fix(janitor): tolerate a legacy DB with no tasks table

scripts/kanban_janitor.py

@@ -140,12 +140,27 @@ def row_to_comment(row: sqlite3.Row) -> Comment:
     )
 
 
+def _table_exists(con: sqlite3.Connection, name: str) -> bool:
+    """True if ``name`` is a table in this SQLite DB."""
+    return con.execute(
+        "SELECT 1 FROM sqlite_master WHERE type='table' AND name=?", (name,)
+    ).fetchone() is not None
+
+
 def fetch_tasks(con: sqlite3.Connection) -> list[Task]:
+    # A legacy/profile DB may have no `tasks` table at all — the default
+    # --legacy-db (profiles/daily/kanban.db) is exactly such a DB. Treat it as
+    # empty rather than crashing the whole janitor run on its default args with
+    # ``OperationalError: no such table: tasks``.
+    if not _table_exists(con, "tasks"):
+        return []
     return [row_to_task(r) for r in con.execute("SELECT * FROM tasks ORDER BY created_at ASC, id ASC")]
 
 
 def fetch_comments(con: sqlite3.Connection) -> dict[str, list[Comment]]:
     comments: dict[str, list[Comment]] = defaultdict(list)
+    if not _table_exists(con, "task_comments"):
+        return comments
     for row in con.execute("SELECT * FROM task_comments ORDER BY created_at ASC, id ASC"):
         comment = row_to_comment(row)
         comments[comment.task_id].append(comment)

tests/scripts/test_kanban_janitor_legacy_skip.py

@@ -0,0 +1,103 @@
+"""Tests for the kanban janitor's tolerance of a tableless legacy DB.
+
+The default ``--legacy-db`` (``~/.hermes/profiles/daily/kanban.db``) is a
+per-profile DB that has NO ``tasks`` table. Before this fix ``build_scan`` ran
+``SELECT * FROM tasks`` unconditionally, so the whole janitor crashed with
+``sqlite3.OperationalError: no such table: tasks`` on its DEFAULT arguments —
+any unattended (cron/triager) run produced no report at all (live proof:
+day-30 verification 2026-05-17).
+
+These tests pin the invariant: a DB missing ``tasks`` / ``task_comments`` is
+scanned as empty, never raised on.
+"""
+
+from __future__ import annotations
+
+import importlib.util
+import sqlite3
+import sys
+from pathlib import Path
+
+
+def _load_janitor():
+    """Import scripts/kanban_janitor.py by path (it is a loose script)."""
+    name = "_kanban_janitor_legacy_under_test"
+    spec = importlib.util.spec_from_file_location(
+        name,
+        Path(__file__).resolve().parents[2] / "scripts" / "kanban_janitor.py",
+    )
+    assert spec and spec.loader
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[name] = module
+    spec.loader.exec_module(module)
+    return module
+
+
+janitor = _load_janitor()
+
+
+def _tableless_db(path: Path) -> Path:
+    """A real DB file with a connection but no kanban tables."""
+    con = sqlite3.connect(path)
+    con.execute("CREATE TABLE unrelated (x INTEGER)")
+    con.commit()
+    con.close()
+    return path
+
+
+def test_table_exists_helper(tmp_path):
+    db = _tableless_db(tmp_path / "k.db")
+    con = sqlite3.connect(db)
+    try:
+        assert janitor._table_exists(con, "unrelated") is True
+        assert janitor._table_exists(con, "tasks") is False
+        assert janitor._table_exists(con, "task_comments") is False
+    finally:
+        con.close()
+
+
+def test_fetch_tasks_missing_table_returns_empty(tmp_path):
+    db = _tableless_db(tmp_path / "k.db")
+    con = janitor.connect(db)
+    try:
+        assert janitor.fetch_tasks(con) == []
+    finally:
+        con.close()
+
+
+def test_fetch_comments_missing_table_returns_empty(tmp_path):
+    db = _tableless_db(tmp_path / "k.db")
+    con = janitor.connect(db)
+    try:
+        assert janitor.fetch_comments(con) == {}
+    finally:
+        con.close()
+
+
+def test_build_scan_on_tableless_legacy_db_does_not_crash(tmp_path):
+    """The actual bug: build_scan(legacy=True) on a tasks-less DB must not raise."""
+    db = _tableless_db(tmp_path / "legacy.db")
+    scan = janitor.build_scan(db, legacy=True)
+    assert scan["legacy"] is True
+    assert scan["task_count"] == 0
+    assert scan["status_counts"] == {}
+    assert scan["close_decisions"] == []
+    assert scan["phantom_completed_at"] == []
+
+
+def test_build_scan_still_works_on_a_real_tasks_db(tmp_path):
+    """Regression guard: the table-exists check must not break a normal DB."""
+    db = tmp_path / "real.db"
+    con = sqlite3.connect(db)
+    con.execute(
+        "CREATE TABLE tasks (id TEXT, title TEXT, status TEXT, created_at INTEGER)"
+    )
+    con.execute(
+        "INSERT INTO tasks (id, title, status, created_at) VALUES "
+        "('t_aaaaaaaa', 'Real task', 'in_progress', 1000)"
+    )
+    con.commit()
+    con.close()
+    scan = janitor.build_scan(db, legacy=False)
+    assert scan["task_count"] == 1
+    assert scan["status_counts"] == {"in_progress": 1}