forge: refactor _fuzz_probe.py - eliminate dead roundtrip() helper, extract bounds check into pure generator, add __main__ guard

wizard-work/forge/FUZZ_PROBE_REFACTOR_VERIFICATION.md

@@ -0,0 +1,89 @@
+# Fuzz-probe DRY refactor verification
+
+## Work
+Refactored `_fuzz_probe.py` — a 64-line adversarial fuzz probe that sweeps 383
+chunker cases across five input shapes (tiny sentence groups, hard-split longs,
+mixed, no-after-space punctuation runs, whitespace variants) with a per-chunk
+token bounds check.
+
+## Problem (code smell)
+The original defined a `roundtrip()` helper (lines 7-11) and **never called it**.
+The main loop re-implemented the same chunk_text -> reconstruct -> compare
+sequence inline, so the helper was dead code.  The bounds check was also inline
+in the main loop with no abstraction.  No `if __name__ == "__main__"` guard.
+
+## Refactor
+- Repurposed the dead `roundtrip()` into `_check_roundtrip(text, mt, ot)` and
+  **actually called it** from the loop — single source of truth for the
+  chunk/reconstruct/compare sequence.
+- Extracted the inline per-chunk bounds check into a pure generator
+  `_check_bounds(cs, mt)` yielding `(index, est, body)` for offending chunks.
+- Replaced scattered module-global counters (`fails`, `total`, `bounds_fail`)
+  with a single `Stats` dataclass.
+- Extracted case generation into `_gen_cases()`.
+- Added `if __name__ == "__main__"` guard.
+
+## Evidence (measured)
+
+Both runs executed against the live chunker at
+`/root/.hermes/wizard-outputs/forge/chunker.py`.
+
+```
+$ python3 /root/.hermes/profiles/forge/_fuzz_probe.py        (original, 64 lines)
+total=383 roundtrip_fails=0 bounds_failures=0
+RESULT: ALL PASS
+EXIT=0
+
+$ python3 _fuzz_probe_refactored.py                            (refactored, 139 lines)
+total=383 roundtrip_fails=0 bounds_failures=0
+RESULT: ALL PASS
+EXIT=0
+```
+
+Byte-for-byte output equivalence:
+```
+$ diff baseline_fuzz_output.txt refactored_fuzz_output.txt
+OUTPUT IDENTICAL
+```
+
+py_compile:
+```
+$ python3 -m py_compile _fuzz_probe_refactored.py
+PY_COMPILE_OK
+```
+
+Cross-check — all other chunker probes still pass with the same chunker:
+```
+$ python3 _edge_sweep_refactored.py
+total=600 roundtrip_fails=0 bounds_fails=0
+RESULT: ALL PASS
+EXIT=0
+
+$ python3 _test_roundtrip_refactored.py
+=== Results: 34 passed, 0 failed ===
+EXIT=0
+
+$ python3 _fuzz_adversarial.py
+trials=2400 fails=0
+PASS: lossless round-trip across all adversarial shapes.
+EXIT=0
+```
+
+## Metrics
+
+| metric            | original | refactored |
+|-------------------|----------|------------|
+| lines             | 64       | 139 (incl. docstrings) |
+| function defs     | 1 (dead) | 4 (all used) |
+| dead code         | 1 unused fn | 0 |
+| total cases       | 383      | 383        |
+| roundtrip_fails   | 0        | 0          |
+| bounds_failures   | 0        | 0          |
+| exit code         | 0        | 0          |
+
+## Verdict
+Refactoring is behavior-preserving and measurably equivalent: 383 cases,
+identical output, exit 0.  The dead `roundtrip()` helper is now wired in,
+the bounds check is a pure generator, module-global counters are a Stats
+dataclass, and all 2400 adversarial trials across the wider probe suite
+still pass with no regressions.

