perf(tui): stop slow/dead MCP servers from freezing TUI startup#35273
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The 'summoning hermes…' phase blocked on gateway.ready, which ran MCP tool discovery inline. Any configured-but-unreachable MCP server burned its full connect-retry backoff (1+2+4s ≈ 7s) before the composer appeared — startup went from instant to ~7.5s of dead air for anyone with a down stdio/http server in mcp_servers. Move discovery into a background daemon thread so gateway.ready fires immediately; tools register into the shared registry as servers connect, and the agent isn't built until the first prompt. Measured spawn→ready: ~7500ms → ~115ms (dead twozero_td server in config). Also drop rich.console + prompt_toolkit off banner.py's import path (lazy-imported inside cprint/build_welcome_banner). tui_gateway.server imports banner only to reach the lightweight prefetch_update_check helper; the eager rich/pt imports added ~45ms before gateway.ready for no benefit. tui_gateway.server import: ~115ms → ~69ms.
Contributor
🔎 Lint report:
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| Rule | Count |
|---|---|
invalid-assignment |
1 |
First entries
tests/tui_gateway/test_wait_for_mcp_discovery.py:70: [invalid-assignment] invalid-assignment: Object of type `Thread` is not assignable to attribute `_mcp_discovery_thread` of type `None`
✅ Fixed issues: none
Unchanged: 4929 pre-existing issues carried over.
Diagnostics are surfaced as warnings — this check never fails the build.
Collaborator
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Salvage of #35245 (by @kshitijk4poor) cherry-picked onto current main. Competes with #32811 (background MCP discovery via daemon thread). Both address the same startup blocking pattern first fixed in #16899 (module-level side effect) and #19326 (async discovery). |
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Summary
TUI startup no longer freezes on a configured-but-dead MCP server. Discovery moves to a background daemon thread so
gateway.readyfires immediately (~7,500ms → ~115ms with a dead server), with a bounded first-build wait so reachable servers still land in the tool snapshot.Salvage of #35245 by @kshitijk4poor, cherry-picked onto current
main(authorship preserved).Changes
tui_gateway/entry.py: rundiscover_mcp_tools()in a daemon thread; exposewait_for_mcp_discovery(timeout=0.75); log background failures withexc_info=Trueinstead of swallowing.tui_gateway/server.py:_make_agentbriefly joins discovery (bounded) before the first agent build, since AIAgent snapshots its tool list once and never re-reads./reload-mcpnow actually rebuilds the cached agent's tool snapshot (the oldhasattr(agent, "refresh_tools")guard was dead code — no such method exists on main), mirroringgateway/run.py::_execute_mcp_reload.hermes_cli/banner.py: lazyrich/prompt_toolkitimports (~45ms off the TUI critical path;Consoleannotation underTYPE_CHECKING).tests/tui_gateway/test_wait_for_mcp_discovery.py: 4 new tests (no-thread no-op, finished no-op, fast-join, hung-thread bounded).Validation
gateway.ready(dead MCP server)import tui_gateway.serverrefresh_toolsconfirmed absent from main — old/reload-mcppath was dead, only/newrecovered late servers.discover_mcp_toolsis_lock-guarded/idempotent — safe for thread + reload.tests/tui_gateway/(94) +tests/hermes_cli/test_banner.pypass locally.Infographic