Replace custom tool dispose() with shutdown session event

Breaking change: CustomAgentTool.dispose() removed. Use onSession with
reason 'shutdown' instead for cleanup.

- Add 'shutdown' to SessionEvent.reason for custom tools
- Remove dispose() method from CustomAgentTool interface
- Make emitToolSessionEvent() public on AgentSession
- Emit shutdown event to tools in InteractiveMode.shutdown()
- Update custom-tools.md with new API and examples

packages/coding-agent/docs/custom-tools.md

@@ -82,7 +82,7 @@ Custom tools can import from these packages (automatically resolved by pi):
 | Package | Purpose |
 |---------|---------|
 | `@sinclair/typebox` | Schema definitions (`Type.Object`, `Type.String`, etc.) |
-| `@mariozechner/pi-coding-agent` | Types (`CustomToolFactory`, `ToolSessionEvent`, etc.) |
+| `@mariozechner/pi-coding-agent` | Types (`CustomToolFactory`, `ToolSessionEvent` (alias for `SessionEvent`), etc.) |
 | `@mariozechner/pi-ai` | AI utilities (`StringEnum` for Google-compatible enums) |
 | `@mariozechner/pi-tui` | TUI components (`Text`, `Box`, etc. for custom rendering) |
 
@@ -116,14 +116,17 @@ const factory: CustomToolFactory = (pi) => ({
   },
 
   // Optional: Session lifecycle callback
-  onSession(event) { /* reconstruct state from entries */ },
+  onSession(event) {
+    if (event.reason === "shutdown") {
+      // Cleanup resources (close connections, save state, etc.)
+      return;
+    }
+    // Reconstruct state from entries for other events
+  },
 
   // Optional: Custom rendering
   renderCall(args, theme) { /* return Component */ },
   renderResult(result, options, theme) { /* return Component */ },
-
-  // Optional: Cleanup on session end
-  dispose() { /* save state, close connections */ },
 });
 
 export default factory;
@@ -139,15 +142,18 @@ The factory receives a `ToolAPI` object (named `pi` by convention):
 interface ToolAPI {
   cwd: string;  // Current working directory
   exec(command: string, args: string[], options?: ExecOptions): Promise<ExecResult>;
-  ui: {
-    select(title: string, options: string[]): Promise<string | null>;
-    confirm(title: string, message: string): Promise<boolean>;
-    input(title: string, placeholder?: string): Promise<string | null>;
-    notify(message: string, type?: "info" | "warning" | "error"): void;
-  };
+  ui: ToolUIContext;
   hasUI: boolean;  // false in --print or --mode rpc
 }
 
+interface ToolUIContext {
+  select(title: string, options: string[]): Promise<string | undefined>;
+  confirm(title: string, message: string): Promise<boolean>;
+  input(title: string, placeholder?: string): Promise<string | undefined>;
+  notify(message: string, type?: "info" | "warning" | "error"): void;
+  custom(component: Component & { dispose?(): void }): { close: () => void; requestRender: () => void };
+}
+
 interface ExecOptions {
   signal?: AbortSignal;  // Cancel the process
   timeout?: number;      // Timeout in milliseconds
@@ -182,11 +188,11 @@ async execute(toolCallId, params, signal) {
 Tools can implement `onSession` to react to session changes:
 
 ```typescript
-interface ToolSessionEvent {
+interface SessionEvent {
   entries: SessionEntry[];      // All session entries
-  sessionFile: string | null;   // Current session file
-  previousSessionFile: string | null;  // Previous session file
-  reason: "start" | "switch" | "branch" | "new";
+  sessionFile: string | undefined;   // Current session file (undefined with --no-session)
+  previousSessionFile: string | undefined;  // Previous session file
+  reason: "start" | "switch" | "branch" | "new" | "tree";
 }
 ```
 
@@ -195,6 +201,8 @@ interface ToolSessionEvent {
 - `switch`: User switched to a different session (`/resume`)
 - `branch`: User branched from a previous message (`/branch`)
 - `new`: User started a new session (`/new`)
+- `tree`: User navigated to a different point in the session tree (`/tree`)
+- `shutdown`: Process is exiting (Ctrl+C, Ctrl+D, or SIGTERM) - use to cleanup resources
 
 ### State Management Pattern
 
@@ -387,13 +395,16 @@ const factory: CustomToolFactory = (pi) => {
   // Shared state
   let connection = null;
 
