feat(matrix): add outbound media uploads and unify media limits with maxMediaBytes

- Use OutboundMessage.media for Matrix file/image/audio/video sends
- Apply effective media limit as min(m.upload.size, maxMediaBytes)
- Rename matrix config key maxInboundMediaBytes -> maxMediaBytes (no legacy fallback)

README.md

@@ -304,7 +304,7 @@ nanobot gateway
 <details>
 <summary><b>Matrix (Element)</b></summary>
 
-Uses Matrix sync via `matrix-nio` (including inbound media support).
+Uses Matrix sync via `matrix-nio` (inbound media + outbound file attachments).
 
 **1. Create/choose a Matrix account**
 
@@ -335,7 +335,7 @@ Uses Matrix sync via `matrix-nio` (including inbound media support).
       "groupPolicy": "open",
       "groupAllowFrom": [],
       "allowRoomMentions": false,
-      "maxInboundMediaBytes": 20971520
+      "maxMediaBytes": 20971520
     }
   }
 }
@@ -356,6 +356,9 @@ Uses Matrix sync via `matrix-nio` (including inbound media support).
 > - With `e2eeEnabled=false`, encrypted room messages may be undecryptable and E2EE send safeguards are not applied.
 > - With `e2eeEnabled=true`, the bot sends with `ignore_unverified_devices=true` (more compatible, less strict than verified-only sending).
 > - Changing `accessToken`/`deviceId` effectively creates a new device and may require session re-establishment.
+> - Outbound attachments are sent from `OutboundMessage.media`.
+> - Effective media limit (inbound + outbound) uses the stricter value of local `maxMediaBytes` and homeserver `m.upload.size` (if advertised).
+> - If `tools.restrictToWorkspace=true`, Matrix outbound attachments are limited to files inside the workspace.
 
 **4. Run**
 

nanobot/channels/manager.py

@@ -38,6 +38,7 @@ class ChannelManager:
         if self.config.channels.telegram.enabled:
             try:
                 from nanobot.channels.telegram import TelegramChannel
+
                 self.channels["telegram"] = TelegramChannel(
                     self.config.channels.telegram,
                     self.bus,
@@ -51,9 +52,8 @@ class ChannelManager:
         if self.config.channels.whatsapp.enabled:
             try:
                 from nanobot.channels.whatsapp import WhatsAppChannel
-                self.channels["whatsapp"] = WhatsAppChannel(
+
-                    self.config.channels.whatsapp, self.bus
+                self.channels["whatsapp"] = WhatsAppChannel(self.config.channels.whatsapp, self.bus)
-                )
                 logger.info("WhatsApp channel enabled")
             except ImportError as e:
                 logger.warning(f"WhatsApp channel not available: {e}")
@@ -62,9 +62,8 @@ class ChannelManager:
         if self.config.channels.discord.enabled:
             try:
                 from nanobot.channels.discord import DiscordChannel
-                self.channels["discord"] = DiscordChannel(
+
-                    self.config.channels.discord, self.bus
+                self.channels["discord"] = DiscordChannel(self.config.channels.discord, self.bus)
-                )
                 logger.info("Discord channel enabled")
             except ImportError as e:
                 logger.warning(f"Discord channel not available: {e}")
@@ -73,9 +72,8 @@ class ChannelManager:
         if self.config.channels.feishu.enabled:
             try:
                 from nanobot.channels.feishu import FeishuChannel
-                self.channels["feishu"] = FeishuChannel(
+
-                    self.config.channels.feishu, self.bus
+                self.channels["feishu"] = FeishuChannel(self.config.channels.feishu, self.bus)
-                )
                 logger.info("Feishu channel enabled")
             except ImportError as e:
                 logger.warning(f"Feishu channel not available: {e}")
@@ -85,9 +83,7 @@ class ChannelManager:
             try:
                 from nanobot.channels.mochat import MochatChannel
 
