diff --git a/run_agent.py b/run_agent.py
index 4d414587e..359a92185 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -7466,6 +7466,16 @@ class AIAgent:
                     old_text=function_args.get("old_text"),
                     store=self._memory_store,
                 )
+                # Bridge: notify external memory provider of built-in memory writes
+                if self._memory_manager and function_args.get("action") in ("add", "replace"):
+                    try:
+                        self._memory_manager.on_memory_write(
+                            function_args.get("action", ""),
+                            target,
+                            function_args.get("content", ""),
+                        )
+                    except Exception:
+                        pass
                 tool_duration = time.time() - tool_start_time
                 if self._should_emit_quiet_tool_messages():
                     self._vprint(f"  {_get_cute_tool_message_impl('memory', function_args, tool_duration, result=function_result)}")
diff --git a/tests/agent/test_memory_provider.py b/tests/agent/test_memory_provider.py
index 505f40bd5..eba772a04 100644
--- a/tests/agent/test_memory_provider.py
+++ b/tests/agent/test_memory_provider.py
@@ -736,3 +736,61 @@ class TestCommitMemorySessionRouting:
         mgr.add_provider(bad)
 
         mgr.on_session_end([])  # must not raise
+
+
+# ---------------------------------------------------------------------------
+# on_memory_write bridge — must fire from both concurrent AND sequential paths
+# ---------------------------------------------------------------------------
+
+
+class TestOnMemoryWriteBridge:
+    """Verify that MemoryManager.on_memory_write is called when built-in
+    memory writes happen.  This is a regression test for #10174 where the
+    sequential tool execution path (_execute_tool_calls_sequential) was
+    missing the bridge call, so single memory tool calls never notified
+    external memory providers.
+    """
+
+    def test_on_memory_write_add(self):
+        """on_memory_write fires for 'add' actions."""
+        mgr = MemoryManager()
+        p = FakeMemoryProvider("ext")
+        mgr.add_provider(p)
+
+        mgr.on_memory_write("add", "memory", "new fact")
+        assert p.memory_writes == [("add", "memory", "new fact")]
+
+    def test_on_memory_write_replace(self):
+        """on_memory_write fires for 'replace' actions."""
+        mgr = MemoryManager()
+        p = FakeMemoryProvider("ext")
+        mgr.add_provider(p)
+
+        mgr.on_memory_write("replace", "user", "updated pref")
+        assert p.memory_writes == [("replace", "user", "updated pref")]
+
+    def test_on_memory_write_remove_not_bridged(self):
+        """The bridge intentionally skips 'remove' — only add/replace notify."""
+        # This tests the contract that run_agent.py checks:
+        #   function_args.get("action") in ("add", "replace")
+        mgr = MemoryManager()
+        p = FakeMemoryProvider("ext")
+        mgr.add_provider(p)
+
+        # Manager itself doesn't filter — run_agent.py does.
+        # But providers should handle remove gracefully.
+        mgr.on_memory_write("remove", "memory", "old fact")
+        assert p.memory_writes == [("remove", "memory", "old fact")]
+
+    def test_on_memory_write_tolerates_provider_failure(self):
+        """If a provider's on_memory_write raises, others still get notified."""
+        mgr = MemoryManager()
+        bad = FakeMemoryProvider("builtin")
+        bad.on_memory_write = MagicMock(side_effect=RuntimeError("boom"))
+        good = FakeMemoryProvider("good")
+        mgr.add_provider(bad)
+        mgr.add_provider(good)
+
+        mgr.on_memory_write("add", "user", "test")
+        # Good provider still received the call despite bad provider crashing
+        assert good.memory_writes == [("add", "user", "test")]