fix(cache): complete atomic shard writes on Windows

[Nanako0129]

Fixes #913

Summary

• Release the temporary cache shard writer before atomic replacement so the cache does not keep its own source handle open across MoveFileExW.
• Reopen the installed shard with read and write access before the final durability sync, matching the access requirements of Windows FlushFileBuffers.
• Add a direct shard write/read regression without changing cache format, parser versions, shard identity, retry policy, or TUI warning behavior.

Current-upstream adaptation

Validated downstream behavior	Current upstream location	Adaptation
Flush and sync the monolithic temporary cache, then drop its writer before replacement	write_shard_with_limit temporary envelope writer	Apply the same handle ordering to each shard writer
Reopen the installed cache read/write before sync_all()	Final shard durability sync	Use OpenOptions::new().read(true).write(true)
Monolithic cache layout and schema	Sharded envelopes and per-parser versions	Deliberately excluded; no format or identity change
Atomic replacement implementation	Shared fs_atomic::replace_file with #906 retry behavior	Deliberately unchanged

The source behavior was recovered into TokenBar PR #59. The Windows validation ancestry and full downstream evidence are recorded in the handoff comment.

Verification

• cargo test -p tokscale-core test_write_shard_round_trips_after_atomic_replace -- --test-threads=1
• cargo test -p tokscale-core test_save_if_dirty_marks_cache_clean -- --test-threads=1
• cargo fmt --all -- --check
• cargo clippy --locked --workspace --all-features -- -D warnings
• cargo test --workspace --all-features
• cargo build --release -p tokscale-cli
• git diff --check

Windows evidence boundary

The downstream handle-ordering fix was executed and validated on Windows. This PR adapts that invariant to the current shard writer. Upstream Build Native checks Windows x64 and arm64 compilation only; it does not execute this regression on Windows. Unless an additional Windows runner runs the test, this PR does not claim independent upstream Windows runtime verification.

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Summary by cubic

Fixes atomic shard writes on Windows by closing the temp writer before replacement and reopening the final shard for a proper flush. Prevents handle conflicts and ensures cache durability after writes.

• Bug Fixes
  • Drop the temporary shard writer before atomic replace to avoid carrying an open source handle into MoveFileExW.
  • Reopen the installed shard with read+write before the final sync_all() to satisfy Windows FlushFileBuffers.
  • Add a regression test to verify shard write/read round-trip after replace.
  • No changes to cache format, shard identity, parser versions, retry policy, or TUI behavior.

^{Written for commit e15e66b. Summary will update on new commits.}

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
tokscale	Ignored	Preview	Jul 17, 2026 3:07pm

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[junhoyeo]

Thanks a lot!