-                self.channels["mochat"] = MochatChannel(
+                self.channels["mochat"] = MochatChannel(self.config.channels.mochat, self.bus)
-                    self.config.channels.mochat, self.bus
-                )
                 logger.info("Mochat channel enabled")
             except ImportError as e:
                 logger.warning(f"Mochat channel not available: {e}")
@@ -96,9 +92,8 @@ class ChannelManager:
         if self.config.channels.dingtalk.enabled:
             try:
                 from nanobot.channels.dingtalk import DingTalkChannel
-                self.channels["dingtalk"] = DingTalkChannel(
+
-                    self.config.channels.dingtalk, self.bus
+                self.channels["dingtalk"] = DingTalkChannel(self.config.channels.dingtalk, self.bus)
-                )
                 logger.info("DingTalk channel enabled")
             except ImportError as e:
                 logger.warning(f"DingTalk channel not available: {e}")
@@ -107,9 +102,8 @@ class ChannelManager:
         if self.config.channels.email.enabled:
             try:
                 from nanobot.channels.email import EmailChannel
-                self.channels["email"] = EmailChannel(
+
-                    self.config.channels.email, self.bus
+                self.channels["email"] = EmailChannel(self.config.channels.email, self.bus)
-                )
                 logger.info("Email channel enabled")
             except ImportError as e:
                 logger.warning(f"Email channel not available: {e}")
@@ -118,9 +112,8 @@ class ChannelManager:
         if self.config.channels.slack.enabled:
             try:
                 from nanobot.channels.slack import SlackChannel
-                self.channels["slack"] = SlackChannel(
+
-                    self.config.channels.slack, self.bus
+                self.channels["slack"] = SlackChannel(self.config.channels.slack, self.bus)
-                )
                 logger.info("Slack channel enabled")
             except ImportError as e:
                 logger.warning(f"Slack channel not available: {e}")
@@ -129,6 +122,7 @@ class ChannelManager:
         if self.config.channels.qq.enabled:
             try:
                 from nanobot.channels.qq import QQChannel
+
                 self.channels["qq"] = QQChannel(
                     self.config.channels.qq,
                     self.bus,
@@ -188,10 +182,7 @@ class ChannelManager:
 
         while True:
             try:
-                msg = await asyncio.wait_for(
+                msg = await asyncio.wait_for(self.bus.consume_outbound(), timeout=1.0)
-                    self.bus.consume_outbound(),
-                    timeout=1.0
-                )
 
                 channel = self.channels.get(msg.channel)
                 if channel:
@@ -214,10 +205,7 @@ class ChannelManager:
     def get_status(self) -> dict[str, Any]:
         """Get status of all channels."""
         return {
-            name: {
+            name: {"enabled": True, "running": channel.is_running}
-                "enabled": True,
-                "running": channel.is_running
-            }
             for name, channel in self.channels.items()
         }
 

nanobot/channels/matrix.py

@@ -10,6 +10,7 @@ from mistune import create_markdown
 from nio import (
     AsyncClient,
     AsyncClientConfig,
+    ContentRepositoryConfigError,
     DownloadError,
     InviteEvent,
     JoinError,
@@ -22,6 +23,7 @@ from nio import (
     RoomSendError,
     RoomTypingError,
     SyncError,
+    UploadError,
 )
 from nio.crypto.attachments import decrypt_attachment
 from nio.exceptions import EncryptionError
@@ -44,6 +46,7 @@ MATRIX_HTML_FORMAT = "org.matrix.custom.html"
 MATRIX_ATTACHMENT_MARKER_TEMPLATE = "[attachment: {}]"
 MATRIX_ATTACHMENT_TOO_LARGE_TEMPLATE = "[attachment: {} - too large]"
 MATRIX_ATTACHMENT_FAILED_TEMPLATE = "[attachment: {} - download failed]"
+MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE = "[attachment: {} - upload failed]"
 MATRIX_DEFAULT_ATTACHMENT_NAME = "attachment"
 
