feat(mls/database): add expected_field_value to UpdateMetadataData.V1

[tylerhawkes]

Adds a compare-and-swap guard to the local metadata-update intent payload.

Why

UpdateMetadataData.V1 is the payload libxmtp stores for a queued metadata-update intent. It carries an absolute field_value frozen at queue time. When a client's published intent loses an epoch race, libxmtp rebuilds the commit from that same frozen payload and republishes it on the new epoch — so a concurrent change from another member is applied, observed, and then silently overwritten by the stale local value.

That is fine for last-writer-wins fields. It is not fine for app_data, where clients hold structured state they reconcile themselves: the overwrite discards another member's write with no signal to either side.

expected_field_value lets the publisher express "set this field to X, but only if it is still Y". libxmtp abandons the intent instead of republishing when the guard does not match, and surfaces that to the caller so it can re-merge against the value that actually landed.

Compatibility

• New optional field on a new tag — buf breaking against main passes.
• Absent means last-writer-wins, which is the existing behavior, so already-queued intents and older clients are unaffected.
• This message lives in the xmtp.mls.database package: it is local intent storage, never sent on the wire. Nothing about the MLS commit format changes.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AdY7WKkNbJmdzpmUWvW1my

Note

Add expected_field_value field to UpdateMetadataData.V1 proto message

Adds an optional string field expected_field_value (tag 3) to the UpdateMetadataData.V1 message in intents.proto. The field acts as a compare-and-swap guard, allowing callers to conditionally update metadata only when the current field value matches the expected value. The field is backward compatible and is omitted from the wire when not set.

^{Macroscope summarized 625e8c1.}

[macroscopeapp]

Approvability

Verdict: Approved at 625e8c1

Macroscope's review found this PR approvable — Additive, backwards-compatible protobuf schema change - adding one optional field to an existing message. The author owns this file per CODEOWNERS, and the change is well-documented with clear intent.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

^{You can add or adjust custom eligibility rules. Learn more.}

[github-actions]

🎉 This PR is included in version 3.96.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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