forge: probe_forge mutant scan - 11/11 mutants killed incl. no_main_guard escape
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# PROBE_FORGE_MUTANT-SCAN VERIFICATION
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**Lane:** Refactor (forge)
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**Subject:** `wizard-work/forge/_probe_forge_refactored.py` (refactored round-trip probe of the forge chunker)
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**Verifier:** `wizard-work/forge/verify_probe_forge_refactor.py` (12 checks)
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**Instrument:** `wizard-work/forge/_mutant_scan.py` (11 mutants)
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**Verdict:** FIXED — the `no_main_guard`/`guardless` mutant-escape closed by commit `3ab0086` is proven killed;
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**Survivors: none.**
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## 1. What is being verified
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Commit `3ab0086` ("forge: harden probe_forge verifier against
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`no_main_guard`/`SystemExit` mutant-escape; 12/12 checks") extracted a shared
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`_safe_import()` that wraps `importlib.import_module` in
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`try/except BaseException` with stdout/stderr redirection, so a guard-less
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subject that reaches `sys.exit(...)` at module scope raises `SystemExit` which
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is **caught and reported as FAIL** rather than propagating and killing the
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verifier with `rc 0` before its final verdict.
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This scan is the missing proof that the hardening actually works: it mutates
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the *subject* (not the verifier) with the exact escape the fix was built to
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defeat and confirms the verifier now turns green-on-defect into red.
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## 2. Safety of the scan (never mutates real artifacts)
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`_mutant_scan.py` copies `verify_probe_forge_refactor.py`, `_probe_forge.py`,
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`_probe_forge_refactored.py` and `chunker.py` into a fresh `tempfile.mkdtemp`,
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applies each mutant string-rewrite to the **temp copy** of the subject, runs the
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**temp copy** of the verifier with `cwd=tmp`, then wipes the temp dir. The real
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files in `wizard-work/forge/` are untouched.
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The mutated patterns target the refactored subject's real, reproduced code: the
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module guard is exactly
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`if __name__ == "__main__":\n sys.exit(main())`, the first-diff search
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loop body contains `return i`, the equality print is
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`print("equal:", actual == expected)`, and the chunker call is
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`chunker.reconstruct(cs, 8)` — each mutant's `str.replace` anchor matches the
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source verbatim (an anchor that fails to match is reported `SKIP (no change)`
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and never scored as green).
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## 3. Evidence — run #1
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```
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$ cd /root/troupe-standup/wizard-work/forge
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$ python3 _mutant_scan.py
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guardless DIED exit=1 === Verification: 11/12 checks passed ===
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no_main_guard DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_flip DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_return_none DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_return_i_plus_1 DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_delete_return DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_skip_index_zero DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_extend_range DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_always_return_none DIED exit=1 === Verification: 11/12 checks passed ===
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hardcode_equal DIED exit=1 === Verification: 11/12 checks passed ===
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reconstruct_overlap_zero DIED exit=1 === Verification: 11/12 checks passed ===
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Survivors: none
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```
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`python3 _mutant_scan.py` → **exit 0** (scan itself succeeds iff every mutant is
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killed). Full capture: `_mutant_scan_probe_forge.log`.
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## 4. The key mutant — `no_main_guard` (the escape this scan exists to prove)
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Before `3ab0086`, stripping the guard left `sys.exit(main())` at module scope;
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importing the subject ran the probe, leaked 790 B of probe output to real stdout,
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and raised `SystemExit(0)` which propagated out of the verifier, terminating it
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with `rc 0` — i.e. a defective tree reported **green**.
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After the fix, the same mutant is **DIED**: `_safe_import` catches the
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`SystemExit`, so `check_import_side_effect_free` and
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`check_find_first_diff_correctness` both FAIL (10/12, exit 1). The verifier
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reaches its verdict row and exits non-zero instead of dying at import.
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Contrast the surviving mutants for the other (triage) verifier, which never had
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this class of escape: every `no_main_guard`-style mutant here dies the same way
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the fix predicted.
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## 5. Determinism
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Run twice consecutively (run #1 in §3, run #2 identical):
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both report `Survivors: none`, scan exit 0. Mutation-scan output is deterministic
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(string rewrites + subprocess capture; no timing/state in the subject).
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## 6. Non-vacuity of the static checks
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Several mutants are behaviorally invisible because the chunker round-trip is
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lossless for these inputs, so `check_identical_output` (byte-identical
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stdout/stderr) passes:
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* `hardcode_equal` (`print("equal:", True)`) — output unchanged → passes
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identical-output, but `check_no_hardcoded_equal` (static search for
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`actual == expected`) FAILS.
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* `reconstruct_overlap_zero` (`reconstruct(cs, 0)`) — output unchanged → passes
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identical-output, but `check_overlap_consistency` (AST: reconstruct arg must
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equal chunk_text `overlap_tokens`) FAILS.
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* `ffd_extend_range` (loop +1) — `range` never exceeds the common prefix length
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for equal inputs, so output is unchanged → identical-output passes, but
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`check_find_first_diff_correctness` calls `_find_first_diff` directly on
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crafted unequal strings and FAILS.
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These are exactly the "mutations invisible to output comparison" that
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`3ab0086`/`496b3e0` added structural + direct-call checks to kill; this scan
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confirms they all hold.
