fix(api): progress checkpoints past the int4 column are a 422, and idle HLS sessions are reaped on a timer

Deep-review round 3 of bug hunt 2026-09.

- The YouTube and Plex progress bodies are bounded by POSITION_MAX_S (the int4 position columns): a
  finite position of 2^31 or more was a DataError, i.e. a 500 — the sibling of round 2's non-finite
  fix.
- plex/stream.py promised "a periodic reaper", but reap_idle ran only inside the NEXT session
  request: after the last playback an abandoned session (its ffmpeg still working, its directory a
  whole segmented copy of the film) lived until someone pressed play again. A lifespan task reaps
  every 60 s.
- Tests for what round 2 left untested: the 422's body keeps the list shape the UI localizes, and
  stream_session refuses non-finite start/aoff.

backend/app/main.py

@@ -81,6 +81,7 @@ async def lifespan(app: FastAPI):
     # alone doesn't buy that; not waiting does. The sweep only touches directories no live session
     # owns, so racing it against early playback is safe.
     sweep = asyncio.create_task(_sweep_hls_orphans())
+    reaper = asyncio.create_task(_reap_hls_sessions())
     start_scheduler()
     try:
         yield
@@ -90,15 +91,33 @@ async def lifespan(app: FastAPI):
         # pending ("Task was destroyed but it is pending!" — noise that reads like a bug during
         # triage). Cancelling does NOT interrupt the rmtree thread itself; this only makes our own
         # bookkeeping honest.
-        sweep.cancel()
+        for task in (sweep, reaper):
+            task.cancel()
             with suppress(asyncio.CancelledError):
-            await sweep
+                await task
         shutdown_scheduler()
         # Kills a running subtitle extraction: its worker would otherwise hold interpreter exit for
         # the rest of the read (see plex_subtitles.shutdown).
         plex_subtitles.shutdown()
 
 
+# How often idle HLS sessions are reaped (see plex/stream.py `reap_idle`).
+_HLS_REAP_EVERY_S = 60.0
+
+
+async def _reap_hls_sessions() -> None:
+    """The periodic reaper plex/stream.py's docstring promises. `reap_idle` used to run only inside
+    the NEXT session request, so after the last playback of the day an abandoned session — its
+    ffmpeg still working through the film, its directory a whole segmented copy of it — lived until
+    somebody pressed play again or the process restarted."""
+    while True:
+        await asyncio.sleep(_HLS_REAP_EVERY_S)
+        try:
+            await asyncio.to_thread(plex_stream.reap_idle)
+        except Exception:
+            log.exception("HLS session reap failed")
+
+
 async def _sweep_hls_orphans() -> None:
     """Background half of the startup HLS sweep (see lifespan). Owns its own errors: a failure here
     must never take the app down, and a cancelled shutdown is not one."""

backend/app/models.py

@@ -24,6 +24,11 @@ from app.db import Base
 from app.utils import canonical_email
 
 
+# The resume-position columns (VideoState / PlexState.position_seconds) are int4. The checkpoint
+# routes bound their bodies by this, so an out-of-range position is a 422 rather than a 500.
+POSITION_MAX_S = 2**31 - 1
+
+
 class TimestampMixin:
     """Adds a server-defaulted `created_at`. Models that index created_at or order it
     differently (QuotaEvent, Notification, Message) keep their own column on purpose."""
@@ -423,6 +428,7 @@ class VideoState(Base, UpdatedAtMixin):
     # status: a partially-watched video keeps status "new" but a non-zero position, so
     # it can render a progress bar and match the "in progress" feed filter. 0 = not
     # started / finished (trivially-early and near-finished positions are not stored).
+    # int4: a checkpoint body must stay under POSITION_MAX_S, or the flush is a DataError (a 500).
     position_seconds: Mapped[int] = mapped_column(
         Integer, default=0, server_default="0", nullable=False
     )

backend/app/routes/feed.py

@@ -1,7 +1,7 @@
 from datetime import date, datetime, timezone
 
 from fastapi import APIRouter, Depends, HTTPException, Query
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, Field
 from sqlalchemy import and_, func, or_, select
 from sqlalchemy.dialects.postgresql import insert as pg_insert
 from sqlalchemy.orm import Session
@@ -22,6 +22,7 @@ from app.feedquery import (
     sort_keys,
 )
 from app.models import (
+    POSITION_MAX_S,
     ChannelTag,
     Tag,
     User,
@@ -310,8 +311,9 @@ class VideoProgressIn(BaseModel):
     # Accept a float and truncate (below) — the player may post a raw currentTime (a float), which
     # the old `int(payload.get(...))` silently truncated. A plain `int` field would 422 that on the
     # 10s progress hot path, losing the resume position; `float` keeps the old tolerance.
-    position_seconds: float = 0
-    duration_seconds: float = 0
+    # Bounded above by the int4 column (see POSITION_MAX_S): past it the flush was a 500.
+    position_seconds: float = Field(0, le=POSITION_MAX_S)
+    duration_seconds: float = Field(0, le=POSITION_MAX_S)
 
