diff --git a/pyre/bench/synth/arith_int_bool.cranelift.jitstats b/pyre/bench/synth/arith_int_bool.cranelift.jitstats
index fa378545d43..78bfa392038 100644
--- a/pyre/bench/synth/arith_int_bool.cranelift.jitstats
+++ b/pyre/bench/synth/arith_int_bool.cranelift.jitstats
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diff --git a/pyre/bench/synth/arith_int_bool.dynasm.jitstats b/pyre/bench/synth/arith_int_bool.dynasm.jitstats
index fa378545d43..78bfa392038 100644
--- a/pyre/bench/synth/arith_int_bool.dynasm.jitstats
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diff --git a/pyre/bench/synth/ast_compile_roundtrip.cranelift.jitstats b/pyre/bench/synth/ast_compile_roundtrip.cranelift.jitstats
index 4665b398e2f..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/ast_compile_roundtrip.cranelift.jitstats
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diff --git a/pyre/bench/synth/ast_compile_roundtrip.dynasm.jitstats b/pyre/bench/synth/ast_compile_roundtrip.dynasm.jitstats
index 4665b398e2f..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/ast_compile_roundtrip.dynasm.jitstats
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diff --git a/pyre/bench/synth/gc_deque_backing_list.cranelift.jitstats b/pyre/bench/synth/gc_deque_backing_list.cranelift.jitstats
index 162e2a91482..b611ca52361 100644
--- a/pyre/bench/synth/gc_deque_backing_list.cranelift.jitstats
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diff --git a/pyre/bench/synth/gc_deque_backing_list.dynasm.jitstats b/pyre/bench/synth/gc_deque_backing_list.dynasm.jitstats
index 162e2a91482..b611ca52361 100644
--- a/pyre/bench/synth/gc_deque_backing_list.dynasm.jitstats
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diff --git a/pyre/bench/synth/imp_lock_rlock_semantics.cranelift.jitstats b/pyre/bench/synth/imp_lock_rlock_semantics.cranelift.jitstats
index 9cf2e63b4a5..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/imp_lock_rlock_semantics.cranelift.jitstats
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diff --git a/pyre/bench/synth/imp_lock_rlock_semantics.dynasm.jitstats b/pyre/bench/synth/imp_lock_rlock_semantics.dynasm.jitstats
index 9cf2e63b4a5..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/imp_lock_rlock_semantics.dynasm.jitstats
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diff --git a/pyre/bench/synth/import_from_name_path.cranelift.jitstats b/pyre/bench/synth/import_from_name_path.cranelift.jitstats
index 4665b398e2f..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/import_from_name_path.cranelift.jitstats
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diff --git a/pyre/bench/synth/import_from_name_path.dynasm.jitstats b/pyre/bench/synth/import_from_name_path.dynasm.jitstats
index 4665b398e2f..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/import_from_name_path.dynasm.jitstats
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diff --git a/pyre/bench/synth/inline_freevar_after_mayforce.cranelift.jitstats b/pyre/bench/synth/inline_freevar_after_mayforce.cranelift.jitstats
index 713c188c498..14fb6a41520 100644
--- a/pyre/bench/synth/inline_freevar_after_mayforce.cranelift.jitstats
+++ b/pyre/bench/synth/inline_freevar_after_mayforce.cranelift.jitstats
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diff --git a/pyre/bench/synth/inline_freevar_after_mayforce.dynasm.jitstats b/pyre/bench/synth/inline_freevar_after_mayforce.dynasm.jitstats
index 713c188c498..14fb6a41520 100644
--- a/pyre/bench/synth/inline_freevar_after_mayforce.dynasm.jitstats
+++ b/pyre/bench/synth/inline_freevar_after_mayforce.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=1
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index 0d405c3ac22..06609531fb7 100644
--- a/pyre/bench/synth/list_append_write_barrier_gc.wasm.jitstats
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diff --git a/pyre/bench/synth/module_getattr_descr_error.cranelift.jitstats b/pyre/bench/synth/module_getattr_descr_error.cranelift.jitstats
index dcfe18e854a..4665b398e2f 100644
--- a/pyre/bench/synth/module_getattr_descr_error.cranelift.jitstats
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diff --git a/pyre/bench/synth/module_getattr_descr_error.dynasm.jitstats b/pyre/bench/synth/module_getattr_descr_error.dynasm.jitstats
index dcfe18e854a..4665b398e2f 100644
