perf(sqlite-native): avoid cloning cached read chunks

[NathanFlurry]

Description

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• 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

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• 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]

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• chore(engine): publish engine bases in ci #4649
• 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 👈 (View in Graphite)
• 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]

Review: perf(sqlite-native): avoid cloning cached read chunks\n\nThe optimization is correct and well-targeted. The core idea — storing &[u8] slices in buffered_chunks instead of owned Vec<u8> clones — eliminates allocations on read-cache and dirty-buffer hits.\n\n### Correctness\n\nRead-cache slices (cached.as_slice()): The borrow of state.read_cache through buffered_chunks ends when the chunk loop exits. The mutable borrow for read_cache.insert() comes after the loop. NLL handles this correctly, so there is no borrow conflict.\n\nDeferred cache population: Moving read_cache.insert() to after the chunk loop is semantically equivalent to the original. resp only contains keys that were not already in the cache (those keys were never added to chunk_keys_to_fetch), so the same entries are written either way.\n\n### Issues\n\nDouble lookup for dirty-buffer chunks (minor perf regression): The prep loop now does contains_key to skip KV fetching, and the retrieval loop does a second get to obtain the slice. Storing the slice directly in buffered_chunks from the prep loop would close the gap and let the retrieval loop drop the if state.batch_mode branch entirely.\n\nLifetime invariant not documented: buffered_chunks holds slices that borrow from state.read_cache. A short comment near the declaration would make this explicit and prevent confusion for future readers.\n\n### Nits\n\n- read_start is still shadowed twice later in the function (pre-existing).\n- The new comment about resp being empty is accurate and helpful.