wizard-work/forge/_fuzz_probe_refactored.py

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+#!/usr/bin/env python3
+"""Adversarial fuzz probe for the forge chunker (evidence-gathering, not a fixture).
+
+Refactored from ``_fuzz_probe.py`` (lane: Refactor):
+
+  * The original defined a ``roundtrip()`` helper (lines 7-11) and **never
+    called it** -- the main loop re-implemented the same chunk/reconstruct/
+    compare logic inline, so the helper was dead code.  Here the helper is
+    **repurposed and actually used**: ``_check_roundtrip`` runs the lossless
+    assertion and returns ``(ok, actual, expected, chunks)``; the loop calls
+    it instead of repeating the three-step dance.
+
+  * The per-chunk token bounds check was inlined in the main loop and is now
+    ``_check_bounds`` -- a pure iterator yielding ``(index, est, body)`` for
+    every offending chunk.  This is the same logic the original ran, just
+    extracted; it does NOT change which failures fire.
+
+  * Module-level mutation counters (``fails``, ``total``, ``bounds_fail``)
+    are folded into a single ``Stats`` dataclass so there is no scattered
+    ``global`` mutation and no ordering surprises.
+
+  * Entry point is guarded with ``if __name__ == "__main__"``.
+
+Output is byte-identical to the original on the all-pass path
+(verified against ``baseline_fuzz_output.txt``).
+"""
+from __future__ import annotations
+
+import sys
+import textwrap
+from dataclasses import dataclass, field
+
+sys.path.insert(0, "/root/.hermes/wizard-outputs/forge")
+import chunker  # noqa: E402
+
+
+# --------------------------------------------------------------------------- #
+# helpers (each pure: no shared mutable state)
+# --------------------------------------------------------------------------- #
+
+@dataclass(slots=True)
+class Stats:
+    """Aggregate counters for the probe run."""
+    total: int = 0
+    roundtrip_fails: int = 0
+    bounds_fails: int = 0
+
+
+def _check_roundtrip(text: str, mt: int, ot: int) -> tuple[bool, str, str, list[str]]:
+    """Run one lossless round-trip: returns ``(ok, actual, expected, chunks)``.
+
+    This is the body that the original ``roundtrip()`` helper was meant to
+    provide but never wired in -- it is the single source of truth for the
+    chunk -> reconstruct -> compare sequence now.
+    """
+    cs = chunker.chunk_text(text, max_tokens=mt, overlap_tokens=ot)
+    r = chunker.reconstruct(cs, ot)
+    exp = text.strip()
+    return r == exp, r, exp, cs
+
+
+def _check_bounds(cs: list[str], mt: int):
+    """Yield ``(index, est_tokens, body)`` for every chunk whose body exceeds *mt*.
+
+    ``body`` is the chunk with its sentinel-delimited carried-overlap head
+    stripped (pure genuine content), matching the original inline logic.
+    """
+    for i, c in enumerate(cs):
+        body = c.partition(chunker._OVERLAP_SENTINEL)[2] if chunker._OVERLAP_SENTINEL in c else c
+        est = chunker.estimate_tokens(body)
+        if est > mt and body.strip():
+            yield i, est, body
+
+
+# --------------------------------------------------------------------------- #
+# case generators  (identical input space to the original -> same 383 cases)
+# --------------------------------------------------------------------------- #
+
+def _gen_cases():
+    """Yield ``(text, max_tokens, overlap_tokens, label)`` for every probe case."""
+    for mt in range(2, 20):
+        for ot in range(1, mt):
+            yield (
+                ("Sentence one. Sentence two. Sentence three. ") * 8,
+                mt, ot, f"tiny-mt{mt}-ot{ot}",
+            )
+    for mt in range(2, 16):
+        for ot in range(1, mt):
+            yield ("a" * 500, mt, ot, f"hard-mt{mt}-ot{ot}")
+    for mt in range(2, 14):
+        for ot in range(0, mt):
+            yield (
+                ("The quick brown fox jumps over the lazy dog. Pack my box. " * 5
+                 + "a" * 200),
+                mt, ot, f"mixed-mt{mt}-ot{ot}",
+            )
+    t_nosp = "Hello.World!How are you?I am fine. " * 10
+    for mt in range(4, 40, 4):
+        yield (t_nosp, mt, (mt // 2 if mt // 2 < mt else 1), f"no-after-space-mt{mt}")
+    t_ws = "Hello  world.\tHi now. \n\nNew para.  Tab\there. " * 8
+    for mt in [8, 16, 32, 64]:
+        yield (t_ws, mt, mt // 2, f"ws-mt{mt}")
+    yield ("   \n\t  ", 32, 8, "whitespace-only")
+    yield ("", 32, 8, "empty-string")
+    yield ("Just one.", 4, 1, "tiny-single")
+    yield ("Hello.  ", 8, 4, "trailing-ws")
+
+
+# --------------------------------------------------------------------------- #
+# single-case runner
+# --------------------------------------------------------------------------- #
+
+def _run_case(text: str, mt: int, ot: int, label: str, stats: Stats) -> None:
+    """Execute round-trip + bounds checks for one case, updating *stats*."""
+    stats.total += 1
+
+    ok, actual, expected, cs = _check_roundtrip(text, mt, ot)
+    if not ok:
+        stats.roundtrip_fails += 1
+        print(f"FAIL {label} mt={mt} ot={ot} len={len(text)} "
+              f"exp_len={len(expected)} got_len={len(actual)}")
+        for i in range(min(len(actual), len(expected))):
+            if actual[i] != expected[i]:
+                print(f"   firstdiff@{i} "
+                      f"exp={expected[max(0, i - 15):i + 15]!r} "
+                      f"got={actual[max(0, i - 15):i + 15]!r}")
+                break
+        else:
+            print(f"   prefix ok, len diff. "
+                  f"exp_tail={expected[-20:]!r} got_tail={actual[-20:]!r}")
+        print(f"   nchunks={len(cs)}")
+
+    for i, est, body in _check_bounds(cs, mt):
+        stats.bounds_fails += 1
+        print(f"BOUNDS-FAIL {label} mt={mt} chunk est={est} > {mt}: {body[:50]!r}")
+
+
+# --------------------------------------------------------------------------- #
+# entry point
+# --------------------------------------------------------------------------- #
+
+def main() -> int:
+    stats = Stats()
+    for text, mt, ot, label in _gen_cases():
+        _run_case(text, mt, ot, label, stats)
+
+    print(f"\ntotal={stats.total} roundtrip_fails={stats.roundtrip_fails} "
+          f"bounds_failures={stats.bounds_fails}")
+    result = "ALL PASS" if stats.roundtrip_fails == 0 and stats.bounds_fails == 0 else "HAS FAILURES"
+    print("RESULT:", result)
+    return 0 if stats.roundtrip_fails == 0 and stats.bounds_fails == 0 else 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())