fix(downloads): a download larger than the space left says so, not "processing failed"

yt-dlp refuses a file announced over `max_filesize` by logging one line and returning with no file
(measured, and pinned in test_formats against a local server): the worker found no output and
failed the job as `postprocess`. `formats.watching_size_cap` now sees that line through our yt-dlp
logger, and the download (and, should it ever happen, a YouTube clip's range fetch) fails as the
owner's refusal with DOWNLOAD_TOO_BIG_MESSAGE, classified `quota_exceeded`. The download's quota
copy says it does not fit in what is left — true at a full cap too — instead of "Storage full".
A pre-existing type error the change touched is fixed (baseline down by one).

backend/tests/test_download_limits.py

@@ -11,7 +11,8 @@ its OWN session, so every test COMMITS its setup before calling it.
 """
 
 from app.config import settings
-from app.downloads import pipeline, quota
+from app.downloads import errors as dlerrors
+from app.downloads import formats, pipeline, quota
 from app.models import DownloadJob, DownloadQuota, MediaAsset, User
 from app.worker import _claim_job
 
@@ -297,3 +298,49 @@ def test_a_refusal_for_one_user_does_not_poison_the_shared_asset(db, monkeypatch
     assert db.get(MediaAsset, shared.id).status == "pending"
     assert db.get(MediaAsset, shared.id).error is None
     assert db.get(DownloadJob, theirs.id).status == "queued"
+
+
+def test_a_download_over_the_space_left_says_so_and_releases_the_shared_asset(
+    db, monkeypatch, tmp_path
+):
+    # yt-dlp refuses a file over `max_filesize` by saying so and returning with no file (pinned in
+    # test_formats). That is the owner's storage, not a processing fault: their refusal, in words
+    # true of a cap with space still left, and the shared asset goes back for the next job.
+    monkeypatch.setattr(settings, "download_root", str(tmp_path))
+    u = User(email="nearcap@example.com")
+    db.add(u)
+    db.flush()
+    db.add(
+        DownloadQuota(user_id=u.id, max_bytes=1000, max_concurrent=2, max_jobs=100, unlimited=False)
+    )
+    held = _sized_asset(db, 400, "near-held")
+    _job(db, u.id, queue_pos=0, status="done", asset_id=held.id)
+    shared = MediaAsset(
+        source_kind="youtube",
+        source_ref="y" * 11,
+        format_sig="s",
+        status="downloading",
+        ref_count=1,
+    )
+    db.add(shared)
+    db.flush()
+    mine = _job(db, u.id, queue_pos=1, status="running", asset_id=shared.id)
+    db.commit()
+    caps = []
+
+    def refuses_over_the_cap(*args, max_bytes=None, **kwargs):
+        caps.append(max_bytes)
+        formats._YDL_LOG.debug(
+            f"[download] File is larger than max-filesize (2000 bytes > {max_bytes} bytes). Aborting."
+        )
+        return {"id": "y" * 11, "requested_downloads": [{}]}
+
+    monkeypatch.setattr(pipeline, "_extract_with_fallback", refuses_over_the_cap)
+    pipeline._download(mine.id, shared.id, "youtube", "y" * 11, {}, u.id)
+
+    db.expire_all()
+    job = db.get(DownloadJob, mine.id)
+    assert caps == [600]
+    assert (job.status, job.error_code) == ("error", "quota_exceeded")
+    assert job.error == dlerrors.DOWNLOAD_TOO_BIG_MESSAGE
+    assert db.get(MediaAsset, shared.id).status == "pending"