Recover browser MCP calls after broken-pipe transport failures

[swordfish444]

Summary

• make MCP browser-tool recovery robust when the transport dies with Transport send error / Broken pipe (not just literal Transport closed)
• keep one-shot restart + retry behavior in McpConnectionManager
• add targeted unit coverage for transport-error matching

Why

On macOS, browser MCP transports (notably chrome-devtools and playwright) can die mid-session, surfacing as broken-pipe send errors. The previous matcher only recognized Transport closed, so recovery did not trigger for these common failures.

Changes

• broadened is_transport_closed_error(...) in
  codex-rs/core/src/mcp_connection_manager.rs to match:
  • transport closed
  • transport send error
  • transport receive error
  • transport errors containing broken pipe / connection reset
• added tests:
  • is_transport_closed_error_matches_transport_closed
  • is_transport_closed_error_matches_transport_broken_pipe
  • is_transport_closed_error_does_not_match_non_transport_error

Validation

Automated

• just fmt
• just fix -p codex-core
• cargo test -p codex-core is_transport_closed_error
• cargo test -p codex-core mcp_tool_call_recovers_from_transport_closed

End-to-end (macOS, patched app-server)

Server:

• ./target/debug/codex app-server --listen ws://127.0.0.1:4322

Chrome DevTools MCP:

1. first turn tool call succeeds (mcp__chrome-devtools__new_page)
2. force-close child MCP process (kill -9 10162)
3. second turn in same thread succeeds without app restart
4. server log confirms recovery path:
   • MCP transport closed for server chrome-devtools; restarting

Playwright MCP:

1. first turn tool call succeeds (mcp__playwright__browser_tabs)
2. force-close child MCP process (kill -9 10154 11782)
3. second turn in same thread succeeds without app restart
4. server log confirms recovery path:
   • MCP transport closed for server playwright; restarting

Related: #6649

[swordfish444]

Adding additional routing based on issue history + MCP ownership signals: @etraut-openai @mzeng-openai. This PR includes macOS E2E repro + validation for browser MCP transport drops (Chrome DevTools and Playwright), with forced process-kill recovery in-session and no Codex app restart required.

[etraut-openai]

@swordfish444 Please do not submit PRs. If you want to suggest a new feature, file a feature request.