fix(antigravity): update handling for new Antigravity API structure (#25)

Author: safzanpirani

bun.lock

@@ -11,6 +11,43 @@ export function generateRequestId(): string {
   return `agent-${randomUUID()}`;
 }
 
+export const ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION =
+  "You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding.You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.**Absolute paths only****Proactiveness**";
+
+export function applyAntigravitySystemInstruction(payload: Record<string, unknown>, model: string): void {
+  const normalizedModel = model.toLowerCase();
+  const needsInjection = normalizedModel.includes("claude")
+    || normalizedModel.includes("gemini-3-pro")
+    || normalizedModel.includes("gemini-3-flash");
+  if (!needsInjection) {
+    return;
+  }
+
+  const existing = payload.systemInstruction;
+  let existingParts: Array<Record<string, unknown>> = [];
+  let existingRecord: Record<string, unknown> | undefined;
+
+  if (typeof existing === "string") {
+    if (existing.length > 0) {
+      existingParts = [{ text: existing }];
+    }
+  } else if (existing && typeof existing === "object") {
+    existingRecord = existing as Record<string, unknown>;
+    const parts = existingRecord.parts;
+    if (Array.isArray(parts)) {
+      existingParts = parts.filter(
+        (part): part is Record<string, unknown> => typeof part === "object" && part !== null,
+      );
+    }
+  }
+
+  const nextParts = [{ text: ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION }, ...existingParts];
+
+  payload.systemInstruction = existingRecord
+    ? { ...existingRecord, role: "user", parts: nextParts }
+    : { role: "user", parts: nextParts };
+}
+
 const GEMINI_PREVIEW_LINK = "https://goo.gle/enable-preview-features";
 
 export interface GeminiApiError {

src/plugin/request-helpers.ts

@@ -132,6 +132,20 @@ describe("URL Transformation", () => {
 
     expect(result.requestedModel).toBe("gemini-3-flash");
   });
+
+  test("aliases gemini-3-flash-preview to gemini-3-flash", async () => {
+    const url = "https://generativelanguage.googleapis.com/v1beta/models/gemini-3-flash-preview:generateContent";
+
+    const result = await prepareAntigravityRequest(
+      url,
+      { method: "POST", body: JSON.stringify({ contents: [] }) },
+      "dummy-token",
+      "dummy-project"
+    );
+
+    const body = JSON.parse(result.init.body as string);
+    expect(body.model).toBe("gemini-3-flash");
+  });
 });
 
 describe("Endpoint Fallback Override", () => {

src/plugin/request.test.ts

@@ -29,6 +29,7 @@ const MODEL_ALIASES: Record<string, string> = {
   "gemini-2.5-computer-use-preview-10-2025": "rev19-uic3-1p",
   "gemini-3-pro-image-preview": "gemini-3-pro-image",
   "gemini-3-pro-preview": "gemini-3-pro-high",
+  "gemini-3-flash-preview": "gemini-3-flash",
   "gemini-claude-sonnet-4-5": "claude-sonnet-4-5",
   "gemini-claude-sonnet-4-5-thinking": "claude-sonnet-4-5-thinking",
   "gemini-claude-opus-4-5-thinking": "claude-opus-4-5-thinking",

src/plugin/request.ts

@@ -1,7 +1,7 @@
 import { randomUUID } from "node:crypto";
 import { cacheSignature, getCachedSignature } from "../cache";
 import { createLogger } from "../logger";
-import { normalizeThinkingConfig } from "../request-helpers";
+import { applyAntigravitySystemInstruction, normalizeThinkingConfig } from "../request-helpers";
 import { cacheToolSchemas } from "../tool-schema-cache";
 import type { RequestPayload, TransformContext, TransformResult } from "./types";
 
@@ -161,6 +161,8 @@ export function transformClaudeRequest(
     delete requestPayload.system_instruction;
   }
 
+  applyAntigravitySystemInstruction(requestPayload, context.model);
+
   const cachedContentFromExtra =
     typeof requestPayload.extra_body === "object" && requestPayload.extra_body
       ? (requestPayload.extra_body as Record<string, unknown>).cached_content ??
@@ -316,6 +318,7 @@ export function transformClaudeRequest(
     project: context.projectId,
     model: context.model,
     userAgent: "antigravity",
+    requestType: "agent",
     requestId: context.requestId,
     request: requestPayload,
   };

src/plugin/transform/claude.ts

@@ -1,6 +1,6 @@
 import { getCachedSignature } from "../cache";
 import { createLogger } from "../logger";
-import { normalizeThinkingConfig } from "../request-helpers";
+import { applyAntigravitySystemInstruction, normalizeThinkingConfig } from "../request-helpers";
 import { cacheToolSchemas } from "../tool-schema-cache";
 import type { RequestPayload, TransformContext, TransformResult } from "./types";
 