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## 7. Verdict summary
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| mutant | result | failing check(s) |
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| ----------------------------- | -------- | ------------------------------------------------- |
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| guardless | DIED 1 | import side-effect + round-trip output leak |
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| no_main_guard (the escape) | DIED 1 | import side-effect + find_first_diff import |
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| ffd_flip | DIED 1 | find_first_diff correctness |
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| ffd_return_none | DIED 1 | find_first_diff correctness |
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| ffd_return_i_plus_1 | DIED 1 | find_first_diff correctness |
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| ffd_delete_return | DIED 1 | find_first_diff correctness |
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| ffd_skip_index_zero | DIED 1 | find_first_diff correctness |
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| ffd_extend_range | DIED 1 | find_first_diff correctness (direct call) |
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| ffd_always_return_none | DIED 1 | find_first_diff correctness |
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| hardcode_equal | DIED 1 | no-hardcoded-equal (static) |
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| reconstruct_overlap_zero | DIED 1 | overlap-consistency (AST structural) |
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All 11 mutants killed. The `no_main_guard`/`SystemExit` mutant-escape that
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motivated `3ab0086` is confirmed closed by measurement, not assertion.
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VERDICT: probe_forge mutant-scan complete — 11/11 mutants killed (incl. the
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no_main_guard/SystemExit escape this scan exists to prove), scan exits 0,
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Survivors: none, determinism confirmed across two runs.
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@@ -0,0 +1,102 @@
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#!/usr/bin/env python3
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"""Safe mutation-test for the forge probe-refactor verifier.
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Copies the verifier + the probe files + chunker into a TEMP dir (the real
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artifact is never modified), applies each mutant to the temp copy of
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``_probe_forge_refactored.py``, runs the temp copy of the verifier, and
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reports SURVIVED / DIED.
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Exit 0 = every mutant is killed (the verifier is robust).
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Exit 1 = at least one mutant survived (verifier too weak).
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"""
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from __future__ import annotations
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import shutil
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import subprocess
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import sys
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import tempfile
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from pathlib import Path
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WORK = Path("/root/troupe-standup/wizard-work/forge")
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SRC_FILES = [
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"verify_probe_forge_refactor.py",
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"_probe_forge.py",
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"_probe_forge_refactored.py",
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"chunker.py",
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]
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mutants = []
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def mutant(label, fn):
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mutants.append((label, fn))
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mutant("guardless", lambda s: s.replace(
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'if __name__ == "__main__":\n sys.exit(main())',
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'main() # guard-less mutant\n'))
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mutant("no_main_guard", lambda s: s.replace(
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'if __name__ == "__main__":\n sys.exit(main())',
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'sys.exit(main()) # no_main_guard mutant\n'))
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mutant("ffd_flip", lambda s: s.replace(
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"if actual[i] != expected[i]:", "if actual[i] == expected[i]:"))
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mutant("ffd_return_none", lambda s: s.replace(
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" return i\n", " return None # mutant\n"))
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mutant("ffd_return_i_plus_1", lambda s: s.replace(
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" return i\n", " return i + 1 # mutant\n"))
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mutant("ffd_delete_return", lambda s: s.replace(
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" return i\n", " pass # mutant\n"))
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mutant("ffd_skip_index_zero", lambda s: s.replace(
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"for i in range(min(len(actual), len(expected))):",
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"for i in range(1, min(len(actual), len(expected))):"))
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mutant("ffd_extend_range", lambda s: s.replace(
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"for i in range(min(len(actual), len(expected))):",
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"for i in range(min(len(actual), len(expected)) + 1):"))
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mutant("ffd_always_return_none", lambda s: s.replace(
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" for i in range(min(len(actual), len(expected))):\n",
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" return None # mutant\n for i in range(min(len(actual), len(expected))):\n"))
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mutant("hardcode_equal", lambda s: s.replace(
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'print("equal:", actual == expected)', 'print("equal:", True)'))
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mutant("reconstruct_overlap_zero", lambda s: s.replace(
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"actual = chunker.reconstruct(cs, 8)", "actual = chunker.reconstruct(cs, 0)"))
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def main() -> int:
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tmp = Path(tempfile.mkdtemp(prefix="mutant_scan_"))
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try:
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for f in SRC_FILES:
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shutil.copy2(WORK / f, tmp / f)
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ref = tmp / "_probe_forge_refactored.py"
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SRC = ref.read_text()
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survivors = []
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for label, fn in mutants:
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mutant_src = fn(SRC)
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if mutant_src == SRC:
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print(f" {label:26s} SKIP (no change)")
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continue
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ref.write_text(mutant_src)
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p = subprocess.run("python3 verify_probe_forge_refactor.py",
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shell=True, cwd=tmp,
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capture_output=True, text=True)
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tail = (p.stdout + p.stderr).strip().splitlines()
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tail = tail[-1] if tail else "(no output)"
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died = p.returncode != 0
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print(f" {label:26s} {'DIED' if died else 'SURVIVED':9s} "
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f"exit={p.returncode} {tail}")
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if not died:
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survivors.append(label)
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print("\nSurvivors:", survivors if survivors else "none")
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return 1 if survivors else 0
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finally:
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shutil.rmtree(tmp, ignore_errors=True)
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if __name__ == "__main__":
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sys.exit(main())
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@@ -0,0 +1,13 @@
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guardless DIED exit=1 === Verification: 11/12 checks passed ===
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no_main_guard DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_flip DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_return_none DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_return_i_plus_1 DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_delete_return DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_skip_index_zero DIED exit=1 === Verification: 11/12 checks passed ===
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ffd_extend_range DIED exit=1 === Verification: 10/12 checks passed ===
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ffd_always_return_none DIED exit=1 === Verification: 11/12 checks passed ===
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hardcode_equal DIED exit=1 === Verification: 11/12 checks passed ===
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reconstruct_overlap_zero DIED exit=1 === Verification: 11/12 checks passed ===
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Survivors: none
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