 
 @router.post("/videos/{video_id}/progress")

backend/app/routes/plex/playback.py

@@ -15,13 +15,14 @@ from fastapi import (
     Response,
 )
 from fastapi.responses import FileResponse
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, Field
 from sqlalchemy import select
 from sqlalchemy.orm import Session
 
 from app.auth import current_user, resolved_user_id
 from app.db import SessionLocal, get_db
 from app.models import (
+    POSITION_MAX_S,
     PlexItem,
     PlexSeason,
     PlexShow,
@@ -293,8 +294,9 @@ class ItemProgressIn(BaseModel):
 
     # float, truncated in the handler — the player may post a raw currentTime (a float); a plain
     # `int` field would 422 it on the periodic progress checkpoint (the old `int(...)` truncated).
-    position_seconds: float = 0
-    duration_seconds: float = 0
+    # Bounded above by the int4 column (see POSITION_MAX_S): past it the flush was a 500.
+    position_seconds: float = Field(0, le=POSITION_MAX_S)
+    duration_seconds: float = Field(0, le=POSITION_MAX_S)
     final: bool = False
 
 

backend/tests/test_hls_reaper.py

@@ -0,0 +1,41 @@
+"""Idle HLS sessions are reaped on a timer, not only when the next session is requested.
+
+plex/stream.py promises "a periodic reaper kills idle ones", but `reap_idle` ran only inside
+POST /session: after the last playback, an abandoned session (its ffmpeg still working through the
+film, its directory a whole segmented copy of it) lived until somebody pressed play again.
+"""
+
+import asyncio
+
+import app.main as app_main
+from app.main import app
+
+
+class _Configured:
+    def __enter__(self):
+        return None
+
+    def __exit__(self, *exc):
+        return False
+
+
+def test_idle_sessions_are_reaped_while_nobody_starts_a_new_one(monkeypatch):
+    async def _no_sweep():
+        return None
+
+    reaped: list[int] = []
+    monkeypatch.setattr(app_main, "SessionLocal", _Configured)
+    monkeypatch.setattr(app_main.state, "is_configured", lambda db: True)
+    monkeypatch.setattr(app_main, "_sweep_hls_orphans", _no_sweep)
+    monkeypatch.setattr(app_main, "start_scheduler", lambda: None)
+    monkeypatch.setattr(app_main, "shutdown_scheduler", lambda: None)
+    monkeypatch.setattr(app_main.plex_subtitles, "shutdown", lambda: None)
+    monkeypatch.setattr(app_main, "_HLS_REAP_EVERY_S", 0.01)
+    monkeypatch.setattr(app_main.plex_stream, "reap_idle", lambda: reaped.append(1) or 0)
+
+    async def _cycle():
+        async with app_main.lifespan(app):
+            await asyncio.sleep(0.2)
+
+    asyncio.run(_cycle())
+    assert len(reaped) >= 2, "no periodic reap ran while the app was up"

backend/tests/test_progress_bounds.py

@@ -32,3 +32,32 @@ def test_a_non_finite_position_is_refused(client, path, raw):
         headers={"content-type": "application/json"},
     )
     assert r.status_code == 422, r.text
+
+
+@pytest.mark.parametrize("path", ["/api/videos/v1/progress", "/api/plex/item/98614/progress"])
+@pytest.mark.parametrize("field", ["position_seconds", "duration_seconds"])
+def test_a_position_past_the_int4_column_is_refused_not_a_500(client, path, field):
+    """Finite but past the int4 column: the flush was a DataError, i.e. a 500 with a traceback."""
+    body = {"position_seconds": 10, "duration_seconds": 3000, field: 2**31}
+    assert client.post(path, json=body).status_code == 422
+
+
+def test_the_refusal_keeps_the_shape_the_ui_reads(client):
+    """The handler replaces FastAPI's own for every validation error in the app, and the UI turns
+    exactly this shape — a LIST of errors — into its localized "check your input" sentence. The
+    refused value is echoed by its name, because JSON cannot carry NaN."""
+    r = client.post(
+        "/api/videos/v1/progress",
+        content='{"position_seconds": NaN, "duration_seconds": 3000}',
+        headers={"content-type": "application/json"},
+    )
+    detail = r.json()["detail"]
+    assert isinstance(detail, list) and detail[0]["loc"] == ["body", "position_seconds"]
+    assert detail[0]["input"] == "nan"
+
+
+@pytest.mark.parametrize("q", ["start=inf", "start=nan", "aoff=inf", "aoff=-inf", "aoff=nan"])
+def test_a_session_at_an_impossible_offset_is_refused(client, q):
+    """`start=inf` reached `int()` in the session builder (a 500); `aoff=inf` spawned an ffmpeg
+    with a non-finite offset."""
+    assert client.post(f"/api/plex/stream/98614/session?{q}").status_code == 422