FLAG-1 unified task_attempts schema (single canonical DDL + 3-shape migration)

User decision 2026-11-05: unified schema, rejecting the rehearsal
runtime column-union workaround and a ledger rename. One definition
(cloud.attempt_ledger.TASK_ATTEMPTS_DDL, 12 columns) shared by
cloud.attempts and cloud.db.POSTGRES_SCHEMA; ensure builds the
unified table fresh and migrates old resume, gap-3 ledger, and
rehearsal shapes in place with rows intact. aggregate counts
ledger rows only (outcome NULL = resume row, never counted).
SQLite verified by 8 new tests; Postgres real-DB upgrade path
explicitly NOT verified (see batch summary). Local commit only:
no merge, no push, no deploy.

cloud/tests/test_v2cov_gaps_a.py

@@ -223,9 +223,14 @@ class LedgerOnboardingGapTestCase(unittest.TestCase):
         finally:
             conn.close()
         self.assertFalse(out["tables_ready"])
+        # Unified schema: the required set is all 12 columns, so a
+        # gap-3-shaped table is missing corrects_attempt_no AND
+        # the five resume columns, not just the one column.
         self.assertEqual(
             out["missing"],
-            ["task_attempts missing columns: corrects_attempt_no"])
+            ["task_attempts missing columns: corrects_attempt_no, "
+             "kind, interrupted_reason, checkpoint_round, "
+             "result_text, error_text"])
 
     def test_verify_marker_missing_column(self):
         conn = self._sqlite(
@@ -237,9 +242,15 @@ class LedgerOnboardingGapTestCase(unittest.TestCase):
         finally:
             conn.close()
         self.assertFalse(out["tables_ready"])
+        # Unified schema: the gap-3-shaped ledger table is also
+        # missing the five resume columns, reported before the
+        # marker table's own missing column.
         self.assertEqual(
             out["missing"],
-            ["task_attempt_origin_markers missing columns: queued_at"])
+            ["task_attempts missing columns: kind, "
+             "interrupted_reason, checkpoint_round, result_text, "
+             "error_text",
+             "task_attempt_origin_markers missing columns: queued_at"])
 
 
 class LedgerOutboxGapTestCase(unittest.TestCase):