feat: Add last update time to Task

[lkawka]

The new task/list method's specification dictates that tasks must be ordered by the last update time. However, the current data model lacks a direct way to determine when a task was last updated. To resolve this, a new field with last update time is being added to the Task message.

Addressing potential concerns:

1. The timestamp field in the TaskStatus message already exists: There are two issues with this field:
   1. Not all task updates are necessarily status updates.
   2. The field is optional, which can lead to unstable ordering when sorting by this field alone.
2. Backends can just incorporate this information into their internal data models: While true, including this in the public API offers significant advantages by allowing clients to readily access and display this value to users.

Fixes #1207

[gemini-code-assist]

Summary of Changes

Hello @lkawka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Task data model by introducing a new update_time field. This addition is essential to fulfill the task/list method's requirement for ordering tasks by their last update, providing a dedicated and reliable timestamp for all task modifications, distinct from just status changes. The change is propagated across the gRPC protobuf definition, the JSON schema, and the TypeScript type definitions to ensure consistency and client accessibility.

Highlights

• Task Message Update: Introduced an update_time field to the Task message in a2a.proto to track the last modification time, crucial for ordering tasks.
• JSON Schema and TypeScript Updates: The updateTime field was added to the Task definition in a2a.json (as a required ISO 8601 string) and to the Task interface in types.ts to ensure consistency across all definitions.
• Minor Formatting Adjustment: A small formatting change was applied to the ListTaskPushNotificationConfigParams interface in types/src/types.ts.

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[gemini-code-assist]

Code Review

This pull request introduces an update_time field to the Task message across the Protobuf, JSON, and TypeScript specifications. This change is well-justified by the need to order tasks by their last update time. The implementation is consistent and correct across all modified files. I have one minor suggestion to revert a purely stylistic change to keep the pull request focused on its primary goal. Otherwise, the changes look good.

[darrelmiller]

/vote

[git-vote]

Vote created

@darrelmiller has called for a vote on feat: Add last update time to Task`` (#1206).

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@a2aproject/a2a-tsc

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[git-vote]

Vote status

So far 12.50% of the users with binding vote are in favor and 0.00% are against (passing threshold: 51%).

Summary

In favor	Against	Abstain	Not voted
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Binding votes (1)

User	Vote	Timestamp
geneknit	In favor	2025-12-02 17:59:29.0 +00:00:00
@muscariello	Pending
@darrelmiller	Pending
@lerhaupt	Pending
@hughesthe1st	Pending
@ToddSegal	Pending
@000-000-000-000-000	Pending
@SivaNSAP	Pending