Follow-up to PR #2509/#2510. The defensive v1-detection branches in
extract_attached_files (Python) and extractFilesFromTask (TypeScript)
were merged with comments claiming they fix a "v0→v1 silent-drop"
bug that surfaced as the 2026-05-01 hongming "no text content"
incident. Live test disproved that hypothesis: a2a-sdk's JSON-RPC
layer validates inbound requests against the v0 Pydantic union, so
v1 shapes are rejected at the request boundary — the v1 detection
branch is unreachable on the JSON-RPC ingress path. The actual root
cause of the hongming incident was the missing /workspace chown
fixed by CP PR #381 + test #382.
Update the comments to honestly describe these branches as
defensive future-proofing (kept against an eventual SDK schema
migration or in-process callers that construct Parts directly from
protobuf), not as fixes for an observed bug. Also trims
ChatTab.tsx's outbound-shape comment block from ~21 lines to a
3-line pointer to the SDK union.
Comment-only change. No behavior change. 86 workspace tests + 91
canvas tests still pass.
fc33cf1131