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/webhooks/plane.py

@@ -18,6 +18,7 @@ from ..db import (
     enqueue_job,
     insert_event_dedup,
     create_task_atomic,
+    set_task_track,
 )
 from ._dedup import plane_delivery_id
 from ..stages import get_next_stage, get_agent_for_stage, get_qg_for_stage, get_previous_stage
@@ -648,6 +649,42 @@ async def start_pipeline(data: dict, project_id: str = ""):
         return
     task_id = task_row["id"]
 
+    # ORCH-019 (FR-1/FR-2, ADR-001 D1/D2): classify the task as a bug-fix and put it
+    # on the cheaper bug-fast-track (skips the `architecture` stage downstream). The
+    # gate idiom is `applies(repo) and is_bug_task(...)`: the LOCAL, network-free
+    # `bug_fast_track_applies` is checked FIRST so a disabled kill-switch / out-of-scope
+    # repo costs ZERO network (no has_label call). The Plane `Bug` label is the source
+    # of truth (read here at start, NEVER in the hot claim_next_job — NFR-4); the type
+    # is persisted in tasks.track so advance_stage routes off the DB, not the network.
+    # never-raise / fail-safe: ANY error -> task stays track='full' (full cycle, AC-6).
+    try:
+        from .. import bug_fast_track
+        if bug_fast_track.bug_fast_track_applies(repo) and bug_fast_track.is_bug_task(
+            work_item_id, plane_project_id
+        ):
+            set_task_track(task_id, "bug")
+            logger.info(
+                f"Task {work_item_id}: classified as BUG -> bug-fast-track "
+                f"(architecture stage will be skipped, ORCH-019)"
+            )
+            try:
+                from ..plane_sync import add_comment as _bug_comment
+                _bug_comment(
+                    work_item_id,
+                    "\U0001f41e Багфикс-трек: "
+                    "упрощённый маршрут "
+                    "(пропуск стадии architecture). "
+                    "Все Quality Gate исполняются.",
+                    author="analyst",
+                )
+            except Exception:
+                pass
+    except Exception as e:
+        logger.warning(
+            f"Task {work_item_id}: bug-fast-track classification skipped "
+            f"(fail-safe -> full cycle): {e}"
+        )
+
     # ORCH-088 (FR-1/AC-6, ADR-001 D1): DEFER the branch cut for an applicable repo.
     # Creating the Gitea branch here (T0, issue -> analysis) would cut it from `main`
     # BEFORE the predecessor is merged -> stale base. When the serial gate applies we