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>

plugin/skills/using-scribe/SKILL.md

@@ -220,6 +220,15 @@ Two constraints on *how* that's achieved:
    either: `verify_snippet` compares the recorded location and code against the
    repo, which is richer and already wired to drift detection.
 
+11. **Report back in a shape the operator can read.** They were not there while
+   you worked, so organise the reply around **where the work stands**, not the
+   order you did things in: which task or milestone it belongs to, what now
+   works, what needs them, and what comes next. Take the placement from the
+   `placement` block that `create_task` / `update_task` return — the milestone,
+   step N of M, the next open step — rather than from memory. The
+   `reporting-back` skill holds the shape for each kind of reply: completions,
+   findings, decisions, handoffs, "where are we".
+
 ## Stay inside the active project's scope
 
 Once a project is in scope — you called `enter_project`, or the working repo is
@@ -300,6 +309,6 @@ nothing will tell you it drifted.
 
 ## Other Scribe process-skills
 
-This plugin also ships focused process-skills — writing-plans, systematic
-debugging, verification, and brainstorming. Reach for the matching one when its
+This plugin also ships focused process-skills — writing-plans, reporting-back,
+systematic debugging, verification, and brainstorming. Reach for the matching one when its
 situation arises, the same way you reach for this skill.