fix(telemetry): a surface that stopped recording is not one that never ran (#3720)

`out["sources"]` was built only from the windowed aggregate, so a source
with rows in `retrieval_logs` but none inside the window got no bucket at
all. Absent is exactly how a source that never existed renders, so a
surface that WAS recording and went silent became unreadable — #2663 one
level up, the failure that looks like the correct answer.

Two queries at different scopes, and only one shaped the output.
`_complete_from` reads all-time and knows every source the table has ever
held; the windowed loop dropped whatever it did not return.

Every such source now gets a zero bucket. Zero is a real measurement here
rather than a manufactured one: the all-time query proves the source was
recording, and it made no calls across a window it fully covers. No
`covers_window` special case is needed either — a source whose first row
fell after `since` would have that row IN the window and already hold a
bucket, so anything reaching this branch began before it.

The counts are 0 and everything else is null. A sampled distribution is
not the same claim as a call count, and rendering p50 as 0.0 for a source
nobody sampled would assert a measurement — #3311's mistake, in the
readout built to prevent it.

Found while fixing #3712's fixture, which failed with KeyError for this
exact reason.

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

src/scribe/services/retrieval_telemetry.py

@@ -213,6 +213,15 @@ def _bucket(rows: list) -> dict:
     }
 
 
+# The aggregate row Postgres would have returned for a source with no rows in
+# the window: nothing counted, nothing scored. Positional, matching the SELECT
+# `_bucket` unpacks — calls, zero, cleared, p10, p50, p90, min, max, avg_n,
+# dur, measured, supp_calls, supp_zero. The three counts are 0 because zero
+# calls is a real observation; everything else is None because a distribution
+# nobody sampled has no value, and rendering it as 0.0 would state one.
+_NO_ROWS_IN_WINDOW = [0, 0, 0, None, None, None, None, None, None, None, 0, 0, 0]
+
+
 def _round(v, places: int = 4):
     return None if v is None else round(float(v), places)
 
@@ -375,6 +384,25 @@ async def retrieval_summary(user_id: int | None, *, days: int = 30) -> dict:
                 bucket.update(_coverage(log_complete.get(source), since))
                 out["sources"][source] = bucket
 
+            # A source with rows in the table but NONE in this window would
+            # otherwise be absent from the readout — and absent is exactly how
+            # a source that never existed renders, so a surface that WAS
+            # recording and went silent is unreadable (#3720). That is #2663
+            # one level up: the failure that looks like the correct answer.
+            #
+            # Zero here is a real measurement, not a manufactured one. The
+            # all-time query proves the source was recording, and it made no
+            # calls across a window it fully covers — which is why no
+            # `covers_window` special case is needed: a source whose first row
+            # fell after `since` would have that row IN the window and already
+            # hold a bucket, so anything reaching here began before it.
+            for src, first_row in log_complete.items():
+                if src == "*" or first_row is None or src in out["sources"]:
+                    continue
+                quiet = _bucket(list(_NO_ROWS_IN_WINDOW))
+                quiet.update(_coverage(first_row, since))
+                out["sources"][src] = quiet
+
             # The corpus side, at its own grain. `ambient` mirrors
             # note_usage.usage_for_notes: an ambient surfacing was not a scored
             # CHOICE, so folding it into pull-through would understate it.