feat(plugin): compaction-hygiene guidance — recommend safe compaction at seams

#834. The pre-compaction complement to the shipped post-compaction re-grounding
banner. Because Scribe records progress as you go (task status, work-logs,
decision notes), a compaction at a clean work-seam is lossless — so guide the
model to recommend it proactively rather than letting auto-compact fire mid-task.

Placed in the ALWAYS-loaded channels (operator wants it consistently in context,
not relevance-gated like a skill): MCP _INSTRUCTIONS (every handshake) + the
static SessionStart floor (every session, MCP-independent). Behavior: at the end
of a block of work in a long session, ensure in-flight state is logged, then tell
the operator it's a safe moment to /compact (naming what was logged); recommend
at seams, not every turn; the model can't run /compact itself.

plugin.json 0.1.8 → 0.1.9 so clients re-pull the static-context change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/scribe/mcp/server.py

@@ -94,6 +94,21 @@ Keep task state honest — this is what makes the project a trustworthy record:
   (tag it `issue`) so it's findable later — even one solved in passing is worth
   two lines, so it isn't diagnosed from scratch next time.
 
+Compaction hygiene — recommend compacting at clean seams. Because you record
+progress as you go, a context compaction is SAFE: the durable state lives in
+Scribe (task status, work-logs, decision notes), not the transcript, so it
+survives the summary. Use this rather than letting auto-compaction fire mid-task:
+- At the end of a coherent block of work (a task closed, a plan phase finished)
+  in a long session, first make sure in-flight state is actually in Scribe —
+  update task status, add a work-log, capture any decision as a note. Surface
+  the few things worth logging before suggesting the compact.
+- Then tell the operator it's a good, safe moment to /compact, naming what you
+  logged ("logged to #X/#Y — safe to /compact, nothing will be lost"). You
+  cannot run /compact yourself; surface the recommendation and let them decide.
+- Recommend it at genuine seams, not every turn. The next session's start will
+  prompt you to reload your bearings from Scribe — so a clean-seam compact plus
+  that reload loses nothing.
+
 Scribe maintains a Rulebook system (Rulebook -> Topic -> Rule). Rules carry
 an actionable statement plus optional Why and How-to-apply context. At the
 start of any session that touches Scribe, call list_always_on_rules() to