 # Runtime callback filter for nio event dispatch (checked via isinstance).
@@ -227,11 +230,22 @@ class MatrixChannel(BaseChannel):
 
     name = "matrix"
 
-    def __init__(self, config: Any, bus):
+    def __init__(
+        self,
+        config: Any,
+        bus,
+        *,
+        restrict_to_workspace: bool = False,
+        workspace: Path | None = None,
+    ):
         super().__init__(config, bus)
         self.client: AsyncClient | None = None
         self._sync_task: asyncio.Task | None = None
         self._typing_tasks: dict[str, asyncio.Task] = {}
+        self._restrict_to_workspace = restrict_to_workspace
+        self._workspace = workspace.expanduser().resolve() if workspace else None
+        self._server_upload_limit_bytes: int | None = None
+        self._server_upload_limit_checked = False
 
     async def start(self) -> None:
         """Start Matrix client and begin sync loop."""
@@ -313,21 +327,266 @@ class MatrixChannel(BaseChannel):
         if self.client:
             await self.client.close()
 
-    async def send(self, msg: OutboundMessage) -> None:
+    @staticmethod
+    def _path_dedupe_key(path: Path) -> str:
+        """Return a stable deduplication key for attachment paths."""
+        expanded = path.expanduser()
+        try:
+            return str(expanded.resolve(strict=False))
+        except OSError:
+            return str(expanded)
+
+    def _is_workspace_path_allowed(self, path: Path) -> bool:
+        """Enforce optional workspace-only outbound attachment policy."""
+        if not self._restrict_to_workspace:
+            return True
+
+        if self._workspace is None:
+            return False
+
+        try:
+            path.resolve(strict=False).relative_to(self._workspace)
+            return True
+        except ValueError:
+            return False
+
+    def _collect_outbound_media_candidates(self, media: list[str]) -> list[Path]:
+        """Collect unique outbound attachment paths from OutboundMessage.media."""
+        candidates: list[Path] = []
+        seen: set[str] = set()
+
+        for raw in media:
+            if not isinstance(raw, str) or not raw.strip():
+                continue
+            path = Path(raw.strip()).expanduser()
+            key = self._path_dedupe_key(path)
+            if key in seen:
+                continue
+            seen.add(key)
+            candidates.append(path)
+
+        return candidates
+
+    @staticmethod
+    def _build_outbound_attachment_content(
+        *,
+        filename: str,
+        mime: str,
+        size_bytes: int,
+        mxc_url: str,
+    ) -> dict[str, Any]:
+        """Build Matrix content payload for an uploaded file/image/audio/video."""
+        msgtype = "m.file"
+        if mime.startswith("image/"):
+            msgtype = "m.image"
+        elif mime.startswith("audio/"):
+            msgtype = "m.audio"
+        elif mime.startswith("video/"):
+            msgtype = "m.video"
+
+        return {
+            "msgtype": msgtype,
+            "body": filename,
+            "filename": filename,
+            "url": mxc_url,
+            "info": {
+                "mimetype": mime,
+                "size": size_bytes,
+            },
+            "m.mentions": {},
+        }
+
+    async def _send_room_content(self, room_id: str, content: dict[str, Any]) -> None:
+        """Send Matrix m.room.message content with configured E2EE send options."""
         if not self.client:
             return
 
         room_send_kwargs: dict[str, Any] = {
-            "room_id": msg.chat_id,
+            "room_id": room_id,
             "message_type": "m.room.message",
-            "content": _build_matrix_text_content(msg.content),
+            "content": content,
         }
         if self.config.e2ee_enabled:
             # TODO(matrix): Add explicit config for strict verified-device sending mode.
             room_send_kwargs["ignore_unverified_devices"] = True
 