--- a/pyre/bench/synth/module_getattr_descr_error.dynasm.jitstats
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diff --git a/pyre/bench/synth/module_getattr_surrogate_cls.cranelift.jitstats b/pyre/bench/synth/module_getattr_surrogate_cls.cranelift.jitstats
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diff --git a/pyre/bench/synth/module_getattr_surrogate_cls.dynasm.jitstats b/pyre/bench/synth/module_getattr_surrogate_cls.dynasm.jitstats
index dcfe18e854a..4665b398e2f 100644
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diff --git a/pyre/bench/synth/operator_set_inplace_ops.cranelift.jitstats b/pyre/bench/synth/operator_set_inplace_ops.cranelift.jitstats
index dcfe18e854a..4665b398e2f 100644
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diff --git a/pyre/bench/synth/operator_set_inplace_ops.dynasm.jitstats b/pyre/bench/synth/operator_set_inplace_ops.dynasm.jitstats
index dcfe18e854a..4665b398e2f 100644
--- a/pyre/bench/synth/operator_set_inplace_ops.dynasm.jitstats
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index 4665b398e2f..d9b4b4c7bd6 100644
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 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=1163
+guard_failures=1161
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=6
+loops_compiled=5
diff --git a/pyre/bench/synth/sre_wasm_min.dynasm.jitstats b/pyre/bench/synth/sre_wasm_min.dynasm.jitstats
index 940c8316a9e..98b6be5cbb1 100644
--- a/pyre/bench/synth/sre_wasm_min.dynasm.jitstats
+++ b/pyre/bench/synth/sre_wasm_min.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=5
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=1163
+guard_failures=1161
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=6
+loops_compiled=5
diff --git a/pyre/bench/synth/sre_wasm_min1.cranelift.jitstats b/pyre/bench/synth/sre_wasm_min1.cranelift.jitstats
index b40b78fef38..10408dc3f7d 100644
--- a/pyre/bench/synth/sre_wasm_min1.cranelift.jitstats
+++ b/pyre/bench/synth/sre_wasm_min1.cranelift.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=3
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=605
+guard_failures=603
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=5
+loops_compiled=4
diff --git a/pyre/bench/synth/sre_wasm_min1.dynasm.jitstats b/pyre/bench/synth/sre_wasm_min1.dynasm.jitstats
index b40b78fef38..10408dc3f7d 100644
--- a/pyre/bench/synth/sre_wasm_min1.dynasm.jitstats
+++ b/pyre/bench/synth/sre_wasm_min1.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=3
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=605
+guard_failures=603
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=5
+loops_compiled=4
diff --git a/pyre/bench/synth/str_encode_text_codec.cranelift.jitstats b/pyre/bench/synth/str_encode_text_codec.cranelift.jitstats
index 97609658080..1c772772091 100644
--- a/pyre/bench/synth/str_encode_text_codec.cranelift.jitstats
+++ b/pyre/bench/synth/str_encode_text_codec.cranelift.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=1
+guard_failures=0
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=2
+loops_compiled=1
diff --git a/pyre/bench/synth/str_encode_text_codec.dynasm.jitstats b/pyre/bench/synth/str_encode_text_codec.dynasm.jitstats
index 97609658080..1c772772091 100644
--- a/pyre/bench/synth/str_encode_text_codec.dynasm.jitstats
+++ b/pyre/bench/synth/str_encode_text_codec.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=1
+guard_failures=0
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=2
+loops_compiled=1
diff --git a/pyre/bench/synth/struct_pack_unpack.cranelift.jitstats b/pyre/bench/synth/struct_pack_unpack.cranelift.jitstats
index dcfe18e854a..4665b398e2f 100644
--- a/pyre/bench/synth/struct_pack_unpack.cranelift.jitstats
+++ b/pyre/bench/synth/struct_pack_unpack.cranelift.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=2
+guard_failures=1
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=2
+loops_compiled=1
diff --git a/pyre/bench/synth/struct_pack_unpack.dynasm.jitstats b/pyre/bench/synth/struct_pack_unpack.dynasm.jitstats
index dcfe18e854a..4665b398e2f 100644
--- a/pyre/bench/synth/struct_pack_unpack.dynasm.jitstats
+++ b/pyre/bench/synth/struct_pack_unpack.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=2
+guard_failures=1
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=2
+loops_compiled=1
