Send A2A ErrorContent as text instead of a JSON blob

[PratikDhanave (PratikDhanave)]

When converting framework contents to A2A parts, contentsToParts had no case for *message.ErrorContent, so it fell through to the default branch and was json.Marshaled into an opaque text part like {"Message":"boom","Type":"error"} instead of the human-readable error text.

The Python client maps an error to a text part carrying content.message: case "error": parts.append(A2APart(text=content.message or "An error occurred.")).

Change

• Add a *message.ErrorContent case that emits cmp.Or(c.Message, "An error occurred.") as a text part. contentsToParts is the shared outbound converter, so both client and hosting paths benefit.

Test

• TestRunSendsErrorContentAsText: an input message carrying an ErrorContent{Message:"boom"} now sends a text part "boom". Fails before (the JSON blob), passes after.

[Copilot]

Copilot review overview

🟢 Approval recommended

The functional change is small, targeted, and covered by a new regression test; only a minor test comment placement issue was found.

Review effort: Lite
Findings: 1

Open (1)

• Update misleading test comment · New

What changed in this PR

This PR updates the A2A provider’s outbound content conversion so *message.ErrorContent is emitted as a human-readable text part (instead of falling back to JSON-marshaled text), aligning behavior with the Python client and improving readability for downstream consumers.

Changes:

• Add an explicit *message.ErrorContent case in contentsToParts to emit cmp.Or(c.Message, "An error occurred.") as a text part.
• Add a regression test verifying ErrorContent{Message:"boom"} is sent as the text part "boom".

File	Description
provider/​a2aprovider/​a2a.go	Adds explicit outbound conversion for *message.ErrorContent to a readable text part.
provider/​a2aprovider/​a2a_test.go	Adds a test ensuring ErrorContent is sent as text, not JSON-blob text.

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[github-actions]

Scope: user-visible behavior (bug fix)

Changed Go contract: No exported Go API added, changed, or removed. contentsToParts (internal helper in provider/a2aprovider/a2a.go) is a private function; the user-visible change is the wire-format output of the A2A outbound converter — *message.ErrorContent now serializes to a plain text part (cmp.Or(c.Message, "An error occurred.")) instead of an opaque JSON blob ({"Message":"...","Type":"error"}) via the default branch's json.Marshal.

Upstream evidence reviewed:

• Python: python/packages/a2a/agent_framework_a2a/_agent.py, _prepare_message_for_a2a, case "error": branch (~line 1047-1052): A2APart(text=content.message or "An error occurred.", metadata=content.additional_properties or {}).
• .NET: searched dotnet/src/Microsoft.Agents.AI.A2A/Extensions/A2AAIContentExtensions.cs (ToPart/ToParts) — the concrete per-content-type ToPart() implementation is not present in this repo (likely supplied by the external A2A SDK), so no .NET evidence could be located for this specific mapping. No equivalent found in-repo.

Result: aligned. The Go fix (cmp.Or(c.Message, "An error occurred.") as a text part) exactly mirrors the Python content.message or "An error occurred." text-part behavior, including the same fallback string. This is a bug fix restoring parity that was previously broken (error content fell through to the JSON-blob default case), not a new public API or behavior divergence. No exported Go symbols changed, so public-api-change is not applicable; no label added/removed.

Generated by Go API Consistency Review Agent · copilot · auto · 31.3 AIC · ⌖ 6.94 AIC · ⊞ 9.2K · ◷