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>

tests/test_db_migrations.py

@@ -0,0 +1,79 @@
+"""ORCH-019 (TC-15) — additive, idempotent tasks.track migration.
+
+The bug-fast-track stores the task type in an additive ``tasks.track`` column
+(``TEXT DEFAULT 'full'``) created via ``_ensure_column`` (idempotent). A repeated
+``init_db`` must not crash, existing rows must default to ``'full'``, and the
+helpers must round-trip.
+"""
+import os
+import tempfile
+
+import pytest
+
+os.environ.setdefault(
+    "ORCH_DB_PATH", os.path.join(tempfile.gettempdir(), "test_db_migrations.db")
+)
+os.environ.setdefault("ORCH_GITEA_TOKEN", "test-token")
+os.environ.setdefault("ORCH_PLANE_API_TOKEN", "test-token")
+
+import src.db as db  # noqa: E402
+from src.db import init_db, get_db, set_task_track, get_task_track  # noqa: E402
+
+
+@pytest.fixture(autouse=True)
+def fresh_db(tmp_path, monkeypatch):
+    dbfile = tmp_path / "m.db"
+    monkeypatch.setattr(db.settings, "db_path", str(dbfile))
+    init_db()
+    yield
+
+
+def _columns(table):
+    conn = get_db()
+    try:
+        return [r[1] for r in conn.execute(f"PRAGMA table_info({table})").fetchall()]
+    finally:
+        conn.close()
+
+
+def test_tc15_track_column_present_with_default():
+    assert "track" in _columns("tasks")
+    # A row inserted WITHOUT track gets the DEFAULT 'full'.
+    conn = get_db()
+    conn.execute(
+        "INSERT INTO tasks (plane_id, work_item_id, repo, branch, stage, title) "
+        "VALUES ('p','ORCH-1','orchestrator','feature/x','analysis','t')"
+    )
+    conn.commit()
+    row = conn.execute("SELECT track FROM tasks WHERE work_item_id='ORCH-1'").fetchone()
+    conn.close()
+    assert row["track"] == "full"
+
+
+def test_tc15_init_db_idempotent():
+    # Running init_db again is a no-op on the existing column (no crash).
+    init_db()
+    init_db()
+    assert "track" in _columns("tasks")
+
+
+def test_tc15_helpers_round_trip():
+    conn = get_db()
+    cur = conn.execute(
+        "INSERT INTO tasks (plane_id, work_item_id, repo, branch, stage, title) "
+        "VALUES ('p2','ORCH-2','orchestrator','feature/y','analysis','t')"
+    )
+    tid = cur.lastrowid
+    conn.commit()
+    conn.close()
+
+    assert get_task_track(tid) == "full"          # default
+    set_task_track(tid, "bug")
+    assert get_task_track(tid) == "bug"
+    set_task_track(tid, "full")
+    assert get_task_track(tid) == "full"
+
+
+def test_tc15_get_task_track_missing_row_failsafe():
+    # Unknown task id -> 'full' (fail-safe -> full cycle), never raises.
+    assert get_task_track(999999) == "full"