diff --git a/plugins/platforms/simplex/adapter.py b/plugins/platforms/simplex/adapter.py
index 21c2f1de8c7..0b241d588f3 100644
--- a/plugins/platforms/simplex/adapter.py
+++ b/plugins/platforms/simplex/adapter.py
@@ -625,6 +625,11 @@ class SimplexAdapter(BasePlatformAdapter):
                 msg_type = MessageType.VOICE
             elif any(mt.startswith("image/") for mt in media_types):
                 msg_type = MessageType.PHOTO
+            else:
+                # Catch-all: non-image/non-audio files (tagged
+                # application/octet-stream above) are documents so run.py's
+                # document-context injection surfaces the file to the agent.
+                msg_type = MessageType.DOCUMENT
 
         # Timestamp
         ts_str = meta.get("itemTs") or meta.get("createdAt", "")
diff --git a/tests/gateway/test_simplex_plugin.py b/tests/gateway/test_simplex_plugin.py
index 286f2291034..66242438f8e 100644
--- a/tests/gateway/test_simplex_plugin.py
+++ b/tests/gateway/test_simplex_plugin.py
@@ -396,3 +396,74 @@ def test_register_calls_register_platform():
     assert callable(kwargs["setup_fn"])
     # SimpleX uses opaque IDs only — no PII to redact.
     assert kwargs["pii_safe"] is True
+
+
+# ---------------------------------------------------------------------------
+# Inbound attachment message type classification
+# ---------------------------------------------------------------------------
+
+def _make_file_chat_item(file_path: str, file_name: str) -> dict:
+    """Minimal direct-chat rcvMsgContent item carrying a completed file."""
+    return {
+        "chatInfo": {
+            "type": "direct",
+            "contact": {"contactId": 42, "localDisplayName": "tester"},
+        },
+        "chatItem": {
+            "chatDir": {"type": "directRcv"},
+            "meta": {"itemTs": "2026-01-01T00:00:00Z"},
+            "content": {
+                "type": "rcvMsgContent",
+                "msgContent": {"type": "file", "text": "here you go"},
+            },
+            "file": {
+                "fileId": 7,
+                "fileName": file_name,
+                "fileSource": {"filePath": file_path},
+            },
+        },
+    }
+
+
+@pytest.mark.asyncio
+async def test_document_file_sets_document_type():
+    """A non-image/non-audio file must classify as DOCUMENT, not TEXT,
+    so run.py's document-context injection surfaces the path to the agent."""
+    from gateway.config import PlatformConfig
+    from gateway.platforms.base import MessageType
+
+    cfg = PlatformConfig(enabled=True, extra={"ws_url": "ws://localhost:5225"})
+    adapter = SimplexAdapter(cfg)
+    dispatched = []
+
+    async def _capture(event):
+        dispatched.append(event)
+
+    adapter.handle_message = _capture
+    await adapter._handle_chat_item(_make_file_chat_item("/tmp/report.pdf", "report.pdf"))
+
+    assert dispatched, "_handle_chat_item did not dispatch any event"
+    assert dispatched[0].message_type == MessageType.DOCUMENT
+    assert dispatched[0].media_urls == ["/tmp/report.pdf"]
+    assert dispatched[0].media_types == ["application/octet-stream"]
+
+
+@pytest.mark.asyncio
+async def test_image_file_still_sets_photo_type():
+    """Regression guard: image files keep classifying as PHOTO after the
+    document catch-all was added."""
+    from gateway.config import PlatformConfig
+    from gateway.platforms.base import MessageType
+
+    cfg = PlatformConfig(enabled=True, extra={"ws_url": "ws://localhost:5225"})
+    adapter = SimplexAdapter(cfg)
+    dispatched = []
+
+    async def _capture(event):
+        dispatched.append(event)
+
+    adapter.handle_message = _capture
+    await adapter._handle_chat_item(_make_file_chat_item("/tmp/pic.jpg", "pic.jpg"))
+
+    assert dispatched, "_handle_chat_item did not dispatch any event"
+    assert dispatched[0].message_type == MessageType.PHOTO