docs(README): add RM/SHS API endpoint section + fix Spark 集成 row

- Drop the now-stale "`yarn logs`" from the 技术栈 table; the service
  no longer shell-outs the yarn CLI, all cluster calls go via httpx
  (yarn_client.py).
- New "RM / SHS API 端点" section between 提交流程 and 配置项:
  - RM: 4 endpoints (/ws/v1/cluster/apps, /{appid},
    /{appid}/aggregated-logs, PUT /{appid}/state) with the
    triggering tool for each.
  - Documents the amContainerLogs 3xx-follow fallback (manual,
    3-hop max) and why (httpx drops Authorization across hosts).
  - SHS: explicitly notes zero built-in calls; history_server_url
    is stored-for-future, today SHS access goes through fetch_url
    + url_allowlist only.

.gitignore

@@ -20,3 +20,6 @@ data/
 .pytest_cache/
 .coverage
 htmlcov/
+
+# macOS
+.DS_Store

README.md

@@ -40,7 +40,7 @@
 | MCP 暴露 | fastapi-mcp |
 | 数据模型 | Pydantic v2 |
 | HTTP 客户端 | httpx、httpx-kerberos |
-| Spark 集成 | `spark-submit`、YARN REST API、`yarn logs` |
+| Spark 集成 | `spark-submit`、YARN REST API (httpx 直连) |
 | 日志 | loguru |
 | 进程管理 | uvicorn、gunicorn |
 | 包管理 | uv |
@@ -104,6 +104,7 @@ MCP 客户端需要先执行 `initialize` 握手，拿到 `mcp-session-id` 后
 | `list_connections` | 列出所有连接配置 |
 | `get_connection` | 按名称读取连接配置 |
 | `delete_connection` | 删除连接配置 |
+| `update_connection` | 部分更新一个已存在的连接 (PATCH 语义, 只改提供的字段) |
 | `write_job_file` | 将 LLM 已生成的 PySpark 代码写入服务端文件 |
 | `read_job_file` | 读取已存在的 PySpark 脚本内容 |
 | `update_job_file` | 覆盖更新已存在的 PySpark 脚本 |
@@ -117,6 +118,11 @@ MCP 客户端需要先执行 `initialize` 握手，拿到 `mcp-session-id` 后
 | `get_job_result` | 查询终态结果视图 |
 | `get_job_logs` | 拉取 YARN 聚合日志 |
 | `kill_job` | Kill YARN application |
+| `get_external_job_status` | 查询**非本服务提交**的外部 YARN application 状态（按 `application_id` + `connection_name`） |
+| `get_external_job_result` | 查询外部 YARN application 终态结果视图 |
+| `get_external_job_logs` | 拉取外部 YARN application 的聚合日志 |
+| `list_applications` | 列出 YARN 上所有应用（按 `state` / `queue` / `limit` 过滤），绕过 JobStore |
+| `fetch_url` | 代理 HTTP GET 到集群内网 URL (host 受 `Connection.url_allowlist` glob allowlist 约束, 空则全拒) |
 
 ### Files MCP 工具
 
@@ -215,6 +221,30 @@ get_job_logs
 kill_job
 ```
 
+## RM / SHS API 端点
+
+本服务**不再 shell-out `yarn` CLI**,所有集群交互都通过 `httpx` 直接打 REST(由 `spark_executor/core/yarn_client.py` 统一封装)。鉴权走 `Connection.auth_type`(`none` / `simple` / `basic` / `kerberos` + SPNEGO),SSL 走 `Connection.ssl_verify` / `ssl_ca_bundle`。
+
+### YARN ResourceManager
+
+| 方法 | 端点 | 用途 |
+| --- | --- | --- |
+| `GET` | `/ws/v1/cluster/apps?state=&queue=&limit=` | 列出 YARN 应用(支持 `state` / `queue` / `limit` 过滤),由 `list_applications` 触发 |
+| `GET` | `/ws/v1/cluster/apps/{appid}` | 取单个 app 的 state + amContainerLogs;日志降级路径会复用 |
+| `GET` | `/ws/v1/cluster/apps/{appid}/aggregated-logs` | 拉聚合后的 container 日志,404/501 时自动降级到 amContainerLogs 路径 |
+| `PUT` | `/ws/v1/cluster/apps/{appid}/state`,body `{"state":"KILLED"}` | 杀应用,由 `kill_job` 触发 |
+
+> **日志降级路径**会**手动**跟随 3xx Location 跳到 NodeManager(最多 3 次)抓 AM driver 的 `/stdout`。原因:httpx 默认跨主机重定向会丢掉 `Authorization`,RM→NM 的 307 在很多集群会因此 401/403。driver 日志可以这样取,**executor 日志仍然依赖 `yarn.log-aggregation-enable=true`**,这个不走降级。
+
+### Spark History Server
+
+**当前没有任何内置调用。** `Connection.history_server_url` 字段只是原样存储,留作未来 SHS 专用工具消费(`models.py` 的 docstring 明确写明)。
+
+要走 SHS API(典型路径 `/api/v1/applications/{id}/jobs`、`/api/v1/applications/{id}/stages` 等),**唯一**方式是用 `fetch_url` 工具:
+
+1. 把 SHS 主机 glob 加到对应 `Connection.url_allowlist`(单标签主机如 `ccam*`,或多级域名如 `*.hadoop.internal`)。
+2. 调用 `fetch_url` 时传入完整 SHS URL,鉴权和 SSL 复用同一条 Connection 的配置。
+
 ## 配置项
 
 ### 应用配置

spark_executor/core/connection_store.py

@@ -77,6 +77,29 @@ class ConnectionStore:
             self._dump(records)
         logger.info(f"connection saved name={conn.name} master={conn.master}")
 
+    def update(self, name: str, **fields) -> Connection:
+        """Apply `fields` to the existing Connection identified by `name` and persist.
+
+        PATCH semantics: only fields explicitly passed in `fields` are changed.
+        Use Pydantic's `model_copy(update=fields)` to apply the patch.
+
+        Raises KeyError if no Connection with `name` exists.
+        Raises pydantic.ValidationError if the patched Connection is invalid
+        (e.g. `master='http://...'` fails the master validator).
+        """
+        with self._lock:
+            records = self._load()
+            if name not in records:
+                raise KeyError(f"Connection not found: {name}")
+            existing = records[name]
+            patched = Connection.model_validate(existing.model_copy(update=fields).model_dump())
+            records[name] = patched
+            self._dump(records)
+        logger.info(
+            f"connection updated name={name} fields={sorted(fields.keys())}"
+        )
+        return patched
+
     def delete(self, name: str) -> bool:
         with self._lock:
             records = self._load()

spark_executor/core/job_writer.py

@@ -14,7 +14,7 @@ Resolution order for the output directory:
 """
 import os
 import secrets
-from datetime import datetime
+from datetime import datetime, timezone
 
 from common.config import settings
 from common.logging import logger
@@ -63,7 +63,7 @@ def write_job_file(code: str, jobs_dir: str | None = None) -> str:
 
     effective_dir = resolve_jobs_dir(jobs_dir)
     os.makedirs(effective_dir, exist_ok=True)
-    stamp = datetime.utcnow().strftime("%Y%m%d%H%M%S")
+    stamp = datetime.now(timezone.utc).strftime("%Y%m%d%H%M%S")
     name = f"job_{stamp}_{secrets.token_hex(3)}.py"
     path = os.path.join(effective_dir, name)
     abs_path = os.path.abspath(path)

spark_executor/core/pending_store.py

@@ -37,7 +37,7 @@ class PendingStore:
         return Path(self._data_dir) / self._dir_name
 
     def _date_path(self, created_at: datetime) -> Path:
-        # created_at is datetime.utcnow(), so the shard date is a UTC date.
+        # created_at is timezone-aware UTC, so the shard date is a UTC date.
         return self.dir_path / f"{created_at.date().isoformat()}.json"
 
     def _legacy_path(self) -> Path:

spark_executor/core/yarn_client.py

@@ -121,13 +121,14 @@ def _base_url(yarn_rm_url: str | None) -> str:
 
 
 def _request(method: str, url: str, *, json_body: dict | None = None,
-             timeout: float = 30.0, verify: bool | str = True,
-             auth: httpx.Auth | None = None) -> httpx.Response:
+             params: dict[str, str] | None = None, timeout: float = 30.0,
+             verify: bool | str = True, auth: httpx.Auth | None = None) -> httpx.Response:
     headers = {"Accept": "application/json"}
     logger.debug(f"YARN {method} {url}" + (f" body={json_body}" if json_body else ""))
     try:
         resp = httpx.request(
-            method, url, json=json_body, headers=headers, timeout=timeout, verify=verify, auth=auth
+            method, url, json=json_body, params=params, headers=headers,
+            timeout=timeout, verify=verify, auth=auth
         )
     except httpx.HTTPError as exc:
         logger.error(f"YARN {method} {url} failed: {exc}")
@@ -257,3 +258,51 @@ def kill_application(application_id: str, config: YarnClientConfig) -> None:
         logger.error(f"YARN PUT {url} -> {resp.status_code}: {resp.text[:500]}")
         raise YarnError(f"YARN kill returned HTTP {resp.status_code}: {resp.text}")
     logger.info(f"YARN kill {application_id} -> ok")
+
+
+def list_applications(
+    config: YarnClientConfig,
+    *,
+    state: str | None = None,
+    queue: str | None = None,
+    limit: int | None = None,
+) -> list[dict]:
+    """List YARN applications, optionally filtered.
+
+    YARN endpoint: GET /ws/v1/cluster/apps?state=...&queue=...&limit=...
+
+    Filters:
+      - state: YARN application state. Common values:
+        "NEW", "NEW_SAVING", "SUBMITTED", "ACCEPTED", "RUNNING",
+        "FINISHED", "FAILED", "KILLED".
+        Note: "FINISHED" is the umbrella state covering SUCCEEDED/FAILED/KILLED.
+      - queue: YARN queue name
+      - limit: cap on number of returned apps (YARN has no pagination;
+        callers that need a full enumeration should make multiple
+        calls with state=... filters or accept the cap)
+
+    Returns a list of YARN app dicts (each with id, name, user, queue,
+    state, finalStatus, applicationType, startedTime, finishedTime,
+    trackingUrl, progress, etc). Empty list if no apps match.
+
+    Raises YarnError on transport / 4xx / 5xx.
+    """
+    params: dict[str, str] = {}
+    if state is not None:
+        params["state"] = state
+    if queue is not None:
+        params["queue"] = queue
+    if limit is not None:
+        params["limit"] = str(limit)
+
+    url = f"{_base_url(config.yarn_rm_url)}/ws/v1/cluster/apps"
+    resp = _request("GET", url, params=params,
+                    verify=config.verify_for_httpx(),
+                    auth=config.auth_for_httpx())
+    if resp.status_code >= 400:
+        raise YarnError(
+            f"YARN list applications failed: {resp.status_code} {resp.text[:200]}"
+        )
+    data = resp.json()
+    apps_container = data.get("apps") or {}
+    return apps_container.get("app", []) or []

spark_executor/models.py

@@ -40,6 +40,35 @@ class SubmitResult(BaseModel):
     tracking_url: str | None = None
 
 
+class FetchUrlResult(BaseModel):
+    url: str
+    status_code: int
+    content_type: str
+    body: str
+
+
+class ApplicationSummary(BaseModel):
+    """A YARN application summary from /ws/v1/cluster/apps.
+
+    Field names are mapped from the YARN JSON keys to clearer
+    snake_case names by the tool function. Unused YARN fields
+    (memorySeconds, vcoreSeconds, preemptedResource*, etc.) are
+    not exposed — the LLM doesn't need them.
+    """
+    application_id: str
+    name: str
+    user: str
+    queue: str
+    state: str
+    final_status: str | None = None
+    application_type: str | None = None
+    application_tags: str = ""
+    started_time: int = 0
+    finished_time: int = 0
+    tracking_url: str | None = None
+    progress: float | None = None
+
+
 class Connection(BaseModel):
     name: str
     # Defaults to "yarn" because that's the literal string spark-submit wants
@@ -61,6 +90,35 @@ class Connection(BaseModel):
     auth_principal: str | None = None
     auth_keytab: str | None = None
 
+    url_allowlist: list[str] = Field(
+        default_factory=list,
+        description=(
+            "List of fnmatch glob patterns for hosts the fetch_url tool may access. "
+            "The list is mandatory-opt-in: an empty list (the default) denies all "
+            "hosts, so you must populate it before fetch_url can access any URL. "
+            "Set or change via save_connection (pass url_allowlist on create) or "
+            "update_connection (PATCH the field on an existing connection). "
+            "Useful for clusters whose hostnames do NOT share a common suffix — "
+            "e.g. single-label hosts like 'ccam1'-'ccam99' (configure ['ccam*']) "
+            "or HDFS namenode on a different subdomain ('*.hadoop.internal'). "
+            "Patterns are matched against the URL host only (no port, no path). "
+            "fnmatch rules apply: '*' does NOT match '.', so 'ccam*' matches "
+            "'ccam50' but not 'ccam50.evil.com'."
