diff --git a/docs/design/ANTIGRAVITY_LOCAL_SCHEMA_REFS.md b/docs/design/ANTIGRAVITY_LOCAL_SCHEMA_REFS.md
new file mode 100644
index 00000000..d3ae9cc5
--- /dev/null
+++ b/docs/design/ANTIGRAVITY_LOCAL_SCHEMA_REFS.md
@@ -0,0 +1,20 @@
+# Antigravity Local Schema References
+
+Status: validated
+Created: 2026-09-08
+Verified: 2026-09-08
+Issue: [#465](https://github.com/openpi-dev/openpi/issues/465)
+
+The Antigravity boundary expands only same-document JSON Pointer references
+before applying Cloud Code Assist's unsupported-keyword sanitizer. External,
+unresolved, recursive, or over-limit references fail before a model request.
+Expansion is bounded by depth, nodes, and serialized bytes. The original Pi
+schema remains the authority for local validation; this only preserves its
+meaning in the provider declaration.
+
+The ablation is explicit: removing expansion reproduces the original empty
+`{}` property for a `$ref` result contract, while allowing references without
+bounds could make provider preparation unbounded. Both the expansion and
+limits are retained.
+
+Validation: `node --test --experimental-strip-types tests/extensions/ai-providers/antigravity.test.ts` (39/39) and `bun run check` passed.
diff --git a/extensions/ai-providers/antigravity/google-conversion.ts b/extensions/ai-providers/antigravity/google-conversion.ts
index 1c1165e3..89c093c9 100644
--- a/extensions/ai-providers/antigravity/google-conversion.ts
+++ b/extensions/ai-providers/antigravity/google-conversion.ts
@@ -34,6 +34,10 @@ const JSON_SCHEMA_META_DECLARATIONS = new Set([
   "definitions",
 ]);
 
+const MAX_SCHEMA_REF_DEPTH = 24;
+const MAX_SCHEMA_REF_NODES = 10_000;
+const MAX_SCHEMA_REF_BYTES = 256 * 1024;
+
 interface GoogleFunctionCall {
   id?: string;
   name: string;
@@ -394,6 +398,141 @@ export function convertMessages(
   return contents;
 }
 
+function expandLocalSchemaRefs(schema: unknown): unknown {
+  if (typeof schema !== "object" || schema === null || Array.isArray(schema)) {
+    return schema;
+  }
+  const root = schema as Record<string, unknown>;
+  const hasRef = (value: unknown) => {
+    const pending = [value];
+    const seen = new WeakSet<object>();
+    while (pending.length > 0) {
+      const entry = pending.pop();
+      if (!entry || typeof entry !== "object" || seen.has(entry)) continue;
+      seen.add(entry);
+      if (
+        Object.prototype.hasOwnProperty.call(entry, "$ref") &&
+        typeof (entry as Record<string, unknown>).$ref === "string"
+      ) {
+        return true;
+      }
+      pending.push(...Object.values(entry));
+    }
+    return false;
+  };
+  if (!hasRef(schema)) return schema;
+
+  const pointer = (ref: string) => {
+    if (!ref.startsWith("#/") && ref !== "#") {
+      throw new Error(`Antigravity tool schema has unsupported external $ref: ${ref}`);
+    }
+    let value: unknown = root;
+    for (const segment of ref === "#" ? [] : ref.slice(2).split("/")) {
+      const key = segment.replaceAll("~1", "/").replaceAll("~0", "~");
+      if (
+        !value ||
+        typeof value !== "object" ||
+        !Object.prototype.hasOwnProperty.call(value, key)
+      ) {
+        throw new Error(`Antigravity tool schema has unresolved $ref: ${ref}`);
+      }
+      value = (value as Record<string, unknown>)[key];
+    }
+    return value;
+  };
+  const assertDepth = (depth: number) => {
+    if (depth > MAX_SCHEMA_REF_DEPTH) {
+      throw new Error("Antigravity tool schema exceeds local $ref expansion limits");
+    }
+  };
+  const siblingsOf = (object: Record<string, unknown>) =>
+    Object.entries(object).filter(([key]) => key !== "$ref");
+
+  // Count the JSON that expansion will emit before cloning any referenced tree.
