test(telemetry): the old surface needs a row in the window to have a bucket at all (#3712)

The per-source grain test gave `auto_inject` a single row 90 days back and
`pre_tool_rule` one 2 days back, then asserted on both buckets. Only the
young arm got a bucket: `out["sources"]` is built from the WINDOWED query,
so a source with no rows inside the window is absent entirely, and the
assertion died on KeyError before it could test anything.

`complete_from` and the bucket come from different queries — all-time for
the first, windowed for the second — and the fixture only satisfied one of
them. Gave `auto_inject` a second row inside the window, which is also the
shape being described: an old surface that is STILL recording. The 90-day
row still sets its `complete_from`.

Still discriminating: auto_inject reads True and pre_tool_rule False, and a
per-table `_complete_from` would make both 90 days and fail the second
assertion — the regression this test is for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011cPyzNnegXHr5iRMzzy5KJ

tests/test_services_retrieval_telemetry.py

@@ -706,11 +706,19 @@ async def test_coverage_is_per_source_because_the_table_is_older_than_its_arms(
     UID = 990077
     now = datetime.now(timezone.utc)
     async with async_session() as s:
-        # An old surface, recording since well before any window we ask for.
+        # An old surface, recording since well before any window we ask for,
+        # AND still recording inside it. Both rows are needed: `complete_from`
+        # comes from the all-time query, but a source only gets a bucket at all
+        # if it has rows in the window, so the 90-day row alone would leave
+        # nothing to assert on.
         s.add(RetrievalLog(
             user_id=UID, source="auto_inject", result_count=1,
             created_at=now - timedelta(days=90),
         ))
+        s.add(RetrievalLog(
+            user_id=UID, source="auto_inject", result_count=1,
+            created_at=now - timedelta(days=1),
+        ))
         # A young arm, first written INSIDE the window below.
         s.add(RetrievalLog(
             user_id=UID, source="pre_tool_rule", result_count=1,