Vote: Add branch/tag metadata field and tag timestamps

[majin1102]

I'd like to call a vote on adding the necessary metadata fields to TagContents and BranchContents.

A dedicated discussion for this proposal is here: #6361
The implementation PR is here: #6364

This thread is for voting only. Please keep detailed design discussion in #6361.

Proposal

This proposal updates the ref metadata stored in branch and tag files.

Specifically:

• BranchContents.metadata becomes a structured string-to-string map
• TagContents.metadata becomes a structured string-to-string map
• missing metadata remains backward-compatible and is treated as an empty map
• TagContents gains createdAt and updatedAt timestamps

The changed spec would be like:

Branch metadata file

{
  "parent_branch": "feature/base",
  "parent_version": 42,
  "create_at": 1712312312,
  "manifest_size": 4096,
  "metadata": {
    "owner": "search-team",
    "purpose": "experiments"
  }
}

Tag metadata file

  {
    "branch": "feature/base",
    "version": 42,
    "createdAt": "2026-04-01T08:00:00Z",
    "updatedAt": "2026-04-01T08:00:00Z",
    "manifest_size": 4096,
    "metadata": {
      "stage": "prod",
      "source": "release-cut"
    }
  }

Backward Compatibility

• missing metadata remains supported and is interpreted as an empty map
• this proposal does not preserve legacy string-shaped metadata

Motivation

This makes branch and tag metadata structured and extensible, and makes tag lifecycle metadata explicit in the format.

Vote

Please vote with one of the following:

• +1 approve
• 0 abstain / no strong opinion
• -1 do not approve

If you vote -1, please include the blocking concern.

[yanghua]

+1

[wojiaodoubao]

+1, this is useful in agent memory.

[jja725]

+1