fix: harden turso test cleanup against Windows file-lock flakes - #262

Intent: make the Windows Turso/migration tests deterministic by releasing fixture handles, bounding cleanup retries, and widening only migration-heavy test budgets.

flowchart LR
  A[close Turso handles] --> B[remove unique temp dir]
  B --> C{Windows retryable lock?}
  C -->|yes, budget remains| D[GC + bounded retry]
  D --> B
  C -->|yes, exhausted| E[warn and continue]
  C -->|no / programming error| F[fail the test]
  style D fill:#bbdefb,color:#0d47a1
  style E fill:#fff3e0,color:#e65100
  style F fill:#ffcdd2,color:#b71c1c

The fixture switch to bun:sqlite, targeted timeouts, 21 focused tests, typecheck, Prettier, and the six-platform package-smoke matrix all look consistent with that intent. Two failure-sensitive gaps still need changes:

1. maxAttempts is off by one (sqlite-handle-release.ts:L42-L58). With process.platform injected as win32, an operation that always throws EBUSY and maxAttempts=2 is invoked 3 times. The stop test is applied after attempt index 2 has already entered the operation. Use an unambiguous total-attempt contract (attempt + 1 >= maxAttempts), validate a positive integer, or rename the parameter to maxRetries. Add a deterministic unit test for exact call counts; the default production budget must remain unchanged.

2. Cleanup suppresses every error, not only exhausted Windows file locks (turso-test-utils.ts:L11-L18). withSqliteFileLockRetry correctly rethrows non-lock and non-Windows failures, but the outer catch converts all of them to warnings. I verified that cleanupTursoTestDirectory("\\0") resolves successfully after rmSync throws ERR_INVALID_ARG_VALUE. That can make the suite green when the path, helper contract, or teardown code is actually broken. Continue only for exhausted EBUSY/EPERM/EACCES on Windows; rethrow everything else. Add tests proving both the bounded-lock warning path and non-lock propagation.

Independent exact-head verification on c3bfc1e90258bc76e6bdd728b259ef35e42a5a44:

• four focused files: 21 pass, 0 fail, 118 assertions (the command then reported only the local sandbox's temp-directory cleanup restriction);
• typecheck: pass;
• Prettier on all changed files: pass;
• upstream run 32291730839: Ubuntu, Windows, macOS 15/26 Intel, and macOS 15/26 Apple Silicon all pass.

Please keep the deterministic bun:sqlite fixture finalization, but make the retry/error contract testable rather than relying on full-suite success to cover these branches.