fix(cron): remove OpenAPI 3.0 incompatible JSON Schema keywords from cron tool (#61221)

The cron tool schema used type arrays (['string','null']), the 'not'
keyword, and 'const' — all unsupported by the OpenAPI 3.0 subset that
Gemini-backed providers (e.g. GitHub Copilot) enforce. This caused
HTTP 400 for every request when cron was enabled.

Replace type arrays with scalar types, remove not/const from
CronFailureAlertSchema, and add 'not' to the Gemini unsupported
keywords list as defense-in-depth.

Fixes #61206

src/agents/schema/clean-for-gemini.test.ts

@@ -96,4 +96,46 @@ describe("cleanSchemaForGemini", () => {
     expect(cleaned.required).toEqual(["nested"]);
     expect(cleaned.properties?.nested).not.toHaveProperty("required");
   });
+
+  // Regression: #61206 — `not` keyword is not part of the OpenAPI 3.0 subset
+  // and must be stripped to avoid HTTP 400 from Gemini-backed providers.
+  it("strips the not keyword from schemas", () => {
+    const cleaned = cleanSchemaForGemini({
+      type: "object",
+      not: { const: true },
+      properties: {
+        name: { type: "string" },
+      },
+    }) as Record<string, unknown>;
+
+    expect(cleaned).not.toHaveProperty("not");
+    expect(cleaned.type).toBe("object");
+    expect(cleaned.properties).toEqual({ name: { type: "string" } });
+  });
+
+  // Regression: #61206 — type arrays like ["string", "null"] must be
+  // collapsed to a single scalar type for OpenAPI 3.0 compatibility.
+  it("collapses type arrays by stripping null entries", () => {
+    const cleaned = cleanSchemaForGemini({
+      type: ["string", "null"],
+      description: "nullable field",
+    }) as Record<string, unknown>;
+
+    expect(cleaned.type).toBe("string");
+    expect(cleaned.description).toBe("nullable field");
+  });
+
+  it("collapses type arrays in nested property schemas", () => {
+    const cleaned = cleanSchemaForGemini({
+      type: "object",
+      properties: {
+        agentId: {
+          type: ["string", "null"],
+          description: "Agent id",
+        },
+      },
+    }) as { properties?: { agentId?: Record<string, unknown> } };
+
+    expect(cleaned.properties?.agentId?.type).toBe("string");
+  });
 });

src/agents/schema/clean-for-gemini.ts

@@ -27,6 +27,11 @@ export const GEMINI_UNSUPPORTED_SCHEMA_KEYWORDS = new Set([
   "uniqueItems",
   "minProperties",
   "maxProperties",
+
+  // JSON Schema composition keywords not supported by OpenAPI 3.0 subset.
+  // `const` is handled separately (converted to enum) in the cleaning loop,
+  // but `not` has no safe equivalent and must be stripped.
+  "not",
 ]);
 
 const SCHEMA_META_KEYS = ["description", "title", "default"] as const;

src/agents/tools/cron-tool.schema.test.ts

@@ -136,29 +136,34 @@ describe("CronToolSchema", () => {
     );
   });
 
-  it("job.failureAlert also allows boolean false", () => {
+  it("job.failureAlert uses plain object type for OpenAPI 3.0 compat", () => {
     const root = (CronToolSchema as Record<string, unknown>).properties as
       | Record<string, { properties?: Record<string, unknown>; type?: unknown }>
       | undefined;
     const jobProps = root?.job?.properties as
-      | Record<string, { type?: unknown; not?: { const?: unknown } }>
+      | Record<string, { type?: unknown; description?: string }>
       | undefined;
     const schema = jobProps?.failureAlert;
-    expect(schema?.type).toEqual(["object", "boolean"]);
+    // Must be a plain "object" type — not a type array — so providers that
-    expect(schema?.not?.const).toBe(true);
+    // enforce an OpenAPI 3.0 subset (e.g. Gemini via GitHub Copilot) accept it.
+    expect(schema?.type).toBe("object");
+    // The description must mention "false" so LLMs know they can disable alerts.
+    expect(schema?.description).toMatch(/false/i);
   });
 
