feat(bug-fast-track): cheaper/shorter pipeline route for bug-fix tasks (ORCH-019)

A task carrying the Plane `Bug` label takes a shortened route that skips the
`architecture` stage (one opus architect run + ADR + check_architecture_done),
replacing heavy analysis with a lite package (bug-report + mandatory regression
test plan). EVERY Quality Gate / sub-gate runs UNCHANGED — the route is a
scheduler property, not a gate (root invariant NFR-1): STAGE_TRANSITIONS /
QG_CHECKS / check_* / machine-verdict keys are byte-for-byte preserved.

- src/bug_fast_track.py: new leaf (never-raise) — bug_fast_track_applies (local,
  network-free, checked first), is_bug_task (labels.has_label, Plane API source),
  skips_architecture (pure DB-backed routing predicate), snapshot.
- src/db.py: additive idempotent tasks.track column (TEXT DEFAULT 'full') +
  set_task_track / get_task_track helpers (missing/NULL -> 'full', fail-safe).
- src/stage_engine.py: routing-override on the analysis-exit edge (track='bug' ->
  development/developer, skipping architect); brd-review-clock stamp extended to
  analysis->development. get_next_stage/get_agent_for_stage stay pure.
- src/webhooks/plane.py: classify task as bug in start_pipeline (applies-first
  short-circuit; never-raise -> full cycle on any error).
- src/main.py: additive bug_fast_track block in GET /queue + POST
  /bug-fast-track/escalate (reset 'bug'->'full' to return to the full cycle).
- src/config.py: bug_fast_track_enabled / _label / _repos flags (empty CSV ->
  self-hosting only).
- src/notifications.py: optional 🐞 marker on the bug-track card (never-raise).
- Prompts: analyst.md (lite bug package + escalation), reviewer.md (regression-
  test axis) — 52d canon preserved.
- Docs: CLAUDE.md, README.md (env + API + section), docs/architecture/README.md,
  CHANGELOG.md, .env.example.
- Tests: tests/test_bug_fast_track*.py + test_db_migrations.py + queue block
  (TC-01..TC-15). Full regression green (1551 passed).

Kill-switch ORCH_BUG_FAST_TRACK_ENABLED=false -> 1:1 pre-ORCH-019 (zero
regression; residual track column harmless).

Refs: ORCH-019

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/config.py

@@ -794,6 +794,34 @@ class Settings(BaseSettings):
     auto_label_repos: str = ""
     auto_label_states_ttl_s: int = 300
 
+    # ORCH-019: bug-fast-track — a cheaper/shorter pipeline route for bug-fix tasks.
+    # A task carrying the Plane label `bug_fast_track_label` (default `Bug`) skips
+    # the whole `architecture` stage (one opus `architect` run + ADR + the
+    # check_architecture_done exit-gate): the routing-override in advance_stage maps
+    # the analysis -> architecture edge to analysis -> development for a task whose
+    # tasks.track == 'bug'. EVERY Quality Gate / sub-gate (CI/review/tester/staging/
+    # deploy + security/merge/coverage/image-freshness/merge-verify) runs UNCHANGED
+    # — the route is a scheduler property, NOT a gate (root invariant NFR-1).
+    # Recognition reuses the proven ORCH-089 label apparatus (labels.has_label ->
+    # plane_sync), read ONLY in start_pipeline (never in the hot claim_next_job).
+    # Additive leaf (src/bug_fast_track.py, never-raise) + an additive idempotent
+    # tasks.track column; STAGE_TRANSITIONS / QG_CHECKS / check_* / verdict-keys are
+    # NOT touched. fail-safe -> full cycle on any error/ambiguity/disabled flag. See
+    # docs/work-items/ORCH-019/06-adr/ADR-001-bug-fast-track.md and the cross-cutting
+    # docs/architecture/adr/adr-0032-bug-fast-track.md.
+    #   bug_fast_track_enabled -> kill-switch (env ORCH_BUG_FAST_TRACK_ENABLED).
+    #                             False -> start_pipeline AND advance_stage are 1:1 as
+    #                             before ORCH-019 (skips_architecture always False,
+    #                             has_label never consulted) — zero regression (AC-6).
+    #   bug_fast_track_label   -> Plane label name that activates the track (env
+    #                             ORCH_BUG_FAST_TRACK_LABEL; default `Bug`).
+    #   bug_fast_track_repos   -> CSV scope (env ORCH_BUG_FAST_TRACK_REPOS). Empty ->
+    #                             self-hosting only (orchestrator), the safe default
+    #                             (D6); non-empty -> only the listed repos.
+    bug_fast_track_enabled: bool = True
+    bug_fast_track_label: str = "Bug"
+    bug_fast_track_repos: str = ""
+
     # Telegram notifications
     telegram_bot_token: str = ""
     telegram_chat_id: str = ""