yellowjacket/.planning/phases/15-schema-migration-write-safety/15-02-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, requirements-completed, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	requirements-completed	duration	completed
15-schema-migration-write-safety	02	database	atomic-write file-safety os-rename temp-file	phase provides none standalone utility package	General-purpose AtomicWrite function for safe file modifications ErrCrossDevice sentinel for cross-filesystem detection Orphan .yj-tmp cleanup on each write operation	16-tag-writing-database-sync 19-ogg-vorbis-tag-writing	added patterns write-to-temp-then-rename callback-API deterministic-temp-suffix	created modified backend/fileutil/atomicwrite.go backend/fileutil/atomicwrite_test.go	Used *slog.Logger as first parameter for consistency with codebase conventions Deterministic .yj-tmp suffix (not random) enables reliable orphan cleanup Cross-device rejection via ErrCrossDevice sentinel wrapping syscall.EXDEV — no copy fallback Default 0644 permissions for new files; stat-and-preserve for existing files	AtomicWrite callback API: AtomicWrite(logger, path, func(tmp *os.File) error) error Deterministic temp file suffix .yj-tmp for all atomic writes	SCHEMA-02 WRITE-05	16min	2026-03-16

Phase 15 Plan 02: Atomic Write Utility Summary

General-purpose AtomicWrite function with write-to-temp-then-rename, permission preservation, orphan cleanup, and cross-device rejection

Performance

• Duration: 16 min
• Started: 2026-03-16T21:57:34Z
• Completed: 2026-03-16T22:13:45Z
• Tasks: 2
• Files modified: 2

Accomplishments

• Created backend/fileutil package with exported AtomicWrite function using callback API pattern
• Implemented deterministic .yj-tmp temp file suffix with automatic orphan cleanup
• Permission preservation (stat existing target, apply mode before rename) with 0644 default for new files
• Cross-device rejection via ErrCrossDevice sentinel wrapping syscall.EXDEV
• 7 comprehensive test functions covering success, new file, callback error rollback, orphan cleanup, same-dir constraint, permission preservation (3 modes), and 1MiB sync verification

Task Commits

Each task was committed atomically:

1. Task 1: Create backend/fileutil package with AtomicWrite - 4d64b5d (feat)
2. Task 2: Add comprehensive tests for AtomicWrite - 0cdfe48 (test)

Files Created/Modified

• backend/fileutil/atomicwrite.go - AtomicWrite function with ErrCrossDevice sentinel, orphan cleanup, permission preservation, cross-device rejection
• backend/fileutil/atomicwrite_test.go - 7 test functions: success, new file, callback error, orphan cleanup, same-dir temp, permission preservation (table-driven), sync and close

Decisions Made

• Used *slog.Logger as the first parameter for consistency with the codebase convention (all packages accept logger as first arg)
• Deterministic .yj-tmp suffix instead of random temp file names — enables reliable orphan cleanup without directory scanning
• Cross-device rejection wraps both ErrCrossDevice and syscall.EXDEV using Go 1.20+ multi-%w in fmt.Errorf
• Default 0644 permissions for new files (target doesn't exist); stat-and-preserve for existing files

Deviations from Plan

Auto-fixed Issues

1. [Rule 1 - Bug] Fixed errorlint violation in cross-device error wrapping

• Found during: Task 1 (AtomicWrite implementation)
• Issue: fmt.Errorf("%w: %s", ErrCrossDevice, err) used %s for the second error, violating the errorlint linter rule that requires %w for all error format verbs
• Fix: Changed to fmt.Errorf("%w: %w", ErrCrossDevice, err) using Go 1.20+ multi-wrapping
• Files modified: backend/fileutil/atomicwrite.go
• Verification: golangci-lint run passes with 0 issues
• Committed in: 4d64b5d (Task 1 commit)

2. [Rule 1 - Bug] Fixed err113 lint violation in test code

• Found during: Task 2 (test implementation)
• Issue: errors.New("simulated write failure") defined inline in test function violated err113 linter (dynamic error creation)
• Fix: Extracted to package-level var errSimulatedFailure = errors.New("simulated write failure")
• Files modified: backend/fileutil/atomicwrite_test.go
• Verification: golangci-lint run passes with 0 issues
• Committed in: 0cdfe48 (Task 2 commit)

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Total deviations: 2 auto-fixed (2 bugs — linter violations) Impact on plan: Both auto-fixes necessary for lint compliance. No scope creep.

Issues Encountered

None

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• AtomicWrite utility ready for Phase 16 tag writers to import
• No blockers — Phase 15 infrastructure complete (Plan 01: FTS5 migration, Plan 02: atomic write)

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Phase: 15-schema-migration-write-safety Completed: 2026-03-16