diff --git a/apps/web/src/app/setup/page.tsx b/apps/web/src/app/setup/page.tsx
index 423eb25c..da16ff00 100644
--- a/apps/web/src/app/setup/page.tsx
+++ b/apps/web/src/app/setup/page.tsx
@@ -1902,7 +1902,8 @@ export default function SetupPage() {
                                   setGeminiError("");
                                 }}
                                 onPaste={(e) => {
-                                  const pasted = e.clipboardData.getData("text");
+                                  e.preventDefault();
+                                  const pasted = e.clipboardData.getData("text").trim();
                                   if (pasted) {
                                     setGeminiKey(pasted);
                                     setGeminiValidated(false);
diff --git a/packages/agent-adapters/src/gemini.ts b/packages/agent-adapters/src/gemini.ts
index 37a7c0e5..9b0ddfdb 100644
--- a/packages/agent-adapters/src/gemini.ts
+++ b/packages/agent-adapters/src/gemini.ts
@@ -164,6 +164,13 @@ export class GeminiAdapter implements AgentAdapter {
     let hasError = false;
     let lastAssistantMessage: string | undefined;
 
+    // Check for JSON error messages embedded in non-JSON output
+    const apiKeyErrorMatch = logs.match(/API key not valid|API_KEY_INVALID/i);
+    if (apiKeyErrorMatch) {
+      errorMessage = "API key not valid. Please pass a valid API key.";
+      hasError = true;
+    }
+
     for (const line of logs.split("\n")) {
       if (!line.trim()) continue;
 
diff --git a/packages/shared/src/error-classifier.test.ts b/packages/shared/src/error-classifier.test.ts
index dfc847f2..22a8d277 100644
--- a/packages/shared/src/error-classifier.test.ts
+++ b/packages/shared/src/error-classifier.test.ts
@@ -157,4 +157,11 @@ describe("classifyError", () => {
     expect(result.category).toBe("auth");
     expect(result.title).toBe("Authentication token expired");
   });
+
+  it("classifies invalid API key error", () => {
+    const result = classifyError("API_KEY_INVALID error from Gemini API");
+    expect(result.category).toBe("auth");
+    expect(result.title).toBe("Invalid API key");
+    expect(result.retryable).toBe(false);
+  });
 });
diff --git a/packages/shared/src/error-classifier.ts b/packages/shared/src/error-classifier.ts
index 4a8041e8..396c4470 100644
--- a/packages/shared/src/error-classifier.ts
+++ b/packages/shared/src/error-classifier.ts
@@ -234,6 +234,18 @@ const ERROR_PATTERNS: Array<{
       retryable: true,
     }),
   },
+  {
+    pattern: /API key not valid|API_KEY_INVALID/i,
+    classify: () => ({
+      category: "auth",
+      title: "Invalid API key",
+      description:
+        "The provided API key is invalid. This can affect Gemini, Anthropic, or OpenAI depending on which agent was running.",
+      remedy:
+        "Go to Secrets and verify your API keys (GEMINI_API_KEY, ANTHROPIC_API_KEY, etc.) are valid and have not been revoked.",
+      retryable: false,
+    }),
+  },
   {
     pattern: /exit code: (\d+)/i,
     classify: (match) => ({