diff --git a/pyre/bench/synth/type_dotted_name.cranelift.jitstats b/pyre/bench/synth/type_dotted_name.cranelift.jitstats
index 9d7d0e11958..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/type_dotted_name.cranelift.jitstats
+++ b/pyre/bench/synth/type_dotted_name.cranelift.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=2
+guard_failures=0
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=1
+loops_compiled=0
diff --git a/pyre/bench/synth/type_dotted_name.dynasm.jitstats b/pyre/bench/synth/type_dotted_name.dynasm.jitstats
index 9d7d0e11958..d9b4b4c7bd6 100644
--- a/pyre/bench/synth/type_dotted_name.dynasm.jitstats
+++ b/pyre/bench/synth/type_dotted_name.dynasm.jitstats
@@ -2,7 +2,7 @@ bridges_compiled=0
 descr_set_absent=0
 descr_set_ambiguous=0
 descr_set_stale_absent=0
-guard_failures=2
+guard_failures=0
 internal_compile_panics=0
 loops_aborted=0
-loops_compiled=1
+loops_compiled=0
diff --git a/pyre/check.py b/pyre/check.py
index 1b87dcd5806..f634a34c298 100644
--- a/pyre/check.py
+++ b/pyre/check.py
@@ -179,6 +179,7 @@ def _detect_pyre_stdlib():
 # ── ANSI helpers ─────────────────────────────────────────────────────
 
 def red(s):    return f"\033[31m{s}\033[0m"
+def yellow(s): return f"\033[33m{s}\033[0m"
 def green(s):  return f"\033[32m{s}\033[0m"
 def dim(s):    return f"\033[2m{s}\033[0m"
 def bold(s):   return f"\033[1m{s}\033[0m"
@@ -401,6 +402,35 @@ def pyre_env():
     # compute anyway, so pinning it costs nothing there and makes a macOS
     # recorder agree with them.
     env.setdefault("PYPY_GC_NURSERY", str(4 * 1024 * 1024))
+    # Keep the bench directory off `sys.path` (`-P`), so the jit-stats counters
+    # describe the fixture rather than the directory it happens to sit in.
+    #
+    # `sys.path[0]` is the script's own directory, and `pyre/bench/synth` holds
+    # well over a thousand entries. The import machinery's scan of that entry is
+    # itself a Python loop, and at that size it crosses the 1039 compile
+    # threshold — so a fixture with no loop at all in its body still records
+    # `loops_compiled=1`, produced by a single `import` statement. Measured, one
+    # fixture unchanged and only the directory it runs from varied: 400 files
+    # compile nothing, 800 compile that loop, and the real directory is well past
+    # both. It is invariant to PYPY_GC_NURSERY (1MB..16MB), so it is not the
+    # collection schedule.
+    #
+    # That is what made the counters disagree between platforms: path handling
+    # differs per OS, so the same ambient loop lands either side of the
+    # threshold. Every jit-stats diff CI reported was a uniform +-1 on
+    # `loops_compiled` — and setting this flag reproduces the Linux numbers
+    # exactly on macOS (`arith_int_bool` 8 -> 7 with guard_failures 2213 -> 2211,
+    # `gc_deque_backing_list` 6 -> 5 / 204 -> 203, `struct_pack_unpack`
+    # 2 -> 1 / 2 -> 1).
+    #
+    # `-P` alone, not `-I`: the latter also implies `-E`, which drops
+    # PYTHONIOENCODING and so changes how the child resolves its stdio encoding —
+    # not something to fold into a run whose stdout is diffed against an oracle.
+    #
+    # An explicit PYTHONSAFEPATH in the environment wins, so the old behaviour
+    # stays reachable for an A/B: pyre reads the variable as a presence flag, so
+    # passing it empty is what turns the flag back off.
+    env.setdefault("PYTHONSAFEPATH", "1")
     # Pin the vendored, `_sre.MAGIC`-matched stdlib so pyre never picks up a
     # version-mismatched host `python3` off the PATH. An explicit PYRE_STDLIB
     # in the environment wins.
@@ -666,8 +696,51 @@ def _parse_jit_stats(snapshot):
 )
 
 
+# Which way each counter has to move to be a regression rather than a gain.
+# Both outcomes fail — a baseline that stopped describing the tree has to be
+# re-recorded either way, and letting a gain pass is how the eight baselines
+# this split was written for went stale. The labels exist so a reader can tell
+# the two apart at a glance: REGRESSED is "something got worse, go look",
+# IMPROVED is "something got better, re-record it".
+#
+# `loops_compiled` is inverted against the badness fields: it is the counter
+# that falls when the tracer stops admitting a frame at all, which aborts
+# nothing and *lowers* `guard_failures`, so a fall is the regression and a rise
+# is the gain.
