feat(410): the server orients with a client-neutral index; the live context carries live state only (#4030)

Step 3 of milestone 410 "One owner per piece of guidance".

_INSTRUCTIONS is rewritten as an index for every MCP client (1,597 of 2,000
chars): orient, rules, recall, record, plan, ids, reuse, UI, report. Each
line names its tool, and the block says every reflex is stated in full in
the using-scribe skill and in each tool description.
- names no client: CLAUDE.md, auto-memory and "the client injects ~2k
  chars" are gone
- gains the two reflexes it lacked: records that cite each other go through
  create_records with {{ref:N}}, and reports start from `placement`

The comment block above it now explains ownership (decision #4027) instead of
accumulating per-milestone trade history, and keeps the budget and its
reason (#2562).

build_session_context states only what the server knows about this session:
the active project and open work, its design system, an unbound-repo hint,
or that no project is bound. Removed: the "you are not holding the
operator's rules" section, the closing "Reflex: search Scribe" line, the
design-system usage sentence, and the plugin-specific header. using-scribe
owns all of that. The truncation note no longer restates the rules ask.

Tests: a pin that the live context carries no rules reflex; the cap test
drives truncation through the unbound-repo hint, since a bare session is now
one line; the budget test message describes the index.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_instruction_surfaces_agree.py

@@ -166,11 +166,11 @@ INSTRUCTIONS_BUDGET = 2000
 def test_instructions_fit_the_fold():
     text = _instructions_text()
     assert len(text) <= INSTRUCTIONS_BUDGET, (
-        f"_INSTRUCTIONS is {len(text)} chars; the client injects only ~2,048 "
-        f"and silently cuts the rest (#2562). This block is a MAP — move the "
-        f"detail to the tool's docstring (delivered at reach-for time), the "
-        f"plugin static context (always delivered), or a skill; see the "
-        f"comment above _INSTRUCTIONS."
+        f"_INSTRUCTIONS is {len(text)} chars; Claude Code injects only ~2,048 "
+        f"and silently cuts the rest (#2562). This block is an INDEX — state "
+        f"the topic in full on its owner (a skill or the tool's docstring, "
+        f"decision #4027) and give it at most a line here; see the comment "
+        f"above _INSTRUCTIONS."
     )
 
 
@@ -289,8 +289,8 @@ def test_a_surface_claiming_rules_bind_also_names_what_does_not():
 # The reporting-back skill carries the shapes, but a skill only helps if it
 # fires. The reflex that sends a session to it lives on the two plugin
 # surfaces a session always reads; the in-band cue on update_task is the half
-# that reaches clients with no plugin at all. _INSTRUCTIONS took no line, on
-# purpose — server.py's comment block records why.
+# that reaches clients with no plugin at all. Since milestone 410 the server's
+# index carries a REPORT line too, pointing at `placement`.
 
 REPORT_REFLEX = "report back in a shape the operator can read"
 REPORT_SURFACES = (