feat(fetch_url): per-Connection allowed_url_hosts glob allowlist

The default 'URL host shares >= 2 labels of suffix with yarn_rm_url
host' rule is too strict for clusters whose hostnames are single-label
(e.g. 'ccam1' through 'ccam99'). The user's cluster is reachable at
http://ccam1:8088, and they want fetch_url to work for any ccamN
host — but ccam1 and ccam50 share 0 suffix labels, so the existing
rule rejects everything.

Add an opt-in allowlist field on Connection:

  allowed_url_hosts: list[str] | None

Each entry is an fnmatch glob pattern. The URL host is allowed if it
matches ANY pattern, regardless of the suffix rule. Save a Connection
with ['ccam*'] to allow ccam1, ccam2, ..., ccam99.

SSRF safety: the implementation does NOT use vanilla fnmatch on the
flat host string (because '*' in fnmatch crosses '.', so 'ccam*' would
match 'ccam50.evil.com' — a security hole). Instead, both the pattern
and the host are split on '.' and matched LABEL-BY-LABEL with the
label counts required to match exactly. So 'ccam*' matches 'ccam50'
but NOT 'ccam50.evil.com' (different label counts).

Test coverage:
- 8 new tests in tests/unit/test_fetch_url.py (glob allow, glob deny,
  dot-boundary SSRF test, multiple globs, empty list, None fallback,
  error message hint)
- All 21 fetch_url tests pass; 377 total.

- spark_executor/models.py: Connection.allowed_url_hosts (with description)
- spark_executor/tools/requests.py: SaveConnectionRequest.allowed_url_hosts
- spark_executor/tools/fetch_url.py: new _host_matches_any_glob helper;
  _validate_url_host now takes allowed_hosts and checks globs BEFORE
  the suffix rule
- tests/unit/test_fetch_url.py: 8 new tests
- README.md: fetch_url row mentions the allowlist

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/unit/test_fetch_url.py

@@ -1,4 +1,5 @@
 # coding=utf-8
+from pathlib import Path
 from unittest.mock import patch
 
 import httpx
@@ -19,6 +20,12 @@ def _fresh_stores(tmp_path, monkeypatch):
     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(tmp_path, monkeypatch):
     _fresh_stores(tmp_path, monkeypatch)
     fetch_url.conn_store.save(
@@ -162,3 +169,118 @@ def test_fetch_url_follows_redirects(tmp_path, monkeypatch):
     with patch("spark_executor.tools.fetch_url.httpx.get", return_value=resp) as m:
         fetch_url.fetch_url("http://nm01.prod.internal:8042/node", "prod")
     assert m.call_args.kwargs["follow_redirects"] is True
+
+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",
+            allowed_url_hosts=["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",
+            allowed_url_hosts=["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",
+            allowed_url_hosts=["ccam*"],
+        )
+    )
+    with pytest.raises(ValueError, match="does not share enough suffix|no allowed_url_hosts pattern matched"):
+        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",
+            allowed_url_hosts=["ccam*"],
+        )
+    )
+    with pytest.raises(ValueError, match="does not share enough suffix"):
+        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",
+            allowed_url_hosts=["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_empty_allowed_hosts_falls_back_to_suffix_rule(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal",
+            allowed_url_hosts=[],
+        )
+    )
+    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://nm.prod.internal/", "prod")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+def test_fetch_url_none_allowed_hosts_falls_back_to_suffix_rule(fresh_stores):
+    fetch_url.conn_store.save(
+        Connection(
+            name="prod",
+            master="yarn",
+            yarn_rm_url="http://rm.prod.internal",
+            allowed_url_hosts=None,
+        )
+    )
+    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://nm.prod.internal/", "prod")
+    assert out.status_code == 200
+    assert out.body == "hello"
+    assert m.call_count == 1
+
+def test_fetch_url_error_message_hints_at_allowed_url_hosts(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="allowed_url_hosts"):
+        fetch_url.fetch_url("http://evil.com/foo", "prod")