fix(pegboard): skip protocol version keys in runner pool backfill

[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]

• fix(pegboard): isolate runner config dc lookup failures #4625 : 2 dependent PRs (#4626 , #4630 )
• 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 👈 (View in Graphite)
• fix(pegboard): create missing normal runner configs #4619
• fix(epoxy): reuse cached optimistic value #4618
• main

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[claude]

PR Review: fix(pegboard): skip protocol version keys in runner pool backfill

Summary

This PR fixes a bug in runner_pool_backfill.rs where a range scan over the runner_config_subspace was inadvertently pulling in ProtocolVersionKey entries alongside the intended DataKey entries. Without the fix, the backfill would attempt to deserialize a ProtocolVersionKey value (a u16) as a RunnerConfig, causing the activity to fail.

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Correctness

runner_config.rs - ProtocolVersionKey unpack validation

The new validation is correct. DataKey packs as a 5-element tuple (RUNNER, CONFIG, DATA, namespace_id, name) while ProtocolVersionKey packs as a 6-element tuple with the additional PROTOCOL_VERSION constant appended. Because of the length difference:

• Attempting to unpack a DataKey entry as a ProtocolVersionKey will fail (only 5 elements, 6 expected) so is_ok() returns false and the entry is processed normally.
• Attempting to unpack a ProtocolVersionKey entry will succeed after the new data != PROTOCOL_VERSION guard so is_ok() returns true and the entry is skipped.

No false positives or false negatives appear possible.

runner_pool_backfill.rs - skip ordering

The new_last_key is updated before the skip check (line 101 vs lines 103-108). This is correct. Pagination must advance past the current entry regardless of whether it is processed or skipped. If new_last_key were only set for non-skipped entries, a chunk full of protocol-version keys could loop infinitely.

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Minor observations

Error message could include context (runner_config.rs line 274)

The current message is a static string. Including the actual vs expected value would make debugging easier if the constant ever changes.

Unrelated formatting changes in database.rs

The database.rs diff is purely cosmetic: reordered imports and collapsed multi-line expressions. Per CLAUDE.md, cargo fmt should not be run automatically, and mixing formatting-only changes into a bug-fix PR adds diff noise. Consider omitting these or landing them as a separate commit.

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Overall

The fix is correct, well-scoped, and addresses the root cause. The two observations above are minor.

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