refactor(retrieval): the specs are the registry - SURFACES, the ranked POINTS rows and RANKED_SOURCES are read off the pipeline specs (milestone 456 step 5, #4907)

Each arm spec now carries its tuning pair (Surface, moved verbatim into
retrieval_pipeline) and a Declared block - what the telemetry readout
must know and cannot read off its rows. The two ranked stages that are
not arms (preference_slot, rule_via_lesson) are RankedSource specs, and
the note slots carry their own declaration.

- retrieval_surfaces.SURFACES = the TUNED_ARMS tuning, same order
- retrieval_registry.POINTS ranked rows = one per spec in RANKED; the
  lookups, asked, ambient and pull rows stay declared there
- rule_usage.RANKED_SOURCES = RULE_RANKED_SOURCES + moment_rule

Settings keys, defaults, prose and order are unchanged (checked field by
field against HEAD). tests/test_retrieval_specs.py pins the derivation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_retrieval_specs.py

@@ -0,0 +1,71 @@
+"""The specs are the registry (milestone 456 step 5).
+
+Three lists used to be kept by hand beside the arms — the tuning table, the
+ranked rows of the telemetry registry, and the rule-usage denominator — with
+tests to make them agree. They are now read off the pipeline's specs. These
+pin the derivation itself: every arm is tunable, every ranked source is
+measured with the declaration its spec carries, and the rule-usage
+denominator counts exactly the rule surfaces a ranker chose.
+"""
+from __future__ import annotations
+
+from scribe.services import retrieval_pipeline as rp
+from scribe.services.retrieval_registry import POINTS, UNBIDDEN
+from scribe.services.retrieval_surfaces import SURFACES
+from scribe.services.rule_usage import RANKED_SOURCES, is_ambient
+
+
+def test_every_arm_is_one_tunable_surface_in_the_order_settings_lists_them():
+    assert [arm.source for arm in rp.TUNED_ARMS] == list(SURFACES)
+    for arm in rp.TUNED_ARMS:
+        assert arm.tuning is not None, f"{arm.source} has no floor or budget"
+        # The join key: the surface a tuner moves and the rows it is judged by
+        # must name the same arm.
+        assert arm.tuning.name == arm.source
+        assert SURFACES[arm.source] is arm.tuning
+
+
+def test_every_ranked_source_is_measured_as_its_spec_declares():
+    sources = [spec.source for spec in rp.RANKED]
+    assert len(sources) == len(set(sources)), f"a source is declared twice: {sources}"
+    for spec in rp.RANKED:
+        d = spec.declared
+        assert d is not None and d.what.strip(), f"{spec.source} declares nothing"
+        point = POINTS[spec.source]
+        assert point.kind == UNBIDDEN
+        assert point.what == d.what
+        assert point.fixed_query == d.fixed_query
+        # A quiet source must say why, and only a quiet source may (#2475).
+        assert point.expects_traffic == (not d.quiet_because)
+        assert point.quiet_because == d.quiet_because
+
+
+def test_the_slots_are_measured_but_never_tuned():
+    for slot in (rp.PREFERENCE_SLOT, *rp.NOTE_SLOTS):
+        assert slot.source in POINTS
+        assert slot.source not in SURFACES
+
+
+def test_the_rule_denominator_is_every_rule_surface_a_ranker_chose():
+    rule_arms = {arm.source for arm in rp.RULE_ARMS}
+    assert rule_arms <= set(RANKED_SOURCES)
+    assert set(RANKED_SOURCES) == (
+        rule_arms | {rp.PREFERENCE_SLOT_SOURCE, rp.VIA_LESSON_SOURCE,
+                     rp.MOMENT_RULE_SOURCE}
+    )
+    # And a notes arm is not a RULE surface: its lines are not rules, so a
+    # rule pull cannot confirm them.
+    for arm in rp.NOTE_ARMS:
+        assert is_ambient(arm.source)
+
+
+def test_an_arm_added_without_tuning_would_be_caught():
+    """Rule 167: the first test has to be able to bite. SURFACES skips an arm
+    with no tuning rather than raising, so an arm added without one would
+    silently be untunable — and the order-equality assertion is what notices,
+    as this replays with one such arm appended."""
+    bare = rp.RuleArm("x_rule", band=False, compact_tail=False,
+                      checkpoint=False, preference_slot=False)
+    arms = (*rp.TUNED_ARMS, bare)
+    derived = {a.tuning.name: a.tuning for a in arms if a.tuning is not None}
+    assert [a.source for a in arms] != list(derived)