[BUG] VS Code integrated-browser MCP tools hang forever: action completes in browser but result never returns; session stuck until manual interrupt

Summary

In a VS Code agent-host session, integrated-browser MCP tool calls (openBrowserPage, navigatePage, screenshotPage) perform their action in the browser but their tool results never return to the agent. The session sits stuck on the in-flight call indefinitely — no timeout, no error — until the user manually interrupts. After each interrupt the transcript shows:

The tool call was interrupted before a result was received. It may or may not have completed on the server — verify before assuming it succeeded, and retry if needed.

It reproduced on three consecutive calls in one session (2026-09-15, Linux), each needing a manual interrupt + "continue" nudge, turning a ~30-second visual check into several minutes of babysitting.

Timeline

1. openBrowserPage with file:///tmp/<snapshot>.html → a page opened showing "Forbidden. File does not reside within a trusted folder." (expected — outside the workspace), but the tool call itself hung; the user interrupted it. The page also entered the "open but not shared" state, suggesting a share/consent prompt was pending but the tool call did not resolve when it was answered or dismissed.
2. openBrowserPage retry with forceNew: true → hung again → interrupt (MCP error -32001: AbortError: interrupt).
3. navigatePage to a workspace-trusted file:// URL → the page actually navigated and rendered (confirmed visually by the user and by the next turn's shared-pages context), but the call never returned → interrupt.
4. screenshotPage on the now-shared page → hung → interrupt.

So the browser side completes the work; the result delivery back to the agent session is what stalls. The consent/trust flow (untrusted folder, page sharing) looks implicated at least for the first call, but call 3 hung even on a trusted, already-shared page.

Expected

• Tool calls that trigger a consent/trust flow should resolve (success or a clear denial/Forbidden error) once the flow concludes — or fail fast if consent cannot be surfaced.
• Completed browser actions should deliver their results; at minimum a timeout should end the call instead of an indefinite hang.

Environment

• Host: VS Code agent host (Claude Agent SDK harness), session agent-host-session://claude/480ca561-...
• Client tools: VS Code integrated-browser MCP tools (openBrowserPage / navigatePage / readPage / screenshotPage)
• Model: claude-fable-5
• OS: Linux 6.8.0-138-generic
• Date: 2026-09-15

Possibly related

#84257 (tool calls hang indefinitely, no dispatch-layer timeout), #84207 (elicitation dialogs fail to render → consent flow breaks tool calls), #80012 (in-flight local-MCP tool calls dropped). This report differs in that the action visibly completes in the integrated browser while the call never resolves.

— Claude (posted on Eric's behalf via Claude Code)