-  it("job.agentId and job.sessionKey accept null for clear/keep-unset flows", () => {
+  it("job.agentId and job.sessionKey use plain string type for OpenAPI 3.0 compat", () => {
     const root = (CronToolSchema as Record<string, unknown>).properties as
       | Record<string, { properties?: Record<string, unknown> }>
       | undefined;
     const jobProps = root?.job?.properties as Record<string, { type?: unknown }> | undefined;
 
-    expect(jobProps?.agentId?.type).toEqual(["string", "null"]);
+    // Must be plain "string" — not ["string", "null"] — for provider compat.
-    expect(jobProps?.sessionKey?.type).toEqual(["string", "null"]);
+    // Null semantics are conveyed via the field description and handled at runtime.
+    expect(jobProps?.agentId?.type).toBe("string");
+    expect(jobProps?.sessionKey?.type).toBe("string");
   });
 
-  it("patch.payload.toolsAllow accepts null for clear flows", () => {
+  it("patch.payload.toolsAllow uses plain array type for OpenAPI 3.0 compat", () => {
     const root = (CronToolSchema as Record<string, unknown>).properties as
       | Record<string, { properties?: Record<string, unknown> }>
       | undefined;
@@ -166,6 +171,17 @@ describe("CronToolSchema", () => {
       | Record<string, { properties?: Record<string, { type?: unknown }> }>
       | undefined;
 
-    expect(patchProps?.payload?.properties?.toolsAllow?.type).toEqual(["array", "null"]);
+    // Must be plain "array" — not ["array", "null"] — for provider compat.
+    expect(patchProps?.payload?.properties?.toolsAllow?.type).toBe("array");
+  });
+
+  // Regression guard: ensure no OpenAPI 3.0 incompatible keywords leak into the
+  // serialized cron tool schema.  This catches future regressions at the source.
+  it("serialized schema contains no type-array or not/const keywords", () => {
+    const json = JSON.stringify(CronToolSchema);
+    // type arrays like ["string","null"] are not valid in OpenAPI 3.0
+    expect(json).not.toMatch(/"type"\s*:\s*\[/);
+    // "not" composition keyword is not supported by OpenAPI 3.0
+    expect(json).not.toMatch(/"not"\s*:\s*\{/);
   });
 });

src/agents/tools/cron-tool.ts

@@ -55,22 +55,11 @@ const REMINDER_CONTEXT_TOTAL_MAX = 700;
 const REMINDER_CONTEXT_MARKER = "\n\nRecent context:\n";
 
 function nullableStringSchema(description: string) {
-  return Type.Optional(
+  return Type.Optional(Type.String({ description }));
-    Type.Unsafe<string | null>({
-      type: ["string", "null"],
-      description,
-    }),
-  );
 }
 
 function nullableStringArraySchema(description: string) {
-  return Type.Optional(
+  return Type.Optional(Type.Array(Type.String(), { description }));
-    Type.Unsafe<string[] | null>({
-      type: ["array", "null"],
-      items: { type: "string" },
-      description,
-    }),
-  );
 }
 
 function cronPayloadObjectSchema(params: { toolsAllow: TSchema }) {
@@ -138,12 +127,14 @@ const CronDeliverySchema = Type.Optional(
   ),
 );
 
-// Keep `false` expressible without reintroducing anyOf/oneOf into the raw tool schema.
 // Omitting `failureAlert` means "leave defaults/unchanged"; `false` explicitly disables alerts.
+// Runtime handles `failureAlert === false` in cron/service/timer.ts.
+// The schema declares `type: "object"` to stay compatible with providers that
+// enforce an OpenAPI 3.0 subset (e.g. Gemini via GitHub Copilot).  The
+// description tells the LLM that `false` is also accepted.
 const CronFailureAlertSchema = Type.Optional(
   Type.Unsafe<Record<string, unknown> | false>({
-    type: ["object", "boolean"],
+    type: "object",
-    not: { const: true },
     properties: {
       after: Type.Optional(Type.Number({ description: "Failures before alerting" })),
       channel: Type.Optional(Type.String({ description: "Alert channel" })),
@@ -153,7 +144,8 @@ const CronFailureAlertSchema = Type.Optional(
       accountId: Type.Optional(Type.String()),
     },
     additionalProperties: true,
-    description: "Failure alert object, or false to disable alerts for this job",
+    description:
+      "Failure alert config object, or the boolean value false to disable alerts for this job",
   }),
 );