python-cli-relative-child-path-vs-spawn-cwd
Wrote the solution to ~/python-cli-relative-child-path-vs-spawn-cwd.md.
Root cause: When neither --config nor --cwd is given, scripts/probe_mcp_stdio.py creates a fresh tempfile.mkdtemp() config dir and spawns the child with that as cwd. subprocess resolves a relative executable after the child chdirs, so .venv/bin/chimera-mcp is looked up under the temp dir → FileNotFoundError. The earlier chimera config init provisioning step had the same flaw. Absolute paths were unaffected, matching the report.
Fix (test-side, no production code): a pure helper
resolve_child_command(cmd, *, base_dir, exists=os.path.isfile) -> (resolved_cmd, usage_error)
called in main() right after option parsing and before planning/provisioning, with base_dir=os.getcwd(). Only argv[0] is rewritten; rest of argv is the child's. Absolute tokens pass through verbatim; bare names (no separator) stay for PATH lookup and are never joined onto base_dir; a missing relative-with-separator returns a named usage error that main prints to stderr and turns into exit 2 (no traceback).
Verification performed here (the actual <project> repo/venv is absent in this sandbox — the ~/.local/bin/chimera* symlinks are broken, so I could not edit the real files):
- /tmp/verify_solution.py — 12 hermetic tests, 12/12 pass.
- /tmp/e2e_probe.py — live subprocess.Popen with cwd=<temp dir> reproduces the exact FileNotFoundError pre-fix; post-fix prints PROBE OK; missing path yields the named error.
The doc records the repo-side verification numbers from the work commit (109 focused / 1149 passed / 62 skipped, Tier 1 PASS 5/5, RED-proved 10/12 failing pre-fix) and manual smoke commands.
# Evidence - Problem class: python-cli-relative-child-path-vs-spawn-cwd - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-17T22:33:03.383Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "VERIFIED ANSWER (<project>, work commit 6546f56, 2026-09-17). Symptom: a stdio probe script whose own usage examples pass the child executable RELATIVELY (python3 scripts/probe_mcp_stdio.py .venv/bin/chimera-mcp) died with a raw FileNotFoundError: [Errno 2] No such file or directory: '.venv/bin/chimera-mcp' raised inside subprocess.Popen, while the identical call with an ABSOLUTE path worked. Root cause: when neither --config nor --cwd is given the probe generates a config in a fresh tempfile.mkdtemp() directory and spawns the child with THAT directory as cwd, so a relative child token is resolved against the temp dir instead of the invoking cwd. The same unresolvable bin dir also broke the earlier provisioning step, which runs the child's sibling CLI (<bin-dir>/chimera config init) with cwd set to the same temp dir. Fix (test-side, no production code): a pure helper resolve_child_command(cmd, *, base_dir, exists=os.path.isfile) -> (resolved_cmd, usage_error_or_None) called in main() immediately after option parsing and BEFORE planning/provisioning the config. Arms: empty cmd untouched; an absolute token returned verbatim (so the CI gate's absolute form is byte-for-byte unchanged); a relative token containing a path separator that exists under base_dir is absolutized (only the executable token is ever rewritten, the rest of the argv is the child's); a relative token with a separator that does not exist returns a NAMED usage error ('child command not found: <token> (resolved against <base_dir>); pass an absolute path') which main prints to stderr and turns into exit 2 with no traceback; a bare command name (no separator) is left untouched so PATH lookup still happens and is never joined onto base_dir. Verification: live relative-exists run exit 0 PROBE OK with CHILD_CMD absolutized and zero tracebacks; relative-missing exit 2 with the named message; absolute form unchanged; 12 new hermetic tests, RED-proved (10 fail against the pre-fix script), focused file 109 passed, full suite 1149 passed / 62 skipped; gitreins guard --full Tier 1 PASS 5/5. Related prior art in the corpus: answer 541 (go-cli-cwd-relative-default-path) and answer 2002 (release-gate-probe-spawns-configless-cwd). Generalizable rule: never let a cwd-relative path reach a consumer that runs with a different cwd - resolve it against the INVOKING cwd once, early, and fail fast with a named error when it does not exist.", "environment": "<project> repo root, Python 3.11 venv; a probe script that spawns a child MCP server with cwd set to a generated temp dir", "language": "python", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "python-cli-relative-child-path-vs-spawn-cwd", "provider": "openrouter", "solved_at": "2026-09-17T22:33:03.383Z", "version": "<project> 0.2.6"}Wrote the solution to ~/python-cli-relative-child-path-vs-spawn-cwd.md.
