fix(udb): add txn tagging

[MasterPtato]

Description

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• This change requires a documentation update

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[MasterPtato]

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This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• chore: bump rivetkit protocol version #4329
• fix(udb): add txn tagging #4328 👈 (View in Graphite)
• fix(api): make actor destroy wait for ack #4327
• chore: flatten runtime config #4326
• chore: deploy patch #4324
• main

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[claude]

Review: fix(udb): add txn tagging

This is a small, focused PR that adds a tag method to TransactionDriver and Transaction. Here's my feedback:

Observations

No driver implementations

Neither PostgresTransactionDriver nor RocksDbTransactionDriver override the tag method, so calling txn.tag("my-tag") silently does nothing in both supported backends. Given the existing metrics infrastructure (TRANSACTION_TOTAL, TRANSACTION_PENDING, TRANSACTION_DURATION all use a name label), it would be worth clarifying whether this is a follow-up stub (with implementations coming in a subsequent PR) or if the intent is different.

If it's a stub, that's fine — but consider whether the silent no-op could cause confusion for callers who expect tagging to affect observability.

Relationship to Database::txn

database.rs already has a txn(name, closure) API that threads the name through to metrics. The new Transaction::tag method would complement this for transactions created via create_trx() or where the name can only be determined dynamically inside the closure. A small comment in either tag or the docstring clarifying this relationship would help future readers.

Comment style (minor)

Per the project conventions, the comment // No-op unless implemented documents an absence/delta, which the style guide cautions against unless it's unintuitive why something isn't there. Since the trait already has other methods without default implementations, the no-op default is self-evident from the trait definition. Consider removing the comment or replacing it with a sentence explaining the intent (e.g., // Default implementation for drivers that do not support transaction tagging.).

Missing docstring on the trait method

The Transaction::tag method has a doc comment but the TransactionDriver::tag trait method has none. Since this is the primary extension point, adding a brief /// explaining what a tag is used for (observability? tracing? metrics?) would help implementors.

Summary

The interface is clean and consistent with the rest of the module. The main open question is whether this is intentionally a no-op stub (to be wired up to metrics/tracing in a follow-up) or if there's a concrete use case where the default no-op is expected to be sufficient. If the former, a TODO comment pointing to the intended implementation would add clarity.

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commit: edf0cfc

[MasterPtato]

This change is part of the following stack:

• chore: deploy patch #4324
  • chore: flatten runtime config #4326
    • fix(api): make actor destroy wait for ack #4327
      • fix(udb): add txn tagging #4328 ◀
        • chore: bump rivetkit protocol version #4329

_{Change managed by git-spice.}