Add before/after session events with cancellation support

- Merge branch event into session with before_branch/branch reasons
- Add before_switch, before_clear, shutdown reasons
- before_* events can be cancelled with { cancel: true }
- Update RPC commands to return cancelled status
- Add shutdown event on process exit
- New example hooks: confirm-destructive, dirty-repo-guard, auto-commit-on-exit

fixes #278

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## [Unreleased]
 
+### Breaking
+
+- **Session hooks API redesign**: Merged `branch` event into `session` event. `BranchEvent`, `BranchEventResult` types and `pi.on("branch", ...)` removed. Use `pi.on("session", ...)` with `reason: "before_branch" | "branch"` instead. `AgentSession.branch()` returns `{ cancelled }` instead of `{ skipped }`. `AgentSession.reset()` and `switchSession()` now return `boolean` (false if cancelled by hook). RPC commands `reset`, `switch_session`, and `branch` now include `cancelled` in response data. ([#278](https://github.com/badlogic/pi-mono/issues/278))
+
+### Added
+
+- **Session lifecycle hooks**: Added `before_*` variants (`before_switch`, `before_clear`, `before_branch`) that fire before actions and can be cancelled with `{ cancel: true }`. Added `shutdown` reason for graceful exit handling. ([#278](https://github.com/badlogic/pi-mono/issues/278))
+
 ### Fixed
 
 - **File tab completion display**: File paths no longer get cut off early. Folders now show trailing `/` and removed redundant "directory"/"file" labels to maximize horizontal space. ([#280](https://github.com/badlogic/pi-mono/issues/280))