+  let bytes = 0;
+  const append = (text: string) => {
+    bytes += Buffer.byteLength(text);
+    if (bytes > MAX_SCHEMA_REF_BYTES) {
+      throw new Error("Antigravity tool schema exceeds local $ref expansion byte limit");
+    }
+  };
+  const measure = (value: unknown, depth: number, active: Set<string>): void => {
+    assertDepth(depth);
+    if (value === null || typeof value !== "object") {
+      append(JSON.stringify(value) ?? "null");
+      return;
+    }
+    if (Array.isArray(value)) {
+      append("[");
+      value.forEach((entry, index) => {
+        if (index > 0) append(",");
+        measure(entry, depth + 1, active);
+      });
+      append("]");
+      return;
+    }
+    const object = value as Record<string, unknown>;
+    if (typeof object.$ref === "string") {
+      const ref = object.$ref;
+      if (active.has(ref)) throw new Error(`Antigravity tool schema has recursive $ref: ${ref}`);
+      active.add(ref);
+      const siblings = siblingsOf(object);
+      if (siblings.length === 0) measure(pointer(ref), depth + 1, active);
+      else {
+        append('{"allOf":[');
+        measure(pointer(ref), depth + 1, active);
+        append(",{");
+        siblings.forEach(([key, entry], index) => {
+          if (index > 0) append(",");
+          append(`${JSON.stringify(key)}:`);
+          measure(entry, depth + 2, active);
+        });
+        append("}]}");
+      }
+      active.delete(ref);
+      return;
+    }
+    append("{");
+    Object.entries(object).forEach(([key, entry], index) => {
+      if (index > 0) append(",");
+      append(`${JSON.stringify(key)}:`);
+      measure(entry, depth + 1, active);
+    });
+    append("}");
+  };
+  measure(schema, 0, new Set());
+
+  let nodes = 0;
+  const active = new Set<string>();
+  const visit = (value: unknown, depth: number): unknown => {
+    assertDepth(depth);
+    if (++nodes > MAX_SCHEMA_REF_NODES) {
+      throw new Error("Antigravity tool schema exceeds local $ref expansion limits");
+    }
+    if (Array.isArray(value)) return value.map((entry) => visit(entry, depth + 1));
+    if (value === null || typeof value !== "object") return value;
+    const object = value as Record<string, unknown>;
+    if (typeof object.$ref === "string") {
+      const ref = object.$ref;
+      if (active.has(ref)) throw new Error(`Antigravity tool schema has recursive $ref: ${ref}`);
+      active.add(ref);
+      try {
+        const target = visit(pointer(ref), depth + 1);
+        const siblings = Object.fromEntries(
+          siblingsOf(object).map(([key, entry]) => [key, visit(entry, depth + 2)]),
+        );
+        return Object.keys(siblings).length === 0 ? target : { allOf: [target, siblings] };
+      } finally {
+        active.delete(ref);
+      }
+    }
+    return Object.fromEntries(
+      Object.entries(object).map(([key, entry]) => [key, visit(entry, depth + 1)]),
+    );
+  };
+  return visit(schema, 0);
+}
+
 function sanitizeForOpenApi(
   schema: unknown,
   insidePropertiesMap = false,
@@ -425,7 +564,11 @@ export function convertTools(
         name: tool.name,
         description: tool.description,
         ...(useParameters
-          ? { parameters: sanitizeForOpenApi(tool.parameters) }
+          ? {
+              parameters: sanitizeForOpenApi(
+                expandLocalSchemaRefs(tool.parameters),
+              ),
+            }
           : { parametersJsonSchema: tool.parameters }),
       })),
     },
diff --git a/tests/extensions/ai-providers/antigravity.test.ts b/tests/extensions/ai-providers/antigravity.test.ts
index ea83c49c..b6a19910 100644
--- a/tests/extensions/ai-providers/antigravity.test.ts
+++ b/tests/extensions/ai-providers/antigravity.test.ts
@@ -21,6 +21,7 @@ import {
 import { fetchAntigravityModels } from "../../../extensions/ai-providers/antigravity/discovery.ts";
 import {
   convertMessages,
+  convertTools,
   isThinkingPart,
   mapStopReasonString,
   retainThoughtSignature,
@@ -442,6 +443,201 @@ test("sanitizeSchemaForCca preserves property names that match schema keywords",
   );
 });
 
+test("convertTools expands bounded local refs before CCA sanitization", () => {
+  const declarations = convertTools(
+    [
+      {
+        name: "structured_output",
+        description: "Return the result",
+        parameters: {
+          type: "object",
+          properties: { answer: { $ref: "#/$defs/Answer" } },
+          required: ["answer"],
+          $defs: {
+            Answer: {
+              type: "object",
+              properties: {
+                verdict: { type: "string", enum: ["pass", "fail"] },
+              },
+              required: ["verdict"],
+            },
+          },
+        },
+      } as never,