+        ),
+    )
+    history_server_url: str | None = Field(
+        default=None,
+        description=(
+            "Optional Spark History Server (SHS) base URL, e.g. "
+            "'http://history.prod.internal:18080'. Stored as part of the "
+            "connection for reference and to be consumed by future SHS-"
+            "specific tools. Currently **not consumed by any tool** — to "
+            "fetch SHS endpoints today, use fetch_url with the SHS host "
+            "added to url_allowlist. The SHS host and the YARN RM host "
+            "are usually different, so this is independent of yarn_rm_url."
+        ),
+    )
+
     @field_validator("master")
     @classmethod
     def _check_master(cls, v: str) -> str:

spark_executor/server.py

@@ -6,26 +6,41 @@
 from fastapi import FastAPI, Request
 from fastapi.responses import JSONResponse
 
+from spark_executor.core.yarn_client import YarnError
 from spark_executor.tools.connections import (
     delete_connection,
     get_connection,
     list_connections,
     save_connection,
+    update_connection,
 )
 from spark_executor.tools.write_job import write_job_file
 from spark_executor.tools.job_file import read_job_file, update_job_file
 from spark_executor.tools.kill import kill_job
 from spark_executor.tools.logs import get_job_logs
+from spark_executor.tools.external_jobs import (
+    get_external_job_logs,
+    get_external_job_status,
+    get_external_job_result,
+    list_applications,
+)
+from spark_executor.tools.fetch_url import fetch_url
 from spark_executor.tools.requests import (
     ConnectionNameRequest,
     EmptyRequest,
     WriteJobFileRequest,
+    ExternalJobLogsRequest,
+    ExternalJobStatusRequest,
+    ExternalJobResultRequest,
+    ListApplicationsRequest,
+    FetchUrlRequest,
     GetJobLogsRequest,
     JobIdRequest,
     PendingIdRequest,
     PrepareSubmitJobRequest,
     ReadJobFileRequest,
     SaveConnectionRequest,
+    UpdateConnectionRequest,
     UpdateJobFileRequest,
     UpdatePendingJobRequest,
 )
@@ -69,6 +84,20 @@ async def _valueerror_handler(_request: Request, exc: ValueError) -> JSONRespons
     return JSONResponse(status_code=400, content={"detail": str(exc)})
 
 
+@app.exception_handler(YarnError)
+async def _yarnerror_handler(_request: Request, exc: YarnError) -> JSONResponse:
+    """YARN RM unreachable or returned an error.
+
+    Surfaces as HTTP 502 Bad Gateway (we are a gateway to YARN). The
+    detail includes whatever yarn_client put in the YarnError message
+    (host:port unreachable, HTTP status from YARN, parse failure,
+    etc). The LLM can act on this to distinguish "YARN is down" from
+    "the request was bad" (the latter would be a 400 from
+    _valueerror_handler instead).
+    """
+    return JSONResponse(status_code=502, content={"detail": str(exc)})
+
+
 @app.get("/health")
 def health_check():
     return {"status": "ok"}
@@ -117,7 +146,9 @@ def _prepare_submit_job(req: PrepareSubmitJobRequest):
         "Actually invoke spark-submit for the PendingSubmission identified "
         "by pending_id. Requires status=PENDING. On success, transitions the "
         "pending entry to SUBMITTED and creates a Job record. On failure, "
-        "marks the entry FAILED and re-raises."
+        "marks the entry FAILED and re-raises. A FAILED pending can be "
+        "re-confirmed — it resets to PENDING for a single fresh attempt — so "
+        "transient failures (e.g. YARN RM was down) are recoverable."
     ),
 )
 def _confirm_submit_job(req: PendingIdRequest):
@@ -128,7 +159,13 @@ def _confirm_submit_job(req: PendingIdRequest):
     "/list_pending_jobs",
     operation_id="list_pending_jobs",
     summary="List all pending submissions",
-    description="Return every PendingSubmission in any status (PENDING, SUBMITTED, CANCELLED, FAILED).",
+    description=(
+        "Return every PendingSubmission in any status (PENDING, SUBMITTED, "
+        "CANCELLED, FAILED). Call this before prepare_submit_job to check if a "
+        "submission with the same parameters is already in flight, or after a "
+        "batch of confirm_submit_job calls to inspect the lifecycle of recent "
+        "submissions."
+    ),
 )
 def _list_pending_jobs(_req: EmptyRequest = EmptyRequest()):
     return list_pending_jobs()
@@ -138,7 +175,13 @@ def _list_pending_jobs(_req: EmptyRequest = EmptyRequest()):
     "/get_pending_job",
     operation_id="get_pending_job",
     summary="Get a single pending submission",
-    description="Return the PendingSubmission identified by pending_id, including its current status and outcome fields.",
+    description=(
+        "Return the PendingSubmission identified by pending_id, including its "
+        "current status and outcome fields. Use this to inspect a pending "
+        "submission between prepare_submit_job and confirm_submit_job (e.g. "
+        "to confirm the snapshotted connection), or to read the error field "
+        "of a FAILED submission before re-confirming."
+    ),
 )
 def _get_pending_job(req: PendingIdRequest):
     return get_pending_job(req.pending_id)
@@ -186,7 +229,13 @@ def _cancel_pending_job(req: PendingIdRequest):
         "confirm_submit_job: the local job_id (12-char hex, e.g. "
         "'a1b2c3d4e5f6') and the YARN application_id (e.g. "
         "'application_17400000001_0001'). The lookup is by job_id first, "
-        "then by application_id."
+        "then by application_id. **If you pass a YARN application_id and "
+        "the app is NOT in the local JobStore, this tool returns HTTP 400** "
+        "(not 404) with a hint message naming the right external tool. "
+        "**For YARN applications NOT submitted through this service** "
+        "(no local JobStore record), use "
+        "`get_external_job_status(application_id, connection_name)` "
+        "directly — it bypasses the local registry and queries YARN."
     ),
 )
 def _get_job_status(req: JobIdRequest):
@@ -206,7 +255,13 @@ def _get_job_status(req: JobIdRequest):
         "confirm_submit_job: the local job_id (12-char hex, e.g. "
         "'a1b2c3d4e5f6') and the YARN application_id (e.g. "
         "'application_17400000001_0001'). The lookup is by job_id first, "
-        "then by application_id."
+        "then by application_id. **If you pass a YARN application_id and "
+        "the app is NOT in the local JobStore, this tool returns HTTP 400** "
+        "(not 404) with a hint message naming the right external tool. "
+        "**For YARN applications NOT submitted through this service** "
+        "(no local JobStore record), use "
+        "`get_external_job_result(application_id, connection_name)` "
+        "directly — it bypasses the local registry and queries YARN."
     ),
 )
 def _get_job_result(req: JobIdRequest):
@@ -225,7 +280,13 @@ def _get_job_result(req: JobIdRequest):
         "confirm_submit_job: the local job_id (12-char hex, e.g. "
         "'a1b2c3d4e5f6') and the YARN application_id (e.g. "
         "'application_17400000001_0001'). The lookup is by job_id first, "
-        "then by application_id."
+        "then by application_id. **If you pass a YARN application_id and "
+        "the app is NOT in the local JobStore, this tool returns HTTP 400** "
+        "(not 404) with a hint message naming the right external tool. "
+        "**For YARN applications NOT submitted through this service** "
+        "(no local JobStore record), use "
+        "`get_external_job_logs(application_id, connection_name, tail_chars)` "
+        "directly — it bypasses the local registry and queries YARN."
     ),
 )
 def _get_job_logs(req: GetJobLogsRequest):
@@ -240,13 +301,96 @@ def _get_job_logs(req: GetJobLogsRequest):
         "PUT state=KILLED to YARN REST API for the job's application_id. "
         "**job_id accepts BOTH identifiers** returned by "
         "confirm_submit_job: the local job_id (12-char hex) and the YARN "
-        "application_id. The lookup is by job_id first, then by application_id."
+        "application_id. The lookup is by job_id first, then by application_id. "
+        "**If you pass a YARN application_id and the app is NOT in the "
+        "local JobStore, this tool returns HTTP 400** (not 404) with a "
+        "hint pointing to the YARN CLI / UI. **This tool only works for "
+        "jobs submitted through this service**; there is no external "
+        "equivalent. For YARN applications you did not submit here, use "
+        "the YARN CLI / UI directly to kill them."
     ),
 )
 def _kill_job(req: JobIdRequest):
     return kill_job(req.job_id)
 
 
+# --- External YARN job tools (bypass JobStore) ---
+
+@app.post(
+    "/get_external_job_logs",
+    operation_id="get_external_job_logs",
+    summary="Query YARN logs for an application not submitted through this service",
+    description=(
+        "Fetch aggregated container logs for a YARN application using its "
+        "application_id and a saved Connection. This bypasses the local JobStore, "
+        "so it works for jobs submitted outside this MCP service. "
+        "application_id format is 'application_<14-digit-timestamp>_<sequence>'. "
+        "For jobs submitted via this service, use get_job_logs(job_id=...) instead."
+    ),
+)
+def _get_external_job_logs(req: ExternalJobLogsRequest):
+    return get_external_job_logs(req.application_id, req.connection_name, req.tail_chars)
+
+
+@app.post(
+    "/get_external_job_status",
+    operation_id="get_external_job_status",
+    summary="Query YARN status for an application not submitted through this service",
+    description=(
+        "Return the YARN application state and raw REST response for an "
+        "application using its application_id and a saved Connection. "
+        "This bypasses the local JobStore, so it works for jobs submitted "
+        "outside this MCP service. For jobs submitted via this service, "
+        "use get_job_status(job_id=...) instead."
+    ),
+)
+def _get_external_job_status(req: ExternalJobStatusRequest):
+    return get_external_job_status(req.application_id, req.connection_name)
+
+
+@app.post(
+    "/get_external_job_result",
+    operation_id="get_external_job_result",
+    summary="Query YARN terminal result for an application not submitted through this service",
+    description=(
+        "Return a terminal-oriented view (final_status, diagnostics, tracking_url, "
+        "started_time, finished_time) for a YARN application using its application_id "
+        "and a saved Connection. This bypasses the local JobStore. "
+        "For jobs submitted via this service, use get_job_result(job_id=...) instead."
+    ),
+)
+def _get_external_job_result(req: ExternalJobResultRequest):
+    return get_external_job_result(req.application_id, req.connection_name)
+
+
+@app.post(
+    "/list_applications",
+    operation_id="list_applications",
+    summary="List YARN applications on a cluster, optionally filtered",
+    description=(
+        "Query YARN's /ws/v1/cluster/apps endpoint through the named "
+        "Connection, returning a list of ApplicationSummary records. "
+        "Bypasses the local JobStore — useful for enumerating apps that "
+        "were not submitted through this service.\n\n"
+        "**Filters:** state (YARN state, e.g. 'RUNNING', 'FINISHED', "
+        "'FAILED'), queue (YARN queue name), limit (default 100, max ~10000). "
+        "YARN has no offset-based pagination, so for large clusters combine "
+        "state/queue filters to scope the result. The `FINISHED` state "
+        "covers SUCCEEDED/FAILED/KILLED.\n\n"
+        "Returns an empty list if no apps match. The Connection's auth_type "
+        "/ auth_user / auth_password / ssl_verify / ssl_ca_bundle are reused "
+        "for the request."
+    ),
+)
+def _list_applications(req: ListApplicationsRequest):
+    return list_applications(
+        req.connection_name,
+        state=req.state,
+        queue=req.queue,
+        limit=req.limit,
+    )
+
+
 # --- Connection management tools ---
 
 @app.post(
@@ -254,21 +398,39 @@ def _kill_job(req: JobIdRequest):
     operation_id="save_connection",
     summary="Save or update a named Spark connection",
     description=(
-        "Upsert a Connection record (master URL, deploy mode, optional YARN RM URL, "
-        "spark_conf K/V) keyed by name. Used by prepare_submit_job via the "
-        "connection parameter."
+        "Upsert a Connection record (master URL, deploy mode, optional YARN "
+        "RM URL, spark_conf K/V) keyed by name. Referenced by "
+        "prepare_submit_job via the connection parameter, and by the 3 "
+        "get_external_* tools via connection_name. **The Connection's "
+        "yarn_rm_url is required for get_external_* to work** — spark-submit "
+        "can discover the RM for submissions, but direct YARN REST queries "
+        "need an explicit URL. Saving with an existing name overwrites the "
+        "record in place (no version history). When the name already exists, "
+        "only the provided fields are changed (PATCH semantics); omitted "
+        "fields keep their previous values."
     ),
 )
 def _save_connection(req: SaveConnectionRequest):
-    # exclude_none so we don't overwrite the function's default with explicit None
-    return save_connection(**req.model_dump(exclude_none=True))
+    fields = req.model_dump(exclude_none=True)
+    name = fields.pop("name")
+    try:
+        get_connection(name)
+    except KeyError:
+        # exclude_none so we don't overwrite the function's default with explicit None
+        return save_connection(name=name, **fields)
+    return update_connection(name=name, **fields)
 
 
 @app.post(
     "/list_connections",
     operation_id="list_connections",
     summary="List all saved Spark connections",
-    description="Return every Connection in the registry (model_dump form).",
+    description=(
+        "Return every Connection in the registry (model_dump form). Call "
+        "this before save_connection to see existing names (saving with an "
+        "existing name overwrites), or after save_connection to verify the "
+        "record you just stored."
