worker: auto-resume falls back to fresh goal for never-started tasks

2026-10-29 live test: task A was interrupted 61s after claim but had
never written anything (no host-state entry, no worktree, no trace,
no checkpoint); auto-resume ran goal-resume, which host rightly
refused, and the task failed. Refusal only makes sense for tasks
with progress but a lost breakpoint (those go through the P0
checkpoint rebuild); for a never-started task the only meaningful
outcome is a fresh run, identical to its first attempt (same task
id, same goal, worktree does not exist yet so nothing is
overwritten).

Change (claim path only, via _resolve_breakpoint_resume):
- rebuild from checkpoint first, unchanged;
- if rebuild fails AND _task_never_started holds (state entry,
  checkpoint row, worktree dir, trace file all absent), clear the
  breakpoint flag so the run takes the fresh goal path, with a
  worker_fresh_restart audit event;
- any evidence of prior execution, or any check failure,
  keeps the old refusal path (fail-closed); the auto-resume
  count cap and no-progress stall guard still bound retries.

Tests: cloud/tests/test_neverstart_fresh.py, 10 items (fallback
holds, entry/checkpoint/worktree/trace presence each block it,
corrupt state blocks it, rebuild still wins when a checkpoint
exists); test_goal_resume's breakpoint-routing test now sets up
a task with a checkpoint so it still exercises goal-resume.
Full suites: cloud 1178 (skipped 4), host 104, deploy 39, green.

cloud/tests/test_goal_resume.py

@@ -170,6 +170,20 @@ class GoalResumeTestCase(unittest.TestCase):
             "POST", "/tasks/%s/goal-resume" % task["id"],
             {}, self.owner_key)
         self.assertEqual(status, 200, body)
+        # 本测试测的是“有断点的任务走 goal-resume”：先给任务补
+        # 一行库断点（模拟跑过一轮），否则按从未启动回落规则，
+        # 它会被当成从未启动而走全新 goal（见
+        # test_neverstart_fresh.py）。
+        conn = sqlite3.connect(self.db_path)
+        try:
+            conn.execute(
+                "INSERT INTO task_checkpoints(task_id, round_no,"
+                " thread_id, goal_status, state_sha, verify_out,"
+                " created_at) VALUES(?, ?, ?, ?, ?, ?, ?)",
+                (task["id"], 1, "th-test", "goal-running", "sha", "", 0))
+            conn.commit()
+        finally:
+            conn.close()
         seen = []
 
         def fake(cmd):