feat(worker): smooth download % from adapter byte-level progress

The Floor bar used a file-count poller that jumps 0→~99% for small/fast albums
(streamrip reports only 0/1). But yt-dlp and slskd already emit real byte-level
progress via the on_progress callback the pipeline was discarding
(lambda _pct: None).

- Thread a throttled on_progress → Job.downloadProgress (write on a >=1% move or
  every 0.5s; clamped 0..1; write failures swallowed). Called synchronously from
  adapter.download on the pipeline thread, so it reuses the main conn safely.
- The file-count poller stays as the FALLBACK: it skips writing while a
  `reports` flag is set (an adapter is driving real progress), and the flag is
  cleared per attempt so a fall-through to streamrip still gets the estimate.
- Smooth bars for YouTube + Soulseek now; Qobuz/streamrip keeps the file-count
  estimate until its per-track callback is hooked later.

worker 216 tests / 7-skip (on_progress write/throttle/clamp covered; existing
pipeline tests now exercise the fake's on_progress end-to-end).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/lyra_worker/pipeline.py

@@ -1,6 +1,7 @@
 import os
 import shutil
 import threading
+import time
 from dataclasses import replace
 from typing import Sequence
 
@@ -26,16 +27,20 @@ def _count_staged_audio(staging: str) -> int:
     return n
 
 
-def _poll_download_progress(job_id: str, staging: str, expected: int, stop: "threading.Event") -> None:
+def _poll_download_progress(job_id: str, staging: str, expected: int, stop: "threading.Event",
+                            reports: "threading.Event") -> None:
     """Until `stop`, periodically write Job.downloadProgress = files-in-staging / expected
-    (capped 0.99). Uses its own short-lived connection (psycopg conns aren't shareable across
-    threads). A missing DSN or expected<=0 just no-ops."""
+    (capped 0.99) — the FALLBACK for adapters (streamrip/Qobuz) that report no byte-level
+    progress. Skips writing while `reports` is set, i.e. the in-flight adapter is driving
+    progress itself via on_progress (yt-dlp/slskd). Uses its own short-lived connection
+    (psycopg conns aren't shareable across threads). A missing DSN or expected<=0 just no-ops."""
     dsn = os.environ.get("DATABASE_URL")
     if not dsn or expected <= 0:
         return
     conn = psycopg.connect(dsn)
     try:
         while not stop.is_set():
+            if not reports.is_set():  # the adapter isn't reporting real progress → estimate
                 frac = min(_count_staged_audio(staging) / expected, 0.99)
                 with conn.cursor() as cur:
                     cur.execute('UPDATE "Job" SET "downloadProgress" = %s WHERE id = %s', (frac, job_id))
@@ -62,6 +67,29 @@ def _set_download_progress(conn: psycopg.Connection, job_id: str, frac: float) -
     conn.commit()
 
 
+def _make_on_progress(conn: psycopg.Connection, job_id: str, reports: "threading.Event"):
+    """Build the on_progress(pct) callback threaded into adapter.download. It marks the
+    adapter as reporting real byte-level progress (so the file-count poller yields) and
+    throttle-writes Job.downloadProgress. Called synchronously from adapter.download on the
+    pipeline's own thread, so it safely reuses `conn`."""
+    state = {"frac": -1.0, "t": 0.0}
+
+    def on_progress(pct: float) -> None:
+        reports.set()
+        frac = 0.0 if pct < 0 else 1.0 if pct > 1 else float(pct)
+        now = time.monotonic()
+        # throttle DB writes: on a >=1% move or every 0.5s, not once per received byte
+        if frac - state["frac"] >= 0.01 or (now - state["t"]) >= 0.5:
+            state["frac"] = frac
+            state["t"] = now
+            try:
+                _set_download_progress(conn, job_id, frac)
+            except Exception as e:  # a progress write must never fail the download
+                print(f"pipeline: on_progress write failed: {e}", flush=True)
+
+    return on_progress
+
+
 def _request_id(conn: psycopg.Connection, job_id: str) -> str:
     with conn.cursor() as cur:
         cur.execute('SELECT "requestId" FROM "Job" WHERE id = %s', (job_id,))
@@ -245,8 +273,9 @@ def run_pipeline(
     _set_download_progress(conn, job_id, 0.0)  # reset for this run
     expected = target.track_count or (ranked[0].track_count if ranked else 0)
     _stop = threading.Event()
+    _reports = threading.Event()  # set while the in-flight adapter reports real byte progress
     _poller = threading.Thread(
-        target=_poll_download_progress, args=(job_id, staging, expected, _stop), daemon=True
+        target=_poll_download_progress, args=(job_id, staging, expected, _stop, _reports), daemon=True
     )
     _poller.start()
     try:
@@ -257,7 +286,8 @@ def run_pipeline(
                     continue
                 _mark_chosen(conn, job_id, candidate.source_ref)  # reflect the source now in flight
                 shutil.rmtree(staging, ignore_errors=True)  # clean slate per attempt
-                result = adapter.download(candidate, staging, lambda _pct: None)
+                _reports.clear()  # this attempt hasn't reported yet → poller estimates until it does
+                result = adapter.download(candidate, staging, _make_on_progress(conn, job_id, _reports))
                 if result.ok:
                     winner = candidate
                     break

worker/tests/test_download_progress.py

@@ -1,6 +1,41 @@
 import os
+import threading
 
-from lyra_worker.pipeline import _count_staged_audio
+from lyra_worker.pipeline import _count_staged_audio, _make_on_progress
+from tests.conftest import insert_request
+
+
+def _dp(conn, job_id):
+    with conn.cursor() as cur:
+        cur.execute('SELECT "downloadProgress" FROM "Job" WHERE id = %s', (job_id,))
+        return cur.fetchone()[0]
+
+
+def test_on_progress_marks_reporting_and_writes(conn):
+    job_id = insert_request(conn)
+    reports = threading.Event()
+    cb = _make_on_progress(conn, job_id, reports)
+    cb(0.3)
+    assert reports.is_set()  # signals the poller to yield
+    assert _dp(conn, job_id) == 0.3
+
+
+def test_on_progress_throttles_tiny_moves(conn):
+    job_id = insert_request(conn)
+    cb = _make_on_progress(conn, job_id, threading.Event())
+    cb(0.30)
+    cb(0.305)  # <1% and <0.5s later → throttled, not written
+    assert _dp(conn, job_id) == 0.3
+    cb(0.6)  # >=1% move → written
+    assert _dp(conn, job_id) == 0.6
+
+
+def test_on_progress_clamps_out_of_range(conn):
+    job_id = insert_request(conn)
+    _make_on_progress(conn, job_id, threading.Event())(1.5)
+    assert _dp(conn, job_id) == 1.0
+    _make_on_progress(conn, job_id, threading.Event())(-0.2)
+    assert _dp(conn, job_id) == 0.0
 
 
 def test_count_staged_audio_counts_nested_audio_files_only(tmp_path):