fix(logs): deep-review round 2 — a stack names code, not data, and survives a failed write

- A failure keeps its traceback unless it is yt-dlp's or our own StatedFailure (a
  message that is the whole story). A plain RuntimeError, RecursionError or OSError
  is also what a bug of ours raises, and its stack is the only lead.
- The stack is scrubbed link by link (logs.scrubbed_stack): a chained DownloadError
  under a DB error no longer prints yt-dlp's text unscrubbed.
- Engine hide_parameters: a DB error's message no longer carries the title or path
  it was writing.
- The download and edit failure lines go out even when their DB write fails.
- The worker's child_exit/crash/supervisor lines say download.job.failed only when
  the job failed there; a crash the DB will not record no longer ends the thread.
  Stopping a paused child is download.child.stopped, not a second abort.
- log_safe also covers generic ids with spaces, playlist titles and bare ids.
- The ffmpeg image steps log the failure kind, not the argv with its path.
- The consent contract accepts only the body of a plain consented_trace() check,
  and any level that may be TRACE.
- Tests for each; every one mutation-checked.

backend/tests/test_download_failure_catalog.py

@@ -125,6 +125,25 @@ def test_the_download_child_knows_the_cookie_went_with_it(db, monkeypatch, tmp_p
     assert (job.error_code, job.error_detail) == ("login_required", "facebook.cookie_rejected")
 
 
+def test_the_failure_line_goes_out_even_when_its_write_fails(db, monkeypatch, tmp_path):
+    """The database is often what failed; the write of the failure then fails too, and the line
+    that says so must not go down with it."""
+    u = _user(db, "fb-dbdown@example.com")
+    a, j = _asset_and_job(db, u, sig="dbdown", asset_status="downloading", job_status="running")
+    _fail_the_child(monkeypatch, tmp_path, cookie=False)
+    said = []
+    monkeypatch.setattr(pipeline, "_log_download_failed", lambda job_id, *rest: said.append(job_id))
+
+    def db_down(*a, **k):
+        raise ConnectionError("the database went away")
+
+    monkeypatch.setattr(pipeline.service, "finalize_if_running", db_down)
+
+    with pytest.raises(ConnectionError):
+        pipeline._download(j.id, a.id, "url", _REEL, {}, u.id)
+    assert said == [j.id]
+
+
 def test_a_job_meeting_a_failed_shared_asset_gets_the_same_explanation(db):
     # Before the catalog this path wrote the text and NO code: "Download failed" for the second
     # job, "Facebook sign-in required" for the first.