feat: integrate antigravity adapter

src/lib/antigravity/SignatureStore.ts

@@ -0,0 +1,66 @@
+/**
+ * Global thought_signature storage shared by all endpoints
+ * Used to capture and replay signatures for Gemini 3+ function calls when clients don't pass them back.
+ */
+
+class SignatureStoreImpl {
+  private static instance: SignatureStoreImpl;
+  private signature: string | null = null;
+
+  private constructor() {}
+
+  public static getInstance(): SignatureStoreImpl {
+    if (!SignatureStoreImpl.instance) {
+      SignatureStoreImpl.instance = new SignatureStoreImpl();
+    }
+    return SignatureStoreImpl.instance;
+  }
+
+  /**
+   * Store thought_signature to global storage.
+   * Only stores if the new signature is longer than the existing one,
+   * to avoid short/partial signatures overwriting valid ones.
+   */
+  public store(sig: string) {
+    if (!sig) return;
+
+    const existingLen = this.signature ? this.signature.length : 0;
+    const newLen = sig.length;
+
+    if (newLen > existingLen) {
+      console.log(
+        `[ThoughtSig] Storing new signature (length: ${newLen}, replacing old: ${existingLen})`,
+      );
+      this.signature = sig;
+    } else {
+      console.debug(
+        `[ThoughtSig] Skipping shorter signature (new length: ${newLen}, existing: ${existingLen})`,
+      );
+    }
+  }
+
+  /**
+   * Get the stored thought_signature without clearing it.
+   */
+  public get(): string | null {
+    return this.signature;
+  }
+
+  /**
+   * Get and clear the stored thought_signature.
+   */
+  public take(): string | null {
+    const sig = this.signature;
+    this.signature = null;
+    return sig;
+  }
+
+  /**
+   * Clear the stored thought_signature.
+   */
+  public clear() {
+    this.signature = null;
+  }
+}
+
+export const SignatureStore = SignatureStoreImpl.getInstance();