[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/.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)