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_retrieval_miss_route.py

@@ -139,20 +139,19 @@ def test_writing_a_new_record_asks_what_already_covers_the_moment():
     assert "no bar" in text
 
 
-def test_the_index_points_at_the_route_without_restating_it():
+def test_the_route_stays_off_the_index():
     """`_INSTRUCTIONS` is the only surface every MCP client gets (decision #4027).
 
-    It indexes; using-scribe states. A client with no Agent Skills support still
-    learns the ordering exists and which tool opens it.
+    It carried a one-line MISSED pointer to this route until #4389, which found
+    the index was being used as a rulebook: a missed rule is noticed mid-work,
+    not at session start, and the spec asks server instructions for the
+    workflow across tools, not stance. using-scribe states the route (the tests
+    above pin it); the index keeps what_might_apply, the tool that opens it.
 
-    Whitespace-flattened before matching. The block is hard-wrapped to fit a
-    2,000-character budget, so a phrase straddles a line break the moment
-    anything before it changes length — #4103 shipped a guard that broke
-    exactly that way, on text nobody had touched.
+    Whitespace-flattened before matching: the block is hard-wrapped, so a
+    phrase straddles a line break the moment anything before it changes length
+    (#4103).
     """
-    text = " ".join(_instructions().split())
-    assert "retrieval_telemetry" in text
-    assert "not a floor to move" in text
-    # The route itself must NOT be here — 2,000 characters is the whole budget
-    # and Claude Code cuts the rest mid-word (#2562).
-    assert "take it to the record first" not in text.lower()
+    text = " ".join(_instructions().split()).lower()
+    assert "what_might_apply" in text
+    assert "take it to the record first" not in text