align(4909c): the command and write rule arms reserve a line for a preference

PRE_TOOL_RULE and WRITE_PATH_RULE now take preference_slot=True, like
PROMPT_RULE. When no preference placed on score, the arm asks once more for
the best preference over the same bar, and shows it as one extra line.

Operator ruling (2026-10-05): yes. A preference about how to act ("let each
action land before the next") is ranked against every rule whose trigger
names the same command; the act is its last chance to shape anything.

Cost: one kind-filtered search per call that placed no preference. The
query embedding is memoised per request on both hook routes, so no extra
model call. Expect a new stream of preference_slot rows from the two act
arms; preference_slot's call count will rise roughly by pre_tool_rule's and
write_path_rule's (~23k calls over 14 days before this change), and its
zero-result share will rise with it, since most commands have no matching
preference.

Tests: the tool-arm call-row tests count rows under pre_tool_rule only (the
slot logs under its own name), and the write-arm bar test reads the arm's
own search, which is the first.

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

src/grimoire/services/retrieval_pipeline.py

@@ -474,9 +474,10 @@ class RuleArm:
 RULE_FLOOR_KEY = "kb_rule_threshold"
 RULE_FLOOR_DEFAULT = 0.70
 
-# The arms differ on purpose where these flags differ. Whether the prompt arm
-# should band, and whether the act arms should reserve a preference, are open
-# questions to settle on telemetry, not by symmetry.
+# The arms differ on purpose where these flags differ: the prompt arm takes no
+# band, so its budget alone decides how many hits it shows, and the act arms
+# band and may hold the act. Every arm that annotates reserves a line for a
+# preference.
 PROMPT_RULE = RuleArm(
     "prompt_rule", band=False, compact_tail=False, checkpoint=False,
     preference_slot=True,
@@ -494,7 +495,7 @@ PROMPT_RULE = RuleArm(
 )
 PRE_TOOL_RULE = RuleArm(
     "pre_tool_rule", band=True, compact_tail=True, checkpoint=True,
-    preference_slot=False,
+    preference_slot=True,
     tuning=Surface(
         name="pre_tool_rule",
         floor_key=RULE_FLOOR_KEY,
@@ -509,7 +510,7 @@ PRE_TOOL_RULE = RuleArm(
 )
 WRITE_PATH_RULE = RuleArm(
     "write_path_rule", band=True, compact_tail=True, checkpoint=True,
-    preference_slot=False,
+    preference_slot=True,
     tuning=Surface(
         name="write_path_rule",
         floor_key=RULE_FLOOR_KEY,
@@ -703,6 +704,13 @@ async def _reserve_slot_for_preference(
     same shape one corpus over, where snippets lose to project records that
     merely resemble the query.
 
+    The act arms reserve the slot for the same reason one step later. A
+    preference about how to act ("let each action land before the next") is
+    ranked against every rule whose trigger names the same command, and the
+    act is its last chance: once the command has run there is nothing left
+    for it to shape. The slot's query reuses the arm's query, so it costs one
+    kind-filtered search and no extra embedding.
+
     THE SLOT BUYS POSITION, NOT A LOWER BAR — same as `reuse_slot`, which also
     reserves at `cfg["threshold"]`. A weak preference cannot buy the slot, so
     silence stays the default and the reserved line is never worse than the