{"record":{"id":"fbaa2a23777cec0d","repo":"Hmbown/CodeWhale","slug":"failed-to-capture-stderr","errorCode":null,"errorMessage":"Failed to capture stderr","messagePattern":"Failed to capture stderr","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"crates/tui/src/tools/shell.rs","lineNumber":2723,"sourceCode":"                if let (Some(reader), Some(output)) = (combined_reader, bounded_output.as_ref()) {\n                    (\n                        Some(spawn_bounded_reader_thread(reader, Arc::clone(output))),\n                        None,\n                    )\n                } else {\n                    let stdout_handle = child.stdout.take().ok_or_else(|| {\n                        #[cfg(windows)]\n                        terminate_unregistered_process(&mut child, windows_job.as_ref());\n                        #[cfg(not(windows))]\n                        terminate_unregistered_process(&mut child);\n                        anyhow!(\"Failed to capture stdout\")\n                    })?;\n                    let stderr_handle = child.stderr.take().ok_or_else(|| {\n                        #[cfg(windows)]\n                        terminate_unregistered_process(&mut child, windows_job.as_ref());\n                        #[cfg(not(windows))]\n                        terminate_unregistered_process(&mut child);\n                        anyhow!(\"Failed to capture stderr\")\n                    })?;\n                    (\n                        Some(spawn_reader_thread(\n                            stdout_handle,\n                            Arc::clone(&stdout_buffer),\n                        )),\n                        stderr_buffer\n                            .as_ref()\n                            .map(|buffer| spawn_reader_thread(stderr_handle, Arc::clone(buffer))),\n                    )\n                };\n\n            (\n                ShellChild::Process(child),\n                stdin_handle,\n                stdout_thread,\n                stderr_thread,\n            )","sourceCodeStart":2705,"sourceCodeEnd":2741,"githubUrl":"https://github.com/Hmbown/CodeWhale/blob/73e0f67d83c59909b571efdfc88c4bc28c309cb1/crates/tui/src/tools/shell.rs#L2705-L2741","documentation":"Same failure class as the stdout case but for the child's stderr: after spawning a non-TTY child, `child.stderr.take()` returned None, so output capture is impossible. The tool kills the unregistered child immediately and errors out rather than running a process whose diagnostics would be silently lost.","triggerScenarios":"Spawning a synchronous non-TTY command where the OS failed to create the stderr pipe (fd exhaustion, resource limits, platform spawn anomaly), making `Child::stderr` None.","commonSituations":"File-descriptor exhaustion on busy systems; containers or sandboxes restricting pipe allocation; concurrent processes leaking descriptors.","solutions":["Raise the file-descriptor limit (ulimit -n) and retry the command","Re-run — transient pipe-creation failures may not recur","Check that the sandbox/job-object configuration preserves stdio for children","Investigate descriptor leaks in long-running sessions if it reproduces"],"exampleFix":"// caller-side mitigation: ensure fd headroom before spawning\n// before\nshell.run(\"cargo test\", { \"background\": false })\n// after\n// raise fd limit (ulimit -n 4096) or free leaked descriptors, then retry the same call","handlingStrategy":"retry","validationCode":"// ensure fd headroom before spawning (stderr pipe needs an fd too)\n// ulimit -n should comfortably exceed current usage + per-child pipe fds","typeGuard":null,"tryCatchPattern":"// treat it as transient spawn failure\nmatch result {\n    Err(e) if e.to_string().contains(\"Failed to capture stderr\") => retry_with_backoff(cmd, 2),\n    other => other,\n}","preventionTips":["Raise the file-descriptor limit before large concurrent runs","Audit for fd leaks (unjoined reader threads, unclosed handles)","Verify sandbox/job configurations always allocate stdio for children"],"tags":["shell","process-spawn","stderr","pipe"],"backgroundTag":"broken-pipe","analyzedSha":"73e0f67d83c59909b571efdfc88c4bc28c309cb1","analyzedAt":"2026-09-22T01:30:00.501Z","contentChangedAt":"2026-09-22T01:30:00.501Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}