+JITSTATS_REGRESSION_ON_RISE = JITSTATS_BADNESS_FIELDS + ("guard_failures",)
+JITSTATS_REGRESSION_ON_FALL = ("loops_compiled",)
+
+# How many fresh runs a disagreeing fixture gets before its counters are called
+# stable. Only a fixture that already disagrees pays this, so the common path is
+# untouched.
+#
+# The gate's premise is that these counters are a function of the program. Where
+# that holds, a repeat reproduces the first run exactly and the disagreement is
+# gated as before. Where it does not — measured on this tree: two runs of the
+# same `pyre-dynasm` binary, minutes apart on a loaded machine, disagreed by
+# `loops_compiled` +2 on five unrelated fixtures — the number being compared is
+# not a property of the tree, and failing on it reports load as if it were a
+# code change.
+#
+# So instability is MEASURED, never declared: nothing is annotated as flaky, and
+# a fixture stops being gated only by demonstrating, in this same invocation,
+# that it does not reproduce itself. The cost is that a genuinely
+# nondeterministic regression now warns instead of failing — which is the right
+# trade only because a counter that will not reproduce cannot be gated on
+# exactly anyway, and the warning still names it.
+JITSTATS_STABILITY_RUNS = 2
+
+# `bridges_compiled` is deliberately in neither: it is not interpretable on its
+# own, in either direction. A fall to 0 is the dead-bridge regression this gate
+# was built to catch when guards still fail, and a gain when the guards stopped
+# failing (`list_length_hint_validate` fell 4 -> 0 as guard_failures fell
+# 828 -> 1). A rise is more guards crossing the bridge threshold, which is
+# either wider coverage or a guard storm. Undecidable counters are reported as
+# regressions, so the ambiguous case is the one a human is asked to look at.
+
+
 def _jit_stats_change(saved, current):
-    """Return a failure reason naming every gated counter that moved, else "".
+    """Return `(regressions, improvements)`, each a list of "field a -> b".
 
     Both directions gate: a rise means the JIT started aborting traces, hitting
     internal compile panics or failing guards it did not before, and a fall
@@ -684,30 +757,44 @@ def _jit_stats_change(saved, current):
     follows."""
     old_fields = _parse_jit_stats(saved)
     new_fields = _parse_jit_stats(current)
-    changes = [
-        f"{field} {old_fields.get(field, '0')} -> {new_fields.get(field, '0')}"
-        for field in JITSTATS_SNAPSHOT_FIELDS
-        if old_fields.get(field, "0") != new_fields.get(field, "0")
-    ]
-    if changes:
-        # Report what the run compiled alongside what moved. A `guard_failures`
-        # change costs nothing to explain when the same run also compiled more
-        # loops or bridges — each new guard fails `trace_eagerness` times before
-        # its bridge attaches — but the gate names only the fields that moved,
-        # so the reader cannot tell that case from a real defect without
-        # re-running the bench. On a platform the developer does not have (the
-        # CI runners), re-running is not an option and the row is unjudgeable
-        # without this.
-        context = " ".join(
-            f"{f}={new_fields[f]}"
-            for f in ("loops_compiled", "bridges_compiled")
-            if f in new_fields
-        )
-        detail = ", ".join(changes)
-        if context:
-            detail += f" (observed {context})"
-        return "jit-stats change: " + detail
-    return ""
+    regressions, improvements = [], []
+    for field in JITSTATS_SNAPSHOT_FIELDS:
+        old, new = old_fields.get(field, "0"), new_fields.get(field, "0")
+        if old == new:
+            continue
+        try:
+            rose = int(new) > int(old)
+        except ValueError:
+            # A counter that stopped being an integer is not a gain.
+            rose = None
+        if rose is not None and (
+            (rose and field in JITSTATS_REGRESSION_ON_FALL)
+            or (not rose and field in JITSTATS_REGRESSION_ON_RISE)
+        ):
+            improvements.append(f"{field} {old} -> {new}")
+        else:
+            regressions.append(f"{field} {old} -> {new}")
+    return regressions, improvements
+
+
+def _jit_stats_context(current):
+    """Return " (observed loops_compiled=N bridges_compiled=M)", or "".
+
+    Report what the run compiled alongside what moved. A `guard_failures` change
+    costs nothing to explain when the same run also compiled more loops or
+    bridges — each new guard fails `trace_eagerness` times before its bridge
+    attaches — but a gate that names only the fields that moved leaves the
+    reader unable to tell that case from a real defect without re-running the
+    bench. On a platform the developer does not have (the CI runners),
+    re-running is not an option and the row is unjudgeable without this.