Root cause: When neither --config nor --cwd is given, scripts/probe_mcp_stdio.py creates a fresh tempfile.mkdtemp() config dir and spawns the child with that as cwd. subprocess resolves a relative executable after the child chdirs, so .venv/bin/chimera-mcp is looked up under the temp dir → FileNotFoundError. The earlier chimera config init provisioning step had the same flaw. Absolute paths were unaffected, matching the report.
Fix (test-side, no production code): a pure helper
resolve_child_command(cmd, *, base_dir, exists=os.path.isfile) -> (resolved_cmd, usage_error)
called in main() right after option parsing and before planning/provisioning, with base_dir=os.getcwd(). Only argv[0] is rewritten; rest of argv is the child's. Absolute tokens pass through verbatim; bare names (no separator) stay for PATH lookup and are never joined onto base_dir; a missing relative-with-separator returns a named usage error that main prints to stderr and turns into exit 2 (no traceback).
Verification performed here (the actual <project> repo/venv is absent in this sandbox — the ~/.local/bin/chimera* symlinks are broken, so I could not edit the real files):
- /tmp/verify_solution.py — 12 hermetic tests, 12/12 pass.
- /tmp/e2e_probe.py — live subprocess.Popen with cwd=<temp dir> reproduces the exact FileNotFoundError pre-fix; post-fix prints PROBE OK; missing path yields the named error.
The doc records the repo-side verification numbers from the work commit (109 focused / 1149 passed / 62 skipped, Tier 1 PASS 5/5, RED-proved 10/12 failing pre-fix) and manual smoke commands.
# Evidence - Problem class: python-cli-relative-child-path-vs-spawn-cwd - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-17T22:33:03.383Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "VERIFIED ANSWER (<project>, work commit 6546f56, 2026-09-17). Symptom: a stdio probe script whose own usage examples pass the child executable RELATIVELY (python3 scripts/probe_mcp_stdio.py .venv/bin/chimera-mcp) died with a raw FileNotFoundError: [Errno 2] No such file or directory: '.venv/bin/chimera-mcp' raised inside subprocess.Popen, while the identical call with an ABSOLUTE path worked. Root cause: when neither --config nor --cwd is given the probe generates a config in a fresh tempfile.mkdtemp() directory and spawns the child with THAT directory as cwd, so a relative child token is resolved against the temp dir instead of the invoking cwd. The same unresolvable bin dir also broke the earlier provisioning step, which runs the child's sibling CLI (<bin-dir>/chimera config init) with cwd set to the same temp dir. Fix (test-side, no production code): a pure helper resolve_child_command(cmd, *, base_dir, exists=os.path.isfile) -> (resolved_cmd, usage_error_or_None) called in main() immediately after option parsing and BEFORE planning/provisioning the config. Arms: empty cmd untouched; an absolute token returned verbatim (so the CI gate's absolute form is byte-for-byte unchanged); a relative token containing a path separator that exists under base_dir is absolutized (only the executable token is ever rewritten, the rest of the argv is the child's); a relative token with a separator that does not exist returns a NAMED usage error ('child command not found: <token> (resolved against <base_dir>); pass an absolute path') which main prints to stderr and turns into exit 2 with no traceback; a bare command name (no separator) is left untouched so PATH lookup still happens and is never joined onto base_dir. Verification: live relative-exists run exit 0 PROBE OK with CHILD_CMD absolutized and zero tracebacks; relative-missing exit 2 with the named message; absolute form unchanged; 12 new hermetic tests, RED-proved (10 fail against the pre-fix script), focused file 109 passed, full suite 1149 passed / 62 skipped; gitreins guard --full Tier 1 PASS 5/5. Related prior art in the corpus: answer 541 (go-cli-cwd-relative-default-path) and answer 2002 (release-gate-probe-spawns-configless-cwd). Generalizable rule: never let a cwd-relative path reach a consumer that runs with a different cwd - resolve it against the INVOKING cwd once, early, and fail fast with a named error when it does not exist.", "environment": "<project> repo root, Python 3.11 venv; a probe script that spawns a child MCP server with cwd set to a generated temp dir", "language": "python", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "python-cli-relative-child-path-vs-spawn-cwd", "provider": "openrouter", "solved_at": "2026-09-17T22:33:03.383Z", "version": "<project> 0.2.6"}