Add fromHook field to CompactionEntry and BranchSummaryEntry

- fromHook: true = hook generated, skip file extraction
- fromHook: undefined/false = pi generated, extract files (backward compatible)
- branchWithSummary now accepts fromHook parameter
- File extraction only runs for !entry.fromHook entries

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

@@ -64,6 +64,8 @@ export interface CompactionEntry<T = unknown> extends SessionEntryBase {
 	tokensBefore: number;
 	/** Hook-specific data (e.g., ArtifactIndex, version markers for structured compaction) */
 	details?: T;
+	/** True if generated by a hook, undefined/false if pi-generated (backward compatible) */
+	fromHook?: boolean;
 }
 
 export interface BranchSummaryEntry<T = unknown> extends SessionEntryBase {
@@ -72,6 +74,8 @@ export interface BranchSummaryEntry<T = unknown> extends SessionEntryBase {
 	summary: string;
 	/** Hook-specific data (not sent to LLM) */
 	details?: T;
+	/** True if generated by a hook, false if pi-generated */
+	fromHook?: boolean;
 }
 
 /**
@@ -872,7 +876,7 @@ export class SessionManager {
 	 * Same as branch(), but also appends a branch_summary entry that captures
 	 * context from the abandoned conversation path.
 	 */
-	branchWithSummary(branchFromId: string | null, summary: string, details?: unknown): string {
+	branchWithSummary(branchFromId: string | null, summary: string, details?: unknown, fromHook?: boolean): string {
 		if (branchFromId !== null && !this.byId.has(branchFromId)) {
 			throw new Error(`Entry ${branchFromId} not found`);
 		}
@@ -885,6 +889,7 @@ export class SessionManager {
 			fromId: branchFromId ?? "root",
 			summary,
 			details,
+			fromHook,
 		};
 		this._appendEntry(entry);
 		return entry.id;