Split HookContext and HookCommandContext to prevent deadlocks

HookContext (all events):
- isIdle() - read-only state check
- hasQueuedMessages() - read-only state check
- abort() - fire-and-forget, does not wait

HookCommandContext (slash commands only):
- waitForIdle() - waits for agent to finish
- newSession(options?) - create new session
- branch(entryId) - branch from entry
- navigateTree(targetId, options?) - navigate session tree

Session control methods moved from HookAPI (pi.*) to HookCommandContext (ctx.*)
because they can deadlock when called from event handlers that run inside
the agent loop (tool_call, tool_result, context events).

packages/coding-agent/src/core/hooks/loader.ts

@@ -62,7 +62,7 @@ export type SendMessageHandler = <T = unknown>(
 export type AppendEntryHandler = <T = unknown>(customType: string, data?: T) => void;
 
 /**
- * New session handler type for pi.newSession().
+ * New session handler type for ctx.newSession() in HookCommandContext.
  */
 export type NewSessionHandler = (options?: {
 	parentSession?: string;
@@ -70,12 +70,12 @@ export type NewSessionHandler = (options?: {
 }) => Promise<{ cancelled: boolean }>;
 
 /**
- * Branch handler type for pi.branch().
+ * Branch handler type for ctx.branch() in HookCommandContext.
  */
 export type BranchHandler = (entryId: string) => Promise<{ cancelled: boolean }>;
 
 /**
- * Navigate tree handler type for pi.navigateTree().
+ * Navigate tree handler type for ctx.navigateTree() in HookCommandContext.
  */
 export type NavigateTreeHandler = (
 	targetId: string,
@@ -100,12 +100,6 @@ export interface LoadedHook {
 	setSendMessageHandler: (handler: SendMessageHandler) => void;
 	/** Set the append entry handler for this hook's pi.appendEntry() */
 	setAppendEntryHandler: (handler: AppendEntryHandler) => void;
-	/** Set the new session handler for this hook's pi.newSession() */
-	setNewSessionHandler: (handler: NewSessionHandler) => void;
-	/** Set the branch handler for this hook's pi.branch() */
-	setBranchHandler: (handler: BranchHandler) => void;
-	/** Set the navigate tree handler for this hook's pi.navigateTree() */
-	setNavigateTreeHandler: (handler: NavigateTreeHandler) => void;
 }
 
 /**
@@ -165,9 +159,6 @@ function createHookAPI(
 	commands: Map<string, RegisteredCommand>;
 	setSendMessageHandler: (handler: SendMessageHandler) => void;
 	setAppendEntryHandler: (handler: AppendEntryHandler) => void;
-	setNewSessionHandler: (handler: NewSessionHandler) => void;
-	setBranchHandler: (handler: BranchHandler) => void;
-	setNavigateTreeHandler: (handler: NavigateTreeHandler) => void;
 } {
 	let sendMessageHandler: SendMessageHandler = () => {
 		// Default no-op until mode sets the handler
@@ -175,18 +166,6 @@ function createHookAPI(
 	let appendEntryHandler: AppendEntryHandler = () => {
 		// Default no-op until mode sets the handler
 	};
-	let newSessionHandler: NewSessionHandler = async () => {
-		// Default no-op until mode sets the handler
-		return { cancelled: false };
-	};
-	let branchHandler: BranchHandler = async () => {
-		// Default no-op until mode sets the handler
-		return { cancelled: false };
-	};
-	let navigateTreeHandler: NavigateTreeHandler = async () => {
-		// Default no-op until mode sets the handler
-		return { cancelled: false };
-	};
 	const messageRenderers = new Map<string, HookMessageRenderer>();
 	const commands = new Map<string, RegisteredCommand>();
 
@@ -213,15 +192,6 @@ function createHookAPI(
 		exec(command: string, args: string[], options?: ExecOptions) {
 			return execCommand(command, args, options?.cwd ?? cwd, options);
 		},
-		newSession(options) {
-			return newSessionHandler(options);
-		},
-		branch(entryId) {
-			return branchHandler(entryId);
-		},
-		navigateTree(targetId, options) {
-			return navigateTreeHandler(targetId, options);
-		},
 	} as HookAPI;
 
 	return {
@@ -234,15 +204,6 @@ function createHookAPI(
 		setAppendEntryHandler: (handler: AppendEntryHandler) => {
 			appendEntryHandler = handler;
 		},
-		setNewSessionHandler: (handler: NewSessionHandler) => {
-			newSessionHandler = handler;
-		},
-		setBranchHandler: (handler: BranchHandler) => {
-			branchHandler = handler;
-		},
-		setNavigateTreeHandler: (handler: NavigateTreeHandler) => {
-			navigateTreeHandler = handler;
-		},
 	};
 }
 
@@ -270,16 +231,10 @@ async function loadHook(hookPath: string, cwd: string): Promise<{ hook: LoadedHo
 
 		// Create handlers map and API
 		const handlers = new Map<string, HandlerFn[]>();
-		const {
-			api,
-			messageRenderers,
-			commands,
-			setSendMessageHandler,
-			setAppendEntryHandler,
-			setNewSessionHandler,
-			setBranchHandler,
-			setNavigateTreeHandler,
-		} = createHookAPI(handlers, cwd);
+		const { api, messageRenderers, commands, setSendMessageHandler, setAppendEntryHandler } = createHookAPI(
+			handlers,
+			cwd,
+		);
 
 		// Call factory to register handlers
 		factory(api);
@@ -293,9 +248,6 @@ async function loadHook(hookPath: string, cwd: string): Promise<{ hook: LoadedHo
 				commands,
 				setSendMessageHandler,
 				setAppendEntryHandler,
-				setNewSessionHandler,
-				setBranchHandler,
-				setNavigateTreeHandler,
 			},
 			error: null,
 		};