diff --git a/nanobot/agent/runner.py b/nanobot/agent/runner.py
index 53f6554a..e5cc579f 100644
--- a/nanobot/agent/runner.py
+++ b/nanobot/agent/runner.py
@@ -257,12 +257,17 @@ class AgentRunner:
             return []
         injected_messages: list[dict[str, Any]] = []
         for item in items:
-            if isinstance(item, dict) and item.get("role") == "user" and "content" in item:
-                injected_messages.append(item)
+            if item is None:
                 continue
-            text = getattr(item, "content", str(item))
-            if text.strip():
-                injected_messages.append({"role": "user", "content": text})
+            if isinstance(item, dict) and item.get("role") == "user" and "content" in item:
+                if self._has_injection_content(item.get("content")):
+                    injected_messages.append(item)
+                continue
+            if isinstance(item, dict):
+                continue
+            content = getattr(item, "content") if hasattr(item, "content") else str(item)
+            if self._has_injection_content(content):
+                injected_messages.append({"role": "user", "content": content})
         if len(injected_messages) > _MAX_INJECTIONS_PER_TURN:
             dropped = len(injected_messages) - _MAX_INJECTIONS_PER_TURN
             logger.warning(
@@ -272,6 +277,16 @@ class AgentRunner:
             injected_messages = injected_messages[:_MAX_INJECTIONS_PER_TURN]
         return injected_messages
 
+    @staticmethod
+    def _has_injection_content(content: Any) -> bool:
+        if content is None:
+            return False
+        if isinstance(content, str):
+            return bool(content.strip())
+        if isinstance(content, list):
+            return bool(content)
+        return True
+
     async def run(self, spec: AgentRunSpec) -> AgentRunResult:
         hook = spec.hook or AgentHook()
         messages = list(spec.initial_messages)
diff --git a/tests/agent/test_runner_injections.py b/tests/agent/test_runner_injections.py
index 3b94569d..637235ba 100644
--- a/tests/agent/test_runner_injections.py
+++ b/tests/agent/test_runner_injections.py
@@ -152,6 +152,70 @@ async def test_drain_injections_skips_empty_content():
     assert result == [{"role": "user", "content": "valid"}]
 
 
+@pytest.mark.asyncio
+async def test_drain_injections_filters_empty_dict_payloads():
+    """Pre-normalized dict injections should obey the same empty-content guard."""
+    from nanobot.agent.runner import AgentRunner, AgentRunSpec
+
+    provider = MagicMock()
+    runner = AgentRunner(provider)
+    tools = MagicMock()
+    tools.get_definitions.return_value = []
+
+    multimodal = [{"type": "image_url", "image_url": {"url": "data:image/png;base64,abc"}}]
+    msgs = [
+        {"role": "user", "content": ""},
+        {"role": "user", "content": "   "},
+        {"role": "user", "content": None},
+        {"role": "assistant", "content": "should not be re-injected as user"},
+        None,
+        {"role": "user", "content": "valid"},
+        {"role": "user", "content": multimodal},
+    ]
+
+    async def cb():
+        return msgs
+
+    spec = AgentRunSpec(
+        initial_messages=[], tools=tools, model="m",
+        max_iterations=1, max_tool_result_chars=1000,
+        injection_callback=cb,
+    )
+    result = await runner._drain_injections(spec)
+    assert result == [
+        {"role": "user", "content": "valid"},
+        {"role": "user", "content": multimodal},
+    ]
+
+
+@pytest.mark.asyncio
+async def test_drain_injections_skips_objects_with_none_content():
+    """Objects exposing content=None should be skipped rather than stringified."""
+    from types import SimpleNamespace
+
+    from nanobot.agent.runner import AgentRunner, AgentRunSpec
+
+    provider = MagicMock()
+    runner = AgentRunner(provider)
+    tools = MagicMock()
+    tools.get_definitions.return_value = []
+
+    async def cb():
+        return [
+            SimpleNamespace(content=None),
+            SimpleNamespace(content=""),
+            SimpleNamespace(content="valid"),
+        ]
+
+    spec = AgentRunSpec(
+        initial_messages=[], tools=tools, model="m",
+        max_iterations=1, max_tool_result_chars=1000,
+        injection_callback=cb,
+    )
+    result = await runner._drain_injections(spec)
+    assert result == [{"role": "user", "content": "valid"}]
+
+
 @pytest.mark.asyncio
 async def test_drain_injections_handles_callback_exception():
     """If the callback raises, return empty list (error is logged)."""
@@ -1155,4 +1219,3 @@ async def test_injection_cycle_cap_on_error_path():
     assert result.had_injections is True
     # Should cap: _MAX_INJECTION_CYCLES drained rounds + 1 final round that breaks
     assert call_count["n"] == _MAX_INJECTION_CYCLES + 1
-