=== 1. guard-page containment sweep (pristine memcchr.c, verbatim) ===
guard sweep: 762160 calls (NULL=317387 ptr=444773), wrong returns=0
RESULT: PASS - no load escaped the valid page (both-side guards); done-filter never leaked a past-end mismatch
=== 2. instrumented over-read measurement + differential (pristine) ===
exhaustive differential : 608384 cases, 0 failures
randomized differential : 2000000 cases, 0 failures
over-read measurement (pristine memcchr.c):
  loads below begin      : 2282570 (max 7 B before begin)
  loads past end         : 61553 (max 7 B past end)
  fully in-range loads   : 11404517
  done-filter rejections : 10948 (mismatch found at p >= end, returned NULL anyway)
  loads outside [align_down(begin), align_up(end)) : 0 (MUST be 0)
RESULT: OVERREAD-CONFIRMED (live, <=7B both directions, granule-contained, result-filtered); semantics exact vs reference
=== 3. fix validation: instrumented loads + differential (fixed) ===
fixed differential: 2608384 cases, 0 failures
fixed loads: below-start=0 past-end=0 in-range=11402250 outside-granule=0 done-filter-rejections=0
RESULT: FIX-PASS - zero loads outside [begin,begin+n), semantics exact
=== 4. fix validation: guard sweep (fixed) ===
guard sweep: 762160 calls (NULL=317387 ptr=444773), wrong returns=0
RESULT: PASS - no load escaped the valid page (both-side guards); done-filter never leaked a past-end mismatch
=== summary ===
RESULT: PASS - no load escaped the valid page (both-side guards); done-filter never leaked a past-end mismatch
RESULT: OVERREAD-CONFIRMED (live, <=7B both directions, granule-contained, result-filtered); semantics exact vs reference
RESULT: FIX-PASS - zero loads outside [begin,begin+n), semantics exact
RESULT: PASS - no load escaped the valid page (both-side guards); done-filter never leaked a past-end mismatch