-        try:
         await self.client.room_send(**room_send_kwargs)
+
+    async def _resolve_server_upload_limit_bytes(self) -> int | None:
+        """Resolve homeserver-advertised upload limit once per channel lifecycle."""
+        if self._server_upload_limit_checked:
+            return self._server_upload_limit_bytes
+
+        self._server_upload_limit_checked = True
+        if not self.client:
+            return None
+
+        try:
+            response = await self.client.content_repository_config()
+        except Exception as e:
+            logger.debug(
+                "Matrix media config lookup failed ({}): {}",
+                type(e).__name__,
+                str(e),
+            )
+            return None
+
+        upload_size = getattr(response, "upload_size", None)
+        if isinstance(upload_size, int) and upload_size > 0:
+            self._server_upload_limit_bytes = upload_size
+            return self._server_upload_limit_bytes
+
+        if isinstance(response, ContentRepositoryConfigError):
+            logger.debug("Matrix media config lookup failed: {}", response)
+            return None
+
+        logger.debug(
+            "Matrix media config lookup returned unexpected response {}",
+            type(response).__name__,
+        )
+        return None
+
+    async def _effective_media_limit_bytes(self) -> int:
+        """
+        Compute effective Matrix media size cap.
+
+        `m.upload.size` (if advertised) is treated as the homeserver-side cap.
+        `maxMediaBytes` is a local hard limit/fallback. Using the stricter value
+        keeps resource usage predictable while honoring server constraints.
+        """
+        local_limit = max(int(self.config.max_media_bytes), 0)
+        server_limit = await self._resolve_server_upload_limit_bytes()
+        if server_limit is None:
+            return local_limit
+        if local_limit == 0:
+            return 0
+        return min(local_limit, server_limit)
+
+    async def _upload_and_send_attachment(
+        self, room_id: str, path: Path, limit_bytes: int
+    ) -> str | None:
+        """Upload one local file to Matrix and send it as a media message."""
+        if not self.client:
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(
+                path.name or MATRIX_DEFAULT_ATTACHMENT_NAME
+            )
+
+        resolved = path.expanduser().resolve(strict=False)
+        filename = safe_filename(resolved.name) or MATRIX_DEFAULT_ATTACHMENT_NAME
+
+        if not resolved.is_file():
+            logger.warning("Matrix outbound attachment missing file: {}", resolved)
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        if not self._is_workspace_path_allowed(resolved):
+            logger.warning(
+                "Matrix outbound attachment denied by workspace restriction: {}",
+                resolved,
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        try:
+            size_bytes = resolved.stat().st_size
+        except OSError as e:
+            logger.warning(
+                "Matrix outbound attachment stat failed for {} ({}): {}",
+                resolved,
+                type(e).__name__,
+                str(e),
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        if limit_bytes and size_bytes > limit_bytes:
+            logger.warning(
+                "Matrix outbound attachment skipped: {} bytes exceeds limit {} for {}",
+                size_bytes,
+                limit_bytes,
+                resolved,
+            )
+            return MATRIX_ATTACHMENT_TOO_LARGE_TEMPLATE.format(filename)
+
+        try:
+            data = resolved.read_bytes()
+        except OSError as e:
+            logger.warning(
+                "Matrix outbound attachment read failed for {} ({}): {}",
+                resolved,
+                type(e).__name__,
+                str(e),
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        mime = mimetypes.guess_type(filename, strict=False)[0] or "application/octet-stream"
+        upload_response = await self.client.upload(
+            data,
+            content_type=mime,
+            filename=filename,
+            filesize=len(data),
+        )
+        if isinstance(upload_response, UploadError):
+            logger.warning(
+                "Matrix outbound attachment upload failed for {}: {}",
+                resolved,
+                upload_response,
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        mxc_url = getattr(upload_response, "content_uri", None)
+        if not isinstance(mxc_url, str) or not mxc_url.startswith("mxc://"):
+            logger.warning(
+                "Matrix outbound attachment upload returned unexpected response {} for {}",
+                type(upload_response).__name__,
+                resolved,
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+
+        content = self._build_outbound_attachment_content(
+            filename=filename,
+            mime=mime,
+            size_bytes=len(data),
+            mxc_url=mxc_url,
+        )
+        try:
+            await self._send_room_content(room_id, content)
+        except Exception as e:
+            logger.warning(
+                "Matrix outbound attachment send failed for {} ({}): {}",
+                resolved,
+                type(e).__name__,
+                str(e),
+            )
+            return MATRIX_ATTACHMENT_UPLOAD_FAILED_TEMPLATE.format(filename)
+        return None
+
+    async def send(self, msg: OutboundMessage) -> None:
+        if not self.client:
+            return
+
+        text = msg.content or ""
+        candidates = self._collect_outbound_media_candidates(msg.media)
+
+        try:
+            failures: list[str] = []
+
+            if candidates:
+                limit_bytes = await self._effective_media_limit_bytes()
+                for path in candidates:
+                    failure_marker = await self._upload_and_send_attachment(
+                        room_id=msg.chat_id,
+                        path=path,
+                        limit_bytes=limit_bytes,
+                    )
+                    if failure_marker:
+                        failures.append(failure_marker)
+
+            if failures:
+                if text.strip():
+                    text = f"{text.rstrip()}\n" + "\n".join(failures)
+                else:
+                    text = "\n".join(failures)
+
+            if text or not candidates:
+                await self._send_room_content(msg.chat_id, _build_matrix_text_content(text))
         finally:
             await self._stop_typing_keepalive(msg.chat_id, clear_typing=True)
 