+    ],
+    true,
+  );
+  assert.deepEqual(declarations?.[0]?.functionDeclarations[0]?.parameters, {
+    type: "object",
+    properties: {
+      answer: {
+        type: "object",
+        properties: { verdict: { type: "string", enum: ["pass", "fail"] } },
+        required: ["verdict"],
+      },
+    },
+    required: ["answer"],
+  });
+});
+
+test("convertTools counts each expanded ref subtree once", () => {
+  const fields = Object.fromEntries(
+    Array.from({ length: 60 }, (_, index) => [
+      `field${index}`,
+      { type: "string" },
+    ]),
+  );
+  const declarations = convertTools(
+    [
+      {
+        name: "structured_output",
+        description: "Return the result",
+        parameters: {
+          type: "object",
+          properties: {
+            first: { $ref: "#/$defs/Result" },
+            second: { $ref: "#/$defs/Result" },
+          },
+          $defs: {
+            Result: { type: "object", properties: fields },
+          },
+        },
+      } as never,
+    ],
+    true,
+  );
+  const parameters = declarations?.[0]?.functionDeclarations[0]?.parameters as {
+    properties?: Record<string, { properties?: Record<string, unknown> }>;
+  };
+  assert.deepEqual(parameters.properties?.first, parameters.properties?.second);
+  assert.equal(
+    parameters.properties?.first?.properties?.field59 !== undefined,
+    true,
+  );
+});
+
+test("convertTools bounds the serialized expanded schema size", () => {
+  assert.throws(
+    () =>
+      convertTools(
+        [
+          {
+            name: "oversized",
+            description: "oversized",
+            parameters: {
+              type: "object",
+              properties: { value: { $ref: "#/$defs/Value" } },
+              $defs: {
+                Value: { type: "string", description: "x".repeat(256 * 1024) },
+              },
+            },
+          } as never,
+        ],
+        true,
+      ),
+    /expansion byte limit/,
+  );
+});
+
+test("convertTools preserves ref sibling conjunctions and boolean schemas", () => {
+  const declarations = convertTools(
+    [
+      {
+        name: "conjunction",
+        description: "conjunction",
+        parameters: {
+          type: "object",
+          properties: {
+            value: {
+              $ref: "#/$defs/Value",
+              properties: { extra: { type: "string" } },
+            },
+            denied: { $ref: "#/$defs/Never" },
+          },
+          $defs: {
+            Value: { type: "object", properties: { required: { type: "string" } } },
+            Never: false,
+          },
+        },
+      } as never,
+    ],
+    true,
+  );
+  const parameters = declarations?.[0]?.functionDeclarations[0]?.parameters as {
+    properties?: Record<string, unknown>;
+  };
+  assert.deepEqual(parameters.properties?.value, {
+    allOf: [
+      { type: "object", properties: { required: { type: "string" } } },
+      { properties: { extra: { type: "string" } } },
+    ],
+  });
+  assert.equal(parameters.properties?.denied, false);
+});
+
+test("convertTools keeps ordinary no-ref schemas outside ref expansion limits", () => {
+  const properties = Object.fromEntries(
+    Array.from({ length: 600 }, (_, index) => [`field${index}`, { type: "string" }]),
+  );
+  assert.doesNotThrow(() =>
+    convertTools(
+      [{ name: "ordinary", description: "ordinary", parameters: { type: "object", properties } } as never],
+      true,
+    ),
+  );
+});
+
+test("convertTools rejects inherited local ref targets", () => {
+  assert.throws(
+    () =>
+      convertTools(
+        [
+          {
+            name: "inherited",
+            description: "inherited",
+            parameters: { $defs: {}, $ref: "#/$defs/toString" },
+          } as never,
+        ],
+        true,
+      ),
+    /unresolved \$ref/,
+  );
+});
+
+test("convertTools rejects unsafe local refs before the request", () => {
+  assert.throws(
+    () =>
+      convertTools(
+        [
+          {
+            name: "bad",
+            description: "bad",
+            parameters: { $ref: "https://example.test/schema" },
+          } as never,
+        ],
+        true,
+      ),
+    /unsupported external \$ref/,
+  );
+  assert.throws(
+    () =>
+      convertTools(
+        [
+          {
+            name: "loop",
+            description: "loop",
+            parameters: {
+              $defs: { Node: { $ref: "#/$defs/Node" } },
+              $ref: "#/$defs/Node",
+            },
+          } as never,
+        ],
+        true,
+      ),
+    /recursive \$ref/,
+  );
+});
+
 test("buildRequestBody strips CCA-rejected keywords and spills constraints into description", () => {
   const contextWithTools = {
     ...SIMPLE_CONTEXT,