fix(guard): serialize gateway actor keys correctly

[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.
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• fix(rivetkit): keep internal error exposure behavior consistent #4661
• fix(test): stabilize lifecycle, sleep, queue, and run edge cases #4660
• test(rivetkit): re-enable gateway URL and direct-registry coverage #4659
• fix(rivetkit): restore hibernatable sockets and hydrate serverless starts #4658
• fix(rivetkit-native): expose full hibernation metadata to JS #4657
• fix(pegboard): persist and replay hibernating requests #4656
• fix(guard): serialize gateway actor keys correctly #4655 👈 (View in Graphite)
• fix(api): subscribe before namespace workflow dispatch #4654
• chore(engine): publish engine bases in ci #4649 : 2 other dependent PRs (#4650 , #4652 )
• chore: lockfile lefthook #4647
• fix(rivetkit): surface native sqlite kv errors to callers #4645
• fix(rivetkit): prevent sleep races during disconnect and db work #4644
• fix(rivetkit): isolate engine envoys and propagate startup failures #4643
• test(rivetkit): remove wasm sqlite-only fixtures and coverage #4642
• chore(sqlite-vfs): remove wasm sqlite packages and workspace wiring #4641
• chore(rivetkit): remove wasm sqlite runtime #4614
• fix(sqlite-native): restore native startup kv preload #4639
• fix(sqlite-native): delete metadata before chunk range #4638
• fix(sqlite-native): keep truncate cache coherent #4637
• fix(sqlite-vfs): use delete range for truncate cleanup #4636
• fix(sqlite-native): restore kv error hook #4635
• perf(sqlite-native): avoid cloning cached read chunks #4634
• perf(sqlite-native): gate kv operation labels #4633
• perf(sqlite-native): reuse read cache for partial writes #4632
• perf(sqlite-native): remove delete file existence probe #4631
• fix(sqlite-native): gate native read cache behind env var #4630
• fix(pegboard): isolate runner config dc lookup failures #4625 : 1 other dependent PR (#4626 )
• docs(pegboard): note runner config upsert split write risk #4624
• fix(pegboard): unpack global runner config keys correctly #4623
• fix(pegboard-gateway): enforce tunnel message state #4622
• fix(pegboard-runner): clear terminal tunnel routes #4621
• fix(pegboard): skip protocol version keys in runner pool backfill #4620
• fix(pegboard): create missing normal runner configs #4619
• fix(epoxy): reuse cached optimistic value #4618
• main

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[claude]

Code Review for PR 4655 - fix(guard): serialize gateway actor keys correctly

Overview

This PR fixes a semantic bug in serialize_actor_key. The original code used EMPTY_KEY in the join() call instead of KEY_SEPARATOR. Both constants share the same string value so there is no observable behavioral change, but the intent was wrong and the naming misleading.

What Changed

The root cause: KEY_SEPARATOR was typed as char, which cannot be passed to slice::join() (requires &str). The workaround was to use EMPTY_KEY (same value) for the join. The fix properly types KEY_SEPARATOR as &str and adds KEY_SEPARATOR_CHAR: char for the replace() call.

• Before: KEY_SEPARATOR as char, escaped_parts.join(EMPTY_KEY) -- wrong constant, coincidentally same value
• After: KEY_SEPARATOR as &str, KEY_SEPARATOR_CHAR as char, escaped_parts.join(KEY_SEPARATOR) -- semantically correct

Assessment

Correct fix. Resolves the semantic confusion without any behavior change.

Minor suggestions:

1. Test coverage: No unit tests exist for serialize_actor_key. Since this function serializes actor keys used in both resolve_query_get_actor_id and resolve_query_get_or_create_actor_id, adding tests would be valuable covering: empty key, single part, multi-part, parts containing slash (escaped), backslash (escaped), and empty string parts.

2. Constant documentation (optional): Having both EMPTY_KEY and KEY_SEPARATOR with the same underlying value '/' is still a little confusing. A short inline comment clarifying that EMPTY_KEY represents the serialized form of an empty key slice (early-return only) while KEY_SEPARATOR is the join delimiter would help future readers avoid the same mix-up.

Verdict

The fix is correct and clean. The only meaningful follow-up is adding unit tests for serialize_actor_key to guard against future regressions.