pi extension: herdr never shows the agent as blocked while a revdiff review is open

Current behavior

With the pi plugin, revdiff_review runs revdiff in-place: runDirectReview in plugins/pi/extensions/revdiff.ts does spawnSync(revdiffBin, ..., { stdio: "inherit" }), so pi is suspended inside the tool call while the user reviews. To anything supervising the agent from outside, the session looks busy rather than waiting on the user.

Concrete case: herdr gets omp/pi lifecycle state from its installed hook integration (which disables herdr's screen-scraping fallback for the pane). The integration reports working for the entire review, because a parked tool call is indistinguishable from active work. Result: no blocked state in the sidebar, no notification, and herdr agent wait <pane> --until blocked never fires — easy to miss that the agent is waiting.

The standalone launcher scripts already integrate with herdr for tab placement (the HERDR_ENV branch in launch-revdiff.sh), so herdr awareness exists in the project; only the pi in-place path lacks any state signal.

Expected behavior

While the revdiff UI owns the terminal, the supervising integration should see the session as blocked/waiting-for-user.

Reproduction

1. herdr integration install omp, start omp (TUI) inside a herdr pane.
2. /revdiff (or let the agent call revdiff_review).
3. While the review UI is open: herdr agent list → agent_status: working until revdiff exits.

Proposed fix

herdr's omp/pi integration listens on pi's shared extension event bus for a herdr:blocked channel. Emitting around the review run is enough:

pi.events.emit("herdr:blocked", { active: true, label: `revdiff review: ${launch.label}` });
try {
  result = await runDirectReview(ctx, launch, cwd);
} finally {
  pi.events.emit("herdr:blocked", { active: false });
}

EventBus.emit with no listener is a no-op, so this is free for non-herdr users and needs no HERDR_ENV gate. PR with this change: #319.

Environment

• revdiff-pi 0.4.1, omp 17.3.5, herdr 0.8.0 (omp integration v6), macOS arm64

(Disclosure: drafted by an AI coding agent on behalf of the human reporter, who reviewed and approved this text before it was posted.)

Start in plugins/pi/extensions/revdiff.ts at runDirectReview and inspect the pi extension event bus used by the herdr integration. Verify the review lifecycle reports a blocked state while the revdiff UI is open and clears it when the review exits, including error or cancellation paths; PR #319 already contains the proposed change.