fix: stale-default-provider test flaky in CI with existing providers

Test assumed no active providers exist after deleting the test one, but
CI DB may have other active providers from previous runs, causing
getActiveProvider() fallback to return a provider instead of undefined.

Fix: temporarily deactivate non-test providers during the assertion,
restore them in a finally block.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: op7418

src/__tests__/unit/stale-default-provider.test.ts

@@ -126,17 +126,29 @@ describe('Stale default_provider_id cleanup', () => {
   });
 
   describe('resolveProvider does NOT auto-heal', () => {
-    it('returns undefined provider when default points to deleted record', () => {
-      const id = createTestProvider('__test_stale');
-      setDefaultProviderId(id);
-      deleteProvider(id);
-      // Now default_provider_id points to a non-existent provider
-
-      const resolved = resolveProvider({});
-
-      // Resolver should NOT have auto-fixed the stale default
-      // (that would cause side effects during Doctor diagnostics)
-      assert.equal(resolved.provider, undefined, 'should return undefined, not auto-heal');
+    it('returns undefined provider when default points to deleted record and no other providers exist', () => {
+      // Deactivate all existing providers so fallback chain doesn't find one
+      const existing = getAllProviders();
+      const deactivated: string[] = [];
+      for (const p of existing) {
+        if (p.is_active && !p.name.startsWith('__test_')) {
+          getDb().prepare('UPDATE api_providers SET is_active = 0 WHERE id = ?').run(p.id);
+          deactivated.push(p.id);
+        }
+      }
+      try {
+        const id = createTestProvider('__test_stale');
+        setDefaultProviderId(id);
+        deleteProvider(id);
+
+        const resolved = resolveProvider({});
+        assert.equal(resolved.provider, undefined, 'should return undefined when no active providers exist');
+      } finally {
+        // Restore deactivated providers
+        for (const pid of deactivated) {
+          getDb().prepare('UPDATE api_providers SET is_active = 1 WHERE id = ?').run(pid);
+        }
+      }
     });
 
     it('does not modify default_provider_id setting on read', () => {