Propagate workspace roots into subagent sessions

Subagents (task tool) now inherit the parent session's
additionalDirectories via ToolSession → ExecutorOptions →
CreateAgentSessionOptions, so delegated agents see the same
<workspace-roots> block and can read/grep/glob added roots.

Co-authored-by: oh-my-pi <https://omp.sh>

packages/coding-agent/src/tools/index.ts

@@ -143,6 +143,8 @@ export interface DeferredDiagnosticsEntry {
 export interface ToolSession {
 	/** Current working directory */
 	cwd: string;
+	/** Additional workspace directories beyond cwd (multi-root), forwarded to subagents. */
+	additionalDirectories?: string[];
 	/** Whether UI is available */
 	hasUI: boolean;
 	/**