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>

plugin/hooks/scribe_static_context.md

@@ -23,6 +23,12 @@ for the operator's work, and as your own working memory across sessions.
   moment it's complete.
 - Do **not** keep the operator's rules, plans, or project notes in local
   memory / CLAUDE.md in parallel with Scribe — Scribe holds the single copy.
+- **Compact at clean seams** — because you record as you go, a context
+  compaction is safe: the durable record lives in Scribe, not the transcript.
+  After finishing a block of work in a long session, make sure in-flight state
+  is logged to Scribe, then tell the operator it's a good, safe moment to
+  `/compact` (name what you logged). You can't run it yourself — surface the
+  recommendation and let them decide. Suggest it at seams, not every turn.
 
 If the Scribe tools are unavailable, say so rather than silently falling back
 to local notes.