refactor(mcp): _INSTRUCTIONS orients the workflow, not a rulebook (#4389)

Spike #4389 read the spec, Claude's docs and a dozen servers: the field is
for how the tools fit together, and the field runs ~600-1,600 characters.
Ours sat at the 2,048 cap as a keyword index that also carried stance.

- JUDGE, REPORT and MISSED leave the index. They fire mid-work, not at
  session start; using-scribe and reporting-back state them in full, and
  `placement`/`report_back` cue reporting in-band. No skill text changes.
- The rest is rewritten as plain practices (1,503 chars) and keeps every
  session-start marker the ownership registry pins.
- INSTRUCTIONS_BUDGET 2000 -> 1600; the three index markers are dropped
  from the registry; the miss-route index test now checks that the index
  keeps what_might_apply and stays off the route.

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

tests/test_guidance_ownership.py

@@ -25,7 +25,10 @@ WHAT IT PINS
    moments declares that in `shared_with`, with the reason beside it.
 3. THE INDEX NAMES THE SESSION-START REFLEXES. `_INSTRUCTIONS` is the one
    surface every MCP client receives, so each reflex it indexes keeps its
-   `index` markers there — a one-line pointer, not a copy.
+   `index` markers there — a one-line pointer, not a copy. Only session-start
+   practices carry `index`: judging, reporting and the missed-rule route fire
+   mid-work, and #4389 took them out of the index (the skills and the in-band
+   responses carry them at the moment they apply).
 
 WHAT IT CANNOT SEE
 
@@ -174,8 +177,7 @@ TOPICS: tuple[Topic, ...] = (
     # returned zero events. Machinery with no route to it.
     Topic("a missed rule is a trigger to fix before a floor to move", U,
           ("retrieval_telemetry", "tune_retrieval", "retrieval_surfaces"),
-          "take it to the record first and the dial second",
-          index=("retrieval_telemetry",)),
+          "take it to the record first and the dial second"),
     Topic("ask what already covers a moment before writing a record", U,
           ("what_might_apply",), "ask what already covers that moment"),
     Topic("reference notes update in place; dev-logs don't", U, ("reference note",),
@@ -193,7 +195,7 @@ TOPICS: tuple[Topic, ...] = (
           ("create_snippet", "when_to_use", "first build", "second copy"),
           "prior art offered beside a write is not noise", index=("create_snippet",)),
     Topic("report back where the work stands", "skill:reporting-back", ("reporting-back", "placement"),
-          "take the placement from the record", index=("placement",)),
+          "take the placement from the record"),
     Topic("the operator's own reply shapes come first", "skill:reporting-back",
           ("reply_preferences", 'content_type="rule"'),
           "the operator's own shapes come first"),
@@ -225,8 +227,7 @@ TOPICS: tuple[Topic, ...] = (
     # that trimming one cannot quietly take the other with it.
     Topic("the agent judges the record, and judging is attended", U,
           ("judge of record", "attended", "classify_shapes"),
-          "a record that is wrong stays wrong until something rewrites it",
-          index=("judge of record",)),
+          "a record that is wrong stays wrong until something rewrites it"),
     Topic("a finding surfaced and not judged is a finding dropped",
           "skill:reporting-back", ("you are the judge", "hard to reverse"),
           "it reads as diligence and functions as a backlog"),