feat(subscriptions): live posts-processed progress on backfill/recovery — #704 step 2

The running badge only showed the chunk counter; now it shows posts walked
— real walk progress. The ingester already reports posts_processed per
chunk (step 1); the backfill lifecycle accumulates it into
config_overrides._backfill_posts across chunks. SourceRecord exposes
backfill_posts; start_backfill/start_recovery clear it (fresh walk); stop
clears it too. SourceRow/SourceCard badge renders "Recovering · 45 posts"
(falls back to "(N)" chunks before any posts are counted).

Per-chunk accumulation (no mid-walk DB write) — simple and race-free; a
small over-count from each chunk re-walking its resumed page is fine for a
progress indicator.

Tests: lifecycle accumulates posts_processed across chunks; start clears a
prior _backfill_posts and the record exposes it.

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

tests/test_download_service.py

@@ -648,6 +648,40 @@ async def test_backfill_stuck_guard_stalls_after_two_no_advance(
     assert "_backfill_cursor" not in co2
 
 
+@pytest.mark.asyncio
+async def test_backfill_accumulates_posts_processed(
+    db, db_sync, tmp_path, seed_artist_and_source,
+):
+    """plan #704 (#5): the lifecycle accumulates DownloadResult.posts_processed
+    into _backfill_posts across chunks for the live progress badge."""
+    from unittest.mock import MagicMock
+
+    from backend.app.services.download_service import DownloadService
+
+    _artist, source = seed_artist_and_source
+    source.config_overrides = {"_backfill_state": "running", "_backfill_posts": 5}
+    source.backfill_runs_remaining = 5
+    await db.commit()
+
+    svc = DownloadService(
+        async_session=db, sync_session=db_sync,
+        gdl=MagicMock(), importer=MagicMock(), cred_service=MagicMock(),
+    )
+    ctx = {
+        "source_id": source.id, "platform": "patreon",
+        "config_overrides": {"_backfill_state": "running", "_backfill_posts": 5},
+        "backfill_runs_remaining": 5,
+    }
+    await svc._apply_backfill_lifecycle(
+        ctx, _make_fake_dl_result(success=False, cursor="C1", posts_processed=10),
+    )
+    await db.commit()
+    co = (await db.execute(
+        select(Source.config_overrides).where(Source.id == source.id)
+    )).scalar_one()
+    assert co.get("_backfill_posts") == 15  # 5 (prior) + 10 (this chunk)
+
+
 @pytest.mark.asyncio
 async def test_backfill_timeout_chunk_reclassified_to_ok(
     db, db_sync, tmp_path, seed_artist_and_source,

tests/test_source_service.py

@@ -238,15 +238,25 @@ async def test_start_recovery_arms_bypass_flag(db):
         artist_id=artist.id, platform="patreon",
         url="https://patreon.com/alice",
     )
+    # Simulate a prior walk's posts counter — start must clear it (plan #704).
+    await db.execute(
+        Source.__table__.update().where(Source.id == rec.id).values(
+            config_overrides={"_backfill_posts": 42},
+        )
+    )
+    await db.commit()
+
     updated = await svc.start_recovery(rec.id)
     assert updated.backfill_state == "running"
     assert updated.backfill_bypass_seen is True
+    assert updated.backfill_posts == 0  # cleared for a fresh walk
     assert updated.backfill_runs_remaining == BACKFILL_MAX_CHUNKS
 
     co = (await db.execute(
         select(Source.config_overrides).where(Source.id == rec.id)
     )).scalar_one()
     assert co.get("_backfill_bypass_seen") is True
+    assert "_backfill_posts" not in co
 
     # Stop clears the bypass flag too (shared lifecycle).
     stopped = await svc.stop_backfill(rec.id)