Three required fixes from the bundle review of 391e1872:
1. workspace/a2a_client.py: substring `type_name in msg` could miss
the diagnostic prefix when an exception's message embedded a
different class name mid-string (e.g. `OSError("see ConnectionError
below")` → printed as plain msg, type lost). Switched to a
prefix-anchored check (`msg.startswith(f"{type_name}:")` etc.) so
the type label is always added when not already at the start of
the message.
2. workspace/a2a_tools.py: `activity_logs.error_detail` is unbounded
TEXT on the platform (handlers/activity.go does not validate
length). A buggy or hostile peer could stream arbitrarily large
error messages into the caller's activity log. Cap at 4096 chars
at the producer — comfortably above any real exception traceback,
well below an obvious-DoS threshold.
3. New regression test for JSON-RPC `code=0` — pins the
`code is not None` semantics so the code is preserved in the
detail rather than collapsing into the no-code path. Code=0 is
not valid per the spec, but a malformed peer can still emit it
and we want it visible for diagnosis.
Plus one optional taken: extracted the A2A-error → hint mapping into
canvas/src/components/tabs/chat/a2aErrorHint.ts. The two prior copies
(AgentCommsPanel.inferCauseHint + ActivityTab.inferA2AErrorHint) had
already drifted — Activity tab gained `not found`/`offline` cases the
chat panel never picked up, AgentCommsPanel handled empty-input
explicitly while Activity didn't. The shared module is the merged
superset, with 10 unit tests pinning each named pattern + the
"most specific first" ordering (Claude SDK wedge wins over generic
timeout).
Skipped (per analysis):
- Unicode-naive 120-char slice — Python str[:N] slices on code
points, not bytes. Safe.
- Nested [A2A_ERROR] confusion — non-issue per reviewer; outer
prefix winning still produces a structured render.
- MessagePreview + JsonBlock dual render on errors — intentional
drilldown; raw JSON is below the fold for operators who need it.
- console.warn dedup — refetches don't happen per-event so spam
risk is low.
- str(data)[:200] materialization — A2A response bodies aren't
typically MB-sized.
Verified: 1005 canvas tests pass (10 new hint tests); 10 Python
send_a2a_message tests pass (1 new for code=0); tsc clean.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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