chore: remove udb as a dependency of envoy-client

[NathanFlurry]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[NathanFlurry]

Warning

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.
Learn more

• chore: remove udb as a dependency of envoy-client #4587 : 2 dependent PRs (#4588 , #4591 ) 👈 (View in Graphite)
• chore: revert actor v2 hack #4586
• fix: fix pool metadata protocol version refresh, rivetkit native ws #4585
• feat: US-001 - Define SqliteKv trait in rivetkit-sqlite-native #4584
• feat(rust/engine-runner): minimal rust engine runner #4289
• chore: delete kv channel #4583
• feat(engine): rust runner #4582
• chore: remove non-engine drivers #4574 : 1 other dependent PR (#4581 )
• feat: dynamic actors #4397
• fix: driver test suite & sqlite reliability #4559
• fix: remove serverless token #4572
• fix: misc token fixes #4569
• fix(pb): clean up actor stop decision handling #4566
• fix(envoy): use global instance, add signal handlers #4565
• chore: misc fixes, add pb snapshot test #4561
• fix(cache): make in memory cache global #4560
• main

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[claude]

Code Review

This PR extracts serde utilities from rivet-util into a new dedicated rivet-util-serde crate so envoy-client no longer drags in the heavy rivet-util dependency tree. The overall approach is sound.

Issues

Missing workspace registration for the new crate

engine/packages/util-serde is added as a new package, but the root Cargo.toml is not updated to include it in either the members list or [workspace.dependencies]. Without these two additions, the package will not build as part of the workspace, and downstream crates using rivet-util-serde.workspace = true will get a "package not found" error.

The diff needs:

# members list (around line 49)
"engine/packages/util-serde",

# workspace.dependencies section
[workspace.dependencies.rivet-util-serde]
path = "engine/packages/util-serde"

build.rs post-processing is fragile

post_process_generated_rust does a raw string replacement of rivet_util::serde::HashableMap in generated files. This approach has a few risks:

• It mutates OUT_DIR files after the code generator runs. If vbare_compiler is ever updated to emit the new path directly this becomes a silent no-op, but if it emits the old path in a context other than a bare identifier (e.g. inside a use statement, a doc comment, or a qualified path like rivet_util::serde::HashableMap::new) the replacement could produce malformed code.
• The better long-term fix is to configure vbare_compiler to emit rivet_util_serde::HashableMap instead, or alias the type in the generated files via a use shim. The build-time post-processing should carry a comment explaining why it exists and when it can be removed.

thiserror is still in util/Cargo.toml removal scope

The PR removes thiserror from rivet-util's Cargo.toml, but thiserror may still be used elsewhere in rivet-util (e.g. other error types in engine/packages/util/src/). It is worth confirming that no remaining code in that crate relies on thiserror before removing it.

Minor Notes

• The commented-out ToSchema/PartialSchema impl block is preserved in the new crate. It has a // TODO: This doesn't work comment. If this is tracked elsewhere it is fine to leave as-is, but it would be cleaner to either delete it or convert it to a tracked issue.
• FakeMap::sort has a redundant where K: Ord bound that duplicates the impl-level bound. This was pre-existing in rivet-util, so not introduced here, but worth noting.
• The new util-serde/src/lib.rs uses ::serde:: (with leading ::) as a qualifier in a few places but plain serde:: in others. Minor style inconsistency, also pre-existing.

Summary

The extraction itself is clean and the import/re-export pattern (pub use rivet_util_serde::* in the old module) maintains backward compatibility for existing callers via rivet-util. The critical blocker is the missing workspace registration; the build will fail without it.