diff --git a/packages/api/src/agents/__tests__/messagePiiFilter.spec.ts b/packages/api/src/agents/__tests__/messagePiiFilter.spec.ts
index dadecde599..d8a6ae7030 100644
--- a/packages/api/src/agents/__tests__/messagePiiFilter.spec.ts
+++ b/packages/api/src/agents/__tests__/messagePiiFilter.spec.ts
@@ -47,7 +47,8 @@ describe('createMessagePiiFilterHooks', () => {
 
       expect(result.updatedPrompt).toBe('key sk-[REDACTED] please');
       expect(result.decision).toBeUndefined();
-      expect(built!.collector.matches).toHaveLength(1);
+      // Silent mode skips collector population (no consumer reads it)
+      expect(built!.collector.matches).toEqual([]);
     });
 
     it('is a no-op when nothing matches', async () => {
@@ -110,7 +111,7 @@ describe('createMessagePiiFilterHooks', () => {
       expect(result.updatedPrompt).toBe('auth Bearer [REDACTED] and key sk-ant-1234567890ABC');
     });
 
-    it('layers customPatterns on top of starters', async () => {
+    it('uses customPatterns only when starterPatterns is empty', async () => {
       const built = createMessagePiiFilterHooks(
         silent({
           starterPatterns: [],
@@ -123,7 +124,25 @@ describe('createMessagePiiFilterHooks', () => {
       });
 
       expect(result.updatedPrompt).toBe('token [REDACTED] ok');
-      expect(built!.collector.matches.map((m) => m.patternId)).toEqual(['acme']);
+    });
+
+    it('layers customPatterns on top of starters (both fire in one prompt)', async () => {
+      const built = createMessagePiiFilterHooks(
+        silent({
+          onMatch: 'warn',
+          customPatterns: [{ id: 'acme', label: 'Acme token', regex: '\\bACME-[A-Z0-9]{6,}' }],
+        }),
+      );
+      const result = await executeHooks({
+        registry: built!.registry,
+        input: promptInput('starter sk-anything-here and custom ACME-DEADBEEF12'),
+      });
+
+      const ids = built!.collector.matches.map((m) => m.patternId).sort();
+      expect(ids).toContain('sk_prefix');
+      expect(ids).toContain('acme');
+      expect(result.updatedPrompt).toContain('sk-[REDACTED]');
+      expect(result.updatedPrompt).toContain('[REDACTED]');
     });
 
     it('honors a custom redactionText', async () => {
diff --git a/packages/api/src/agents/messagePiiFilter.ts b/packages/api/src/agents/messagePiiFilter.ts
index 9879c4e3fd..71919038c7 100644
--- a/packages/api/src/agents/messagePiiFilter.ts
+++ b/packages/api/src/agents/messagePiiFilter.ts
@@ -91,7 +91,9 @@ export function createMessagePiiFilterHooks(
           return {};
         }
 
-        collector.matches.push(...matches);
+        if (mode !== 'silent') {
+          collector.matches.push(...matches);
+        }
 
         if (mode === 'block') {
           logger.info(
@@ -108,13 +110,11 @@ export function createMessagePiiFilterHooks(
         // silent + warn both redact server-side. The difference is
         // that warn surfaces the matches to the UI via the controller
         // (which reads collector.matches after processStream resolves).
-        if (mode === 'warn') {
-          logger.info(
-            `[messagePiiFilter] redacted ${matches.length} match(es) (mode=warn, patterns=${matches
-              .map((m) => m.patternId)
-              .join(',')})`,
-          );
-        }
+        logger.info(
+          `[messagePiiFilter] redacted ${matches.length} match(es) (mode=${mode}, patterns=${matches
+            .map((m) => m.patternId)
+            .join(',')})`,
+        );
 
         return { updatedPrompt: text };
       },