Add setEditorText/getEditorText to hook UI context, improve custom() API

- Add setEditorText() and getEditorText() to HookUIContext for prompt generator pattern
- custom() now accepts async factories for fire-and-forget work
- Add CancellableLoader component to tui package
- Add BorderedLoader component for hooks with cancel UI
- Export HookAPI, HookContext, HookFactory from main package
- Update all examples to import from packages instead of relative paths
- Update hooks.md and custom-tools.md documentation

fixes #350

packages/coding-agent/examples/hooks/README.md

@@ -2,97 +2,53 @@
 
 Example hooks for pi-coding-agent.
 
-## Examples
-
-### permission-gate.ts
-Prompts for confirmation before running dangerous bash commands (rm -rf, sudo, chmod 777, etc.).
-
-### git-checkpoint.ts
-Creates git stash checkpoints at each turn, allowing code restoration when branching.
-
-### protected-paths.ts
-Blocks writes to protected paths (.env, .git/, node_modules/).
-
-### file-trigger.ts
-Watches a trigger file and injects its contents into the conversation. Useful for external systems (CI, file watchers, webhooks) to send messages to the agent.
-
-### confirm-destructive.ts
-Prompts for confirmation before destructive session actions (clear, switch, branch). Demonstrates how to cancel `before_*` session events.
-
-### dirty-repo-guard.ts
-Prevents session changes when there are uncommitted git changes. Blocks clear/switch/branch until you commit.
-
-### auto-commit-on-exit.ts
-Automatically commits changes when the agent exits (shutdown event). Uses the last assistant message to generate a commit message.
-
-### custom-compaction.ts
-Custom context compaction that summarizes the entire conversation instead of keeping recent turns. Uses the `before_compact` hook event to intercept compaction and generate a comprehensive summary using `complete()` from the AI package. Useful when you want maximum context window space at the cost of losing exact conversation history.
-
 ## Usage
 
 ```bash
-# Test directly
+# Load a hook with --hook flag
 pi --hook examples/hooks/permission-gate.ts
 
-# Or copy to hooks directory for persistent use
+# Or copy to hooks directory for auto-discovery
 cp permission-gate.ts ~/.pi/agent/hooks/
 ```
 
+## Examples
+
+| Hook | Description |
+|------|-------------|
+| `permission-gate.ts` | Prompts for confirmation before dangerous bash commands (rm -rf, sudo, etc.) |
+| `git-checkpoint.ts` | Creates git stash checkpoints at each turn for code restoration on branch |
+| `protected-paths.ts` | Blocks writes to protected paths (.env, .git/, node_modules/) |
+| `file-trigger.ts` | Watches a trigger file and injects contents into conversation |
+| `confirm-destructive.ts` | Confirms before destructive session actions (clear, switch, branch) |
+| `dirty-repo-guard.ts` | Prevents session changes with uncommitted git changes |
+| `auto-commit-on-exit.ts` | Auto-commits on exit using last assistant message for commit message |
+| `custom-compaction.ts` | Custom compaction that summarizes entire conversation |
+| `qna.ts` | Extracts questions from last response into editor via `ctx.ui.setEditorText()` |
+| `snake.ts` | Snake game with custom UI, keyboard handling, and session persistence |
+
 ## Writing Hooks
 
 See [docs/hooks.md](../../docs/hooks.md) for full documentation.
 
-### Key Points
-
-**Hook structure:**
 ```typescript
 import type { HookAPI } from "@mariozechner/pi-coding-agent/hooks";
 
 export default function (pi: HookAPI) {
-  pi.on("session", async (event, ctx) => {
-    // event.reason: "start" | "before_switch" | "switch" | "before_clear" | "clear" |
-    //               "before_branch" | "branch" | "shutdown"
-    // event.targetTurnIndex: number (only for before_branch/branch)
-    // ctx.ui, ctx.exec, ctx.cwd, ctx.sessionFile, ctx.hasUI
-
-    // Cancel before_* actions:
-    if (event.reason === "before_clear") {
-      return { cancel: true };
-    }
-    return undefined;
-  });
-
+  // Subscribe to events
   pi.on("tool_call", async (event, ctx) => {
-    // Can block tool execution
-    if (dangerous) {
-      return { block: true, reason: "Blocked" };
+    if (event.toolName === "bash" && event.input.command?.includes("rm -rf")) {
+      const ok = await ctx.ui.confirm("Dangerous!", "Allow rm -rf?");
+      if (!ok) return { block: true, reason: "Blocked by user" };
     }
-    return undefined;
   });
 
-  pi.on("tool_result", async (event, ctx) => {
-    // Can modify result
-    return { result: "modified result" };
+  // Register custom commands
+  pi.registerCommand("hello", {
+    description: "Say hello",
+    handler: async (args, ctx) => {
+      ctx.ui.notify("Hello!", "info");
+    },
   });
 }
 ```
-
-**Available events:**
-- `session` - lifecycle events with before/after variants (can cancel before_* actions)
-- `agent_start` / `agent_end` - per user prompt
-- `turn_start` / `turn_end` - per LLM turn
-- `tool_call` - before tool execution (can block)
-- `tool_result` - after tool execution (can modify)
-
-**UI methods:**
-```typescript
-const choice = await ctx.ui.select("Title", ["Option A", "Option B"]);
-const confirmed = await ctx.ui.confirm("Title", "Are you sure?");
-const input = await ctx.ui.input("Title", "placeholder");
-ctx.ui.notify("Message", "info"); // or "warning", "error"
-```
-
-**Sending messages:**
-```typescript
-pi.send("Message to inject into conversation");
-```