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>

src/scribe/services/rule_usage.py

@@ -89,6 +89,7 @@ from scribe.models.rule_usage import (
     APPLIED, DEPARTED, OUTCOMES, PULLED, SURFACED, RuleUsageEvent,
 )
 from scribe.services.background import report_telemetry_failure, spawn
+from scribe.services.retrieval_pipeline import MOMENT_RULE_SOURCE, RULE_RANKED_SOURCES
 
 logger = logging.getLogger(__name__)
 
@@ -98,31 +99,19 @@ logger = logging.getLogger(__name__)
 # Membership is the whole definition of the pull-through denominator: a ranked
 # surfacing is a claim ("this rule may apply to what you are doing") that a pull
 # can confirm or refute, while an ambient one is a delivery nobody decided on.
-# Add a source here only when a ranker picked it.
+# The ranked half is read off the retrieval pipeline's specs (milestone 456
+# step 5): every rule arm — the reply backstop included, which records only
+# the rule that HELD the reply — the preference slot, which is a ranker's
+# choice twice over, and the rule reached through a confirmed lesson link,
+# whose own source lets its pull-through read apart from a direct match
+# (#4636). An arm added there is counted here by construction.
 RANKED_SOURCES = (
-    "write_path_rule", "pre_tool_rule", "prompt_rule",
-    # The reply backstop records only the rule that HELD the reply — a claim
-    # put in front of the reader as plainly as any line, and one a pull
-    # confirms or refutes the same way.
-    "reply_rule",
+    *RULE_RANKED_SOURCES,
     # A rule mounted on a moment (milestone 458). Not a ranker's pick, but
     # not bulk either: somebody decided this rule applies at this moment, and
     # that is exactly the claim a pull can confirm or refute. Its
     # pull-through is the evidence for whether a mount earns its line.
-    "moment_rule",
-    # A reserved slot is a ranker's choice twice over — it ran a query AND
-    # decided a kind was worth guaranteeing a place. Left out, its line would
-    # be counted as bulk delivery and drop out of the denominator, so the one
-    # surface built because a record class kept losing would be the one whose
-    # hits nobody could confirm.
-    "preference_slot",
-    # The completion-report lookup on update_task (milestone 409 step 4). It
-    # runs its own query and shows only what cleared the bar — a ranker.
-    "report_preference",
-    # A rule reached through a lesson confirmed as an instance of it (#4633).
-    # Its own source so its pull-through reads apart from the rule's direct
-    # match — whether the lesson route earns its line is #4636's question.
-    "rule_via_lesson",
+    MOMENT_RULE_SOURCE,
 )