+  const handleSession = (event: ToolSessionEvent) => {
+    if (event.reason === "shutdown") {
+      connection?.close();
+    }
+  };
+
   return [
-    { name: "db_connect", ... },
-    { name: "db_query", ... },
-    {
-      name: "db_close",
-      dispose() { connection?.close(); }
-    },
+    { name: "db_connect", onSession: handleSession, ... },
+    { name: "db_query", onSession: handleSession, ... },
+    { name: "db_close", onSession: handleSession, ... },
   ];
 };
 ```

packages/coding-agent/src/core/agent-session.ts

@@ -698,7 +698,7 @@ export class AgentSession {
 		}
 
 		// Emit session event to custom tools
-		await this._emitToolSessionEvent("new", previousSessionFile);
+		await this.emitToolSessionEvent("new", previousSessionFile);
 		return true;
 	}
 
@@ -1473,7 +1473,7 @@ export class AgentSession {
 		}
 
 		// Emit session event to custom tools
-		await this._emitToolSessionEvent("switch", previousSessionFile);
+		await this.emitToolSessionEvent("switch", previousSessionFile);
 
 		this.agent.replaceMessages(sessionContext.messages);
 
@@ -1550,7 +1550,7 @@ export class AgentSession {
 		}
 
 		// Emit session event to custom tools (with reason "branch")
-		await this._emitToolSessionEvent("branch", previousSessionFile);
+		await this.emitToolSessionEvent("branch", previousSessionFile);
 
 		if (!skipConversationRestore) {
 			this.agent.replaceMessages(sessionContext.messages);
@@ -1720,7 +1720,7 @@ export class AgentSession {
 		}
 
 		// Emit to custom tools
-		await this._emitToolSessionEvent("tree", this.sessionFile);
+		await this.emitToolSessionEvent("tree", this.sessionFile);
 
 		this._branchSummaryAbortController = undefined;
 		return { editorText, cancelled: false, summaryEntry };
@@ -1875,11 +1875,11 @@ export class AgentSession {
 
 	/**
 	 * Emit session event to all custom tools.
-	 * Called on session switch, branch, and clear.
+	 * Called on session switch, branch, tree navigation, and shutdown.
 	 */
-	private async _emitToolSessionEvent(
+	async emitToolSessionEvent(
 		reason: ToolSessionEvent["reason"],
-		previousSessionFile: string | undefined,
+		previousSessionFile?: string | undefined,
 	): Promise<void> {
 		const event: ToolSessionEvent = {
 			entries: this.sessionManager.getEntries(),

packages/coding-agent/src/core/custom-tools/types.ts

@@ -40,10 +40,10 @@ export interface SessionEvent {
 	entries: SessionEntry[];
 	/** Current session file path, or undefined in --no-session mode */
 	sessionFile: string | undefined;
-	/** Previous session file path, or undefined for "start" and "new" */
+	/** Previous session file path, or undefined for "start", "new", and "shutdown" */
 	previousSessionFile: string | undefined;
 	/** Reason for the session event */
-	reason: "start" | "switch" | "branch" | "new" | "tree";
+	reason: "start" | "switch" | "branch" | "new" | "tree" | "shutdown";
 }
 
 /** Rendering options passed to renderResult */
@@ -85,14 +85,12 @@ export interface RenderResultOptions {
  */
 export interface CustomAgentTool<TParams extends TSchema = TSchema, TDetails = any>
 	extends AgentTool<TParams, TDetails> {
-	/** Called on session start/switch/branch/clear - use to reconstruct state from entries */
+	/** Called on session lifecycle events - use to reconstruct state or cleanup resources */
 	onSession?: (event: SessionEvent) => void | Promise<void>;
 	/** Custom rendering for tool call display - return a Component */
 	renderCall?: (args: Static<TParams>, theme: Theme) => Component;
 	/** Custom rendering for tool result display - return a Component */
 	renderResult?: (result: AgentToolResult<TDetails>, options: RenderResultOptions, theme: Theme) => Component;
-	/** Called when session ends - cleanup resources */
-	dispose?: () => Promise<void> | void;
 }
 
 /** Factory function that creates a custom tool or array of tools */

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -1239,7 +1239,7 @@ export class InteractiveMode {
 
 	/**
 	 * Gracefully shutdown the agent.
-	 * Emits shutdown event to hooks, then exits.
+	 * Emits shutdown event to hooks and tools, then exits.
 	 */
 	private async shutdown(): Promise<void> {
 		// Emit shutdown event to hooks
@@ -1250,6 +1250,9 @@ export class InteractiveMode {
 			});
 		}
 
+		// Emit shutdown event to custom tools
+		await this.session.emitToolSessionEvent("shutdown");
+
 		this.stop();
 		process.exit(0);
 	}