start_background_mcp_discovery() sets _mcp_discovery_started once and never
resets it. If the first background run exits without connecting any MCP
server (startup cancellation, OOM restart, transient network failure), every
later call returns immediately and the process is permanently stuck with
zero MCP tools until a full restart.
Fix: when discovery is marked started but the thread is dead and no server
is connected, reset the flag and spawn a fresh discovery thread. Also log a
WARNING when a discovery run completes with zero connected servers, so the
condition is visible instead of silent.
Caught in production on a long-running gateway fleet where a gateway
restarted under memory pressure and came back with all MCP tools missing.
The backgrounding-contract test (test_prepare_agent_startup_backgrounds_
blocking_mcp_for_chat) failed intermittently on loaded CI shards: it stubs
tools.mcp_tool.discover_mcp_tools but NOT tools.mcp_oauth, so the background
discovery thread paid the real, cold ~0.75s 'import tools.mcp_oauth' (added by
this PR's _discover_mcp_tools_without_interactive_oauth) before calling the
stubbed discovery. On a slow/loaded runner that import plus thread scheduling
exceeded the 1.0s polling deadline, leaving calls['mcp'] == 0.
Fix: stub tools.mcp_oauth with a nullcontext suppress_interactive_oauth (the
same no-op production falls back to when mcp_oauth is unavailable), so the
test exercises the backgrounding contract without paying an unrelated cold
import in its timing window. Bumped the poll deadline 1.0s -> 3.0s as
belt-and-suspenders. Production behaviour is unchanged; the import cost was
always off the main thread.
Verified: 5/5 pass repeatedly via scripts/run_tests.sh (per-file isolation,
matching CI), ruff clean.
When an MCP server requires OAuth, the interactive `hermes` TUI froze on
startup: background MCP discovery hit the OAuth flow, which on an interactive
TTY spawns a daemon thread doing a blocking `sys.stdin.readline()` (the
"paste the redirect URL" fallback in mcp_oauth._wait_for_callback). That
thread competes with the TUI's own stdin reader for the same terminal, so
keystrokes get swallowed and the TUI appears frozen (up to the 300s OAuth
timeout). Reported symptom: "MCP OAuth: authorization required / Open this URL
... the tui is freezing, not respond to typing."
Add a thread-local `suppress_interactive_oauth()` context manager in
tools/mcp_oauth.py; `_is_interactive()` returns False while it's active, so the
stdin paste-thread and prompt are never created. Background discovery
(hermes_cli/mcp_startup.py, tui_gateway/entry.py) now runs discovery inside
that context, so OAuth-requiring servers soft-skip (raise
OAuthNonInteractiveError, already handled) instead of stealing the TUI's stdin.
A real `hermes mcp login` on the main thread is unaffected (thread-local).
Salvaged from #35945 by @zapabob (authorship preserved via cherry-pick;
resolved a conflict against main's new mcp_discovery_timeout / wait_for_mcp_
discovery refactor, keeping both). Verified E2E: with suppression the paste
prompt is NOT printed and no stdin thread spawns (raises OAuthNonInteractive
soft-skip); without it the prompt shows (the freeze). Mutation-verified
(removing the suppress check in _is_interactive fails the regression test).
76 tests pass, ruff clean.
Closes#35927.
SELF-REVIEW FIX: the original #35945 used threading.local(), which does NOT
propagate to the dedicated mcp-event-loop thread where OAuth actually runs
(discover_mcp_tools dispatches the connect via run_coroutine_threadsafe), so
the suppression was a NO-OP in production (the tests passed only by stubbing
out the cross-thread dispatch). Converted to a contextvars.ContextVar, which
asyncio copies onto the scheduled coroutine — empirically verified suppression
now holds on the mcp-event-loop thread through the real _run_on_mcp_loop path.
Added a cross-thread regression test (fails on threading.local, passes on the
ContextVar) so the no-op can't regress.
