Propagate ContinuationToken through Response.ToUpdates so it survives a ToUpdates/Collect round-trip

[PratikDhanave (PratikDhanave)]

What

Response.ToUpdates() copies response-level FinishReason, CreatedAt, AdditionalProperties and Usage onto the emitted ResponseUpdate values, but never set ContinuationToken, even though both Response and ResponseUpdate carry that field.

Because Response.Update() resets resp.ContinuationToken to empty for every update whose token is empty, and every ToUpdates-emitted update had an empty token, a Response{ContinuationToken: tok} converted via ToUpdates and re-collected yielded an empty ContinuationToken.

This extends the trailing extra-update condition to also fire when ContinuationToken is non-empty, and sets extra.ContinuationToken on it so a subsequent Collect reconstructs the token.

Why

Four sibling response-level fields were already copied in the same function while ContinuationToken alone was omitted. This aligns with .NET, where AsChatResponseUpdate copies ContinuationToken, keeping the ToUpdates/Collect round-trip lossless across SDKs.

Testing

Added TestResponse_ToUpdates_PropagatesContinuationToken in agent/response_test.go: it builds a Response with an assistant message and ContinuationToken: tok-123, round-trips it through ToUpdates then Update/Coalesce, and asserts the token is preserved. The test fails before the change (empty token) and passes after. go build ./..., go vet ./agent/... and go test ./agent/... are green.

[Copilot]

Pull request overview

Propagates ContinuationToken through Response.ToUpdates() so a Response can round-trip through ToUpdates + Update/Collect without losing the continuation token, aligning behavior with other SDKs.

Changes:

• Emit an extra metadata ResponseUpdate when Response.ContinuationToken is non-empty, and copy the token onto that update.
• Add a regression test ensuring ContinuationToken survives a ToUpdates → Update/Coalesce round-trip.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
agent/response.go	Include ContinuationToken in the metadata-only “extra update” path so it can be reconstructed by collection.
agent/response_test.go	Add a round-trip test to verify ContinuationToken is preserved.

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[github-actions]

Parity Review — ✅ Approved

Scope: agent/response.go, agent/response_test.go — behavioral bug fix only; no new exported types, methods, or fields introduced.

What changed

1. Response.ToUpdates() — the trailing metadata-only update now carries ContinuationToken when the response has one, so a ToUpdates → Update/Coalesce round-trip is lossless.
2. Response.Update() — a nil RawRepresentation on an incoming ResponseUpdate is now skipped instead of overwriting the accumulated message value. This prevents metadata-only updates (e.g. the token-carrying trailing update from ToUpdates) from corrupting a message's raw provider data.

Cross-repo alignment

The PR description correctly identifies the upstream .NET reference. In dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs, the streaming path wraps and forwards ContinuationToken through every ChatResponseUpdate via WrapContinuationToken(update.ContinuationToken, ...). The fix in this PR closes the equivalent gap in Go, making ToUpdates/Collect round-trips as lossless as the .NET streaming path.

No equivalent Python surface for ContinuationToken-in-streaming was found; this appears to be a .NET ↔ Go concept only, so no Python divergence to flag.

API surface

No exported identifiers were added, removed, or renamed. The public-api-change label is not warranted.

Verdict

The change is a targeted bug fix that moves Go closer to .NET parity. No cross-SDK consistency issues found.

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