@@ -711,13 +970,14 @@ class MatrixChannel(BaseChannel):
             )
             return None, MATRIX_ATTACHMENT_FAILED_TEMPLATE.format(filename)
 
+        limit_bytes = await self._effective_media_limit_bytes()
         declared_size = self._event_declared_size_bytes(event)
-        if declared_size is not None and declared_size > self.config.max_inbound_media_bytes:
+        if declared_size is not None and declared_size > limit_bytes:
             logger.warning(
                 "Matrix attachment skipped in room {}: declared size {} exceeds limit {}",
                 room.room_id,
                 declared_size,
-                self.config.max_inbound_media_bytes,
+                limit_bytes,
             )
             return None, MATRIX_ATTACHMENT_TOO_LARGE_TEMPLATE.format(filename)
 
@@ -733,12 +993,12 @@ class MatrixChannel(BaseChannel):
                 return None, MATRIX_ATTACHMENT_FAILED_TEMPLATE.format(filename)
             data = decrypted
 
-        if len(data) > self.config.max_inbound_media_bytes:
+        if len(data) > limit_bytes:
             logger.warning(
                 "Matrix attachment skipped in room {}: downloaded size {} exceeds limit {}",
                 room.room_id,
                 len(data),
-                self.config.max_inbound_media_bytes,
+                limit_bytes,
             )
             return None, MATRIX_ATTACHMENT_TOO_LARGE_TEMPLATE.format(filename)
 

nanobot/config/schema.py

@@ -76,8 +76,8 @@ class MatrixConfig(Base):
     e2ee_enabled: bool = True
     # Max seconds to wait for sync_forever to stop gracefully before cancellation fallback.
     sync_stop_grace_seconds: int = 2
-    # Max attachment size accepted from inbound Matrix media events.
+    # Max attachment size accepted for Matrix media handling (inbound + outbound).
-    max_inbound_media_bytes: int = 20 * 1024 * 1024
+    max_media_bytes: int = 20 * 1024 * 1024
     allow_from: list[str] = Field(default_factory=list)
     group_policy: Literal["open", "mention", "allowlist"] = "open"
     group_allow_from: list[str] = Field(default_factory=list)

