Symptom: Activity tab and Agent Comms surfaced bare "[A2A_ERROR] "
(prefix + nothing) for failed delegations. Operator had no signal
to act on — no exception type, no target, no hint about what went
wrong, no next step. Fix is in three layers.
1. workspace/a2a_client.py — every error path now produces an
actionable detail string:
- except branch: some httpx exceptions (RemoteProtocolError,
ConnectionReset variants) stringify to "". Pre-fix the catch
was `f"{_A2A_ERROR_PREFIX}{e}"` → bare prefix. Now falls back
to `<TypeName> (no message — likely connection reset or silent
timeout)` and always appends `[target=<url>]` for traceability
in chained delegations.
- JSON-RPC error branch: previously dropped error.code on the
floor and printed "unknown" when message was missing. Now
surfaces both, including the well-defined "JSON-RPC error
with no message (code=N)" path.
- "neither result nor error" branch: pre-fix returned
str(payload) which the canvas rendered as a successful
response block. Now tagged as A2A_ERROR with a payload
snippet so downstream UI routes through the error path.
2. workspace/a2a_tools.py — tool_delegate_task now passes
error_detail (the stripped error message) through to the
activity-log POST. The platform's activity_logs.error_detail
column is the canvas's red error chip source; populating it
makes the failure visible in the row header without the user
having to expand into raw response_body JSON. The summary line
also gets a 120-char prefix of the cause so the collapsed row
reads "React Engineer failed: ConnectionResetError: ... [target=...]"
instead of "React Engineer failed".
3. canvas/src/components/tabs/ActivityTab.tsx — MessagePreview
now detects [A2A_ERROR]-prefixed bodies and renders a
structured error block (red chip, stripped detail, cause hint)
instead of the previous gray text-block that showed the literal
"[A2A_ERROR]" string. inferA2AErrorHint mirrors the patterns
from AgentCommsPanel.inferCauseHint so the same symptom reads
the same way in both surfaces (Claude SDK init wedge → restart
workspace; timeout → busy/stuck; connection-reset → transient
blip then check logs).
Tests: 9 send_a2a_message tests pass (including a new regression
test for the empty-stringifying-exception case that the user
reported); 995 canvas tests pass; tsc clean.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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