docs(6206): retrieval, snippets, notes routes and rule_usage model drop citations

Corrected while reading: routes/notes.py said lessons and snippets pass the
owner to set_record_systems, "a real inconsistency". Every door passes the
caller; the comment now says so.

rule_usage's model docstring states what an outcome measures and why the
row cannot share the note table, without the measurement and record ids
that motivated it.

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

src/scribe/models/rule_usage.py

@@ -7,16 +7,15 @@ from scribe.models.base import CreatedAtMixin, iso
 SURFACED = "surfaced"
 PULLED = "pulled"
 
-# The outcome half (#4212, milestone 419). A rule that was read and then
-# ignored has always been indistinguishable from one that was read and
-# obeyed; these are the two events that can tell them apart.
+# The outcome half. Without these, a rule that was read and then ignored is
+# indistinguishable from one that was read and obeyed; these are the two
+# events that can tell them apart.
 #
 # There is deliberately NO third value for "read and ignored". That state is
-# real and is the whole point of the milestone, but it cannot be reported:
-# an agent that knew it was ignoring a rule would not be ignoring it. It is
+# real and is the point of measuring outcomes, but it cannot be reported: an
+# agent that knew it was ignoring a rule would not be ignoring it. It is
 # DERIVED — a pull with no outcome — and an enum member for it would collect
-# nothing while reading as though it had measured something, which is #3311's
-# failure exactly.
+# nothing while reading as though it had measured something.
 APPLIED = "applied"
 DEPARTED = "departed"
 OUTCOMES = (APPLIED, DEPARTED)
@@ -26,15 +25,14 @@ class RuleUsageEvent(Base, CreatedAtMixin):
     """One row per time a rule was SURFACED to the agent, PULLED in full, or
     ACTED ON — applied, or departed from with a stated reason.
 
-    The sibling `note_usage_events` has had since 2026-07, third in the line
-    after `rule_embeddings` and `rule_versions` — and, like those, it exists
-    because the rule side kept inheriting machinery built for notes and
-    quietly getting the weaker version of it.
+    The rule-side sibling of `note_usage_events`, beside `rule_embeddings`
+    and `rule_versions` — each exists because machinery built for notes gives
+    rules the weaker version of it.
 
     WHY RULES NEED THEIR OWN AND CANNOT SHARE THE NOTE TABLE. Not squeamishness
     about a polymorphic column — the row shares no note-specific fields and the
     aggregate readout is the same shape, which is the strongest case for
-    sharing that note #3163 admits. What decides it is IDENTITY AT RESTORE. A
+    sharing there is. What decides it is IDENTITY AT RESTORE. A
     note id and a rule id are different namespaces resolved through different
     maps, and `note_usage_events`'s importer maps `note_id` through
     `note_id_map` and drops what does not resolve. A rule id parked in that
@@ -42,11 +40,10 @@ class RuleUsageEvent(Base, CreatedAtMixin):
     happened to take that number — telemetry that is not merely lost but wrong,
     and wrong in a way nothing downstream could detect.
 
-    WHAT THIS MEASURES, AND WHY IT DID NOT EXIST. The write-path standing-rule
-    arm is the only retrieval surface in Scribe whose usefulness cannot be
-    observed — and, not coincidentally, the only one that has never declined to
-    fire (#3311: 296 calls, zero zero-result, 100% clearing its threshold).
-    `retrieval_logs` gives it scores; scores say what the ranker thought, never
+    WHAT THIS MEASURES. A standing-rule arm's usefulness cannot be observed
+    from its scores: an arm can fire on every call, clearing its threshold
+    every time, and say nothing about whether it helped. `retrieval_logs`
+    gives it scores; scores say what the ranker thought, never
     whether the hint landed. Without a pull counter no install can tune the arm
     from evidence, only from the shape of a histogram.
 
@@ -58,7 +55,7 @@ class RuleUsageEvent(Base, CreatedAtMixin):
     forty times and opened never, because that evidence is precisely the case
     for having deleted it.
 
-    Cells left deliberately empty (note #3163's step 3): no share ACL — rules
+    Cells left deliberately empty: no share ACL — rules
     have none of their own; no soft delete — nothing restores a telemetry row,
     and the table is append-only; no embedding — an event is not a document.
     """
@@ -76,7 +73,7 @@ class RuleUsageEvent(Base, CreatedAtMixin):
     # 'surfaced' | 'pulled' | 'applied' | 'departed'
     #
     # Plain Text with no CHECK, as created in 0094 — which is why 0106 added
-    # the outcome pair without a DROP/ADD migration. Rule 36 governs
+    # the outcome pair without a DROP/ADD migration — that step is for
     # CHECK-whitelisted columns and this is not one. Said here as well as in
     # the migration because this is where the next person adding a value will
     # look first.
@@ -84,9 +81,9 @@ class RuleUsageEvent(Base, CreatedAtMixin):
 
     # Which surface produced it. A CONVENTION, not a fixed vocabulary, and the
     # note twin's comment explains why this one deliberately does not enumerate
-    # its members: the previous such list went stale, naming a source nothing
-    # wrote while omitting ones that existed, and a half-true enumeration reads
-    # as authoritative in exactly the way that misleads (#2476).
+    # its members: such a list goes stale, naming a source nothing writes while
+    # omitting ones that exist, and a half-true enumeration reads as
+    # authoritative in exactly the way that misleads.
     # `grep -rn record_rule_pulled\|record_rule_surfaced src/` is the
     # authoritative list, and unlike a comment it cannot drift.
     #