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/db.py

@@ -140,6 +140,13 @@ def init_db():
     #                           irreversible step finishes honestly, then applied.
     _ensure_column(conn, "tasks", "cancelled_at", "TEXT")
     _ensure_column(conn, "tasks", "cancel_requested_at", "TEXT")
+    # ORCH-019 (08-data-requirements.md): bug-fast-track task type. Additive,
+    # idempotent (_ensure_column is a no-op once present) -> safe on the live shared
+    # prod DB (enduro untouched). Values: 'full' (DEFAULT — ALL existing and non-bug
+    # tasks) | 'bug' (a task carrying the Plane `Bug` label, set in start_pipeline
+    # after a successful atomic create). Read in advance_stage for the routing-override
+    # (skips architecture) — from the DB, NEVER from the network (NFR-4).
+    _ensure_column(conn, "tasks", "track", "TEXT DEFAULT 'full'")
     # ORCH-026 (Level B): declarative task dependencies. job_deps stores the
     # directed edge "task_id (B) is blocked-by depends_on_task_id (A)". The
     # scheduler gate in claim_next_job keeps B queued until every A reaches
@@ -487,6 +494,48 @@ def update_task_stage(task_id: int, stage: str):
     conn.close()
 
 
+# ---------------------------------------------------------------------------
+# ORCH-019: bug-fast-track task type (tasks.track) helpers
+# ---------------------------------------------------------------------------
+def set_task_track(task_id: int, track: str) -> None:
+    """ORCH-019: persist the task's pipeline track ('full' | 'bug').
+
+    Idempotent overwrite. Called from start_pipeline (after a successful atomic
+    create, when the issue carries the `Bug` label) and from the escalate endpoint
+    (reset 'bug' -> 'full' to return a complex bug to the full cycle).
+    """
+    conn = get_db()
+    try:
+        conn.execute(
+            "UPDATE tasks SET track = ? WHERE id = ?", (track, task_id)
+        )
+        conn.commit()
+    finally:
+        conn.close()
+
+
+def get_task_track(task_id: int) -> str:
+    """ORCH-019: read the task's pipeline track; missing/NULL -> 'full' (fail-safe).
+
+    Read in the hot advance_stage path for the routing-override (skips architecture).
+    A non-existent row, a NULL value, or any read error degrades to 'full' so a bug
+    can never be created by accident (fail-safe -> full cycle).
+    """
+    try:
+        conn = get_db()
+        try:
+            row = conn.execute(
+                "SELECT track FROM tasks WHERE id = ?", (task_id,)
+            ).fetchone()
+        finally:
+            conn.close()
+        if not row:
+            return "full"
+        return row["track"] or "full"
+    except Exception:  # noqa: BLE001 - fail-safe -> full cycle
+        return "full"
+
+
 # ---------------------------------------------------------------------------
 # Telegram live tracker helpers (feat/telegram-live-tracker)
 # ---------------------------------------------------------------------------