Architectural shift driven by user clarification: lazy-loading on first
use causes user-perceptible lag when the user-triggered action (e.g.
provider switch) propagates to a controller method that triggers the
first import. The fix is to pre-import heavy modules on a bg thread
at startup and have functions access them via _require_warmed().
Old design (rejected):
- from google import genai inside _send_gemini (lazy on first call)
- First user action that triggers this pays the cost; UI feels laggy
New design (this commit):
- Top-level heavy imports REMOVED from main-thread-reachable files
- AppController.__init__ submits warmup jobs to _io_pool (4 threads,
named 'controller-io-N')
- Each warmup worker imports its module and updates a thread-safe
warmup_status dict
- Functions access modules via _require_warmed(name), which assumes
the module is in sys.modules (warmed at startup)
- When all jobs complete, _warmup_done_event is set and registered
on_warmup_complete callbacks fire
- GUI shows status indicator + toast when warmup completes
- Hook API exposes /api/warmup_status and /api/warmup_wait
- Tests can call controller.wait_for_warmup() before exercising
warmup-dependent functionality
Phase 2 now bundles job pool + warmup (T2.3+T2.4 add warmup tests +
implementation). Phases 3-5 do 'remove top-level imports' instead of
'lazy-load'. Phase 7 is the notification surface (Hook API + GUI).
Definition of Done includes warmup-completion criteria, the
'no function-body imports' check, and an end-to-end 'provider switch
is INSTANT' smoke test.
No code changes; this is a planning update only.
Fulfills the existing backlog entry at conductor/tracks.md:152
(2026-06-05 root-cause analysis of live_gui wait_for_server timeouts).
Main Thread Purity Invariant: the main thread (entering immapp.run())
must never import a module heavier than imgui_bundle and the lean
gui_2 skeleton. Enforced by:
- static gate: scripts/audit_main_thread_imports.py (CI)
- runtime hook: tests/test_main_thread_purity.py (sys.addaudithook)
Threading constraint: no new threading.Thread(...) calls in src/.
All background work goes through AppController._io_pool
(ThreadPoolExecutor, max_workers=4, thread_name_prefix='controller-io').
9 phases, 57 tasks: audit+baseline, job pool, lazy-load SDKs, lazy-load
FastAPI, lazy-load feature-gated GUI, migrate ad-hoc threads, runtime
enforcement, hook API + diagnostics, verify+checkpoint.
Expected savings: ~2000-2400ms off main-thread import cost.
Target: import src.ai_client < 50ms (from ~1800ms), live_gui fixtures
no longer time out at wait_for_server(timeout=15).
ed