Image-only chats surface "Error: message contained no text content"
because canvas posts v0 `{kind:"file", file:{uri,name,mimeType}}` shapes
that the workspace runtime's a2a-sdk v1 protobuf parser silently drops:
v1 `Part` has fields `[text, raw, url, data, metadata, filename,
media_type]` and `ignore_unknown_fields=True` discards `kind`+`file`,
producing a fully-empty Part. With no text and no extracted file
attachments, the executor's "no text content" guard fires.
Three coordinated changes close the gap:
1. canvas/ChatTab.tsx — outbound file parts now carry the v1 flat
shape `{url, filename, mediaType}` so the v1 protobuf parser
populates Part fields instead of dropping them.
2. workspace/executor_helpers.py — extract_attached_files learns the
v1 detection branch (non-empty `part.url` + `filename` +
`media_type`) alongside the existing v0 RootModel and flat-file
shapes. Defends every runtime that mounts the OSS wheel against
the same drop, including any pre-fix client still on the wire.
3. canvas/message-parser.ts — extractFilesFromTask tolerates the v1
shape on incoming agent responses too, so file chips render in
chat history regardless of which Part shape the runtime emits.
Test pins:
- workspace/tests/test_executor_helpers.py:
+ v1 protobuf shape extraction
+ empty-Part defense (v0→v1 silent-drop fall-through returns [])
- canvas message-parser test:
+ v1 protobuf flat parts
+ filename fallback to URL basename for v1
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