fix(agent): resolve relative media paths in MessageTool

When deployed with Docker and workspace mounted as a volume, sending
media files failed because relative paths (e.g. output/image.png) were
not resolved against the workspace directory. The process CWD differs
from the workspace in containerized environments, causing os.path.isfile
checks to fail in channel handlers. Normalize relative media paths at
the MessageTool entry point using get_workspace_path().

tests/tools/test_message_tool.py

@@ -1,7 +1,10 @@
+import os
+
 import pytest
 
 from nanobot.agent.tools.message import MessageTool
 from nanobot.bus.events import OutboundMessage
+from nanobot.config.paths import get_workspace_path
 
 
 @pytest.mark.asyncio
@@ -85,3 +88,97 @@ async def test_message_tool_does_not_inherit_metadata_for_cross_target() -> None
     await tool.execute(content="channel reply", channel="slack", chat_id="C999")
 
     assert sent[0].metadata == {}
+
+
+@pytest.mark.asyncio
+async def test_message_tool_resolves_relative_media_paths() -> None:
+    sent: list[OutboundMessage] = []
+
+    async def _send(msg: OutboundMessage) -> None:
+        sent.append(msg)
+
+    tool = MessageTool(send_callback=_send)
+
+    await tool.execute(
+        content="see attached",
+        channel="telegram",
+        chat_id="1",
+        media=["output/image.png"],
+    )
+
+    expected = str(get_workspace_path() / "output/image.png")
+    assert sent[0].media == [expected]
+
+
+@pytest.mark.asyncio
+async def test_message_tool_passes_through_absolute_media_paths() -> None:
+    sent: list[OutboundMessage] = []
+
+    async def _send(msg: OutboundMessage) -> None:
+        sent.append(msg)
+
+    tool = MessageTool(send_callback=_send)
+
+    abs_path = os.path.abspath(os.path.join(os.sep, "tmp", "abs_image.png"))
+
+    await tool.execute(
+        content="see attached",
+        channel="telegram",
+        chat_id="1",
+        media=[abs_path],
+    )
+
+    assert sent[0].media == [abs_path]
+
+
+@pytest.mark.asyncio
+async def test_message_tool_passes_through_url_media_paths() -> None:
+    sent: list[OutboundMessage] = []
+
+    async def _send(msg: OutboundMessage) -> None:
+        sent.append(msg)
+
+    tool = MessageTool(send_callback=_send)
+
+    url = "https://example.com/image.png"
+
+    await tool.execute(
+        content="see attached",
+        channel="telegram",
+        chat_id="1",
+        media=[url],
+    )
+
+    assert sent[0].media == [url]
+
+
+@pytest.mark.asyncio
+async def test_message_tool_resolves_mixed_media_paths() -> None:
+    sent: list[OutboundMessage] = []
+
+    async def _send(msg: OutboundMessage) -> None:
+        sent.append(msg)
+
+    tool = MessageTool(send_callback=_send)
+
+    abs_path = os.path.abspath(os.path.join(os.sep, "tmp", "absolute.png"))
+
+    await tool.execute(
+        content="see attached",
+        channel="telegram",
+        chat_id="1",
+        media=[
+            "output/relative.png",
+            abs_path,
+            "https://example.com/url.png",
+            "http://example.com/http.png",
+        ],
+    )
+
+    expected_relative = str(get_workspace_path() / "output/relative.png")
+    assert sent[0].media == [
+        expected_relative,
+        abs_path,
+        "https://example.com/url.png",
+        "http://example.com/http.png",
+    ]