test: clarify distinction between UI display and auto-retry

Added tests that explicitly demonstrate the key distinction:
- hasInterruptedStream = Should RetryBarrier UI be shown?
- isEligibleForAutoRetry = Should system auto-retry?

For non-retryable errors (authentication, quota):
- hasInterruptedStream returns true (show UI)
- isEligibleForAutoRetry returns false (don't auto-retry)
- Result: User sees manual Retry button, not 'Retrying...'

For retryable errors (network, server):
- Both return true
- Result: User sees 'Retrying...' with countdown and exponential backoff

This prevents confusion about why we have two similar-sounding functions.

Author: ammar-agent

src/utils/messages/retryEligibility.test.ts

@@ -286,6 +286,114 @@ describe("hasInterruptedStream", () => {
 });
 
 describe("isEligibleForAutoRetry", () => {
+  describe("hasInterruptedStream vs isEligibleForAutoRetry distinction", () => {
+    // These tests demonstrate the key distinction in our retry system:
+    // - hasInterruptedStream: Should UI show retry barrier? (YES for all errors)
+    // - isEligibleForAutoRetry: Should system auto-retry? (NO for non-retryable errors)
+
+    describe("authentication errors", () => {
+      const messages: DisplayedMessage[] = [
+        {
+          type: "user",
+          id: "user-1",
+          historyId: "user-1",
+          content: "Hello",
+          historySequence: 1,
+        },
+        {
+          type: "stream-error",
+          id: "error-1",
+          historyId: "assistant-1",
+          error: "Invalid API key",
+          errorType: "authentication",
+          historySequence: 2,
+        },
+      ];
+
+      it("hasInterruptedStream returns true (show UI)", () => {
+        expect(hasInterruptedStream(messages)).toBe(true);
+      });
+
+      it("isEligibleForAutoRetry returns false (don't auto-retry)", () => {
+        expect(isEligibleForAutoRetry(messages)).toBe(false);
+      });
+
+      it("behavior: UI shows Retry button, not 'Retrying...'", () => {
+        // This combination means:
+        // - User sees RetryBarrier with manual "Retry" button
+        // - System does NOT auto-retry (infinite loop prevention)
+        // - User can manually retry after fixing API key
+        expect(hasInterruptedStream(messages)).toBe(true);
+        expect(isEligibleForAutoRetry(messages)).toBe(false);
+      });
+    });
+
+    describe("quota errors", () => {
+      const messages: DisplayedMessage[] = [
+        {
+          type: "user",
+          id: "user-1",
+          historyId: "user-1",
+          content: "Hello",
+          historySequence: 1,
+        },
+        {
+          type: "stream-error",
+          id: "error-1",
+          historyId: "assistant-1",
+          error: "Usage quota exceeded",
+          errorType: "quota",
+          historySequence: 2,
+        },
+      ];
+
+      it("hasInterruptedStream returns true (show UI)", () => {
+        expect(hasInterruptedStream(messages)).toBe(true);
+      });
+
+      it("isEligibleForAutoRetry returns false (don't auto-retry)", () => {
+        expect(isEligibleForAutoRetry(messages)).toBe(false);
+      });
+    });
+
+    describe("network errors (retryable)", () => {
+      const messages: DisplayedMessage[] = [
+        {
+          type: "user",
+          id: "user-1",
+          historyId: "user-1",
+          content: "Hello",
+          historySequence: 1,
+        },
+        {
+          type: "stream-error",
+          id: "error-1",
+          historyId: "assistant-1",
+          error: "Network connection failed",
+          errorType: "network",
+          historySequence: 2,
+        },
+      ];
+
+      it("hasInterruptedStream returns true (show UI)", () => {
+        expect(hasInterruptedStream(messages)).toBe(true);
+      });
+
+      it("isEligibleForAutoRetry returns true (auto-retry with backoff)", () => {
+        expect(isEligibleForAutoRetry(messages)).toBe(true);
+      });
+
+      it("behavior: UI shows 'Retrying...' with countdown", () => {
+        // This combination means:
+        // - User sees RetryBarrier with "Retrying... (attempt N)"
+        // - System auto-retries with exponential backoff
+        // - User can stop with Ctrl+C
+        expect(hasInterruptedStream(messages)).toBe(true);
+        expect(isEligibleForAutoRetry(messages)).toBe(true);
+      });
+    });
+  });
+
   it("returns false for empty messages", () => {
     expect(isEligibleForAutoRetry([])).toBe(false);
   });