fix(file): persist workspace writes with atomic replace - #78
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file_write opened the live path with fopen("w"), truncating before
fwrite. Under ENOSPC/EFBIG the original file was wiped, and stdio could
report success after fclose failed on a partial flush. Write via
temp+fsync+rename so a failed write_file leaves prior contents intact.
Co-authored-by: esadrianno <esadrianno@gmail.com>
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Bug and impact
file_write(agentwrite_filetool) opened the live workspace path withfopen("w"), which truncates before any bytes are written. OnENOSPC/EFBIG/crash after truncate, the existing file was wiped. With stdio buffering,fwritecould report a full write whilefcloseflushed only a partial file and was ignored, returning success after destroying the original contents.Trigger: The agent updates an existing workspace file (notes, configs, drafts) while the filesystem cannot complete the new write (disk full, or
RLIMIT_FSIZEin the regression test). The prior file body is gone;write_filemay even report{"status":"ok"}.Distinct from open PR #67 (nested path collapse onto an ancestor) and #77 (
skill_updateskill markdown). Same truncate-then-write class as #71/#77, different path (src/tools/file.cvia the file tool).Root cause
In-place truncate-then-write with unchecked
fclose.Fix
Write content to
path.tmp,fsync, thenrenameover the live file.Validation
./build/test_file— 35 tests passed, includingtest_file_write_failure_preserves_existing(RLIMIT_FSIZE=8)fwritereturned success,fclosefailed, live file shrank to 8 bytes