tests/test_matrix_channel.py

@@ -48,12 +48,16 @@ class _FakeAsyncClient:
         self.room_send_calls: list[dict[str, object]] = []
         self.typing_calls: list[tuple[str, bool, int]] = []
         self.download_calls: list[dict[str, object]] = []
+        self.upload_calls: list[dict[str, object]] = []
         self.download_response: object | None = None
         self.download_bytes: bytes = b"media"
         self.download_content_type: str = "application/octet-stream"
         self.download_filename: str | None = None
+        self.upload_response: object | None = None
+        self.content_repository_config_response: object = SimpleNamespace(upload_size=None)
         self.raise_on_send = False
         self.raise_on_typing = False
+        self.raise_on_upload = False
 
     def add_event_callback(self, callback, event_type) -> None:
         self.callbacks.append((callback, event_type))
@@ -108,6 +112,32 @@ class _FakeAsyncClient:
             filename=self.download_filename,
         )
 
+    async def upload(
+        self,
+        data_provider,
+        content_type: str | None = None,
+        filename: str | None = None,
+        filesize: int | None = None,
+        encrypt: bool = False,
+    ):
+        if self.raise_on_upload:
+            raise RuntimeError("upload failed")
+        self.upload_calls.append(
+            {
+                "data_provider": data_provider,
+                "content_type": content_type,
+                "filename": filename,
+                "filesize": filesize,
+                "encrypt": encrypt,
+            }
+        )
+        if self.upload_response is not None:
+            return self.upload_response
+        return SimpleNamespace(content_uri="mxc://example.org/uploaded")
+
+    async def content_repository_config(self):
+        return self.content_repository_config_response
+
     async def close(self) -> None:
         return None
 
@@ -523,7 +553,7 @@ async def test_on_media_message_respects_declared_size_limit(
 ) -> None:
     monkeypatch.setattr("nanobot.channels.matrix.get_data_dir", lambda: tmp_path)
 
-    channel = MatrixChannel(_make_config(max_inbound_media_bytes=3), MessageBus())
+    channel = MatrixChannel(_make_config(max_media_bytes=3), MessageBus())
     client = _FakeAsyncClient("", "", "", None)
     channel.client = client
 
@@ -552,6 +582,42 @@ async def test_on_media_message_respects_declared_size_limit(
     assert "[attachment: large.bin - too large]" in handled[0]["content"]
 
 
+@pytest.mark.asyncio
+async def test_on_media_message_uses_server_limit_when_smaller_than_local_limit(
+    monkeypatch, tmp_path
+) -> None:
+    monkeypatch.setattr("nanobot.channels.matrix.get_data_dir", lambda: tmp_path)
+
+    channel = MatrixChannel(_make_config(max_media_bytes=10), MessageBus())
+    client = _FakeAsyncClient("", "", "", None)
+    client.content_repository_config_response = SimpleNamespace(upload_size=3)
+    channel.client = client
+
+    handled: list[dict[str, object]] = []
+
+    async def _fake_handle_message(**kwargs) -> None:
+        handled.append(kwargs)
+
+    channel._handle_message = _fake_handle_message  # type: ignore[method-assign]
+
+    room = SimpleNamespace(room_id="!room:matrix.org", display_name="Test room", member_count=2)
+    event = SimpleNamespace(
+        sender="@alice:matrix.org",
+        body="large.bin",
+        url="mxc://example.org/large",
+        event_id="$event2_server",
+        source={"content": {"msgtype": "m.file", "info": {"size": 5}}},
+    )
+
+    await channel._on_media_message(room, event)
+
+    assert client.download_calls == []
+    assert len(handled) == 1
+    assert handled[0]["media"] == []
+    assert handled[0]["metadata"]["attachments"] == []
+    assert "[attachment: large.bin - too large]" in handled[0]["content"]
+
+
 @pytest.mark.asyncio
 async def test_on_media_message_handles_download_error(monkeypatch, tmp_path) -> None:
     monkeypatch.setattr("nanobot.channels.matrix.get_data_dir", lambda: tmp_path)
@@ -690,6 +756,107 @@ async def test_send_clears_typing_after_send() -> None:
     assert client.typing_calls[-1] == ("!room:matrix.org", False, TYPING_NOTICE_TIMEOUT_MS)
 
