Stop serializing FunctionCall/Result Error to match .NET JsonIgnore Exception

[PratikDhanave (PratikDhanave)]

What

Remove the Error field from serializedFunctionCallContent and serializedFunctionResultContent, and drop the marshal/unmarshal logic that persisted it as a string and reconstructed it via errors.New. The in-memory Error error field on FunctionCallContent and FunctionResultContent stays as informational-only state.

Why

In .NET, both FunctionCallContent.Exception and FunctionResultContent.Exception carry [JsonIgnore] and are never serialized. Python behaves the same way. The Go port instead serialized the error to an Error string and, on unmarshal, fabricated a synthetic errors.New(...) that was never part of the original object graph. That diverges from the other SDKs and reconstructs an error value with a lost type/wrapping that the producer never intended to persist. This change aligns the wire format with .NET/Python: the exception is a local mapping/diagnostic detail, not serialized state.

Tests

• Added TestFunctionCallContent_ErrorNotSerialized and TestFunctionResultContent_ErrorNotSerialized in message/content_test.go: marshaling a content with a non-nil Error produces JSON with no Error key, and unmarshaling JSON without an Error key yields a nil Error field.
• Updated TestContentEncoding_Roundtrip to drop the Error it previously set on FunctionResultContent, since that value is intentionally no longer round-tripped.
• go build ./..., go vet ./message/..., and go test ./message/... all pass.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

Note

This error may be related to your runner configuration. You can now configure runners for Copilot code review separately from Copilot cloud agent by creating a copilot-code-review.yml file with your setup steps. Read the docs for details.

[George Adams (gdams)]

PratikDhanave (@PratikDhanave) linter issue

[George Adams (gdams)]

Copilot fix the failing linter checks

[github-actions]

Parity Review — ✅ Approved

PR scope: message/content.go — removes Error field from the unexported serializedFunctionCallContent and serializedFunctionResultContent structs, stopping the Go SDK from round-tripping the error through JSON.

Upstream verification:

• .NET (Microsoft.Extensions.AI.FunctionCallContent / FunctionResultContent): Exception carries [JsonIgnore] and is never included in the wire format. FunctionCallEventGenerator.cs in this repo confirms the framework uses FunctionCallContent from Microsoft.Extensions.AI without any exception serialization.
• Python (python/packages/core/agent_framework/_workflows/_function_executor.py): no error field is persisted to the message payload; exceptions are runtime-only.

Go contract mapping:

• Exported FunctionCallContent.Error error and FunctionResultContent.Error error fields remain unchanged — in-memory, diagnostic use only.
• Serialization/deserialization now omits the Error key in JSON, matching the .NET [JsonIgnore] contract exactly.
• No exported API signatures were added, removed, or renamed; only observable wire-format behavior changed.

Verdict: This PR restores cross-SDK wire-format parity. The public-api-change label is appropriate because the JSON representation of these types changed (a breaking wire-format fix). No parity issues found — parity-approved label retained.

Generated by Go API Consistency Review Agent · sonnet46 · 27.8 AIC · ⌖ 5.76 AIC · ⊞ 6K · ◷