refactor(coding-agent): fix compaction for branched sessions, consolidate hook context types

Compaction API:
- prepareCompaction() now takes (pathEntries, settings) only
- CompactionPreparation restructured: removed cutPoint/messagesToKeep/boundaryStart, added turnPrefixMessages/isSplitTurn/previousSummary/fileOps/settings
- compact() now takes (preparation, model, apiKey, customInstructions?, signal?)
- Fixed token overflow by using getPath() instead of getEntries()

Hook types:
- HookEventContext renamed to HookContext
- HookCommandContext removed, RegisteredCommand.handler takes (args, ctx)
- HookContext now includes model field
- SessionBeforeCompactEvent: removed previousCompactions/model, added branchEntries
- SessionBeforeTreeEvent: removed model (use ctx.model)
- HookRunner.initialize() added for modes to set up callbacks

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

@@ -3,6 +3,7 @@
  */
 
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
+import type { Model } from "@mariozechner/pi-ai";
 import type { ModelRegistry } from "../model-registry.js";
 import type { SessionManager } from "../session-manager.js";
 import type { AppendEntryHandler, LoadedHook, SendMessageHandler } from "./loader.js";
@@ -11,9 +12,9 @@ import type {
 	BeforeAgentStartEventResult,
 	ContextEvent,
 	ContextEventResult,
+	HookContext,
 	HookError,
 	HookEvent,
-	HookEventContext,
 	HookMessageRenderer,
 	HookUIContext,
 	RegisteredCommand,
@@ -72,6 +73,7 @@ export class HookRunner {
 	private modelRegistry: ModelRegistry;
 	private timeout: number;
 	private errorListeners: Set<HookErrorListener> = new Set();
+	private getModel: () => Model<any> | undefined = () => undefined;
 
 	constructor(
 		hooks: LoadedHook[],
@@ -89,6 +91,30 @@ export class HookRunner {
 		this.timeout = timeout;
 	}
 
+	/**
+	 * Initialize HookRunner with all required context.
+	 * Modes call this once the agent session is fully set up.
+	 */
+	initialize(options: {
+		/** Function to get the current model */
+		getModel: () => Model<any> | undefined;
+		/** Handler for hooks to send messages */
+		sendMessageHandler: SendMessageHandler;
+		/** Handler for hooks to append entries */
+		appendEntryHandler: AppendEntryHandler;
+		/** UI context for interactive prompts */
+		uiContext?: HookUIContext;
+		/** Whether UI is available */
+		hasUI?: boolean;
+	}): void {
+		this.getModel = options.getModel;
+		this.setSendMessageHandler(options.sendMessageHandler);
+		this.setAppendEntryHandler(options.appendEntryHandler);
+		if (options.uiContext) {
+			this.setUIContext(options.uiContext, options.hasUI ?? false);
+		}
+	}
+
 	/**
 	 * Set the UI context for hooks.
 	 * Call this when the mode initializes and UI is available.
@@ -217,13 +243,14 @@ export class HookRunner {
 	/**
 	 * Create the event context for handlers.
 	 */
-	private createContext(): HookEventContext {
+	private createContext(): HookContext {
 		return {
 			ui: this.uiContext,
 			hasUI: this.hasUI,
 			cwd: this.cwd,
 			sessionManager: this.sessionManager,
 			modelRegistry: this.modelRegistry,
+			model: this.getModel(),
 		};
 	}
 

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

@@ -88,9 +88,9 @@ export interface HookUIContext {
 }
 
 /**
- * Context passed to hook event handlers.
+ * Context passed to hook event and command handlers.
  */
-export interface HookEventContext {
+export interface HookContext {
 	/** UI methods for user interaction */
 	ui: HookUIContext;
 	/** Whether UI is available (false in print mode) */
@@ -101,6 +101,8 @@ export interface HookEventContext {
 	sessionManager: ReadonlySessionManager;
 	/** Model registry - use for API key resolution and model retrieval */
 	modelRegistry: ModelRegistry;
+	/** Current model (may be undefined if no model is selected yet) */
+	model: Model<any> | undefined;
 }
 
 // ============================================================================
@@ -152,14 +154,12 @@ export interface SessionBranchEvent {
 /** Fired before context compaction (can be cancelled or customized) */
 export interface SessionBeforeCompactEvent {
 	type: "session_before_compact";
-	/** Compaction preparation with cut point, messages to summarize/keep, etc. */
+	/** Compaction preparation with messages to summarize, file ops, previous summary, etc. */
 	preparation: CompactionPreparation;
-	/** Previous compaction entries, newest first. Use for iterative summarization. */
-	previousCompactions: CompactionEntry[];
+	/** Branch entries (root to current leaf). Use to inspect custom state or previous compactions. */
+	branchEntries: SessionEntry[];
 	/** Optional user-provided instructions for the summary */
 	customInstructions?: string;
-	/** Current model */
-	model: Model<any>;
 	/** Abort signal - hooks should pass this to LLM calls and check it periodically */
 	signal: AbortSignal;
 }
@@ -196,9 +196,7 @@ export interface SessionBeforeTreeEvent {
 	type: "session_before_tree";
 	/** Preparation data for the navigation */
 	preparation: TreePreparation;
-	/** Model to use for summarization (conversation model) */
-	model: Model<any>;
-	/** Abort signal - honors Escape during summarization */
+	/** Abort signal - honors Escape during summarization (model available via ctx.model) */
 	signal: AbortSignal;
 }
 
@@ -529,7 +527,7 @@ export interface SessionBeforeTreeResult {
  * Handlers can return R, undefined, or void (bare return statements).
  */
 // biome-ignore lint/suspicious/noConfusingVoidType: void allows bare return statements in handlers
-export type HookHandler<E, R = undefined> = (event: E, ctx: HookEventContext) => Promise<R | void> | R | void;
+export type HookHandler<E, R = undefined> = (event: E, ctx: HookContext) => Promise<R | void> | R | void;
 
 export interface HookMessageRenderOptions {
 	/** Whether the view is expanded */
@@ -546,24 +544,6 @@ export type HookMessageRenderer<T = unknown> = (
 	theme: Theme,
 ) => Component | undefined;
 
-/**
- * Context passed to hook command handlers.
- */
-export interface HookCommandContext {
-	/** Arguments after the command name */
-	args: string;
-	/** UI methods for user interaction */
-	ui: HookUIContext;
-	/** Whether UI is available (false in print mode) */
-	hasUI: boolean;
-	/** Current working directory */
-	cwd: string;
-	/** Session manager (read-only) - use pi.sendMessage()/pi.appendEntry() for writes */
-	sessionManager: ReadonlySessionManager;
-	/** Model registry for API keys */
-	modelRegistry: ModelRegistry;
-}
-
 /**
  * Command registration options.
  */
@@ -571,7 +551,7 @@ export interface RegisteredCommand {
 	name: string;
 	description?: string;
 
-	handler: (ctx: HookCommandContext) => Promise<void>;
+	handler: (args: string, ctx: HookContext) => Promise<void>;
 }
 
 /**