fix(coding-agent): kept todo active for prewalk subagents and fixed prewalk gate deadlock

- Updated prewalk gating in `AgentSession` to key the todo gate on active tools instead of registry presence, so deactivated todo tools no longer block prewalk handoff.
- Changed subprocess tool filtering so `todo` is stripped for normal subagents but retained when prewalk is armed, and propagated the prewalk state through tool-session setup.
- Added regression tests for restricted active-tool slates and prewalk/non-prewalk subagent tool propagation to verify todo is handled correctly in each case.

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

@@ -1750,7 +1750,7 @@ export class AgentSession {
 	#prewalkPlanInjected = false;
 	/** True once any successful `todo` call landed — opens the prewalk
 	 *  trigger gate: the switch fires at the first edit/write AFTER the todo
-	 *  list exists (sessions without a todo tool skip the gate). */
+	 *  list exists (sessions without an ACTIVE todo tool skip the gate). */
 	#prewalkTodoSeen = false;
 	#planYolo: PlanYolo | undefined;
 	#planYoloPreviousTools: string[] | undefined;
@@ -2270,12 +2270,14 @@ export class AgentSession {
 		// todo list from it and start" — so the switch waits until a todo list
 		// exists AND the model has actually started implementing (first
 		// edit/write). The todo call itself never triggers: firing there handed
-		// the fast model the whole implementation cold. Sessions without a todo
-		// tool skip the gate.
+		// the fast model the whole implementation cold. The gate keys on the
+		// ACTIVE tool set, not the registry: a registered-but-deactivated todo
+		// (e.g. a restricted active-tool slate) is uncallable and would
+		// deadlock the switch.
 		if (context.toolResults.some(result => result.toolName === "todo")) {
 			this.#prewalkTodoSeen = true;
 		}
-		const todoGateOpen = this.#prewalkTodoSeen || !this.#toolRegistry.has("todo");
+		const todoGateOpen = this.#prewalkTodoSeen || !this.getActiveToolNames().includes("todo");
 		const action = todoGateOpen
 			? context.toolResults.find(result => PREWALK_ACTION_TOOLS[result.toolName])
 			: undefined;

packages/coding-agent/src/task/executor.ts

@@ -2575,9 +2575,12 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 				});
 			}
 
+			// Todos are parent-owned bookkeeping and stripped from subagents —
+			// except under prewalk, whose plan nudge + todo gate require the
+			// subagent to commit its own todo list before the hand-off.
+			const isParentOwnedTool = (name: string): boolean => !prewalk && name === "todo";
 			const subagentToolNames = session.getActiveToolNames();
-			const parentOwnedToolNames = new Set(["todo"]);
-			const filteredSubagentTools = subagentToolNames.filter(name => !parentOwnedToolNames.has(name));
+			const filteredSubagentTools = subagentToolNames.filter(name => !isParentOwnedTool(name));
 			if (filteredSubagentTools.length !== subagentToolNames.length) {
 				await awaitAbortable(session.setActiveToolsByName(filteredSubagentTools));
 			}
@@ -2635,7 +2638,7 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 						getActiveTools: () => session.getActiveToolNames(),
 						getAllTools: () => session.getAllToolNames(),
 						setActiveTools: (toolNames: string[]) =>
-							session.setActiveToolsByName(toolNames.filter(name => !parentOwnedToolNames.has(name))),
+							session.setActiveToolsByName(toolNames.filter(name => !isParentOwnedTool(name))),
 						getCommands: () => getSessionSlashCommands(session),
 						setModel: model => runExtensionSetModel(session, model),
 						getThinkingLevel: () => session.thinkingLevel,

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

@@ -206,7 +206,6 @@ function renderDescription(
 		agents: renderedAgents,
 		spawningDisabled,
 		defaultAgent: spawnPolicy.defaultAgent,
-		allowedAgentsText: spawnPolicy.allowedPromptText,
 		isolationEnabled,
 		batchEnabled,
 		asyncEnabled,

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

@@ -205,6 +205,9 @@ export interface ToolSession {
 	outputSchema?: unknown;
 	/** Whether to include the yield tool by default */
 	requireYieldTool?: boolean;
+	/** Session starts with a prewalk hand-off armed. Keeps `todo` in yield-gated
+	 *  (subagent) registries: the prewalk plan nudge + todo gate need it. */
+	prewalkArmed?: boolean;
 	/** Task recursion depth (0 = top-level, 1 = first child, etc.) */
 	taskDepth?: number;
 	/** Get shared eval executor session ID. Subagents inherit this to share JS/Python/Ruby/Julia state. */
@@ -612,7 +615,8 @@ export async function createTools(session: ToolSession, toolNames?: string[]): P
 		if (name === "launch") return session.settings.get("launch.enabled");
 		if (name === "eval") return allowEval;
 		if (name === "debug") return session.settings.get("debug.enabled");
-		if (name === "todo") return !includeYield && session.settings.get("todo.enabled");
+		if (name === "todo")
+			return (!includeYield || session.prewalkArmed === true) && session.settings.get("todo.enabled");
 		if (name === "glob") return session.settings.get("glob.enabled");
 		if (name === "grep") return session.settings.get("grep.enabled");
 		if (name === "github") return session.settings.get("github.enabled");