+    ),
 )
 def _list_connections(_req: EmptyRequest = EmptyRequest()):
     return list_connections()
@@ -278,17 +440,58 @@ def _list_connections(_req: EmptyRequest = EmptyRequest()):
     "/get_connection",
     operation_id="get_connection",
     summary="Get a single connection by name",
-    description="Return the Connection record, or 404 if not found.",
+    description=(
+        "Return the full Connection record, or 404 if not found. **Call this "
+        "whenever you need any cluster-level config** — common lookups: "
+        "yarn_rm_url (YARN RM endpoint), history_server_url (Spark History "
+        "Server), url_allowlist (which hosts fetch_url may access), "
+        "auth_type / auth_user / ssl_verify (for any YARN REST or HTTP call), "
+        "master / deploy_mode / spark_conf (for prepare_submit_job).\n\n"
+        "The response is a full Pydantic model dump — all fields including "
+        "secrets (auth_password, auth_keytab). Treat it as sensitive. "
+        "Useful to verify a connection was saved correctly, or to discover "
+        "the right endpoint to call before invoking get_external_*, "
+        "fetch_url, or list_applications."
+    ),
 )
 def _get_connection(req: ConnectionNameRequest):
     return get_connection(req.name)
 
 
+@app.post(
+    "/update_connection",
+    operation_id="update_connection",
+    summary="Update an existing connection's fields",
+    description=(
+        "Apply a partial update (PATCH) to an existing Connection record. "
+        "Only the fields you provide are changed; the rest are kept as-is. "
+        "The `name` is the immutable identifier (use delete_connection + "
+        "save_connection to rename).\n\n"
+        "To CLEAR an optional field (e.g. remove `yarn_rm_url`), use "
+        "delete_connection followed by save_connection with the field omitted. "
+        "This tool cannot clear fields — only replace them.\n\n"
+        "Returns the full updated Connection record. 404 if no Connection "
+        "with the given name exists."
+    ),
+)
+def _update_connection(req: UpdateConnectionRequest):
+    fields = req.model_dump(exclude_none=True)
+    fields.pop("name", None)  # name is the identity, not a field to patch
+    return update_connection(name=req.name, **fields)
+
+
 @app.post(
     "/delete_connection",
     operation_id="delete_connection",
     summary="Delete a saved connection",
-    description="Remove a Connection by name. 404 if not found.",
+    description=(
+        "Remove a Connection by name. 404 if not found. Deleting a "
+        "Connection does NOT affect any pending submission or running job "
+        "that already references it (the connection details are snapshotted "
+        "at prepare_submit_job time, and YARN holds the live submission "
+        "state). New prepare_submit_job calls will fail until you re-save "
+        "the connection with the same name."
+    ),
 )
 def _delete_connection(req: ConnectionNameRequest):
     return delete_connection(req.name)
@@ -301,16 +504,18 @@ def _delete_connection(req: ConnectionNameRequest):
     operation_id="write_job_file",
     summary="Write LLM-authored PySpark code to disk",
     description=(
-        "Takes a PySpark code string the LLM has already composed in its "
-        "context and writes it to a timestamped file under "
-        "SPARK_EXECUTOR_JOBS_DIR (default ./data/jobs/). Returns the absolute "
-        "path for use as the script_path argument of prepare_submit_job — the "
-        "two-step pattern means the LLM writes the file, the user can review "
-        "it (via read_job_file), and only then is the job submitted.\n\n"
-        "Note: this tool does NOT generate PySpark code. The calling LLM is "
-        "expected to have already written the code; this tool only persists "
-        "it. Code is also run through the SQL safety policy (SELECT/INSERT "
-        "only) before being written — forbidden statements cause a 400."
+        "Persist PySpark code you've already written in your context to a "
+        "timestamped file under SPARK_EXECUTOR_JOBS_DIR (default "
+        "./data/jobs/). Returns the absolute path to pass as the "
+        "script_path argument of prepare_submit_job. The two-step pattern "
+        "(write the file, then prepare) means the user can review the "
+        "file via read_job_file before anything runs.\n\n"
+        "Prerequisite: you should have already composed the PySpark code "
+        "in your own context before calling this tool — it only persists "
+        "code, it does not generate it. Code is run through the SQL safety "
+        "policy (SELECT/INSERT only) before being written; forbidden "
+        "statements cause a 400 with details about which line broke the "
+        "policy."
     ),
 )
 def _write_job_file(req: WriteJobFileRequest):
@@ -323,10 +528,9 @@ def _write_job_file(req: WriteJobFileRequest):
     summary="Read the contents of an existing PySpark script",
     description=(
         "Returns the text content of an existing script file at the given "
-        "path. Caps reads at 1 MB. Typical use: after write_job_file "
-        "returns a path, call read_job_file on that path to inspect what "
-        "was actually written, before deciding to prepare_submit_job or "
-        "update_job_file."
+        "path. No size cap. Typical use: after write_job_file returns a "
+        "path, call read_job_file on that path to inspect what was actually "
+        "written, before deciding to prepare_submit_job or update_job_file."
     ),
 )
 def _read_job_file(req: ReadJobFileRequest):
@@ -341,10 +545,41 @@ def _read_job_file(req: ReadJobFileRequest):
         "Replaces the entire content of an existing script file. Path must "
         "be under SPARK_EXECUTOR_JOBS_DIR (the dir write_job_file writes "
         "to) — protects against overwriting host-mounted configs or other "
-        "non-script files. Caps writes at 1 MB. Typical use: read_job_file, "
-        "edit the content (LLM or human), update_job_file, then "
-        "prepare_submit_job with the same path."
+        "non-script files. No size cap. Typical use: read_job_file, edit "
+        "the content (LLM or human), update_job_file, then prepare_submit_job "
+        "with the same path."
     ),
 )
 def _update_job_file(req: UpdateJobFileRequest):
     return update_job_file(req.script_path, req.content)
+
+# --- HTTP fetch proxy (host allowlist via Connection.yarn_rm_url) ---
+
+@app.post(
+    "/fetch_url",
+    operation_id="fetch_url",
+    summary="Fetch a URL on the cluster's network and return the body",
+    description=(
+        "Proxy an HTTP GET to a URL on the cluster's network, returning the "
+        "response body. Useful when the agent is on a different network from "
+        "the cluster and cannot reach YARN tracking pages, Spark History "
+        "Server, or NodeManager web UIs directly.\n\n"
+        "**Security constraints:** the URL host must match one of the fnmatch "
+        "glob patterns in the named Connection's url_allowlist. An empty or "
+        "omitted allowlist denies every host. There are no scheme or IP-literal "
+        "guardrails — the allowlist is the only gate — so keep it tight. The "
+        "Connection's saved auth is reused, so the agent does not need cluster "
+        "credentials.\n\n"
+        "**Limits:** 30s timeout, redirects followed.\n\n"
+        "**Errors:** when the host is unreachable (connect refused, DNS "
+        "failure, TLS handshake error, timeout, etc.) this tool returns "
+        "HTTP 400 with the exception class and message in the response "
+        "detail — e.g. `fetch_url could not reach ...: ConnectError: "
+        "Connection refused`. Upstream HTTP 4xx/5xx responses that DID "
+        "come back are returned in the result body with their status code "
+        "preserved (not translated to an error) so you can see what the "
+        "server actually said."
+    ),
+)
+def _fetch_url(req: FetchUrlRequest):
+    return fetch_url(req.url, req.connection_name)

spark_executor/tools/connections.py

@@ -4,47 +4,98 @@
 @Author :tao.chen
 """
 from common.logging import logger
-from spark_executor.core.connection_store import ConnectionStore, store
+from spark_executor.core.connection_store import store
 from spark_executor.models import Connection
 
 
+_UNSET = object()
+
+
 def save_connection(
     *,
     name: str,
     master: str,
-    deploy_mode: str = "cluster",
-    yarn_rm_url: str | None = None,
-    spark_conf: dict[str, str] | None = None,
-    ssl_verify: bool | None = None,
-    ssl_ca_bundle: str | None = None,
-    auth_type: str = "none",
-    auth_user: str | None = None,
-    auth_password: str | None = None,
-    auth_principal: str | None = None,
-    auth_keytab: str | None = None,
-) -> dict[str, str]:
+    deploy_mode: str = _UNSET,  # type: ignore[assignment]
+    yarn_rm_url: str | None = _UNSET,  # type: ignore[assignment]
+    spark_conf: dict[str, str] | None = _UNSET,  # type: ignore[assignment]
+    ssl_verify: bool | None = _UNSET,  # type: ignore[assignment]
+    ssl_ca_bundle: str | None = _UNSET,  # type: ignore[assignment]
+    auth_type: str = _UNSET,  # type: ignore[assignment]
+    auth_user: str | None = _UNSET,  # type: ignore[assignment]
+    auth_password: str | None = _UNSET,  # type: ignore[assignment]
+    auth_principal: str | None = _UNSET,  # type: ignore[assignment]
+    auth_keytab: str | None = _UNSET,  # type: ignore[assignment]
+    url_allowlist: list[str] | None = _UNSET,  # type: ignore[assignment]
+    history_server_url: str | None = _UNSET,  # type: ignore[assignment]
+) -> dict[str, object]:
     logger.debug(
-        f"save_connection enter name={name} master={master} deploy_mode={deploy_mode} "
-        f"yarn_rm_url={yarn_rm_url} spark_conf_keys={list((spark_conf or {}).keys())}"
-    )
-    conn = Connection(
-        name=name,
-        master=master,
-        deploy_mode=deploy_mode,
-        yarn_rm_url=yarn_rm_url,
-        spark_conf=spark_conf or {},
-        ssl_verify=ssl_verify,
-        ssl_ca_bundle=ssl_ca_bundle,
-        auth_type=auth_type,
-        auth_user=auth_user,
-        auth_password=auth_password,
-        auth_principal=auth_principal,
-        auth_keytab=auth_keytab,
+        f"save_connection enter name={name} master={master} "
+        f"spark_conf_keys={list((spark_conf if isinstance(spark_conf, dict) else {}).keys())}"
     )
+    existing = store.get(name)
+    if existing is not None:
+        fields: dict[str, object] = {"master": master}
+        if deploy_mode is not _UNSET:
+            fields["deploy_mode"] = deploy_mode
+        if yarn_rm_url is not _UNSET:
+            fields["yarn_rm_url"] = yarn_rm_url
+        if spark_conf is not _UNSET:
+            fields["spark_conf"] = spark_conf or {}
+        if ssl_verify is not _UNSET:
+            fields["ssl_verify"] = ssl_verify
+        if ssl_ca_bundle is not _UNSET:
+            fields["ssl_ca_bundle"] = ssl_ca_bundle
+        if auth_type is not _UNSET:
+            fields["auth_type"] = auth_type
+        if auth_user is not _UNSET:
+            fields["auth_user"] = auth_user
+        if auth_password is not _UNSET:
+            fields["auth_password"] = auth_password
+        if auth_principal is not _UNSET:
+            fields["auth_principal"] = auth_principal
+        if auth_keytab is not _UNSET:
+            fields["auth_keytab"] = auth_keytab
+        if url_allowlist is not _UNSET:
+            fields["url_allowlist"] = url_allowlist or []
+        if history_server_url is not _UNSET:
+            fields["history_server_url"] = history_server_url
+        return update_connection(name, **fields)
+    new_fields: dict[str, object] = {
+        "name": name,
+        "master": master,
+        "deploy_mode": deploy_mode if deploy_mode is not _UNSET else "cluster",
+        "yarn_rm_url": yarn_rm_url if yarn_rm_url is not _UNSET else None,
+        "spark_conf": (spark_conf if spark_conf is not _UNSET else None) or {},
+        "ssl_verify": ssl_verify if ssl_verify is not _UNSET else None,
+        "ssl_ca_bundle": ssl_ca_bundle if ssl_ca_bundle is not _UNSET else None,
+        "auth_type": auth_type if auth_type is not _UNSET else "none",
+        "auth_user": auth_user if auth_user is not _UNSET else None,
+        "auth_password": auth_password if auth_password is not _UNSET else None,
+        "auth_principal": auth_principal if auth_principal is not _UNSET else None,
+        "auth_keytab": auth_keytab if auth_keytab is not _UNSET else None,
+        "url_allowlist": (url_allowlist if url_allowlist is not _UNSET else None) or [],
+        "history_server_url": history_server_url if history_server_url is not _UNSET else None,
+    }
+    conn = Connection(**new_fields)
     store.save(conn)
     return {"name": name, "status": "SAVED"}
 
 
+def update_connection(name: str, **fields) -> dict[str, object]:
+    """Update an existing Connection's mutable fields.
+
+    `name` is the identifier (immutable). PATCH semantics: only the fields
+    you pass are changed. To clear an optional field (e.g. `yarn_rm_url`),
+    use `delete_connection(name=...)` followed by `save_connection(...)`.
+
+    Mutable fields: master, deploy_mode, yarn_rm_url, spark_conf,
+    ssl_verify, ssl_ca_bundle, auth_type, auth_user, auth_password,
+    auth_principal, auth_keytab, url_allowlist, history_server_url.
+    """
+    logger.debug(f"update_connection enter name={name} fields={sorted(fields.keys())}")
+    return store.update(name, **fields).model_dump()
+
+
 def list_connections() -> list[dict[str, object]]:
     logger.debug("list_connections enter")
     return [c.model_dump() for c in store.list_all()]

spark_executor/tools/external_jobs.py

@@ -0,0 +1,120 @@
+# coding=utf-8
+"""
+@Time   :2026/7/8
+@Author :tao.chen
+
+Tools for inspecting YARN applications NOT submitted through this service.
