fix(grpc): preserve null values in protobuf Struct

[MyPrototypeWhat]

Summary

• update the ts-proto generator from v2.6.1 to v2.11.0 so generated google.protobuf.Struct wrappers preserve JavaScript null
• encode JavaScript null as google.protobuf.NullValue.NULL_VALUE
• decode the protobuf nullValue case back to JavaScript null
• add a wire-level regression test covering direct, nested, and array metadata values

Root cause

The generated Value.wrap() implementation assigned the literal JavaScript null to a protobuf enum field. @bufbuild/protobuf requires an integer enum value, so gRPC serialization failed with invalid int32: object.

The reverse conversion also returned the enum value 0 instead of restoring JSON null. The newer ts-proto output corrects both directions so google.protobuf.Struct fields preserve JSON semantics across the gRPC wire.

Impact

Tasks, messages, and other A2A gRPC payloads can now contain valid JSON null values in metadata or other Struct-backed fields without crashing or changing them to 0 after deserialization.

Target branch

This PR is rebased onto and directly targets epic/1.0_breaking_changes for the stable 1.0.0 SDK work.

Generation note

The checked-in 1.0 bindings contain post-generation adjustments. A full buf generate currently rewrites those bindings and adds unrelated generated files, so this PR refreshes only the affected Struct artifact together with the generator pin to keep the fix scoped.

Validation

• npm test — 66 files, 1,375 tests passed
• npm run test:edge — 49 files, 1,081 tests passed, 2 skipped
• npm run build — passed
• npm run test-build — passed
• npm run lint:ci — passed in GitHub Actions

Fixes #576

[github-actions]

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[gemini-code-assist]

Code Review

This pull request fixes an issue with protobuf serialization where null values were not correctly preserved. It updates the wrap and unwrap functions in struct.ts and adds a test suite to verify the behavior. Feedback was provided noting that modifying generated files directly is a maintenance risk, and alternative approaches like post-generation scripts or patching were suggested.

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[JakubWorek]

Hi @MyPrototypeWhat, thank you for the fix. As you mentioned in the PR description we are working towards releasing stable 1.0.0 version of a2a-js sdk. Can you please rebase your current branch to epic/1.0 and fix it there directly also updating the base branch of this PR?

[MyPrototypeWhat]

Done — I rebased the PR onto the current epic/1.0_breaking_changes branch and updated the PR base accordingly. I also updated the ts-proto generator pin and adapted the regression test to the 1.0 generated service layout. Validation on the rebased branch: 1,375 main tests passed; 1,081 edge tests passed (2 skipped); build and test-build passed.