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.
MCP tools connected and enabled but never surfaced into the agent's
session toolset on the desktop app + dashboard WebUI (#51587).
There are two independent background MCP discovery thread owners by
surface: tui_gateway.entry (stdio 'hermes --tui') and hermes_cli.mcp_startup
(desktop app + dashboard WS sidecar via tui_gateway/ws.py, and 'hermes
dashboard'). The late-refresh scheduler gates on
tui_gateway.entry.mcp_discovery_in_flight(), which read ONLY the entry
thread global. On the desktop/dashboard surfaces that global is None, so a
server slower than the bounded build-time wait never triggered a late
refresh and its tools stayed invisible for the whole session.
Make mcp_discovery_in_flight() / join_mcp_discovery() consult BOTH thread
owners. Adds the matching in-flight/join helpers to hermes_cli.mcp_startup
and has tui_gateway.entry delegate to them as a second owner.
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.
Second review pass (Codex + Hermes subagent). Codex reproduced a real race with
a two-thread harness; both converged on the remaining issues.
- Generation-aware publish (fixes a lost-update race): two refresh callers (the
late-refresh daemon and the between-turns prologue around turn 1) could each
compute a snapshot outside the lock; a SLOWER caller holding an OLDER registry
generation could acquire the publish lock after a newer caller and clobber it,
deleting just-landed tools. refresh_agent_mcp_tools now captures
registry._generation before computing and refuses to publish a stale set;
agent._tool_snapshot_generation tracks the published generation.
- Context-engine routing names (_context_engine_tool_names) are now staged on a
local and published atomically with the snapshot, and only claimed when this
rebuild actually appended the schema — matching agent_init's dedup so a
registry/plugin tool of the same name keeps its own dispatch. (Previously
mutated live, before the publish lock, and on no-change refreshes.)
- CLI /reload-mcp: self.enabled_toolsets is resolved once at startup, so a
server newly ENABLED in config mid-session wasn't picked up (TUI already
re-resolved). Merge now-connected MCP server names into the override (unless
the user pinned all/*), mirroring startup, and keep self.enabled_toolsets in
sync. Closes the CLI/TUI parity hole.
- ACP (acp_adapter/server.py) routed through the shared helper — it was a 5th
sibling rebuild that re-injected memory tools but NOT context-engine tools and
bypassed the atomic/name-diff path (inert today, fragile).
- mcp_startup._resolve_discovery_timeout pulls its default from DEFAULT_CONFIG
(single source of truth) instead of a stale hardcoded 5.0 literal.
- Tests: stale-generation-no-clobber, _skip_mcp_refresh honored, timeout
fallback uses DEFAULT_CONFIG.
MCP servers that connect after the agent's one-time tool snapshot were
invisible for the whole session. Two root causes, fixed together:
1. The startup discovery wait was a flat 0.75s. HTTP/OAuth servers
commonly take 2-6s on a cold connect, so they missed the window and
their tools never entered the agent's snapshot. `thread.join(timeout)`
already returns the instant discovery completes, so raising the bound
costs ~0s for the common case (no MCP / fast servers) and only ever
blocks for a genuinely-pending server, capped so a dead server can't
freeze startup. The bound is now configurable via
`mcp_discovery_timeout` (config.yaml, default 5.0s).
2. Three call sites duplicated the agent tool-snapshot rebuild (the TUI
`reload.mcp` RPC, the gateway reload, and the TUI late-binding refresh
thread), and the late-refresh detected changes by tool COUNT — missing
an equal-size add/remove swap. Consolidated into one shared
`tools.mcp_tool.refresh_agent_mcp_tools(agent)` helper that diffs by
tool NAME, mutates the agent under a lock (thread-safe), and respects
the agent's own enabled/disabled toolsets.
The late-binding refresh keeps its pre-first-turn cache-safety guard:
it never rebuilds the tool list once a turn has started, so the cached
prompt prefix is never invalidated mid-conversation.
Tests: new tests/tools/test_refresh_agent_mcp_tools.py covers the
name-based diff, in-place mutation, agent-scoped filtering, thread
safety, and the config-driven discovery bound (incl. instant-return
when nothing is pending). 75 passed across the touched areas.