+These bypass the local JobStore and require the caller to supply both the
+YARN application_id and the name of a saved Connection.
+"""
+import json
+
+from common.logging import logger
+from spark_executor.core.yarn_client import (
+    YarnClientConfig,
+    get_application_logs,
+    get_application_status,
+    list_applications as list_applications_yarn,  # alias to avoid collision
+)
+from spark_executor.models import ApplicationSummary, JobResult, JobStatus
+from spark_executor.tools.connections import store as conn_store
+
+
+def get_external_job_logs(application_id: str, connection_name: str, tail_chars: int = 5000) -> str:
+    """Fetch aggregated container logs for a YARN application by ID."""
+    logger.debug(f"get_external_job_logs enter application_id={application_id} connection_name={connection_name} tail_chars={tail_chars}")
+    conn = conn_store.get(connection_name)
+    if conn is None:
+        raise KeyError(f"Connection not found: {connection_name}")
+    config = YarnClientConfig.from_connection(conn)
+    full = get_application_logs(application_id, config)
+    tailed = full[-tail_chars:] if len(full) > tail_chars else full
+    logger.info(
+        f"get_external_job_logs ok application_id={application_id} connection_name={connection_name} "
+        f"full_chars={len(full)} returned_chars={len(tailed)}"
+    )
+    return tailed
+
+
+def get_external_job_status(application_id: str, connection_name: str) -> JobStatus:
+    """Query YARN for an external application's current status."""
+    logger.debug(f"get_external_job_status enter application_id={application_id} connection_name={connection_name}")
+    conn = conn_store.get(connection_name)
+    if conn is None:
+        raise KeyError(f"Connection not found: {connection_name}")
+    config = YarnClientConfig.from_connection(conn)
+    state, raw = get_application_status(application_id, config)
+    logger.info(f"get_external_job_status ok application_id={application_id} connection_name={connection_name} state={state}")
+    return JobStatus(application_id=application_id, state=state, raw=raw)
+
+
+def get_external_job_result(application_id: str, connection_name: str) -> JobResult:
+    """Query YARN for an external application's terminal result view."""
+    logger.debug(f"get_external_job_result enter application_id={application_id} connection_name={connection_name}")
+    conn = conn_store.get(connection_name)
+    if conn is None:
+        raise KeyError(f"Connection not found: {connection_name}")
+    config = YarnClientConfig.from_connection(conn)
+    state, raw = get_application_status(application_id, config)
+    app = json.loads(raw).get("app", {})
+    result = JobResult(
+        application_id=application_id,
+        state=state,
+        final_status=app.get("finalStatus"),
+        diagnostics=app.get("diagnostics"),
+        tracking_url=app.get("trackingUrl"),
+        started_time=app.get("startedTime"),
+        finished_time=app.get("finishedTime"),
+    )
+    logger.info(f"get_external_job_result ok application_id={application_id} connection_name={connection_name} state={state}")
+    return result
+
+
+def list_applications(
+    connection_name: str,
+    state: str | None = None,
+    queue: str | None = None,
+    limit: int = 100,
+) -> list[ApplicationSummary]:
+    """List YARN applications on the named cluster, optionally filtered.
+
+    Bypasses the local JobStore (this is for apps not submitted through
+    this service). The YARN ResourceManager REST endpoint
+    /ws/v1/cluster/apps is queried through the connection's auth/SSL
+    config.
+
+    Defaults: limit=100 (YARN has no offset-based pagination, so large
+    clusters should use state/queue filters to scope the result).
+    """
+    logger.debug(
+        f"list_applications enter connection_name={connection_name} "
+        f"state={state} queue={queue} limit={limit}"
+    )
+    conn = conn_store.get(connection_name)
+    if conn is None:
+        raise KeyError(f"Connection not found: {connection_name}")
+    config = YarnClientConfig.from_connection(conn)
+    raw_apps = list_applications_yarn(
+        config, state=state, queue=queue, limit=limit
+    )
+    summaries = [
+        ApplicationSummary(
+            application_id=app.get("id", ""),
+            name=app.get("name", ""),
+            user=app.get("user", ""),
+            queue=app.get("queue", ""),
+            state=app.get("state", ""),
+            final_status=app.get("finalStatus"),
+            application_type=app.get("applicationType"),
+            application_tags=app.get("applicationTags", ""),
+            started_time=app.get("startedTime", 0),
+            finished_time=app.get("finishedTime", 0),
+            tracking_url=app.get("trackingUrl"),
+            progress=app.get("progress"),
+        )
+        for app in raw_apps
+    ]
+    logger.info(
+        f"list_applications ok connection_name={connection_name} count={len(summaries)}"
+    )
+    return summaries

spark_executor/tools/fetch_url.py

@@ -0,0 +1,136 @@
+# coding=utf-8
+"""
+@Time   :2026/7/9
+@Author :tao.chen
+
+Generic HTTP GET proxy for the agent. Lets the agent fetch URLs on the
+cluster's network when it cannot reach those hosts directly. Security:
+the host is checked against an explicit fnmatch glob allowlist configured
+on the connection (`url_allowlist`). Empty or missing allowlist means no
+URL access; the allowlist is the only gate — scheme and IP-literal checks
+are intentionally NOT performed. Reuses the connection's saved auth/SSL
+config so the agent doesn't need cluster credentials.
+"""
+import fnmatch
+from urllib.parse import urlparse, urljoin
+
+import httpx
+
+from common.logging import logger
+from spark_executor.core.yarn_client import YarnClientConfig
+from spark_executor.models import FetchUrlResult
+from spark_executor.tools.connections import store as conn_store
+
+_REQUEST_TIMEOUT_SECONDS = 30
+
+_MAX_REDIRECTS = 3
+_REDIRECT_STATUSES = frozenset({301, 302, 303, 307, 308})
+
+
+def _host_matches_any_glob(host: str, allowlist: list[str]) -> bool:
+    """True if `host` matches any of the fnmatch glob patterns.
+
+    fnmatch is case-sensitive on Linux (our deployment target). `*` in a
+    pattern does NOT cross '.' boundaries, so 'ccam*' matches 'ccam50' but
+    NOT 'ccam50.evil.com' (which is what we want — domain boundary matters
+    for SSRF).
+    """
+    host_labels = host.split(".")
+    for p in allowlist:
+        pat_labels = p.split(".")
+        if len(pat_labels) != len(host_labels):
+            continue
+        if all(fnmatch.fnmatchcase(h, pat) for h, pat in zip(host_labels, pat_labels)):
+            return True
+    return False
+
+
+def _validate_url_host(url: str, allowlist: list[str] | None) -> None:
+    """Reject the URL unless its host matches a glob in `allowlist`.
+
+    The only check. The url_allowlist is the single source of truth for
+    what fetch_url is allowed to access — no scheme, IP-literal, or
+    "must be the same as yarn_rm_url" guardrails. The caller is
+    responsible for writing a tight allowlist.
+
+    The only structural check: the URL must have a host (otherwise
+    the glob match has nothing to test). Anything else is the
+    allowlist's job.
+    """
+    host = urlparse(url).hostname
+    if not host:
+        raise ValueError(f"URL has no host: {url!r}")
+    if _host_matches_any_glob(host, allowlist or []):
+        return
+    raise ValueError(
+        f"URL host {host!r} is not in Connection.url_allowlist {allowlist!r}. "
+        f"Add the host pattern to url_allowlist (or use a broader glob) "
+        f"and try again."
+    )
+
+
+def fetch_url(url: str, connection_name: str) -> FetchUrlResult:
+    """Proxy an HTTP GET to url using the auth/SSL settings of connection_name."""
+    logger.debug(f"fetch_url enter url={url} connection_name={connection_name}")
+    conn = conn_store.get(connection_name)
+    if conn is None:
+        raise KeyError(f"Connection not found: {connection_name}")
+
+    _validate_url_host(url, conn.url_allowlist)
+
+    config = YarnClientConfig.from_connection(conn)
+    auth = config.auth_for_httpx()
+    verify = config.verify_for_httpx()
+
+    for hop in range(_MAX_REDIRECTS + 1):
+        try:
+            resp = httpx.get(
+                url,
+                auth=auth,
+                verify=verify,
+                timeout=_REQUEST_TIMEOUT_SECONDS,
+                follow_redirects=False,
+            )
+        except httpx.HTTPError as exc:
+            # Network-level failure (no response received). Surface the
+            # exception class + message so the LLM can act on it.
+            # ValueError -> 400 via the existing handler in server.py.
+            # The cause chain (`from exc`) preserves the original
+            # exception for loguru.
+            raise ValueError(
+                f"fetch_url could not reach {url!r}: "
+                f"{type(exc).__name__}: {exc}. "
+                f"Check that the URL is reachable from the MCP service, "
+                f"the host is in Connection.url_allowlist, and the "
+                f"connection's auth/SSL settings are correct."
+            ) from exc
+        if resp.status_code not in _REDIRECT_STATUSES:
+            logger.info(
+                f"fetch_url ok url={url} connection_name={connection_name} "
+                f"status_code={resp.status_code} "
+                f"content_type={resp.headers.get('content-type', '')} "
+                f"body_chars={len(resp.text)}"
+            )
+
+            return FetchUrlResult(
+                url=url,
+                status_code=resp.status_code,
+                content_type=resp.headers.get("content-type", ""),
+                body=resp.text,
+            )
+
+        location = resp.headers.get("Location") or resp.headers.get("location")
+        if not location:
+            raise ValueError(
+                f"HTTP GET returned {resp.status_code} with no Location header at {url}"
+            )
+        next_url = urljoin(url, location)
+        logger.debug(
+            f"fetch_url redirect url={url} status={resp.status_code} to={next_url}"
+        )
+        _validate_url_host(next_url, conn.url_allowlist)
+        url = next_url
+
+    raise ValueError(
+        f"fetch_url exceeded {_MAX_REDIRECTS} redirects (last url: {url})"
+    )

spark_executor/tools/job_file.py

@@ -16,7 +16,10 @@ Safety:
   - update_job_file:  must be under SPARK_EXECUTOR_JOBS_DIR
     (settings.jobs_dir) so the agent cannot overwrite host-mounted
     configs or arbitrary files on the container FS.
-  - 1 MB cap on both read and write payloads to keep MCP responses bounded.
+  - No size cap on read or write payloads — the caller controls the
+    file size. MCP response size is bounded by httpx and the JSON
+    transport; for very large files the LLM should split via
+    write_job_file and read in chunks via read_job_file + update.
 """
 import os
 from pathlib import Path
@@ -24,9 +27,6 @@ from pathlib import Path
 from common.config import settings
 from common.logging import logger
 
-MAX_FILE_BYTES = 1 * 1024 * 1024  # 1 MB
-
-
 class ScriptFileError(ValueError):
     """Raised when read/update fails. -> HTTP 400 via the FastAPI ValueError
     handler in server.py.
@@ -68,16 +68,10 @@ def _check_writable(script_path: str) -> None:
 def read_job_file(script_path: str) -> dict[str, object]:
     """Return the text content of an existing script file.
 
-    Caps the read at 1 MB to keep MCP responses bounded; raises
-    ScriptFileError (-> 400) if the file is missing or too large.
+    No size cap. Raises ScriptFileError (-> 400) if the file is missing.
     """
     _check_readable(script_path)
     size = os.path.getsize(script_path)
-    if size > MAX_FILE_BYTES:
-        raise ScriptFileError(
-            f"Script is too large to read back ({size} bytes > {MAX_FILE_BYTES} "
-            f"byte cap). Edit it via a host volume mount instead."
-        )
     logger.debug(f"read_job_file enter script_path={script_path} size={size}")
     with open(script_path, encoding="utf-8") as f:
         content = f.read()
@@ -88,17 +82,12 @@ def read_job_file(script_path: str) -> dict[str, object]:
 def update_job_file(script_path: str, content: str) -> dict[str, object]:
     """Overwrite an existing script file with new content.
 
-    Restricted to paths under settings.jobs_dir. Caps writes at 1 MB.
-    Raises ScriptFileError (-> 400) if the path is missing, outside
-    the allowed dir, or the content is too large.
+    Restricted to paths under settings.jobs_dir. No size cap.
+    Raises ScriptFileError (-> 400) if the path is missing or outside
+    the allowed dir.
     """
     _check_writable(script_path)
     encoded_size = len(content.encode("utf-8"))
-    if encoded_size > MAX_FILE_BYTES:
-        raise ScriptFileError(
-            f"content is too large ({encoded_size} bytes > {MAX_FILE_BYTES} "
-            f"byte cap). Split the script into multiple files."
-        )
     logger.debug(
         f"update_job_file enter script_path={script_path} "
         f"new_bytes={encoded_size}"

spark_executor/tools/kill.py

@@ -21,7 +21,13 @@ def kill_job(job_id: str) -> dict[str, str]:
     logger.debug(f"kill_job enter job_id={job_id}")
     job = store.get_either(job_id)
     if job is None:
-        raise _unknown_job_error(job_id)
+        raise _unknown_job_error(
+            job_id,
+            external_tool_hint=(
+                "the YARN CLI (`yarn application -kill <app_id>`) or the YARN "
+                "UI directly — this service has no external kill tool"
+            ),
+        )
     conn = conn_store.get(job.connection)
     if conn is None:
         raise KeyError(f"Connection not found: {job.connection}")

spark_executor/tools/logs.py

@@ -11,14 +11,31 @@ from spark_executor.tools.connections import store as conn_store
 store = JobStore()
 
 
-def _unknown_job_error(uid: str) -> KeyError:
-    """Standard "we tried both IDs and found nothing" message.