@@ -531,6 +531,7 @@ export function transformGeminiRequest(
   augmentToolDescriptionsWithStrictParams(requestPayload);
   injectSystemInstructionIfNeeded(requestPayload);
   scrubConversationArtifactsFromModelHistory(requestPayload);
+  applyAntigravitySystemInstruction(requestPayload, context.model);
 
   const contents = requestPayload.contents as Array<Record<string, unknown>> | undefined;
   if (Array.isArray(contents)) {
@@ -638,6 +639,7 @@ export function transformGeminiRequest(
     project: context.projectId,
     model: context.model,
     userAgent: "antigravity",
+    requestType: "agent",
     requestId: context.requestId,
     request: requestPayload,
   };

src/plugin/transform/gemini.ts

@@ -1,7 +1,7 @@
 import { describe, expect, it } from "bun:test";
 
 import { cacheSignature } from "../cache";
-import { normalizeToolCallArgs, recursivelyParseJsonStrings } from "../request-helpers";
+import { ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION, normalizeToolCallArgs, recursivelyParseJsonStrings } from "../request-helpers";
 import { cacheToolSchemas, clearToolSchemaCache } from "../tool-schema-cache";
 import { transformClaudeRequest } from "./claude";
 import { transformGeminiRequest } from "./gemini";
@@ -139,6 +139,38 @@ describe("thoughtSignature handling", () => {
       const userParts = contents[0].parts;
       expect(userParts[0].thoughtSignature).toBe("user-sig-should-stay");
     });
+
+    it("prepends Antigravity systemInstruction and requestType for gemini-3-pro", () => {
+      const payload: RequestPayload = {
+        systemInstruction: { parts: [{ text: "Existing instruction" }] },
+        contents: [{ role: "user", parts: [{ text: "hi" }] }],
+      };
+
+      const context = createContext("gemini-3-pro-high");
+      const result = transformGeminiRequest(context, payload);
+      const parsed = JSON.parse(result.body);
+
+      expect(parsed.requestType).toBe("agent");
+      expect(parsed.request.systemInstruction.role).toBe("user");
+      expect(parsed.request.systemInstruction.parts[0].text).toBe(ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION);
+      expect(parsed.request.systemInstruction.parts[1].text).toBe("Existing instruction");
+    });
+
+    it("prepends Antigravity systemInstruction and requestType for gemini-3-flash-preview", () => {
+      const payload: RequestPayload = {
+        systemInstruction: { parts: [{ text: "Existing instruction" }] },
+        contents: [{ role: "user", parts: [{ text: "hi" }] }],
+      };
+
+      const context = createContext("gemini-3-flash-preview");
+      const result = transformGeminiRequest(context, payload);
+      const parsed = JSON.parse(result.body);
+
+      expect(parsed.requestType).toBe("agent");
+      expect(parsed.request.systemInstruction.role).toBe("user");
+      expect(parsed.request.systemInstruction.parts[0].text).toBe(ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION);
+      expect(parsed.request.systemInstruction.parts[1].text).toBe("Existing instruction");
+    });
   });
 
   describe("tool schema mitigations", () => {
@@ -177,7 +209,10 @@ describe("thoughtSignature handling", () => {
       const result = transformGeminiRequest(context, payload);
       const parsed = JSON.parse(result.body);
 
-      expect(parsed.request.systemInstruction.parts[0].text).toContain("<CRITICAL_TOOL_USAGE_INSTRUCTIONS>");
+      const instructionText = parsed.request.systemInstruction.parts
+        .map((part: any) => part.text ?? "")
+        .join("\n");
+      expect(instructionText).toContain("<CRITICAL_TOOL_USAGE_INSTRUCTIONS>");
       const funcDecl = parsed.request.tools[0].functionDeclarations[0];
       expect(funcDecl.description).toContain("STRICT PARAMETERS:");
       expect(funcDecl.description).toContain("filePath");
@@ -306,6 +341,22 @@ describe("thoughtSignature handling", () => {
   });
 
   describe("claude transformer", () => {
+    it("prepends Antigravity systemInstruction and requestType for claude models", () => {
+      const payload: RequestPayload = {
+        systemInstruction: "Existing instruction",
+        contents: [{ role: "user", parts: [{ text: "Hello" }] }],
+      };
+
+      const context = createContext("gemini-claude-sonnet-4-5");
+      const result = transformClaudeRequest(context, payload);
+      const parsed = JSON.parse(result.body);
+
+      expect(parsed.requestType).toBe("agent");
+      expect(parsed.request.systemInstruction.role).toBe("user");
+      expect(parsed.request.systemInstruction.parts[0].text).toBe(ANTIGRAVITY_BASE_SYSTEM_INSTRUCTION);
+      expect(parsed.request.systemInstruction.parts[1].text).toBe("Existing instruction");
+    });
+
     it("keeps thinking blocks with valid signatures (length > 50)", () => {
       const payload: RequestPayload = {
         contents: [