feat(mcp): restore Inspector E2E browser test for telepath mcp subcommand

[tarotene]

Background

Issue #78 specified the AppError payload format. This issue originally tracked restoring a Playwright-based MCP Inspector UI E2E test for the telepath mcp subcommand. The original E2E infrastructure was removed during PR #33 and the crate was merged into the unified tools/telepath CLI (PR #92).

Scope revision (2026-05-30)

After investigation, the original acceptance criteria cannot be met as stated:

1. Transport gap: The restored Inspector UI test requires --transport loopback, which does not exist in the unified tools/telepath CLI. The current CLI supports rtt and serial only.
2. Known flaky: Inspector UI v0.21.x has a known React render-timing issue where tools/list RPC succeeds but the Tools panel never repopulates — "pass reliably" is not achievable without debugging Inspector internals.
3. Headless coverage already exists: tools/telepath/tests/serial_pty_smoke.rs::serial_pty_mcp_ping_round_trip covers the same acceptance criteria (ping appears in list_tools, call returns 3735928559) over a real hardware-free wire path.

Revised scope: options

• (a) Remove from v0.3.0 milestone. Restore the Inspector UI browser test in a separate issue once:
  • --transport loopback or an equivalent hardware-free CLI entry point exists
  • Inspector UI flakiness is diagnosed against the current Inspector release via playwright codegen http://localhost:6274
• (b) Restore headless mcp.spec.ts only (JSON-RPC over stdio, no browser) + just mcp-e2e recipe + manual "Try it with Inspector" section in docs/mcp-integration.md. This satisfies the spirit of the issue (E2E coverage exists) while acknowledging the UI flakiness. Note: the Rust test serial_pty_smoke.rs already provides equivalent coverage.

Current status

docs/mcp-integration.md line 133:

Inspector E2E browser test removed during initial PR; recovery tracked in #42

This reference will be updated when a decision is made on option (a) or (b).

References

• PR feat(mcp): Stage D — telepath-mcp-server frontend #33: initial MCP server implementation (Inspector E2E removed)
• PR Consolidate telepath-shell and telepath-mcp-server into unified CLI #92: unified CLI consolidation
• tools/telepath/tests/serial_pty_smoke.rs — existing headless MCP E2E coverage
• MCP Inspector: https://github.com/modelcontextprotocol/inspector

[tarotene]

Update (2026-05-25): Since this issue was filed, the MCP server transport architecture changed significantly (PR #66): the in-process loopback transport was removed and build-time Cargo features now select between RTT and serial transports. The recovery steps in this issue are still directionally correct, but the --transport loopback invocation examples are now obsolete — the hardware-free path uses host-pty-server + serial feature instead. Capture this context when re-attempting the Inspector E2E integration.