+def _unknown_job_error(uid: str, external_tool_hint: str | None = None) -> Exception:
+    """Build the right error for a not-found job.
 
     The agent gets this from confirm_submit_job's response:
         {"job_id": "a1b2c3d4e5f6", "application_id": "application_...", ...}
-    and routinely confuses which to pass here. Spelling out that BOTH
-    IDs were tried (and what they look like) saves a round trip.
+    and routinely confuses which to pass here. We differentiate two cases:
+
+    - `uid` looks like a YARN application_id (starts with 'application_')
+      AND the caller passed an `external_tool_hint`: the YARN app likely
+      exists, this tool just can't serve it because it was not submitted
+      through this service. Raise ValueError (-> 400 via the FastAPI
+      handler) pointing the agent at the right external tool.
+    - Otherwise: no local record of either form of id. Raise KeyError
+      (-> 404). Spelling out what both IDs look like saves a round trip.
     """
+    if uid.startswith("application_") and external_tool_hint:
+        return ValueError(
+            f"job_id={uid!r} looks like a YARN application_id (starts with "
+            f"'application_'), but this tool only works for jobs submitted "
+            f"through this MCP service (no local JobStore record). For YARN "
+            f"applications not submitted here, use {external_tool_hint} "
+            f"instead. (If you actually submitted this job through this "
+            f"service, pass the local job_id — it is a 12-char hex like "
+            f"'a1b2c3d4e5f6'.)"
+        )
     return KeyError(
         f"No Job found for id={uid!r} (neither as job_id nor as "
         f"application_id). Pass the job_id from confirm_submit_job's "
@@ -37,7 +54,10 @@ def get_job_logs(job_id: str, tail_chars: int = 5000) -> str:
     logger.debug(f"get_job_logs enter job_id={job_id} tail_chars={tail_chars}")
     job = store.get_either(job_id)
     if job is None:
-        raise _unknown_job_error(job_id)
+        raise _unknown_job_error(
+            job_id,
+            external_tool_hint="get_external_job_logs(application_id, connection_name, tail_chars)",
+        )
     conn = conn_store.get(job.connection)
     if conn is None:
         raise KeyError(f"Connection not found: {job.connection}")

spark_executor/tools/requests.py

@@ -17,22 +17,143 @@ class EmptyRequest(BaseModel):
 
 
 class SaveConnectionRequest(BaseModel):
-    name: str
-    master: str
-    deploy_mode: str = "cluster"
-    yarn_rm_url: str | None = None
-    spark_conf: dict[str, str] | None = None
-    ssl_verify: bool | None = None
-    ssl_ca_bundle: str | None = None
-    auth_type: str = "none"
-    auth_user: str | None = None
-    auth_password: str | None = None
-    auth_principal: str | None = None
-    auth_keytab: str | None = None
+    name: str = Field(
+        ...,
+        description=(
+            "Unique connection name. Referenced by prepare_submit_job.connection "
+            "and get_external_*.connection_name. Saving with an existing name "
+            "overwrites that record."
+        ),
+    )
+    master: str = Field(
+        ...,
+        description=(
+            "Spark master URL. **Required** at the MCP layer (even though "
+            "the underlying Connection model has a default of 'yarn'). "
+            "Other valid values: 'yarn' (default for YARN), 'spark://host:port' "
+            "(Standalone), 'k8s://...', 'mesos://...', 'local[N]' or 'local[*]'. "
+            "The validator rejects 'yarn-cluster' and bare 'http://...' URLs — "
+            "those are common typos. The literal 'yarn' (not 'yarn-cluster') is "
+            "what spark-submit wants for --master."
+        ),
+    )
+    deploy_mode: str = Field(
+        default="cluster",
+        description=(
+            "Spark deploy mode. 'cluster' (default, driver runs in YARN) or "
+            "'client' (driver runs where spark-submit is invoked). Most YARN "
+            "production submissions use 'cluster'."
+        ),
+    )
+    yarn_rm_url: str | None = Field(
+        default=None,
+        description=(
+            "YARN ResourceManager REST base URL, e.g. 'http://rm-host:8088'. "
+            "**Required** for the 3 get_external_* tools to query YARN "
+            "directly. Optional for prepare_submit_job — spark-submit "
+            "discovers the RM via the cluster config when this is unset."
+        ),
+    )
+    spark_conf: dict[str, str] | None = Field(
+        default=None,
+        description=(
+            "Dict of Spark conf key→value pairs, passed as --conf flags to "
+            "spark-submit. Example: {'spark.executor.memory': '4g', "
+            "'spark.sql.shuffle.partitions': '200'}. None or empty means "
+            "no extra --conf flags."
+        ),
+    )
+    ssl_verify: bool | None = Field(
+        default=None,
+        description=(
+            "Whether to verify the YARN RM TLS certificate. None (default) "
+            "falls back to the global setting; explicit True/False overrides "
+            "the global default for this connection. Set False only for "
+            "self-signed dev clusters."
+        ),
+    )
+    ssl_ca_bundle: str | None = Field(
+        default=None,
+        description=(
+            "Absolute path to a CA bundle file for YARN RM TLS verification. "
+            "Only relevant when the RM uses a private CA. Ignored when "
+            "ssl_verify=False."
+        ),
+    )
+    auth_type: str = Field(
+        default="none",
+        description=(
+            "Authentication mode for YARN REST calls. One of: 'none' "
+            "(default, no auth header), 'simple' (pseudo-auth, "
+            "auth_user required), 'basic' (HTTP Basic, auth_user + "
+            "auth_password required), 'kerberos' (SPNEGO via the system "
+            "ticket cache — run kinit beforehand)."
+        ),
+    )
+    auth_user: str | None = Field(
+        default=None,
+        description=(
+            "Username for auth_type='simple' or 'basic'. Ignored when "
+            "auth_type='none' or 'kerberos'."
+        ),
+    )
+    auth_password: str | None = Field(
+        default=None,
+        description=(
+            "Password for auth_type='basic'. Ignored otherwise. Sent on "
+            "every YARN REST request — store with care."
+        ),
+    )
+    auth_principal: str | None = Field(
+        default=None,
+        description=(
+            "Kerberos principal (e.g. 'user@REALM'). Display/audit only; "
+            "the actual SPNEGO handshake uses the system ticket cache. "
+            "Run `kinit <principal>` on the host before invoking the tools."
+        ),
+    )
+    auth_keytab: str | None = Field(
+        default=None,
+        description=(
+            "Absolute path to a Kerberos keytab file. Optional convenience "
+            "for 'kinit -kt' workflows. The service does NOT auto-initialize "
+            "from the keytab — you must `kinit -kt <auth_keytab> <auth_principal>` "
+            "yourself before calling the tools."
+        ),
+    )
 
+    url_allowlist: list[str] | None = Field(
+        default=None,
+        description=(
+            "Optional list of fnmatch glob patterns for hosts the fetch_url tool "
+            "may access. See Connection.url_allowlist for full semantics. "
+            "Example for single-label host clusters: ['ccam*'] allows any host "
+            "starting with 'ccam' (ccam1, ccam2, ..., ccam99). If omitted, None, "
+            "or empty, the saved connection will have url_allowlist=[] (the "
+            "default), meaning fetch_url will reject every URL until the list is "
+            "populated via update_connection."
+        ),
+    )
+    history_server_url: str | None = Field(
+        default=None,
+        description=(
+            "Optional Spark History Server (SHS) base URL, e.g. "
+            "'http://history.prod.internal:18080'. Stored for reference. "
+            "Currently not consumed by any tool — see Connection.history_server_url."
+        ),
+    )
 
 class PrepareSubmitJobRequest(BaseModel):
-    connection: str
+    connection: str = Field(
+        ...,
+        description=(
+            "Name of a saved Connection (call save_connection first, or "
+            "list_connections to see available names). The Connection's "
+            "master / deploy_mode / spark_conf / yarn_rm_url are snapshotted "
+            "into the pending submission at prepare time, so editing the "
+            "Connection afterwards does NOT retarget this pending job."
+        ),
+    )
     app_name: str = Field(
         ...,
         description="Human-readable application name for tracking the pending submission.",
@@ -72,34 +193,115 @@ class PrepareSubmitJobRequest(BaseModel):
 
 
 class PendingIdRequest(BaseModel):
-    pending_id: str
+    pending_id: str = Field(
+        ...,
+        description=(
+            "ID of a pending submission. Format: 'p_' + 12 hex chars, "
+            "e.g. 'p_a1b2c3d4e5f6'. Returned by prepare_submit_job; "
+            "visible via list_pending_jobs."
+        ),
+    )
 
 
 class UpdatePendingJobRequest(BaseModel):
-    pending_id: str
+    pending_id: str = Field(
+        ...,
+        description=(
+            "ID of the pending submission to modify. Format: 'p_' + 12 hex "
+            "chars, e.g. 'p_a1b2c3d4e5f6'. Only PENDING submissions can "
+            "be updated — once SUBMITTED, CANCELLED, or FAILED, the "
+            "pending is terminal."
+        ),
+    )
     script_path: str | None = Field(
         default=None,
-        description="Optional new absolute path to the PySpark script. If provided, the file must exist and pass SQL guard.",
+        description=(
+            "Optional new absolute path to the PySpark script. If provided, "
+            "the file must exist and pass the SQL guard. Omit to keep the "
+            "current script_path."
+        ),
+    )
+    queue: str | None = Field(
+        default=None,
+        description=(
+            "New YARN queue name. Omit to keep the current value (PATCH "
+            "semantics: only fields you provide are changed)."
+        ),
+    )
+    executor_memory: str | None = Field(
+        default=None,
+        description=(
+            "New executor memory, e.g. '4G'. Omit to keep the current value."
+        ),
+    )
+    executor_cores: int | None = Field(
+        default=None,
+        description="New cores per executor. Omit to keep the current value.",
+    )
+    num_executors: int | None = Field(
+        default=None,
+        description="New total executor count. Omit to keep the current value.",
+    )
+    app_name: str | None = Field(
+        default=None,
+        description=(
+            "New human-readable application name (visible in YARN UI). "
+            "Omit to keep the current value."
+        ),
+    )
+    extra_args: dict[str, str] | None = Field(
+        default=None,
+        description=(
+            "Replacement dict of additional spark-submit flags (e.g. "
+            "{'jars': '/path/to.jar'}). Unlike the scalar fields, providing "
+            "this REPLACES the entire dict — it is not deep-merged. Omit to "
+            "keep the current value."
+        ),
     )
-    queue: str | None = None
-    executor_memory: str | None = None
-    executor_cores: int | None = None
-    num_executors: int | None = None
-    app_name: str | None = None
-    extra_args: dict[str, str] | None = None
 
 
 class JobIdRequest(BaseModel):
-    job_id: str
+    job_id: str = Field(
+        ...,
+        description=(
+            "Either the local job_id (12-char hex, e.g. 'a1b2c3d4e5f6') or "
+            "the YARN application_id (e.g. 'application_17400000001_0001') of "
+            "a job submitted through this service. The lookup tries job_id "
+            "first, then application_id. For YARN applications not submitted "
+            "here, use the get_external_* tools instead."
+        ),
+    )
 
 
 class GetJobLogsRequest(BaseModel):
-    job_id: str
-    tail_chars: int = 5000
+    job_id: str = Field(
+        ...,
+        description=(
+            "Either the local job_id (12-char hex, e.g. 'a1b2c3d4e5f6') "
+            "or the YARN application_id (e.g. 'application_17400000001_0001') "
+            "of a job submitted through this service. For YARN applications "
+            "not submitted here, use get_external_job_logs instead."
+        ),
+    )
+    tail_chars: int = Field(
+        default=5000,
+        description=(
+            "Return only the last N characters of the aggregated container "
+            "logs. Default 5000. Use a larger value if the head of the log "
+            "(stack traces, driver errors) is being truncated."
+        ),
+    )
 
 
 class ConnectionNameRequest(BaseModel):
-    name: str
+    name: str = Field(
+        ...,
+        description=(
+            "Name of a saved Connection. Use list_connections to see "
+            "available names. Saving with this name updates an existing "
+            "record (see save_connection)."
+        ),
+    )
 
 
 class WriteJobFileRequest(BaseModel):
@@ -142,3 +344,191 @@ class UpdateJobFileRequest(BaseModel):
             "Maximum 1 MB to keep the MCP response bounded."
         ),
     )
+
+
+class ExternalJobLogsRequest(BaseModel):
+    application_id: str = Field(
+        ...,
+        description=(
+            "YARN application_id of the external job, format "
+            "'application_<14-digit-timestamp>_<sequence>' (e.g. "
+            "'application_1740000000001_0001'). This tool is for jobs "
+            "NOT submitted through this MCP service — for those, use "
+            "get_job_logs(job_id=...) instead."
+        ),
+    )
+    connection_name: str = Field(
+        ...,
+        description=(
+            "Name of a saved Connection (see list_connections) pointing "
+            "at the YARN cluster where the application ran."