+    """
+    fields = _parse_jit_stats(current)
+    context = " ".join(
+        f"{f}={fields[f]}"
+        for f in ("loops_compiled", "bridges_compiled")
+        if f in fields
+    )
+    return f" (observed {context})" if context else ""
 
 
 def scaled_timeout(base, scale):
@@ -949,6 +1036,14 @@ def __init__(self, args):
         self.snapshot_diffs = []
         self.snapshot_missing = []
         self.jitstats_diffs = []
+        # Benches whose gated counters all moved the way their field calls a
+        # gain. Still failures — the baseline stopped describing the tree — but
+        # tracked apart so the summary can say which reds need investigating and
+        # which only need re-recording.
+        self.jitstats_improvements = []
+        # Benches whose counters did not reproduce across repeats in this same
+        # invocation. Reported, never failed — see JITSTATS_STABILITY_RUNS.
+        self.jitstats_unstable = []
         self.jitstats_missing = []
         # Benches whose run printed no `[jit-stats]` line at all. Tracked apart
         # from `jitstats_missing` because the two say opposite things: a missing
@@ -1090,14 +1185,57 @@ def _record(self, backend, passed, name, detail):
     def _snapshot_path(self, backend, name, suffix):
         return Path(SNAP_DIR) / backend / f"{name}.{suffix}"
 
+    def _jitstats_repeats(self, backend, script, timeout):
+        """Re-run the fixture and return each repeat's jit-stats snapshot.
+
+        Returns None if a repeat did not exit cleanly, so a crashing re-run
+        cannot argue a real diff away — the caller then gates on the first run
+        as if no repeat had happened.
+        """
+        effective_timeout = scaled_timeout(timeout, self._timeout_scale(backend))
+        snapshots = []
+        for _ in range(JITSTATS_STABILITY_RUNS):
+            _output, _elapsed, code, stderr = run_timed(
+                [self._pyre(backend), script],
+                timeout_s=effective_timeout, env=pyre_env(),
+            )
+            if code != 0:
+                return None
+            snapshots.append(_jit_stats_snapshot(stderr))
+        return snapshots
+
     def _jitstats_baseline_path(self, backend, script):
         # The committed structural-stats baseline sits beside its benchmark
         # source (pyre/bench/<name>.<backend>.jitstats), not in the gitignored
         # check.snap scratch tree that holds the local .out/.time snapshots.
+        #
+        # A `<name>.<backend>.<platform>.jitstats` beside it wins on that
+        # platform. This is for the counter a host genuinely disagrees on, and
+        # it keeps the comparison exact everywhere instead of widening the gate
+        # for everyone: a band that tolerated the disagreement would tolerate it
+        # on all 371 fixtures and all three backends, and the band this gate
+        # replaced is exactly what let eight baselines go stale unnoticed.
+        #
+        # Measured, not assumed. windows-latest cranelift reports
+        # `closure_per_call` guard_failures 416 and
+        # `recursive_call_frame_relocation` 637 where macos-latest and
+        # ubuntu-24.04 both report 415 and 638, on two independent runs, with
+        # every other counter identical. `PYPY_GC_NURSERY` is pinned above, so
+        # the nursery is not the differing variable, and the same windows host
+        # passes its dynasm leg 371/371. What is left is that the allocation
+        # footprint differs, hence when a collection lands, hence how often the
+        # back-edge eval-breaker poll bails out; the specific cause is not
+        # identified. Adding an overlay is therefore recording a fact about the
+        # host, and the shared file still gates the other two.
