fix(gateway): isolate pending native image paths by session

tests/gateway/test_native_image_buffer_isolation.py

@@ -0,0 +1,79 @@
+import pytest
+
+from gateway.config import GatewayConfig, Platform, PlatformConfig
+from gateway.platforms.base import MessageEvent, MessageType
+from gateway.run import GatewayRunner
+from gateway.session import SessionSource, build_session_key
+
+
+def _make_runner() -> GatewayRunner:
+    runner = GatewayRunner.__new__(GatewayRunner)
+    runner.config = GatewayConfig(
+        platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="fake")},
+    )
+    runner.adapters = {}
+    runner._model = "openai/gpt-4.1-mini"
+    runner._base_url = None
+    runner._decide_image_input_mode = lambda: "native"
+    return runner
+
+
+def _source(chat_id: str) -> SessionSource:
+    return SessionSource(
+        platform=Platform.TELEGRAM,
+        chat_id=chat_id,
+        chat_type="private",
+        user_name=f"user-{chat_id}",
+    )
+
+
+def _image_event(source: SessionSource, path: str) -> MessageEvent:
+    return MessageEvent(
+        text="see image",
+        message_type=MessageType.PHOTO,
+        source=source,
+        media_urls=[path],
+        media_types=["image/png"],
+    )
+
+
+@pytest.mark.asyncio
+async def test_native_image_buffer_isolated_per_session():
+    runner = _make_runner()
+    source_a = _source("chat-a")
+    source_b = _source("chat-b")
+
+    await runner._prepare_inbound_message_text(
+        event=_image_event(source_a, "/tmp/a.png"),
+        source=source_a,
+        history=[],
+    )
+    await runner._prepare_inbound_message_text(
+        event=_image_event(source_b, "/tmp/b.png"),
+        source=source_b,
+        history=[],
+    )
+
+    assert runner._consume_pending_native_image_paths(build_session_key(source_a)) == ["/tmp/a.png"]
+    assert runner._consume_pending_native_image_paths(build_session_key(source_b)) == ["/tmp/b.png"]
+
+
+@pytest.mark.asyncio
+async def test_native_image_buffer_not_cleared_by_other_sessions_without_images():
+    runner = _make_runner()
+    source_a = _source("chat-a")
+    source_b = _source("chat-b")
+
+    await runner._prepare_inbound_message_text(
+        event=_image_event(source_a, "/tmp/a.png"),
+        source=source_a,
+        history=[],
+    )
+    await runner._prepare_inbound_message_text(
+        event=MessageEvent(text="plain text", source=source_b),
+        source=source_b,
+        history=[],
+    )
+
+    assert runner._consume_pending_native_image_paths(build_session_key(source_a)) == ["/tmp/a.png"]
+    assert runner._consume_pending_native_image_paths(build_session_key(source_b)) == []