enforce: hard rule + no self-merge in CLAUDE.md (#541)

Co-authored-by: Perplexity Computer <perplexity@tower.local>
Co-committed-by: Perplexity Computer <perplexity@tower.local>

CLAUDE.md

@@ -26,6 +26,12 @@ The Nexus connects to Timmy's backend via WebSocket for live cognitive state:
 - **Outbound**: `chat_message`, `presence`
 - **Graceful degradation**: When WS is offline, agents idle locally, chat shows "OFFLINE"
 
+## The Hard Rule — Read This First
+
+**Every PR: net ≤ 10 added lines.** Add 40, remove 30. Can't remove? Import instead.
+You MUST plan your cuts BEFORE writing new code. See CONTRIBUTING.md.
+Do NOT self-merge. Do NOT submit a PR that violates this.
+
 ## Conventions
 
 - **ES modules only** — no CommonJS, no bundler
@@ -49,10 +55,11 @@ The `nexus-merge-bot.sh` validates PRs before auto-merge:
 
 ## PR Rules
 
+- **Net addition limit: ≤ 10 lines.** No exceptions. Plan cuts before writing.
+- **Do NOT self-merge.** Submit the PR, a different user merges it.
 - Base every PR on latest `main`
 - Squash merge only
-- **Do NOT merge manually** — merge-bot handles merges
-- If merge-bot comments "CONFLICT": rebase onto `main` and force-push your branch
+- Include manual test plan + automated test output in PR body
 - Include `Fixes #N` or `Refs #N` in commit message
 
 ## Running Locally