{"record":{"id":"89413649362f90fb","repo":"ultraworkers/claw-code","slug":"session-file-was-removed-during-write-possible-co","errorCode":null,"errorMessage":"session file was removed during write (possible concurrent modification): {io_err}","messagePattern":"session file was removed during write \\(possible concurrent modification\\): (.+?)","errorType":"exception","errorClass":"SessionError","httpStatus":null,"severity":"error","filePath":"rust/crates/runtime/src/session.rs","lineNumber":251,"sourceCode":"        let snapshot = self.render_jsonl_snapshot()?;\n        // #112: wrap ENOENT during rotate as concurrent modification\n        match rotate_session_file_if_needed(path) {\n            Ok(()) => {}\n            Err(SessionError::Io(ref io_err)) if io_err.kind() == std::io::ErrorKind::NotFound => {\n                return Err(SessionError::Io(std::io::Error::new(\n                    std::io::ErrorKind::NotFound,\n                    format!(\n                        \"session file was removed during save (possible concurrent modification): {io_err}\"\n                    ),\n                )));\n            }\n            Err(e) => return Err(e),\n        }\n        write_atomic(path, &snapshot).map_err(|e| {\n            // #112: wrap ENOENT during write as concurrent modification\n            match &e {\n                SessionError::Io(io_err) if io_err.kind() == std::io::ErrorKind::NotFound => {\n                    SessionError::Io(std::io::Error::new(\n                        std::io::ErrorKind::NotFound,\n                        format!(\"session file was removed during write (possible concurrent modification): {io_err}\"),\n                    ))\n                }\n                _ => e,\n            }\n        })?;\n        cleanup_rotated_logs(path)?;\n        Ok(())\n    }\n\n    pub fn load_from_path(path: impl AsRef<Path>) -> Result<Self, SessionError> {\n        let path = path.as_ref();\n        let contents = fs::read_to_string(path)?;\n        let session = match JsonValue::parse(&contents) {\n            Ok(value)\n                if value\n                    .as_object()","sourceCodeStart":233,"sourceCodeEnd":269,"githubUrl":"https://github.com/ultraworkers/claw-code/blob/08106b0c3771ef5b4a5aa176acccd460e88b7325/rust/crates/runtime/src/session.rs#L233-L269","documentation":"Returned by Session::save_to_path (session.rs:247-258, issue #112) when write_atomic fails with ENOENT during the actual write phase. write_atomic (session.rs:1340) does create_dir_all(parent), writes a temp file session.jsonl.tmp-<ts>-<n> next to the target, then renames it into place; a NotFound at this stage means the freshly created temp file or the parent directory disappeared between those syscalls — the signature of something concurrently deleting the session directory. The wrapper converts the raw ENOENT into this explicit concurrent-modification message.","triggerScenarios":"Session::save_to_path racing against: deletion of the session directory (another process, test tempdir teardown, tmp cleaner), or on platforms where rename(2) fails with ENOENT because the destination parent was removed after create_dir_all. Two savers using the same path are safe against each other (unique temp names) — the trigger is an external unlink/rmdir of the parent or temp file.","commonSituations":"Background autosave thread still running when a test's tempfile::TempDir drops and unlinks the tree; session dir on a network mount with aggressive cache expiry; cleanup scripts removing 'stale' session dirs while a long-lived claw process periodically saves; nested test runs sharing a session directory prefix.","solutions":["Guarantee the session directory outlives every save: keep the TempDir alive until save tasks are joined (drop order matters in tests)","Store sessions outside /tmp and any cleaner-managed location (use the dedicated .claw sessions area)","Verify the parent dir still exists and re-create + retry once if your workload tolerates it: std::fs::create_dir_all(path.parent().unwrap()) then save again","If concurrent claw instances are possible, route all saves through a single owner process or advisory lock"],"exampleFix":"// before — tempdir dropped while autosave task may still run\nlet dir = tempfile::tempdir()?;\nlet handle = spawn_autosave(session.clone(), dir.path().join(\"s.jsonl\"));\ndrop(dir); // directory unlinked; autosave hits ENOENT\n\n// after — join the saver before dropping the dir\nlet dir = tempfile::tempdir()?;\nlet handle = spawn_autosave(session.clone(), dir.path().join(\"s.jsonl\"));\nhandle.join().expect(\"autosave panicked\")?;\ndrop(dir);","handlingStrategy":"retry","validationCode":"fn ensure_session_dir(path: &std::path::Path) -> std::io::Result<()> {\n    if let Some(parent) = path.parent() {\n        std::fs::create_dir_all(parent)?; // recreate if a cleaner removed it\n        std::fs::symlink_metadata(parent)?; // fail fast if it vanishes again\n    }\n    Ok(())\n}\n\nensure_session_dir(&path)?;\nsession.save_to_path(&path)?;","typeGuard":null,"tryCatchPattern":"match session.save_to_path(&path) {\n    Ok(()) => {}\n    Err(e @ SessionError::Io(ref io))\n        if io.kind() == std::io::ErrorKind::NotFound\n            && io.to_string().contains(\"removed during write\") => {\n        std::fs::create_dir_all(path.parent().unwrap())?; // one bounded retry after recreating the dir\n        session.save_to_path(&path).map_err(|_| e)?;\n    }\n    Err(e) => return Err(e),\n}","preventionTips":["Make the session directory's lifetime strictly longer than every task that saves into it (drop order in tests is the usual culprit)","Pin autosave/teardown ordering: stop savers, flush, then delete directories","Avoid network filesystems for session storage — rename-based atomic writes are ENOENT-prone there","After this error, verify the directory still exists before retrying; a second immediate failure means an active deleter"],"tags":["session","persistence","concurrency","atomic-write","enoent","rust"],"backgroundTag":"concurrent-file-modification","analyzedSha":"08106b0c3771ef5b4a5aa176acccd460e88b7325","analyzedAt":"2026-08-18T00:29:38.590Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-14T00:17:10.932Z"}