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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• chore(rivetkit): remove inline tests #4668
• fix(guard): serialize gateway actor keys correctly #4655 👈 (View in Graphite)
• fix(api): subscribe before namespace workflow dispatch #4654
• 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(rivetkit): keep internal error exposure behavior consistent #4661
• test(rivetkit): stabilize actor db driver tests #4664
• fix(test): stabilize lifecycle, sleep, queue, and run edge cases #4660 : 1 other dependent PR (#4665 )
• test(rivetkit): re-enable gateway URL and direct-registry coverage #4659
• fix(rivetkit): add lifecycle error retry and gateway HTTP routing #4666
• 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: fix(guard): serialize gateway actor keys correctly

Overview

This PR fixes a semantic bug in serialize_actor_key in the guard routing layer. The original code called escaped_parts.join(EMPTY_KEY) using the empty-key sentinel constant as the join separator. Both EMPTY_KEY and KEY_SEPARATOR happened to equal "/", so the output was identical before and after, but the code used the wrong constant for the wrong purpose.

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Correctness

No functional change in this PR. Both constants equal "/", so the serialized output is bit-for-bit identical before and after. The fix is a semantic/clarity correction: the join separator should reference the separator constant, not the empty-key sentinel.

This is still the right fix. Had either constant ever drifted (e.g. EMPTY_KEY becoming "" or the separator becoming ":"), the old code would have silently produced wrong keys.

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Minor Suggestion: Eliminate KEY_SEPARATOR_CHAR

The PR adds two constants to work around a type mismatch (char for replace(), &str for join()):

const KEY_SEPARATOR: &str = "/";
const KEY_SEPARATOR_CHAR: char = /;

str::replace accepts any Pattern, and &str implements Pattern, so KEY_SEPARATOR_CHAR is unnecessary. KEY_SEPARATOR (&str) works in both the replace and join calls, removing the extra constant.

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Test Coverage

No unit tests exist for serialize_actor_key. For escape logic, a small test table is worth adding to cover: empty slice, single part, multiple parts joined with /, part containing / escaped to "\/", and empty string part encoded as "\0".

---

Summary

Area	Assessment
Correctness	No functional regression; semantic fix is valid
Code style	Consistent with surrounding code
Suggestion	KEY_SEPARATOR_CHAR can be removed; use &str for both replace and join
Tests	Missing -- worth adding for the escape logic

Small, low-risk fix. Removing KEY_SEPARATOR_CHAR is a nice-to-have, not a blocker.