+        ),
+    )
+    tail_chars: int = Field(
+        default=5000,
+        description="Return only the last N characters of the aggregated container logs.",
+    )
+
+
+class ExternalJobStatusRequest(BaseModel):
+    application_id: str = Field(
+        ...,
+        description=(
+            "YARN application_id of the external job, format "
+            "'application_<14-digit-timestamp>_<sequence>'. Use "
+            "get_job_status(job_id=...) for jobs submitted through this service."
+        ),
+    )
+    connection_name: str = Field(
+        ...,
+        description="Name of a saved Connection pointing at the YARN cluster.",
+    )
+
+
+class ExternalJobResultRequest(BaseModel):
+    application_id: str = Field(
+        ...,
+        description=(
+            "YARN application_id of the external job, format "
+            "'application_<14-digit-timestamp>_<sequence>'. Use "
+            "get_job_result(job_id=...) for jobs submitted through this service."
+        ),
+    )
+    connection_name: str = Field(
+        ...,
+        description="Name of a saved Connection pointing at the YARN cluster.",
+    )
+
+class FetchUrlRequest(BaseModel):
+    url: str = Field(
+        ...,
+        description=(
+            "Absolute URL to fetch. The only access control is the named "
+            "Connection's url_allowlist: the URL host must match one of the "
+            "fnmatch glob patterns in that list. An empty or omitted allowlist "
+            "denies every host. IP literals and non-HTTP schemes are allowed "
+            "if and only if they are matched by the allowlist. The Connection's "
+            "saved auth is reused for the outbound request — the agent does not "
+            "need cluster credentials."
+        ),
+    )
+    connection_name: str = Field(
+        ...,
+        description=(
+            "Name of a saved Connection (see list_connections). The "
+            "Connection's url_allowlist is the host gate for this tool — "
+            "**not yarn_rm_url** (yarn_rm_url is only used by the "
+            "get_external_* tools to locate the YARN RM). The "
+            "Connection's auth_type / auth_user / auth_password / "
+            "ssl_verify / ssl_ca_bundle are reused for the request."
+        ),
+    )
+
+
+class UpdateConnectionRequest(BaseModel):
+    name: str = Field(
+        ...,
+        description=(
+            "Name of the existing Connection to update (immutable identifier). "
+            "If you want to rename, use delete_connection + save_connection."
+        ),
+    )
+    master: str | None = Field(
+        default=None,
+        description="New Spark master URL. Omit to keep current.",
+    )
+    deploy_mode: str | None = Field(
+        default=None,
+        description="New Spark deploy mode ('cluster' or 'client'). Omit to keep current.",
+    )
+    yarn_rm_url: str | None = Field(
+        default=None,
+        description="New YARN ResourceManager REST base URL. Omit to keep current.",
+    )
+    spark_conf: dict[str, str] | None = Field(
+        default=None,
+        description="Replacement Spark conf dict (not merged with existing). Omit to keep current.",
+    )
+    ssl_verify: bool | None = Field(
+        default=None,
+        description="New SSL verify setting. Omit to keep current.",
+    )
+    ssl_ca_bundle: str | None = Field(
+        default=None,
+        description="New SSL CA bundle path. Omit to keep current.",
+    )
+    auth_type: str | None = Field(
+        default=None,
+        description="New auth mode. Omit to keep current.",
+    )
+    auth_user: str | None = Field(
+        default=None,
+        description="New auth username. Omit to keep current.",
+    )
+    auth_password: str | None = Field(
+        default=None,
+        description="New auth password. Omit to keep current.",
+    )
+    auth_principal: str | None = Field(
+        default=None,
+        description="New Kerberos principal. Omit to keep current.",
+    )
+    auth_keytab: str | None = Field(
+        default=None,
+        description="New Kerberos keytab path. Omit to keep current.",
+    )
+    url_allowlist: list[str] | None = Field(
+        default=None,
+        description=(
+            "Replacement url_allowlist list (not merged). Omit to keep current. "
+            "Pass an empty list to deny all hosts (the default for new connections). "
+            "Example: ['ccam*'] allows ccam1-ccam99."
+        ),
+    )
+    history_server_url: str | None = Field(
+        default=None,
+        description=(
+            "New Spark History Server base URL. Omit to keep current. "
+            "Pass None to clear (use delete_connection + save_connection "
+            "if you need explicit clear semantics; same caveat as other "
+            "Optional fields in this tool)."
+        ),
+    )
+
+
+class ListApplicationsRequest(BaseModel):
+    connection_name: str = Field(
+        ...,
+        description=(
+            "Name of a saved Connection (see list_connections) pointing at "
+            "the YARN cluster to query."
+        ),
+    )
+    state: str | None = Field(
+        default=None,
+        description=(
+            "Optional YARN application state filter. One of: 'NEW', "
+            "'NEW_SAVING', 'SUBMITTED', 'ACCEPTED', 'RUNNING', 'FINISHED', "
+            "'FAILED', 'KILLED'. 'FINISHED' is the umbrella state covering "
+            "SUCCEEDED/FAILED/KILLED. None = no state filter (returns all "
+            "states up to `limit`)."
+        ),
+    )
+    queue: str | None = Field(
+        default=None,
+        description=(
+            "Optional YARN queue name filter (e.g. 'default', 'prod'). "
+            "None = no queue filter."
+        ),
+    )
+    limit: int = Field(
+        default=100,
+        ge=1,
+        le=10000,
+        description=(
+            "Maximum number of applications to return. YARN has no "
+            "offset-based pagination, so for large clusters use state/queue "
+            "filters to scope the result. Max 10000 in practice (YARN's own "
+            "limit on the limit param)."
+        ),
+    )

spark_executor/tools/result.py

@@ -24,7 +24,10 @@ def get_job_result(job_id: str) -> JobResult:
     logger.debug(f"get_job_result enter job_id={job_id}")
     job = store.get_either(job_id)
     if job is None:
-        raise _unknown_job_error(job_id)
+        raise _unknown_job_error(
+            job_id,
+            external_tool_hint="get_external_job_result(application_id, connection_name)",
+        )
     conn = conn_store.get(job.connection)
     if conn is None:
         raise KeyError(f"Connection not found: {job.connection}")

spark_executor/tools/status.py

@@ -23,7 +23,10 @@ def get_job_status(job_id: str) -> JobStatus:
     logger.debug(f"get_job_status enter job_id={job_id}")
     job = store.get_either(job_id)
     if job is None:
-        raise _unknown_job_error(job_id)
+        raise _unknown_job_error(
+            job_id,
+            external_tool_hint="get_external_job_status(application_id, connection_name)",
+        )
     conn = conn_store.get(job.connection)
     if conn is None:
         raise KeyError(f"Connection not found: {job.connection}")

spark_executor/tools/submit.py

@@ -6,9 +6,8 @@
 import os
 import secrets
 import uuid
-from datetime import datetime
+from datetime import datetime, timezone
 
-from common.config import settings
 from common.logging import logger
 from common.sql_guard import validate_pyspark_code
 from spark_executor.core.connection_store import store as conn_store
@@ -124,7 +123,7 @@ def prepare_submit_job(
         num_executors=num_executors,
         spark_conf=dict(conn.spark_conf),
         extra_args=dict(extra_args or {}),
-        created_at=datetime.utcnow(),
+        created_at=datetime.now(timezone.utc),
         status="PENDING",
     )
     pending_store.save(pending)
@@ -248,7 +247,7 @@ def confirm_submit_job(*, pending_id: str) -> SubmitResult:
                     application_id=application_id,
                     script_path=pending.script_path,
                     queue=pending.queue,
-                    submit_time=datetime.utcnow(),
+                    submit_time=datetime.now(timezone.utc),
                     connection=pending.connection,
                     yarn_rm_url=pending.yarn_rm_url,
                 )
@@ -282,7 +281,7 @@ def confirm_submit_job(*, pending_id: str) -> SubmitResult:
             application_id=application_id,
             script_path=pending.script_path,
             queue=pending.queue,
-            submit_time=datetime.utcnow(),
+            submit_time=datetime.now(timezone.utc),
             connection=pending.connection,
             yarn_rm_url=pending.yarn_rm_url,
         )

tests/integration/test_mcp_routes.py

@@ -8,6 +8,7 @@ from fastapi.testclient import TestClient
 from spark_executor.core import connection_store, pending_store
 from spark_executor.core.connection_store import ConnectionStore
 from spark_executor.core.pending_store import PendingStore
+from spark_executor.models import Connection
 from spark_executor.server import app
 from spark_executor.tools import connections, submit
 
@@ -64,6 +65,19 @@ def test_seventeen_tool_routes_registered():
     assert "/update_pending_job" in paths
 
 
+def test_twenty_three_tool_routes_registered():
+    paths = {r.path for r in app.routes}
+    for path in (
+        "/get_external_job_logs",
+        "/get_external_job_status",
+        "/get_external_job_result",
+        "/list_applications",
+        "/fetch_url",
+        "/update_connection",
+    ):
+        assert path in paths, f"missing MCP tool route: {path}"
+
+
 # --- operation_id: pin clean MCP tool names (no auto-generated suffixes) ---
 #
 # fastapi-mcp uses each route's OpenAPI `operationId` as the MCP tool name
@@ -531,3 +545,147 @@ def test_update_pending_job_route_rejects_submitted(tmp_path, monkeypatch):
     )
     assert r.status_code == 400
     assert "only PENDING submissions can be updated" in r.json()["detail"]
+
+
+# --- YarnError -> 502 handler ---
+
+
+def test_yarn_error_returns_502_with_detail(tmp_path, monkeypatch):
+    """When a YARN REST call raises YarnError (host unreachable, YARN
+    returned 4xx/5xx, parse failure), the route must surface HTTP 502
+    with the YarnError message in the detail — not 500 'Internal
+    Server Error' with no info. Mirrors the same fix for fetch_url.
+    """
+    from unittest.mock import patch
+    from spark_executor.core.yarn_client import YarnError
+
+    connection_store.store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+        )
+    )
+    c = TestClient(app)
+    with patch(
+        "spark_executor.tools.status.get_application_status",
+        side_effect=YarnError("YARN connection failed: ConnectError: Connection refused"),
+    ):
+        r = c.post(
+            "/get_job_status",
+            json={"job_id": "a1b2c3d4e5f6"},
+        )
+    assert r.status_code == 502
+    detail = r.json()["detail"]
+    assert "YARN connection failed" in detail
+    assert "Connection refused" in detail
+
+
+def test_external_job_status_returns_502_on_yarn_error(tmp_path):
+    """get_external_job_status uses get_application_status under the
+    hood — same handler, same 502, same detail."""
+    from unittest.mock import patch
+    from spark_executor.core.yarn_client import YarnError
+
+    connection_store.store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+        )
+    )
+    c = TestClient(app)
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_status",
+        side_effect=YarnError("YARN application 'application_xxx' not found"),
+    ):
+        r = c.post(
+            "/get_external_job_status",
+            json={"application_id": "application_1740000000001_0001", "connection_name": "prod"},
+        )
+    assert r.status_code == 502
+    assert "not found" in r.json()["detail"]
+
+
+def test_external_job_result_returns_502_on_yarn_error(tmp_path):
+    """get_external_job_result also uses get_application_status (same
+    underlying YARN endpoint), and exercises the same YarnError path."""
+    from unittest.mock import patch
+    from spark_executor.core.yarn_client import YarnError
+
+    connection_store.store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+        )
+    )
+    c = TestClient(app)
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_status",
+        side_effect=YarnError("YARN connection failed: ConnectError: Connection refused"),
+    ):
+        r = c.post(
+            "/get_external_job_result",
+            json={"application_id": "application_1740000000001_0001", "connection_name": "prod"},
+        )
+    assert r.status_code == 502
+    assert "YARN connection failed" in r.json()["detail"]
+
+
+def test_external_job_logs_returns_502_on_yarn_error(tmp_path):
+    """get_external_job_logs uses get_application_logs — different
+    function, but raises YarnError the same way. Handler must catch
+    it the same way."""
+    from unittest.mock import patch
+    from spark_executor.core.yarn_client import YarnError
+
+    connection_store.store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+        )
+    )
+    c = TestClient(app)
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_logs",
+        side_effect=YarnError("YARN GET logs returned HTTP 500: cluster overloaded"),
+    ):
+        r = c.post(
+            "/get_external_job_logs",
+            json={
+                "application_id": "application_1740000000001_0001",
+                "connection_name": "prod",
+                "tail_chars": 5000,
+            },
+        )
+    assert r.status_code == 502
+    assert "YARN GET logs returned HTTP 500" in r.json()["detail"]
+    assert "cluster overloaded" in r.json()["detail"]
+
+
+def test_list_applications_returns_502_on_yarn_error(tmp_path):
+    """list_applications uses list_applications_yarn — yet another
+    YARN-touching tool. Same YarnError -> 502 contract."""
