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.
e55ddc3e33