feat(409): the reporting reflex reaches every surface a session reads (#4012)

Step 3 of milestone 409 "Response shapes". Step 2's reporting-back skill
only helps if it fires, and only exists in the Claude Code plugin.

- scribe_static_context.md and using-scribe (new reflex 11) say: report back
  in a shape the operator can read, placed from the `placement` block rather
  than memory, and point at the reporting-back skill. using-scribe also lists
  it among the sibling process-skills.
- update_task returns a one-line `report_back` cue when a task is closed
  (done or cancelled). A tool response is the only surface every MCP client
  sees, at the moment the report is about to be written.
- _INSTRUCTIONS takes no line: there is no budget without trading out a
  session-start reflex. The decision is recorded in server.py's comment
  block so it is not re-litigated blind.
- Guards: test_instruction_surfaces_agree pins the reflex and the placement
  pointer on both plugin surfaces; a tool test pins the cue on closing
  statuses and its absence on every other update.

Plugin version minted.

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

tests/test_instruction_surfaces_agree.py

@@ -322,3 +322,39 @@ def test_a_surface_claiming_rules_bind_also_names_what_does_not():
         f"'how the operator likes this done' as something it may not proceed "
         f"past. Name the other kind, however briefly."
     )
+
+
+# ── 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. _INSTRUCTIONS took no line, on
+# purpose — server.py's comment block records why.
+
+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():
+    missing = []
+    for path in REPORT_SURFACES:
+        text = " ".join(path.read_text().split()).lower()
+        if REPORT_REFLEX not in text or "reporting-back" not in text:
+            missing.append(str(path.relative_to(ROOT)))
+    assert not missing, (
+        f"these surfaces no longer send a session to the reporting-back skill "
+        f"({REPORT_REFLEX!r} plus the skill's name): {missing}. Without the "
+        f"reflex the skill loads only when its description happens to match."
+    )
+
+
+def test_the_reporting_reflex_takes_placement_from_the_record():
+    """The failure milestone 409 began from: a placement reconstructed from
+    memory reads exactly like a real one when it is wrong."""
+    for path in REPORT_SURFACES:
+        text = " ".join(path.read_text().split())
+        assert "`placement`" in text, f"{path.relative_to(ROOT)} no longer points at the placement block"