feat(410): the Claude Code plugin becomes a thin adapter (#4031)

Step 4 of milestone 410 "One owner per piece of guidance". The plugin's
static session context was a second copy of using-scribe and the server
index. It now says only what Claude Code needs said: 8,705 -> 1,791 chars.

scribe_static_context.md:
- points at using-scribe for how to work with Scribe, and names the process
  skills
- Claude Code specifics: keep one copy in Scribe rather than CLAUDE.md or
  auto-memory (leave auto-memory at its default); injected lines are
  retrieval, not the whole set; compact at clean seams; stored Processes
  arrive as scribe-proc-* skills with /scribe:sync; say so when the tools
  are unavailable
- retired: the restated reflexes, "how the surfaces divide the work", and
  the "follow the surface that assumes least" precedence (decision #4027)

Hook behaviour is unchanged. The SessionStart hook header says what the
static tier now carries, and the unreachable-instance status points at the
using-scribe skill instead of "the standing guidance above".

README and manifest describe the plugin as the Claude Code adapter over the
shared, client-neutral skills. Fixed along the way: the README said the
SessionStart hook "injects your rules" and suggested disabling auto-memory,
both contradicting the product since milestone 394.

Tests: the session-start rules guards now pin the owner (using-scribe) and
the index (_INSTRUCTIONS) rather than every surface; the Systems-reflex and
snippet-trigger guards pin their owners; the reporting-reflex guard pins
using-scribe. The loss guard and client-neutral guard stay green. Plugin
version minted.

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

tests/test_instruction_surfaces_agree.py

@@ -69,13 +69,19 @@ ABSENCE_CLAIMS = (
     "not evidence there is none",
 )
 
-# Surfaces a session loads before substantive work. Hand-written because
-# "is this a session-start surface?" is an editorial fact, not a derivable one —
-# but each entry is asserted to EXIST, so a move or rename fails loudly here
-# instead of quietly dropping that surface from the check.
+# The surfaces that STATE the rules reflex. Hand-written because "who owns
+# this?" is an editorial fact, not a derivable one — but each entry is asserted
+# to EXIST, so a move or rename fails loudly here instead of quietly dropping
+# that surface from the check.
+#
+# Since milestone 410 (decision #4027) that is the owner and the index, not
+# every surface a session loads: `using-scribe` states the reflex in full and
+# the server's `_INSTRUCTIONS` gives it one line for every MCP client. The
+# Claude Code adapter's static context used to be a third copy; it now points
+# at the skill instead, and tests/test_guidance_ownership.py keeps the topic
+# from falling off.
 SESSION_START_SURFACES = (
     ROOT / "src" / "scribe" / "mcp" / "server.py",
-    ROOT / "plugin" / "hooks" / "scribe_static_context.md",
     ROOT / "plugin" / "skills" / "using-scribe" / "SKILL.md",
 )
 
@@ -174,40 +180,42 @@ def test_instructions_fit_the_fold():
     )
 
 
-def test_floor_states_the_systems_reflex():
-    """Write-time tagging guidance must live on the surface that always arrives.
+def test_the_systems_reflex_is_stated_by_its_owner():
+    """Write-time tagging guidance must be stated as a reflex, not only per tool.
 
     #2562's behavioral finding: with the guidance only in tool descriptions,
-    sessions filed records untagged. The static context is the delivery floor,
-    so the tag-as-you-write reflex has to be stated there.
+    sessions filed records untagged. The tag-as-you-write reflex was pinned on
+    the static context then; since milestone 410 its owner is using-scribe
+    (decision #4027), with the in-band `systems_hint` as the half that fires on
+    its own.
     """
-    floor = (ROOT / "plugin" / "hooks" / "scribe_static_context.md").read_text()
-    for needle in ("system_ids", "create_system"):
-        assert needle in floor, (
-            f"plugin/hooks/scribe_static_context.md no longer mentions "
-            f"{needle} — the Systems tagging reflex must be stated on the "
-            f"floor, not only in tool descriptions (#2562)."
+    owner = (ROOT / "plugin" / "skills" / "using-scribe" / "SKILL.md").read_text()
+    for needle in ("system_ids", "create_system", "systems_hint"):
+        assert needle in owner, (
+            f"plugin/skills/using-scribe/SKILL.md no longer mentions "
+            f"{needle} — the Systems tagging reflex must be stated by its "
+            f"owner, not only in tool descriptions (#2562)."
         )
 
 
-def test_floor_names_the_snippet_recording_triggers():
-    """The floor must state the pattern-library recording model, by name.
+def test_the_snippet_recording_triggers_are_stated_by_their_owner():
+    """The pattern-library recording model must be stated, by name.
 
     #2664's behavioral finding: recording guidance as a trailing clause of the
     reuse bullet converted zero times outside snippet-minded sessions. The
     2026-08-16 ruling (decision #2686) then replaced the reactive model
     entirely: every shape is recorded at FIRST build — no "will it recur?"
-    judgment — and second-copy consolidation is only the backstop. The floor
-    is the delivery surface for that reflex, so all three elements must stay
-    stated: the tool, the first-build trigger, and the backstop.
+    judgment — and second-copy consolidation is only the backstop. All three
+    elements must stay stated: the tool, the first-build trigger, and the
+    backstop. Since milestone 410 the owner is the reusing-code skill.
     """
-    floor = (ROOT / "plugin" / "hooks" / "scribe_static_context.md").read_text()
+    owner = " ".join((ROOT / "plugin" / "skills" / "reusing-code" / "SKILL.md").read_text().split())
     for needle in ("create_snippet", "first build", "second copy"):
-        assert needle in floor, (
-            f"plugin/hooks/scribe_static_context.md no longer states the "
+        assert needle in owner, (
+            f"plugin/skills/reusing-code/SKILL.md no longer states the "
             f"snippet-recording model ({needle!r}) — record-every-shape-at-"
             f"first-build with second-copy consolidation as the backstop must "
-            f"be stated on the floor (#2664, decision #2686)."
+            f"be stated by its owner (#2664, decision #2686)."
         )
 
 
@@ -287,19 +295,18 @@ def test_a_surface_claiming_rules_bind_also_names_what_does_not():
 # ── Reporting back (milestone 409 step 3) ──────────────────────────────
 #
 # 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. Since milestone 410 the server's
-# index carries a REPORT line too, pointing at `placement`.
+# fires. The reflex that sends a session to it is stated in using-scribe; the
+# server's index carries a REPORT line pointing at `placement`, and the in-band
+# cue on update_task is the half that fires on its own in every client. The
+# static context was a second plugin-side copy until milestone 410.
 
 REPORT_REFLEX = "report back in a shape the operator can read"
 REPORT_SURFACES = (
-    ROOT / "plugin" / "hooks" / "scribe_static_context.md",
     ROOT / "plugin" / "skills" / "using-scribe" / "SKILL.md",
 )
 
 
-def test_the_reporting_reflex_reaches_every_plugin_surface():
+def test_the_reporting_reflex_is_stated_in_using_scribe():
     missing = []
     for path in REPORT_SURFACES:
         text = " ".join(path.read_text().split()).lower()