fix(agent): steered override-schema subagents

- Marked eval agent schema calls as caller overrides so subagent prompts can revoke native output/yield instructions.\n- Added override-schema prompt guidance telling agents to ignore conflicting native output labels and terminal-yield the caller schema object.\n- Added prompt coverage for the override notice.\n\nRefs #3926

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

@@ -295,6 +295,11 @@ export interface ExecutorOptions {
 	parentActiveModelPattern?: string;
 	thinkingLevel?: ThinkingLevel;
 	outputSchema?: unknown;
+	/**
+	 * Caller supplied a schema that supersedes the agent's native output prompt.
+	 * Eval `agent(..., schema=...)` sets this so built-in agents ignore stale yield labels.
+	 */
+	outputSchemaOverridesAgent?: boolean;
 	/** Parent task recursion depth (0 = top-level, 1 = first child, etc.) */
 	taskDepth?: number;
 	/**
@@ -2141,6 +2146,7 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 						planReferencePath: options.planReference?.path ?? "",
 						worktree: worktree ?? "",
 						outputSchema: normalizedOutputSchema,
+						outputSchemaOverridesAgent: options.outputSchemaOverridesAgent === true,
 						ircPeers: ircEnabled ? renderIrcPeerRoster(id) : "",
 						ircSelfId: ircEnabled ? id : "",
 					});