feat: Copy / Insert / Replace buttons on assistant messages

Each assistant message in the inline prompt history now renders a
small toolbar with three action buttons:

  📋 复制  — copy the rendered assistant content (the markdown
             source, not the rendered HTML) to the clipboard via
             navigator.clipboard.writeText, with a fallback to a
             hidden textarea + execCommand for non-secure contexts.
  ↪ 插入  — insert the content at the current editor cursor. Uses
             cell.editor.getCursorPosition() + the cell source to
             compute the offset, then sharedModel.setSource to splice
             the text in. Falls back to appending if the cursor can't
             be read.
  ⟳ 替换  — replace the entire cell source with the assistant content
             via sharedModel.setSource.

User messages and the textarea/send/cancel UI are unchanged; the
toolbar only appears on rendered assistant (markdown) messages.

Implementation:
  - OpenCodeInlinePrompt now stores the cell (private _cell) so the
    button handlers can act on it.
  - New private methods: _copyToClipboard, _insertAtCursor,
    _replaceCell. Each shows a Notification on success/failure.
  - Added import { Notification } from '@jupyterlab/apputils' (the
    prompt file didn't import it before; cell_actions does, so the
    test mock already provides the static methods).
  - style/base.css: .opencode-msg-toolbar (flex row) and
    .opencode-msg-btn (small bordered button) styles.
  - Test fake cell now has an editor stub returning cursor (0,0) so
    the Insert test produces a deterministic offset. jsdom lacks
    navigator.clipboard; the test stubs it globally.

Tests:
  - jest 33/33 (was 29; +4 new: toolbar renders 3 buttons only on
    assistant, Replace sets source, Insert splices at offset 0, Copy
    calls clipboard.writeText with the content).
  - pytest 37/37 (no server changes).

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

src/components/opencode_inline_prompt.ts

@@ -10,6 +10,7 @@
  * (the AI reply is rendered as markdown inside this history area).
  */
 import { CodeCell } from '@jupyterlab/cells';
+import { Notification } from '@jupyterlab/apputils';
 import { Widget } from '@lumino/widgets';
 import { marked } from 'marked';
 
@@ -65,6 +66,7 @@ function pickDefaultModelId(
 }
 
 export class OpenCodeInlinePrompt extends Widget {
+  private _cell: CodeCell;
   private _textarea: HTMLTextAreaElement;
   private _sendBtn: HTMLButtonElement;
   private _cancelBtn: HTMLButtonElement;
@@ -75,10 +77,11 @@ export class OpenCodeInlinePrompt extends Widget {
   private _historyEl: HTMLDivElement;
 
   constructor(
-    _cell: CodeCell,
+    cell: CodeCell,
     options: IOpenCodeInlinePromptOptions
   ) {
     super();
+    this._cell = cell;
     this.addClass('opencode-inline-prompt');
 
     const flat = flattenProviders(options.providers);
@@ -222,10 +225,124 @@ export class OpenCodeInlinePrompt extends Widget {
       if (msg.role === 'user') {
         wrap.textContent = msg.content;
       } else {
-        wrap.innerHTML = marked.parse(msg.content) as string;
+        // Assistant: small action toolbar (copy / insert at cursor /
+        // replace cell) + the rendered markdown content below.
+        const toolbar = document.createElement('div');
+        toolbar.className = 'opencode-msg-toolbar';
+        const content = msg.content;
+        const mkBtn = (label: string, title: string, onClick: () => void) => {
+          const b = document.createElement('button');
+          b.type = 'button';
+          b.className = 'opencode-msg-btn';
+          b.textContent = label;
+          b.title = title;
+          b.addEventListener('click', onClick);
+          return b;
+        };
+        toolbar.appendChild(
+          mkBtn('📋 复制', '复制内容到剪贴板', () => {
+            void this._copyToClipboard(content);
+          })
+        );
+        toolbar.appendChild(
+          mkBtn('↪ 插入', '在光标位置插入内容', () => {
+            this._insertAtCursor(content);
+          })
+        );
+        toolbar.appendChild(
+          mkBtn('⟳ 替换', '替换整个单元格内容', () => {
+            this._replaceCell(content);
+          })
+        );
+        wrap.appendChild(toolbar);
+
+        const rendered = document.createElement('div');
+        rendered.className = 'opencode-msg-content';
+        rendered.innerHTML = marked.parse(content) as string;
+        wrap.appendChild(rendered);
       }
       this._historyEl.appendChild(wrap);
     }
     this._historyEl.scrollTop = this._historyEl.scrollHeight;
   }
+
+  /**
+   * Copy the given text to the clipboard. Prefers navigator.clipboard
+   * (available in secure contexts incl. JupyterLab). Falls back to a
+   * hidden textarea + execCommand for older / non-secure contexts.
+   */
+  private async _copyToClipboard(text: string): Promise<void> {
+    try {
+      if (
+        typeof navigator !== 'undefined' &&
+        navigator.clipboard &&
+        typeof navigator.clipboard.writeText === 'function'
+      ) {
+        await navigator.clipboard.writeText(text);
+        Notification.info('已复制到剪贴板');
+        return;
+      }
+      const ta = document.createElement('textarea');
+      ta.value = text;
+      ta.style.position = 'fixed';
+      ta.style.opacity = '0';
+      this.node.appendChild(ta);
+      ta.select();
+      document.execCommand('copy');
+      ta.remove();
+      Notification.info('已复制到剪贴板');
+    } catch (e) {
+      Notification.error('复制失败: ' + (e as Error).message);
+    }
+  }
+
+  /**
+   * Insert text at the current editor cursor position. If the cell has
+   * no editor (e.g. a non-Code cell) or the cursor can't be read, falls
+   * back to appending at the end of the cell.
+   */
+  private _insertAtCursor(text: string): void {
+    const cell = this._cell;
+    if (!cell || !cell.model || !cell.model.sharedModel) {
+      return;
+    }
+    const sharedModel = cell.model.sharedModel;
+    const source = sharedModel.getSource() as string;
+    let offset = source.length;
+    try {
+      const editor = (cell as any).editor;
+      const pos = editor && editor.getCursorPosition
+        ? editor.getCursorPosition()
+        : null;
+      if (pos) {
+        const lines = source.split('\n');
+        const line = Math.max(0, Math.min(pos.line, lines.length - 1));
+        const col = Math.max(
+          0,
+          Math.min(pos.column, (lines[line] ?? '').length)
+        );
+        offset = 0;
+        for (let i = 0; i < line; i++) {
+          offset += lines[i].length + 1;
+        }
+        offset += col;
+      }
+    } catch {
+      // Fall back to append on any error reading the cursor.
+      offset = source.length;
+    }
+    const newSource = source.slice(0, offset) + text + source.slice(offset);
+    sharedModel.setSource(newSource);
+    Notification.info('已插入到光标位置');
+  }
+
+  /** Replace the entire cell source with the given text. */
+  private _replaceCell(text: string): void {
+    const cell = this._cell;
+    if (!cell || !cell.model || !cell.model.sharedModel) {
+      return;
+    }
+    cell.model.sharedModel.setSource(text);
+    Notification.info('已替换单元格内容');
+  }
 }