feat(coding-agent): add extension project trust decisions

packages/coding-agent/docs/extensions.md

@@ -270,6 +270,7 @@ Run `npm install` in the extension directory, then imports from `node_modules/`
 ```
 pi starts
   │
+  ├─► project_trust (user/global and CLI extensions only, before project resources load)
   ├─► session_start { reason: "startup" }
   └─► resources_discover { reason: "startup" }
       │
@@ -334,6 +335,24 @@ exit (Ctrl+C, Ctrl+D, SIGHUP, SIGTERM)
   └─► session_shutdown
 ```
 
+### Startup Events
+
+#### project_trust
+
+Fired before pi decides whether to trust a project with trust inputs (`.pi`, `AGENTS.md`/`CLAUDE.md`, or `.agents/skills`). It runs during startup and when session replacement (for example `/resume`) enters a cwd whose trust has not been resolved in the current process. Only user/global extensions and CLI `-e` extensions participate; project-local extensions are not loaded until after trust is resolved.
+
+```typescript
+pi.on("project_trust", async (event, ctx) => {
+  // event.cwd - current working directory
+  // ctx has a limited trust context: cwd, mode, hasUI, and select/confirm/input/notify UI helpers
+  if (await ctx.ui.confirm("Trust project?", event.cwd)) {
+    return { trusted: true, remember: true };
+  }
+});
+```
+
+A `project_trust` handler must return `{ trusted }`; if a user/global or CLI extension registers this handler, it owns the decision. The first returned decision wins and suppresses the built-in trust prompt. Use `remember: true` to persist the decision; otherwise it applies only to the current process. Check `ctx.hasUI` before prompting. If no extension handles `project_trust`, normal trust resolution continues, including the built-in trust prompt when UI is available.
+
 ### Resource Events
 
 #### resources_discover
@@ -2567,6 +2586,7 @@ All examples in [examples/extensions/](../examples/extensions/).
 | `shutdown-command.ts` | Graceful shutdown command | `registerCommand`, `shutdown()` |
 | **Events & Gates** |||
 | `permission-gate.ts` | Block dangerous commands | `on("tool_call")`, `ui.confirm` |
+| `project-trust.ts` | Decide project trust from a user/global or CLI extension | `on("project_trust")`, trust UI, required trust result |
 | `protected-paths.ts` | Block writes to specific paths | `on("tool_call")` |
 | `confirm-destructive.ts` | Confirm session changes | `on("session_before_switch")`, `on("session_before_fork")` |
 | `dirty-repo-guard.ts` | Warn on dirty git repo | `on("session_before_*")`, `exec` |