test(auth): add token expiry tests for 50-min buffer

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/auth/antigravity/token.test.ts

@@ -0,0 +1,78 @@
+import { describe, it, expect } from "bun:test"
+import { isTokenExpired } from "./token"
+import type { AntigravityTokens } from "./types"
+
+describe("Token Expiry with 50-minute Buffer", () => {
+  const createToken = (expiresInSeconds: number): AntigravityTokens => ({
+    type: "antigravity",
+    access_token: "test-access",
+    refresh_token: "test-refresh",
+    expires_in: expiresInSeconds,
+    timestamp: Date.now(),
+  })
+
+  it("should NOT be expired if token expires in 51 minutes", () => {
+    // #given
+    const fiftyOneMinutes = 51 * 60 // 3060 seconds
+    const token = createToken(fiftyOneMinutes)
+
+    // #when
+    const expired = isTokenExpired(token)
+
+    // #then
+    expect(expired).toBe(false)
+  })
+
+  it("should be expired if token expires in 49 minutes", () => {
+    // #given
+    const fortyNineMinutes = 49 * 60 // 2940 seconds
+    const token = createToken(fortyNineMinutes)
+
+    // #when
+    const expired = isTokenExpired(token)
+
+    // #then
+    expect(expired).toBe(true)
+  })
+
+  it("should be expired at exactly 50 minutes (boundary)", () => {
+    // #given
+    const fiftyMinutes = 50 * 60 // 3000 seconds
+    const token = createToken(fiftyMinutes)
+
+    // #when
+    const expired = isTokenExpired(token)
+
+    // #then - at boundary, should trigger refresh
+    expect(expired).toBe(true)
+  })
+
+  it("should be expired if token already expired", () => {
+    // #given
+    const alreadyExpired: AntigravityTokens = {
+      type: "antigravity",
+      access_token: "test-access",
+      refresh_token: "test-refresh",
+      expires_in: 3600, // 1 hour originally
+      timestamp: Date.now() - 4000 * 1000, // 4000 seconds ago
+    }
+
+    // #when
+    const expired = isTokenExpired(alreadyExpired)
+
+    // #then
+    expect(expired).toBe(true)
+  })
+
+  it("should NOT be expired if token has plenty of time", () => {
+    // #given
+    const twoHours = 2 * 60 * 60 // 7200 seconds
+    const token = createToken(twoHours)
+
+    // #when
+    const expired = isTokenExpired(token)
+
+    // #then
+    expect(expired).toBe(false)
+  })
+})