Fix navigateTree API: add missing type updates, handler passthrough, and docs

- Update ExtensionCommandContext.navigateTree type signature
- Pass new options through in print-mode and rpc-mode handlers
- Update docs/extensions.md, docs/sdk.md, docs/tree.md
- Add changelog entry

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

@@ -237,7 +237,10 @@ export interface ExtensionCommandContext extends ExtensionContext {
 	fork(entryId: string): Promise<{ cancelled: boolean }>;
 
 	/** Navigate to a different point in the session tree. */
-	navigateTree(targetId: string, options?: { summarize?: boolean }): Promise<{ cancelled: boolean }>;
+	navigateTree(
+		targetId: string,
+		options?: { summarize?: boolean; customInstructions?: string; replaceInstructions?: boolean; label?: string },
+	): Promise<{ cancelled: boolean }>;
 }
 
 // ============================================================================