 
+@pytest.mark.asyncio
+async def test_send_uploads_media_and_sends_file_event(tmp_path) -> None:
+    channel = MatrixChannel(_make_config(), MessageBus())
+    client = _FakeAsyncClient("", "", "", None)
+    channel.client = client
+
+    file_path = tmp_path / "test.txt"
+    file_path.write_text("hello", encoding="utf-8")
+
+    await channel.send(
+        OutboundMessage(
+            channel="matrix",
+            chat_id="!room:matrix.org",
+            content="Please review.",
+            media=[str(file_path)],
+        )
+    )
+
+    assert len(client.upload_calls) == 1
+    assert client.upload_calls[0]["filename"] == "test.txt"
+    assert client.upload_calls[0]["filesize"] == 5
+    assert len(client.room_send_calls) == 2
+    assert client.room_send_calls[0]["content"]["msgtype"] == "m.file"
+    assert client.room_send_calls[0]["content"]["url"] == "mxc://example.org/uploaded"
+    assert client.room_send_calls[1]["content"]["body"] == "Please review."
+
+
+@pytest.mark.asyncio
+async def test_send_does_not_parse_attachment_marker_without_media(tmp_path) -> None:
+    channel = MatrixChannel(_make_config(), MessageBus())
+    client = _FakeAsyncClient("", "", "", None)
+    channel.client = client
+
+    missing_path = tmp_path / "missing.txt"
+    await channel.send(
+        OutboundMessage(
+            channel="matrix",
+            chat_id="!room:matrix.org",
+            content=f"[attachment: {missing_path}]",
+        )
+    )
+
+    assert client.upload_calls == []
+    assert len(client.room_send_calls) == 1
+    assert client.room_send_calls[0]["content"]["body"] == f"[attachment: {missing_path}]"
+
+
+@pytest.mark.asyncio
+async def test_send_workspace_restriction_blocks_external_attachment(tmp_path) -> None:
+    workspace = tmp_path / "workspace"
+    workspace.mkdir()
+    file_path = tmp_path / "external.txt"
+    file_path.write_text("outside", encoding="utf-8")
+
+    channel = MatrixChannel(
+        _make_config(),
+        MessageBus(),
+        restrict_to_workspace=True,
+        workspace=workspace,
+    )
+    client = _FakeAsyncClient("", "", "", None)
+    channel.client = client
+
+    await channel.send(
+        OutboundMessage(
+            channel="matrix",
+            chat_id="!room:matrix.org",
+            content="",
+            media=[str(file_path)],
+        )
+    )
+
+    assert client.upload_calls == []
+    assert len(client.room_send_calls) == 1
+    assert client.room_send_calls[0]["content"]["body"] == "[attachment: external.txt - upload failed]"
+
+
+@pytest.mark.asyncio
+async def test_send_uses_server_upload_limit_when_smaller_than_local_limit(tmp_path) -> None:
+    channel = MatrixChannel(_make_config(max_media_bytes=10), MessageBus())
+    client = _FakeAsyncClient("", "", "", None)
+    client.content_repository_config_response = SimpleNamespace(upload_size=3)
+    channel.client = client
+
+    file_path = tmp_path / "tiny.txt"
+    file_path.write_text("hello", encoding="utf-8")
+
+    await channel.send(
+        OutboundMessage(
+            channel="matrix",
+            chat_id="!room:matrix.org",
+            content="",
+            media=[str(file_path)],
+        )
+    )
+
+    assert client.upload_calls == []
+    assert len(client.room_send_calls) == 1
+    assert client.room_send_calls[0]["content"]["body"] == "[attachment: tiny.txt - too large]"
+
+
 @pytest.mark.asyncio
 async def test_send_omits_ignore_unverified_devices_when_e2ee_disabled() -> None:
     channel = MatrixChannel(_make_config(e2ee_enabled=False), MessageBus())