refactor mode selection into delegate tool that spawns subagents (#265)

test/agnostic/delegate.ts

@@ -0,0 +1,44 @@
+import type { AgentResult, TestRunnerOptions, ValidationCheck } from "../utils.ts";
+import { defineFixture, getAgentOutput, getStructuredOutput } from "../utils.ts";
+
+/**
+ * delegate test - validates core end-to-end delegation flow.
+ *
+ * the orchestrator delegates to Plan mode with mini effort, passing instructions
+ * that tell the subagent to call set_output with a specific value.
+ * validates that the subagent executed and the result flows back.
+ */
+
+const fixture = defineFixture(
+  {
+    prompt: `Delegate to the Plan mode with mini effort. Pass these instructions to the subagent:
+"This is a delegation test. Your only task is to call set_output with the value 'DELEGATE_BASIC_PASSED'. Do not create plans, branches, or PRs. Just call set_output."`,
+    effort: "mini",
+    timeout: "5m",
+  },
+  { localOnly: true }
+);
+
+function validator(result: AgentResult): ValidationCheck[] {
+  const output = getStructuredOutput(result);
+  const agentOutput = getAgentOutput(result);
+
+  const setOutputCalled = output !== null;
+  const correctValue = setOutputCalled && /DELEGATE_BASIC_PASSED/i.test(output);
+  // check for the specific log line emitted by the delegate tool handler
+  const delegationOccurred = /» delegating to \w+ mode/i.test(agentOutput);
+
+  return [
+    { name: "set_output", passed: setOutputCalled },
+    { name: "correct_value", passed: correctValue },
+    { name: "delegation_occurred", passed: delegationOccurred },
+  ];
+}
+
+export const test: TestRunnerOptions = {
+  name: "delegate",
+  fixture,
+  validator,
+  env: { GITHUB_REPOSITORY: "pullfrog/test-repo" },
+  tags: ["agnostic"],
+};