+    from unittest.mock import patch
+    from spark_executor.core.yarn_client import YarnError
+
+    connection_store.store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+        )
+    )
+    c = TestClient(app)
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        side_effect=YarnError("YARN list applications failed: 503 Service Unavailable"),
+    ):
+        r = c.post(
+            "/list_applications",
+            json={"connection_name": "prod"},
+        )
+    assert r.status_code == 502
+    assert "YARN list applications failed" in r.json()["detail"]

tests/unit/test_connection_tools.py

@@ -1,4 +1,5 @@
 # coding=utf-8
+import json
 from pathlib import Path
 
 import pytest
@@ -120,3 +121,113 @@ def test_delete_connection_returns_status(_fresh_store):
 def test_delete_connection_unknown_raises(_fresh_store):
     with pytest.raises(KeyError):
         connections.delete_connection("missing")
+
+
+def test_save_connection_preserves_url_allowlist_on_existing_record(_fresh_store):
+    connections.save_connection(name="prod", master="yarn", url_allowlist=["ccam*"])
+    out = connections.save_connection(name="prod", master="spark://new:7077")
+    assert out["master"] == "spark://new:7077"
+    assert out["url_allowlist"] == ["ccam*"]
+
+
+def test_update_connection_changes_specified_field(_fresh_store):
+    connections.save_connection(name="prod", master="yarn")
+    out = connections.update_connection(name="prod", master="spark://new:7077")
+    assert out["master"] == "spark://new:7077"
+    assert _fresh_store.get("prod").master == "spark://new:7077"
+
+
+def test_update_connection_keeps_omitted_fields(_fresh_store):
+    connections.save_connection(
+        name="prod",
+        master="yarn",
+        deploy_mode="client",
+        yarn_rm_url="http://rm:8088",
+    )
+    out = connections.update_connection(name="prod", deploy_mode="cluster")
+    assert out["deploy_mode"] == "cluster"
+    assert out["master"] == "yarn"
+    assert out["yarn_rm_url"] == "http://rm:8088"
+
+
+def test_update_connection_with_no_fields_is_noop(_fresh_store):
+    connections.save_connection(name="prod", master="yarn", deploy_mode="client")
+    out = connections.update_connection(name="prod")
+    assert out["master"] == "yarn"
+    assert out["deploy_mode"] == "client"
+
+
+def test_update_connection_changes_url_allowlist(_fresh_store):
+    connections.save_connection(name="prod", master="yarn")
+    out = connections.update_connection(name="prod", url_allowlist=["ccam*"])
+    assert out["url_allowlist"] == ["ccam*"]
+
+
+def test_update_connection_replaces_not_merges_dict(_fresh_store):
+    connections.save_connection(name="prod", master="yarn", spark_conf={"a": "1"})
+    out = connections.update_connection(name="prod", spark_conf={"b": "2"})
+    assert out["spark_conf"] == {"b": "2"}
+
+
+def test_update_connection_replaces_not_merges_url_allowlist(_fresh_store):
+    connections.save_connection(
+        name="prod",
+        master="yarn",
+        url_allowlist=["ccam*"],
+    )
+    out = connections.update_connection(name="prod", url_allowlist=["nm*"])
+    assert out["url_allowlist"] == ["nm*"]
+
+
+def test_update_connection_raises_for_unknown_name(_fresh_store):
+    with pytest.raises(KeyError, match="Connection not found"):
+        connections.update_connection(name="missing", master="yarn")
+
+
+def test_update_connection_validates_patched_connection(_fresh_store):
+    connections.save_connection(name="prod", master="yarn")
+    with pytest.raises(ValueError, match="master must be"):
+        connections.update_connection(name="prod", master="http://bad")
+
+
+def test_update_connection_persists_to_disk(_fresh_store, tmp_path):
+    connections.save_connection(name="prod", master="yarn")
+    connections.update_connection(name="prod", master="spark://new:7077")
+    raw = json.loads((tmp_path / "connections.json").read_text())
+    assert raw["prod"]["master"] == "spark://new:7077"
+
+
+# --- history_server_url ---
+
+def test_save_connection_with_history_server_url(_fresh_store):
+    connections.save_connection(
+        name="prod",
+        master="yarn",
+        history_server_url="http://history.prod.internal:18080",
+    )
+    assert _fresh_store.get("prod").history_server_url == "http://history.prod.internal:18080"
+
+
+def test_save_connection_history_server_url_defaults_to_none(_fresh_store):
+    connections.save_connection(name="prod", master="yarn")
+    assert _fresh_store.get("prod").history_server_url is None
+
+
+def test_update_connection_changes_history_server_url(_fresh_store):
+    connections.save_connection(name="prod", master="yarn")
+    out = connections.update_connection(
+        name="prod",
+        history_server_url="http://history2.prod.internal:18080",
+    )
+    assert out["history_server_url"] == "http://history2.prod.internal:18080"
+    assert _fresh_store.get("prod").history_server_url == "http://history2.prod.internal:18080"
+
+
+def test_update_connection_keeps_history_server_url_when_omitted(_fresh_store):
+    connections.save_connection(
+        name="prod",
+        master="yarn",
+        history_server_url="http://history.prod.internal:18080",
+    )
+    out = connections.update_connection(name="prod", master="spark://new:7077")
+    assert out["history_server_url"] == "http://history.prod.internal:18080"

tests/unit/test_external_jobs.py

@@ -0,0 +1,305 @@
+# coding=utf-8
+import json
+from unittest.mock import patch
+
+import pytest
+
+from spark_executor.core import connection_store
+from spark_executor.core.yarn_client import YarnError
+from spark_executor.models import ApplicationSummary, Connection
+from spark_executor.tools import connections, external_jobs
+from spark_executor.tools.requests import ListApplicationsRequest
+
+
+def _fresh_stores():
+    """Reset connection store singletons for a single test."""
+    store = connection_store.ConnectionStore()
+    connection_store.store = store
+    connections.store = store
+    external_jobs.conn_store = store
+
+
+@pytest.fixture
+def fresh_stores(tmp_path, monkeypatch):
+    """Reset connection store singletons to an isolated tmp_path."""
+    monkeypatch.setattr(connection_store, "DEFAULT_DATA_DIR", str(tmp_path))
+    _fresh_stores()
+
+
+def test_get_external_job_logs_returns_tailed():
+    _fresh_stores()
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    long_log = "LOG" * 3000
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_logs",
+        return_value=long_log,
+    ) as m:
+        out = external_jobs.get_external_job_logs(
+            application_id="application_1", connection_name="prod", tail_chars=100
+        )
+    assert out == long_log[-100:]
+    args = m.call_args.args
+    assert args[0] == "application_1"
+    assert args[1].yarn_rm_url == "http://rm:8088"
+
+
+def test_get_external_job_logs_returns_full_when_short():
+    _fresh_stores()
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    short_log = "short log"
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_logs",
+        return_value=short_log,
+    ):
+        out = external_jobs.get_external_job_logs(
+            application_id="application_1", connection_name="prod", tail_chars=5000
+        )
+    assert out == short_log
+
+
+def test_get_external_job_logs_raises_when_connection_missing():
+    _fresh_stores()
+    with pytest.raises(KeyError, match="Connection not found"):
+        external_jobs.get_external_job_logs(
+            application_id="application_1", connection_name="missing"
+        )
+
+
+def test_get_external_job_status_returns_state():
+    _fresh_stores()
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    raw = json.dumps({"app": {"state": "RUNNING"}})
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_status",
+        return_value=("RUNNING", raw),
+    ) as m:
+        out = external_jobs.get_external_job_status(
+            application_id="application_1", connection_name="prod"
+        )
+    assert out.application_id == "application_1"
+    assert out.state == "RUNNING"
+    assert out.raw == raw
+    args = m.call_args.args
+    assert args[0] == "application_1"
+    assert args[1].yarn_rm_url == "http://rm:8088"
+
+
+def test_get_external_job_status_raises_when_connection_missing():
+    _fresh_stores()
+    with pytest.raises(KeyError, match="Connection not found"):
+        external_jobs.get_external_job_status(
+            application_id="application_1", connection_name="missing"
+        )
+
+
+def test_get_external_job_result_parses_app_fields():
+    _fresh_stores()
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    raw = json.dumps(
+        {
+            "app": {
+                "state": "FINISHED",
+                "finalStatus": "SUCCEEDED",
+                "diagnostics": "",
+                "trackingUrl": "http://rm:8088/proxy/application_1",
+                "startedTime": 100,
+                "finishedTime": 200,
+            }
+        }
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.get_application_status",
+        return_value=("FINISHED", raw),
+    ) as m:
+        out = external_jobs.get_external_job_result(
+            application_id="application_1", connection_name="prod"
+        )
+    assert out.application_id == "application_1"
+    assert out.state == "FINISHED"
+    assert out.final_status == "SUCCEEDED"
+    assert out.diagnostics == ""
+    assert out.tracking_url == "http://rm:8088/proxy/application_1"
+    assert out.started_time == 100
+    assert out.finished_time == 200
+    args = m.call_args.args
+    assert args[0] == "application_1"
+    assert args[1].yarn_rm_url == "http://rm:8088"
+
+
+def test_get_external_job_result_raises_when_connection_missing():
+    _fresh_stores()
+    with pytest.raises(KeyError, match="Connection not found"):
+        external_jobs.get_external_job_result(
+            application_id="application_1", connection_name="missing"
+        )
+
+
+def test_list_applications_returns_summaries(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[
+            {
+                "id": "application_1",
+                "name": "app-one",
+                "user": "alice",
+                "queue": "default",
+                "state": "RUNNING",
+                "finalStatus": "UNDEFINED",
+                "applicationType": "SPARK",
+                "applicationTags": "tag1",
+                "startedTime": 1000,
+                "finishedTime": 0,
+                "trackingUrl": "http://rm:8088/proxy/application_1",
+                "progress": 75.0,
+            },
+            {
+                "id": "application_2",
+                "name": "app-two",
+                "user": "bob",
+                "queue": "research",
+                "state": "FINISHED",
+                "finalStatus": "SUCCEEDED",
+                "applicationType": "SPARK",
+                "applicationTags": "",
+                "startedTime": 2000,
+                "finishedTime": 3000,
+                "trackingUrl": "http://rm:8088/proxy/application_2",
+                "progress": 100.0,
+            },
+        ],
+    ) as m:
+        out = external_jobs.list_applications("prod")
+    assert len(out) == 2
+    assert all(isinstance(item, ApplicationSummary) for item in out)
+    assert out[0].application_id == "application_1"
+    assert out[1].application_id == "application_2"
+    args = m.call_args.args
+    assert args[0].yarn_rm_url == "http://rm:8088"
+
+
+def test_list_applications_passes_state_filter(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[],
+    ) as m:
+        external_jobs.list_applications("prod", state="RUNNING")
+    assert m.call_args.kwargs == {"state": "RUNNING", "queue": None, "limit": 100}
+
+
+def test_list_applications_passes_queue_filter(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[],
+    ) as m:
+        external_jobs.list_applications("prod", queue="research")
+    assert m.call_args.kwargs == {"state": None, "queue": "research", "limit": 100}
+
+
+def test_list_applications_passes_limit_filter(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[],
+    ) as m:
+        external_jobs.list_applications("prod", limit=50)
+    assert m.call_args.kwargs == {"state": None, "queue": None, "limit": 50}
+
+
+def test_list_applications_default_limit_is_100(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[],
+    ) as m:
+        external_jobs.list_applications("prod")
+    assert m.call_args.kwargs == {"state": None, "queue": None, "limit": 100}
+    assert ListApplicationsRequest(connection_name="prod").limit == 100
+
+
+def test_list_applications_returns_empty_list_when_no_apps(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[],
+    ):
+        out = external_jobs.list_applications("prod")
+    assert out == []
+
+
+def test_list_applications_raises_for_missing_connection(fresh_stores):
+    with pytest.raises(KeyError, match="Connection not found"):
+        external_jobs.list_applications("missing")
+
+
+def test_list_applications_maps_yarn_json_to_summary(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    yarn_app = {
+        "id": "application_42",
+        "name": "mapped-app",
+        "user": "carol",
+        "queue": "prod",
+        "state": "ACCEPTED",
+        "finalStatus": "UNDEFINED",
+        "applicationType": "MAPREDUCE",
+        "applicationTags": "batch",
+        "startedTime": 12345,
+        "finishedTime": 0,
+        "trackingUrl": "http://rm:8088/proxy/application_42",
+        "progress": 12.5,
+    }
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        return_value=[yarn_app],
+    ):
+        out = external_jobs.list_applications("prod")
+    assert len(out) == 1
+    summary = out[0]
+    assert summary.application_id == "application_42"
+    assert summary.name == "mapped-app"
+    assert summary.user == "carol"
+    assert summary.queue == "prod"
+    assert summary.state == "ACCEPTED"
+    assert summary.final_status == "UNDEFINED"
+    assert summary.application_type == "MAPREDUCE"
+    assert summary.application_tags == "batch"
+    assert summary.started_time == 12345
+    assert summary.finished_time == 0
+    assert summary.tracking_url == "http://rm:8088/proxy/application_42"
+    assert summary.progress == 12.5
+
+
+def test_list_applications_raises_on_404(fresh_stores):
+    external_jobs.conn_store.save(
+        Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088")
+    )
+    with patch(
+        "spark_executor.tools.external_jobs.list_applications_yarn",
+        side_effect=YarnError("YARN list applications failed: 404"),
+    ):
+        with pytest.raises(YarnError, match="YARN list applications failed"):
+            external_jobs.list_applications("prod")

tests/unit/test_fetch_url.py

@@ -0,0 +1,402 @@
+# coding=utf-8
+from pathlib import Path
+from unittest.mock import patch
+
+import httpx
+import pytest
+from pydantic import ValidationError
+
+from spark_executor.core import connection_store
+from spark_executor.core.connection_store import ConnectionStore
+from spark_executor.models import Connection
+from spark_executor.tools import connections, fetch_url
+from spark_executor.tools.requests import ListApplicationsRequest
+
+
+def _fresh_stores(tmp_path, monkeypatch):
+    """Reset connection store singletons for a single test."""
