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/eval/__tests__/agent-bridge.test.ts

@@ -235,10 +235,12 @@ describe("runEvalAgent", () => {
 		expect(firstOptions.signal).toBe(abortController.signal);
 		expect(firstOptions.parentActiveModelPattern).toBe("p/current");
 		expect(firstOptions.outputSchema).toBe(schema);
+		expect(firstOptions.outputSchemaOverridesAgent).toBe(true);
 		expect(firstOptions.assignment).toBe("hello");
 		expect(firstOptions.description).toBe("My Agent");
 		expect(firstOptions.modelOverride).toEqual(["p/override"]);
 		expect(secondOptions.outputSchema).toBeUndefined();
+		expect(secondOptions.outputSchemaOverridesAgent).toBeUndefined();
 	});
 
 	it("forces LSP off for bridge subagents even when task.enableLsp is on", async () => {

packages/coding-agent/src/eval/agent-bridge.ts

@@ -371,6 +371,7 @@ export async function runEvalAgent(args: unknown, options: EvalAgentBridgeOption
 		parentActiveModelPattern,
 		thinkingLevel: effectiveAgent.thinkingLevel,
 		outputSchema: structured ? parsed.schema : undefined,
+		outputSchemaOverridesAgent: structured,
 		sessionFile,
 		persistArtifacts: Boolean(sessionFile),
 		artifactsDir,

packages/coding-agent/src/prompts/system/subagent-system-prompt.md

@@ -61,6 +61,10 @@ Yield protocol:
 
 This is your only way to return a final result. For structured results, you NEVER put JSON in plain text or substitute a text summary for `result.data`.
 
+{{#if outputSchemaOverridesAgent}}
+Caller schema overrides agent-native output instructions. Ignore ROLE-provided output/yield labels, field names, examples, and procedures that conflict with the interface below. Use ONLY labels/fields from the caller schema; safest path: omit `type` and terminal-yield the full `result.data` object.
+
+{{/if}}
 {{#if outputSchema}}
 Your result MUST match this TypeScript interface:
 ```ts

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 : "",
 					});

packages/coding-agent/test/task/subagent-system-prompt.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from "bun:test";
+import { prompt } from "@oh-my-pi/pi-utils";
+import "../../src/config/prompt-templates";
+import subagentSystemPromptTemplate from "../../src/prompts/system/subagent-system-prompt.md" with { type: "text" };
+
+describe("subagent system prompt", () => {
+	it("revokes native output labels when caller schema overrides the agent", () => {
+		const out = prompt.render(subagentSystemPromptTemplate, {
+			agent: 'Use incremental yield with type: ["findings"].',
+			outputSchemaOverridesAgent: true,
+			outputSchema: {
+				properties: {
+					issue_key: { type: "string" },
+					verdict: { enum: ["clean", "blockers"] },
+				},
+			},
+		});
+
+		expect(out).toContain("Caller schema overrides agent-native output instructions");
+		expect(out).toContain("Ignore ROLE-provided output/yield labels");
+		expect(out).toContain("omit `type` and terminal-yield the full `result.data` object");
+	});
+});