Closes the gap where the Director would say "ZIP is ready at /tmp/foo.zip"
in plain text instead of attaching a download chip — the runtime literally
had no API for outbound file attachments. The canvas + platform's
chat-uploads infrastructure already supported the inbound (user → agent)
direction (commit 94d9331c); this PR wires the outbound side.
End-to-end shape:
agent: send_message_to_user("Done!", attachments=["/tmp/build.zip"])
↓ runtime
POST /workspaces/<self>/chat/uploads (multipart)
↓ platform
/workspace/.molecule/chat-uploads/<uuid>-build.zip
→ returns {uri: workspace:/...build.zip, name, mimeType, size}
↓ runtime
POST /workspaces/<self>/notify
{message: "Done!", attachments: [{uri, name, mimeType, size}]}
↓ platform
Broadcasts AGENT_MESSAGE with attachments + persists to activity_logs
with response_body = {result: "Done!", parts: [{kind:file, file:{...}}]}
↓ canvas
WS push: canvas-events.ts adds attachments to agentMessages queue
Reload: ChatTab.loadMessagesFromDB → extractFilesFromTask sees parts[]
Either path → ChatTab renders download chip via existing path
Files changed:
workspace-server/internal/handlers/activity.go
- NotifyAttachment struct {URI, Name, MimeType, Size}
- Notify body accepts attachments[], broadcasts in payload,
persists as response_body.parts[].kind="file"
canvas/src/store/canvas-events.ts
- AGENT_MESSAGE handler reads payload.attachments, type-validates
each entry, attaches to agentMessages queue
- Skips empty events (was: skipped only when content empty)
workspace/a2a_tools.py
- tool_send_message_to_user(message, attachments=[paths])
- New _upload_chat_files helper: opens each path, multipart POSTs
to /chat/uploads, returns the platform's metadata
- Fail-fast on missing file / upload error — never sends a notify
with a half-rendered attachment chip
workspace/a2a_mcp_server.py
- inputSchema declares attachments param so claude-code SDK
surfaces it to the model
- Defensive filter on the dispatch path (drops non-string entries
if the model sends a malformed payload)
Tests:
- 4 new Python: success path, missing file, upload 5xx, no-attach
backwards compat
- 1 new Go: Notify-with-attachments persists parts[] in
response_body so chat reload reconstructs the chip
Why /tmp paths work even though they're outside the canvas's allowed
roots: the runtime tool reads the bytes locally and re-uploads through
/chat/uploads, which lands the file under /workspace (an allowed root).
The agent can specify any readable path.
Does NOT include: agent → agent file transfer. Different design problem
(cross-workspace download auth: peer would need a credential to call
sender's /chat/download). Tracked as a follow-up under task #114.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
