fix: second-audit gate findings (B1, I1-I8, M1-M10)

B1: gateway capability check now triggers on walking the sub2api
gateway, not on the gateway having filled a model; task-level
explicit models are audited (worker_capability_gateway_explicit)
but never blocked, preserving explicit priority; gateway-default
models still fail-fast under active.
I1: dry-run adds a gateway-model section, sourced only from
CLOUD_SUB2API_DEFAULT_MODEL (never queries the relay); an active
tier whose requires the gateway model fails or cannot verify
blocks, shadow only warns.
I2: shadow review gate now counts completed samples
(completed >= 20), same basis for sample_shortfall; the endpoint
attaches per-tier capability status (read-only policy load) and
flags capability-failing tiers in the recommendation.
I3: configured-but-broken routing policy logs a warning in
load_routing_policy (unconfigured stays silent); the worker sets
routing_policy_load_failed and audits
worker_routing_policy_load_failed per task.
I4: resume preamble wraps prior output/error as data with an
explicit do-not-execute constraint; position verified in run_one
(tree -> preamble -> project -> original) and the docs corrected
from the false 'closest to the original prompt' claim.
I5: decided model is written back with a CAS UPDATE
(model IS NULL OR model=''), so later attempts reuse it;
explicit models are never overwritten.
I6: agent_* columns added to worker._ensure_result_columns and
db.init_postgres_schema backfill; migrations backfills them for
tasks before insert (sender_task_id pattern); column-level tests
for agent_tool_approvals and task_attempts.
I7: coordinator requeue adds AND status=<snapshot> (rowcount 0
skips requeue/audit) and filters paused_by_user / user_cancel /
user_pause children, which are never revived or cleared.
I8: explicit-model tasks (including coordinator children that
inherited a parent model) audit a source=explicit worker_routing
row; evaluate_shadow counts it as per-tier explicit_n only,
never routed_n, never a dedup slot.
M1/M2/M3/M5/M6/M8/M10: dedup slot moved after tier validation,
shadow sort doc fixed, truncated recommendation notes truncation,
seed cleanup on gateway/quota/goal-cap early returns, tools-only
coordinator definitions rejected, preamble goal branch marked
effectively unreachable, DESIGN.md drift corrected (outside repo).
M4/M7/M9: documentation/new-field only (pass_rate_fully_measured,
whitespace-model shadow-drop note, bound-note race note); old
field semantics unchanged.

cloud/migrations.py

@@ -206,6 +206,29 @@ def migrate_sqlite_to_postgres(sqlite_path, pg_conn=None, tables=None):
                 continue
             columns = [d[0] for d in src.execute(
                 'SELECT * FROM "%s" LIMIT 0' % table).description]
+            if table == "tasks":
+                # Audit fix 3（I6）：task_followups.sender_task_id
+                # 同款特殊回填。SQLite 侧 tasks 已有 agent 列，
+                # POSTGRES_SCHEMA 新库建表时一次建齐，但老
+                # PG 库的回填清单此前没有这 5 列；直插前先
+                # 查现有列、缺了再 ALTER 补列，已有列是
+                # no-op。补列失败不吞掉迁移：INSERT 时若列
+                # 仍缺失会直接报错（大声失败，绝不静默丢列）。
+                try:
+                    _existing = {row[1] for row in pg_conn.execute(
+                        "PRAGMA table_info(tasks)").fetchall()}
+                except Exception:
+                    _existing = set()
+                for _col in ("agent_name", "agent_version",
+                             "agent_instructions", "agent_tools",
+                             "agent_tool_approvals"):
+                    if _col not in _existing:
+                        try:
+                            pg_conn.execute(
+                                "ALTER TABLE tasks ADD COLUMN %s TEXT"
+                                % _col)
+                        except Exception:
+                            pass
             if table == "task_followups" and "sender_task_id" in columns:
                 # SQLite 侧有、POSTGRES_SCHEMA 里没有的列：
                 # 与 peer_messages.ensure_followups_table 同款，