fix(telemetry): a warning fired on an arm whose decline rate is arithmetic, not evidence (#4232)

Found by reading a live `retrieval_telemetry` readout after milestone 419
deployed, not by inspection. The readout said:

    cannot_decline / report_preference — "45 calls, 0 of them returned
    nothing. An arm that fires unasked has to be able to say nothing; this one
    never has. Check that it applies its floor at all."

And printed, beside it, that arm's band: p10 = p50 = p90 = min = max = 0.791.

FIVE IDENTICAL PERCENTILES IS THE TELL. That is not a ranking, it is one
record at one score on every call — because `report_preference` searches a
fixed string (`reply_preferences.COMPLETION_QUERY`, a module constant, and
deliberately so).

For a fixed query against a stable corpus the top score is a CONSTANT, so the
arm's decline rate is 0% or 100% and never in between; which of the two it is
depends only on where the bar sits relative to that one number. "Never
returned nothing" is therefore arithmetic, not evidence, and the warning's own
remedy — check whether it applies a floor — cannot be answered from it.

The arm already knew this about itself; the warning did not:

    "a fixed query makes this arm's score a constant and a floor a hair above
     it produces a dead arm no amount of traffic will ever reveal"
        — services/reply_preferences.py

THIS CLASS OF BUG ALREADY HAS A GUARD, which is the argument for the shape of
the fix. `Point.logs_unconditionally` exists because of #3497: both rule arms
once logged only their hits, so their zero count was structurally 0 and this
same warning would have fired on a LOGGING property while sending the reader
to move a threshold that was never involved. This is that one step over — a
QUERY-SHAPE property — and gets the same treatment: a declared field on
`Point`, and exclusion rather than trust.

AND THE WARNING THAT WOULD BE INFORMATIVE HERE DID NOT EXIST. For a fixed-query
arm the dangerous state is the mirror image: every call empty, meaning the bar
is above the constant and no further traffic will ever move it. The arm is off
rather than quiet, and nothing in the readout said so — `expects_traffic`
covers an arm with NO calls, not one with calls and a 100% decline rate. That
state is real and reached: `report_preference` once logged 69 consecutive
declines at 0.0006 under its bar.

So `fixed_query_never_clears` sends the reader to `near_miss_samples` and not
to the dial — because that incident is also the one where the statistic and
the correct action pointed opposite ways. Every percentile said lower the
floor; opening the refused record showed it was rule 77 arriving as a false
positive, and lowering it would have delivered that rule on every completion
report ever written.

Guards in tests/test_retrieval_warnings.py, including the falsifier that
matters most here: `cannot_decline` must still fire on an arm whose query
varies, or this change is a disabled check wearing a narrowed one's clothes.
Both boundaries tested from both sides, per that module's own standard.

The new code is documented in the `retrieval_telemetry` tool docstring beside
the others (rule 33) — an undocumented code in a readout is a reader meeting a
verdict with no way to disagree with it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_retrieval_warnings.py

@@ -446,3 +446,80 @@ def test_a_quiet_arm_is_not_suspended_either_way() -> None:
     ws = warn({"auto_inject": src(calls=1, zero_result_calls=0, p10=0.705)},
               floors={"auto_inject": 0.70}, floor_moves={"auto_inject": MOVED})
     assert "floor_moved_mid_window" not in codes(ws)
+
+
+# ── a fixed-query arm: decline rate is arithmetic, not evidence (#4232) ─────
+#
+# `report_preference` searches one constant string (COMPLETION_QUERY), so it
+# scores against one number on every call. Its decline rate is therefore 0% or
+# 100% and never in between, and which one depends only on where the bar sits
+# relative to that constant.
+#
+# So the two warnings swap roles for these arms. "Never declined" stops being
+# evidence about the floor — `cannot_decline`'s own remedy, "check that it
+# applies its floor", is unanswerable from it. "Always declined" starts being
+# evidence, because for a constant score it means the bar is above it and no
+# further traffic will ever say otherwise.
+
+
+def test_cannot_decline_is_silent_on_a_fixed_query_arm():
+    """The live readout fired this on `report_preference` at 45 calls, 0
+    empty, with p10 = p50 = p90 = min = max = 0.791 — five identical
+    percentiles, which is one record at one score rather than a ranking."""
+    ws = warn({"report_preference": src(calls=45, zero_result_calls=0, p10=0.791)})
+    assert "cannot_decline" not in codes(ws, "report_preference")
+
+
+def test_cannot_decline_still_fires_where_the_rate_means_something():
+    """The falsifier for the case above (rule 167). If this passes only
+    because the check was disabled rather than narrowed, this fails."""
+    ws = warn({"auto_inject": src(calls=N, zero_result_calls=0)})
+    assert "cannot_decline" in codes(ws, "auto_inject")
+
+
+def test_a_fixed_query_arm_that_never_clears_its_bar_is_named():
+    """69 consecutive declines at 0.0006 under the bar is a state this arm has
+    actually been in. Nothing else in the readout would have said so: it looks
+    exactly like an arm with nothing to report."""
+    ws = warn({"report_preference": src(calls=45, zero_result_calls=45)})
+    assert "fixed_query_never_clears" in codes(ws, "report_preference")
+
+    detail = next(w["detail"] for w in ws if w["code"] == "fixed_query_never_clears")
+    assert "near_miss_samples" in detail, (
+        "the last time this fired, every percentile said lower the floor and "
+        "the refused record showed the refusal was right — so the warning has "
+        "to send the reader to the record, not to the dial"
+    )
+
+
+def test_an_ordinary_arm_returning_nothing_all_window_is_not_dead():
+    """For an arm whose score can vary, an empty window means nothing matched,
+    which is an answer rather than a fault."""
+    ws = warn({"auto_inject": src(calls=N, zero_result_calls=N)})
+    assert "fixed_query_never_clears" not in codes(ws, "auto_inject")
+
+
+def test_a_fixed_query_arm_that_sometimes_clears_is_not_dead():
+    """Only ALL-empty says the bar is above the constant. Anything in between
+    means the score is not actually constant, and the premise is wrong."""
+    ws = warn({"report_preference": src(calls=45, zero_result_calls=44)})
+    assert "fixed_query_never_clears" not in codes(ws, "report_preference")
+
+
+def test_the_dead_arm_warning_still_needs_volume():
+    ws = warn({"report_preference": src(calls=N - 1, zero_result_calls=N - 1)})
+    assert "fixed_query_never_clears" not in codes(ws)
+
+
+def test_the_registry_declares_which_arms_ask_a_fixed_question():
+    """Asserted on structure (rule 167), and able to fail: if `fixed_query`
+    is dropped or defaults to True, one of these two halves breaks."""
+    from scribe.services.retrieval_registry import POINTS
+
+    assert POINTS["report_preference"].fixed_query is True, (
+        "services/reply_preferences.py::COMPLETION_QUERY is a module constant"
+    )
+    # An arm whose query is built from the prompt, the file or the command is
+    # not fixed, and marking one would silence a warning that works there.
+    for varying in ("auto_inject", "write_path", "pre_tool_rule", "prompt_rule"):
+        assert POINTS[varying].fixed_query is False, varying