+    monkeypatch.setattr(connection_store, "DEFAULT_DATA_DIR", str(tmp_path))
+    store = ConnectionStore()
+    monkeypatch.setattr(connection_store, "store", store)
+    connections.store = store
+    fetch_url.conn_store = store
+
+
+@pytest.fixture
+def fresh_stores(tmp_path: Path, monkeypatch):
+    """Reset connection store singletons for a single test."""
+    _fresh_stores(tmp_path, monkeypatch)
+    yield
+
+
+def test_fetch_url_returns_body_and_status(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    resp = httpx.Response(200, text="hello", headers={"content-type": "text/html"})
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url("http://nm01.prod.internal:8042/node", "prod")
+    assert out.url == "http://nm01.prod.internal:8042/node"
+    assert out.status_code == 200
+    assert out.content_type == "text/html"
+    assert out.body == "hello"
+    assert "truncated" not in fetch_url.FetchUrlResult.model_fields
+    assert m.call_count == 1
+
+
+def test_fetch_url_raises_for_missing_connection(fresh_stores):
+    with pytest.raises(KeyError, match="Connection not found"):
+        fetch_url.fetch_url("http://rm.prod.internal:8088/", "missing")
+
+
+def test_fetch_url_passes_auth_from_connection(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="auth",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            auth_type="basic",
+            auth_user="u",
+            auth_password="p",
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    resp = httpx.Response(200, text="ok")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        fetch_url.fetch_url("http://nm01.prod.internal:8042/node", "auth")
+    auth = m.call_args.kwargs["auth"]
+    assert isinstance(auth, httpx.BasicAuth)
+    import base64
+
+    creds = base64.b64decode(auth._auth_header.split()[1]).decode()
+    assert creds == "u:p"
+
+
+def test_fetch_url_passes_ssl_verify_from_connection(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="insecure",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            ssl_verify=False,
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    resp = httpx.Response(200, text="ok")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        fetch_url.fetch_url("http://nm01.prod.internal:8042/node", "insecure")
+    assert m.call_args.kwargs["verify"] is False
+
+
+def test_fetch_url_allows_host_matching_glob_pattern(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="ccam",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    resp = httpx.Response(200, text="hello")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url("http://ccam50:8088/foo", "ccam")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+
+def test_fetch_url_allows_host_matching_any_of_multiple_globs(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["ccam*", "*.prod.internal"],
+        )
+    )
+    resp = httpx.Response(200, text="hello")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url(
+            "http://history.prod.internal:18080/api/v1/info", "prod"
+        )
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+
+def test_fetch_url_glob_does_not_match_unrelated_host(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="ccam",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+        fetch_url.fetch_url("http://evil.com/foo", "ccam")
+
+
+def test_fetch_url_glob_does_not_cross_dot_boundary(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="ccam",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+        fetch_url.fetch_url("http://ccam50.evil.com/", "ccam")
+
+
+def test_fetch_url_glob_match_does_not_require_suffix_overlap(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    resp = httpx.Response(200, text="hello")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url("http://ccam50:8088/", "prod")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+
+def test_fetch_url_accepts_ip_literal_when_in_url_allowlist(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            url_allowlist=["*.*.*.*"],
+        )
+    )
+    resp = httpx.Response(200, text="hello")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url("http://10.0.0.1/secret", "prod")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+
+def test_fetch_url_accepts_https_when_in_url_allowlist(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            url_allowlist=["ccam*.example.com"],
+        )
+    )
+    resp = httpx.Response(200, text="hello")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get", return_value=resp
+    ) as m:
+        out = fetch_url.fetch_url("https://ccam1.example.com/secure", "prod")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+
+def test_fetch_url_rejects_when_url_has_no_host(fresh_stores):
+    with pytest.raises(ValueError, match="URL has no host"):
+        fetch_url._validate_url_host("", ["*"])
+    with pytest.raises(ValueError, match="URL has no host"):
+        fetch_url._validate_url_host("not-a-url", ["*"])
+
+
+def test_fetch_url_rejects_when_url_allowlist_empty(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(name="prod", master="yarn", url_allowlist=[])
+    )
+    with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+        fetch_url.fetch_url("http://anything.com/", "prod")
+
+
+def test_fetch_url_error_message_mentions_url_allowlist(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+        )
+    )
+    with pytest.raises(ValueError, match="url_allowlist"):
+        fetch_url.fetch_url("http://evil.com/foo", "prod")
+
+
+def test_fetch_url_omitted_url_allowlist_defaults_to_empty_and_rejects(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal",
+        )
+    )
+    with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+        fetch_url.fetch_url("http://nm.prod.internal/", "prod")
+
+
+def test_fetch_url_rejects_redirect_to_disallowed_host(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="ccam",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    redirect = httpx.Response(302, headers={"Location": "http://evil.com/"})
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get",
+        return_value=redirect,
+    ) as m:
+        with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+            fetch_url.fetch_url("http://ccam50/foo", "ccam")
+    assert m.call_count == 1
+
+
+def test_fetch_url_follows_redirect_to_allowed_host(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["*.internal"],
+        )
+    )
+    redirect = httpx.Response(
+        302, headers={"Location": "http://other.internal/"}
+    )
+    final = httpx.Response(200, text="ok")
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get",
+        side_effect=[redirect, final],
+    ) as m:
+        out = fetch_url.fetch_url("http://foo.internal/", "prod")
+    assert out.status_code == 200
+    assert out.body == "ok"
+    assert m.call_count == 2
+    assert m.call_args_list[1].args[0] == "http://other.internal/"
+
+
+def test_fetch_url_rejects_redirect_to_ip_literal_not_in_allowlist(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="ccam",
+            master="yarn",
+            yarn_rm_url="http://ccam1:8088",
+            url_allowlist=["ccam*"],
+        )
+    )
+    redirect = httpx.Response(302, headers={"Location": "http://10.0.0.1/"})
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get",
+        return_value=redirect,
+    ) as m:
+        with pytest.raises(ValueError, match="is not in Connection.url_allowlist"):
+            fetch_url.fetch_url("http://ccam50/foo", "ccam")
+    assert m.call_count == 1
+
+
+def test_list_applications_request_limit_bounds():
+    assert ListApplicationsRequest(connection_name="prod", limit=10000).limit == 10000
+    with pytest.raises(ValidationError):
+        ListApplicationsRequest(connection_name="prod", limit=0)
+    with pytest.raises(ValidationError):
+        ListApplicationsRequest(connection_name="prod", limit=10001)
+
+
+# --- Network error handling (httpx.HTTPError -> 400 with detail) ---
+
+
+def test_fetch_url_raises_400_with_detail_on_connect_error(fresh_stores):
+    """When httpx.get raises ConnectError (host unreachable / port closed),
+    fetch_url must raise ValueError (-> 400) with the exception class
+    and message in the detail. Previously this bubbled up as a bare
+    500 Internal Server Error with no info."""
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get",
+        side_effect=httpx.ConnectError("Connection refused"),
+    ):
+        with pytest.raises(ValueError) as ei:
+            fetch_url.fetch_url("http://nm01.prod.internal:8042/", "prod")
+    msg = str(ei.value)
+    assert "ConnectError" in msg
+    assert "Connection refused" in msg
+    assert "nm01.prod.internal" in msg
+    # Cause chain preserved for loguru
+    assert isinstance(ei.value.__cause__, httpx.ConnectError)
+
+
+def test_fetch_url_raises_400_with_detail_on_timeout(fresh_stores):
+    """When httpx.get raises TimeoutException (request exceeded 30s),
+    fetch_url must raise ValueError with the exception details surfaced."""
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    with patch(
+        "spark_executor.tools.fetch_url.httpx.get",
+        side_effect=httpx.ReadTimeout("Timed out reading"),
+    ):
+        with pytest.raises(ValueError) as ei:
+            fetch_url.fetch_url("http://nm01.prod.internal:8042/", "prod")
+    msg = str(ei.value)
+    assert "ReadTimeout" in msg
+    assert "Timed out reading" in msg
+    assert isinstance(ei.value.__cause__, httpx.ReadTimeout)
+
+
+def test_fetch_url_returns_body_for_4xx_5xx_upstream(fresh_stores):
+    """Upstream HTTP errors (4xx/5xx responses that DID come back) are
+    NOT translated to ValueError — the FetchUrlResult carries the status
+    code and body so the LLM can see what the server actually said. This
+    is the intentional contrast with the no-response-at-all case."""
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal:8088",
+            url_allowlist=["*.prod.internal"],
+        )
+    )
+    resp = httpx.Response(503, text="Service Unavailable - try again later")
+    with patch("spark_executor.tools.fetch_url.httpx.get", return_value=resp):
+        out = fetch_url.fetch_url("http://nm01.prod.internal:8042/", "prod")
+    assert out.status_code == 503
+    assert "Service Unavailable" in out.body

tests/unit/test_job_file.py

@@ -118,25 +118,17 @@ def test_update_rejects_missing_file(tmp_path: Path):
         update_job_file(str(tmp_path / "nope.py"), "x\n")
 
 
-def test_update_rejects_oversized_content(tmp_path: Path, monkeypatch):
-    """Cap at 1 MB so the MCP response stays bounded."""
+def test_update_accepts_content_larger_than_former_1mb_cap(tmp_path: Path):
+    """The 1 MB cap was removed (commit a5e6d1f and following). Content
+    larger than the old cap must now be accepted; size is bounded by
+    the MCP transport, not the tool."""
     config.settings.jobs_dir = str(tmp_path)
     p = tmp_path / "big.py"
     p.write_text("# small\n")
-    # Synthesize 2 MB of content (don't actually write 2 MB to disk)
     big = "x" * (2 * 1024 * 1024)
-    with pytest.raises(ScriptFileError, match="too large"):
-        update_job_file(str(p), big)
-
-
-def test_update_rejects_1mb_plus_1_byte(tmp_path: Path):
-    """Exactly at the boundary: 1 MB + 1 byte must be rejected."""
-    config.settings.jobs_dir = str(tmp_path)
-    p = tmp_path / "x.py"
-    p.write_text("# t\n")
-    just_over = "x" * (1024 * 1024 + 1)
-    with pytest.raises(ScriptFileError, match="too large"):
-        update_job_file(str(p), just_over)
+    out = update_job_file(str(p), big)
+    assert out["bytes_written"] == len(big)
+    assert p.read_text() == big
 
 
 # --- round-trip: write -> read -> update -> read ---

tests/unit/test_kill_tool.py

@@ -63,6 +63,14 @@ def test_kill_job_raises_for_unknown_job():
         kill.kill_job("missing")
 
 
+def test_kill_job_raises_400_for_external_application_id(fresh_stores):
+    """Input that looks like a YARN application_id but is not in the local
+    JobStore must raise ValueError (-> 400) — kill_job has no external
+    equivalent, so the error points to the YARN CLI / UI."""
+    with pytest.raises(ValueError, match="YARN CLI"):
+        kill.kill_job("application_17400000001_0001")
+
+
 def test_kill_job_raises_when_connection_missing():
     _fresh_stores()
     kill.store.put(

tests/unit/test_logs_tool.py

@@ -68,6 +68,14 @@ def test_get_job_logs_raises_for_unknown_job():
         logs.get_job_logs("missing")
 
 
+def test_get_job_logs_raises_400_for_external_application_id(fresh_stores):
+    """Input that looks like a YARN application_id but is not in the local
+    JobStore must raise ValueError (-> 400) with a hint to use the
+    external tool, NOT a generic KeyError (-> 404)."""
+    with pytest.raises(ValueError, match="get_external_job_logs"):
+        logs.get_job_logs("application_17400000001_0001")
+
+
 def test_get_job_logs_raises_when_connection_missing(fresh_stores):
     logs.store.put(
         Job(

tests/unit/test_result_tool.py

@@ -136,6 +136,14 @@ def test_result_raises_keyerror_for_unknown_job():
     assert "application_id" in msg
 
 
+def test_result_raises_400_for_external_application_id(fresh_stores):
+    """Input that looks like a YARN application_id but is not in the local
+    JobStore must raise ValueError (-> 400) with a hint to use the
+    external tool, NOT a generic KeyError (-> 404)."""
+    with pytest.raises(ValueError, match="get_external_job_result"):
+        result.get_job_result("application_17400000001_0001")
+
+
 def test_result_raises_when_connection_missing():
     _fresh_stores()
     result.store.put(

tests/unit/test_status_tool.py

@@ -66,6 +66,14 @@ def test_get_job_status_raises_for_unknown_job():
         status.get_job_status("missing")
 
 
+def test_get_job_status_raises_400_for_external_application_id(fresh_stores):
+    """Input that looks like a YARN application_id but is not in the local
+    JobStore must raise ValueError (-> 400) with a hint to use the
+    external tool, NOT a generic KeyError (-> 404)."""
+    with pytest.raises(ValueError, match="get_external_job_status"):
+        status.get_job_status("application_17400000001_0001")
+
+
 def test_get_job_status_raises_when_connection_missing():
     _fresh_stores()
     status.store.put(