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_services_plugin_context.py

@@ -114,6 +114,10 @@ async def test_build_session_context_includes_project_when_scoped():
     # No design system on the project -> no design block at all. An install with
     # none is the ordinary case, not a degraded one.
     assert "## Design system" not in out["context"]
+    # Live state only (decision #4027): how to work with Scribe is the
+    # using-scribe skill's to say. A restated reflex here is a copy that drifts.
+    assert 'content_type="rule"' not in out["context"]
+    assert "Reflex:" not in out["context"]
 
 
 @pytest.mark.asyncio
@@ -246,14 +250,16 @@ async def test_build_session_context_caps_length():
 
     Patching the cap rather than manufacturing 9,000 characters keeps the test
     about the TRUNCATION PATH — that it cuts, and that it says it cut — which
-    is the part a reader depends on.
+    is the part a reader depends on. The unbound-repo hint supplies the text:
+    since milestone 410 the block carries live state only, and a bare session
+    is a one-liner.
     """
     from scribe.services import plugin_context as pc
 
-    with patch.object(pc, "_MAX_CHARS", 120):
-        out = await pc.build_session_context(user_id=7)
+    with patch.object(pc, "_MAX_CHARS", 60):
+        out = await pc.build_session_context(user_id=7, unbound_repo="host/owner/repo")
 
-    assert len(out["context"]) <= 120 + 60  # cap + truncation note
+    assert len(out["context"]) <= 60 + 20  # cap + truncation note
     assert "truncated" in out["context"], (
         "the block was cut without saying so — a reader cannot tell a "
         "truncated context from a short one"