         source = Path(script)
+        per_platform = source.with_name(f"{source.stem}.{backend}.{sys.platform}.jitstats")
+        if per_platform.exists():
+            return per_platform
         return source.with_name(f"{source.stem}.{backend}.jitstats")
 
-    def _apply_snapshot_gate(self, backend, name, script, output, stderr, elapsed):
+    def _apply_snapshot_gate(
+        self, backend, name, script, output, stderr, elapsed, timeout,
+    ):
         status, reason = "ok", ""
         out_path = self._snapshot_path(backend, name, "out")
         time_path = self._snapshot_path(backend, name, "time")
@@ -1140,12 +1278,41 @@ def _apply_snapshot_gate(self, backend, name, script, output, stderr, elapsed):
                     f"no committed jit-stats baseline ({jitstats_path.name}) — record it with "
                     f"`pyre/check.py --snapshot --backend {backend}`"
                 )
-            change = _jit_stats_change(
+            regressions, improvements = _jit_stats_change(
                 jitstats_path.read_text(encoding="utf-8"), jitstats
             )
-            if change:
-                self.jitstats_diffs.append(f"{backend}/{name}")
-                return "fail", change
+            if regressions or improvements:
+                repeats = self._jitstats_repeats(backend, script, timeout)
+                drifted = next(
+                    (s for s in repeats or () if s != jitstats), None
+                )
+                if drifted is not None:
+                    moved = _jit_stats_change(jitstats, drifted)
+                    self.jitstats_unstable.append(f"{backend}/{name}")
+                    return "unstable", (
+                        "jit-stats unstable — re-running the same binary moved "
+                        + ", ".join(moved[0] + moved[1])
+                        + ", so this run's counters are not a property of the "
+                        "tree and the baseline comparison ("
+                        + ", ".join(regressions + improvements)
+                        + ") is not gated"
+                    )
+                parts = []
+                if regressions:
+                    parts.append("regressed: " + ", ".join(regressions))
+                if improvements:
+                    parts.append("improved: " + ", ".join(improvements))
+                reason = (
+                    "jit-stats change — " + "; ".join(parts)
+                    + _jit_stats_context(jitstats)
+                    + f" (re-record with `pyre/check.py --snapshot --backend {backend} "
+                    f"--synthetic-pattern {Path(script).stem}`)"
+                )
+                if regressions:
+                    self.jitstats_diffs.append(f"{backend}/{name}")
+                    return "regressed", reason
+                self.jitstats_improvements.append(f"{backend}/{name}")
+                return "improved", reason
 
         if self.args.snapshot_mode == "record":
             out_path.parent.mkdir(parents=True, exist_ok=True)
@@ -1620,12 +1787,24 @@ def _ratio(elapsed_val, pypy_val):
             return
 
         snap_status, snap_reason = self._apply_snapshot_gate(
-            backend, name, script, output, stderr, elapsed,
+            backend, name, script, output, stderr, elapsed, timeout,
         )
-        if snap_status == "fail":
+        if snap_status == "unstable":
+            # Warned, not failed: the counter did not reproduce itself in this
+            # invocation, so there is nothing to gate on.
+            self._record(backend, True, name, f"{elapsed:.2f}s")
+            print(f"{yellow('UNSTABLE')}  {snap_reason}")
+            self._append_comparison(backend, name, t_cpython, t_pypy, "UNSTABLE")
+            return
+
+        if snap_status != "ok":
+            # `improved` is still a failure; the label only tells the reader
+            # whether to investigate or just re-record.
+            label = "IMPROVED" if snap_status == "improved" else "SNAPDIFF"
+            paint = yellow if snap_status == "improved" else red
             self._record(backend, False, name, snap_reason)
-            print(f"{red('SNAPDIFF')}  {snap_reason}")
-            self._append_comparison(backend, name, t_cpython, t_pypy, "SNAPDIFF")
+            print(f"{paint(label)}  {snap_reason}")
+            self._append_comparison(backend, name, t_cpython, t_pypy, label)
             return
 
         self._record(backend, True, name, f"{elapsed:.2f}s")
@@ -1943,14 +2122,16 @@ def print_summary(self):
         # reported on every non-record run — not only under --snapshot-diff,
         # where it used to live and where the bare CI invocation never looked.
         if self.args.snapshot_mode != "record":
-            for label, benches in (
-                ("jit-stats change", self.jitstats_diffs),
-                ("jit-stats baseline missing", self.jitstats_missing),
-                ("jit-stats line absent", self.jitstats_absent),
+            for paint, label, benches in (
+                (red, "jit-stats regressed", self.jitstats_diffs),
+                (yellow, "jit-stats improved (re-record)", self.jitstats_improvements),
+                (yellow, "jit-stats unstable (not gated)", self.jitstats_unstable),
+                (red, "jit-stats baseline missing", self.jitstats_missing),
+                (red, "jit-stats line absent", self.jitstats_absent),
             ):
                 if benches:
                     print(
-                        f"{red(label)}: {len(benches)} bench(es)"
+                        f"{paint(label)}: {len(benches)} bench(es)"
                         f" — {' '.join(benches)}"
                     )
 
diff --git a/pyre/pyre-wasm-runner/src/main.rs b/pyre/pyre-wasm-runner/src/main.rs
index 092fc111620..e349ffd97a0 100644
--- a/pyre/pyre-wasm-runner/src/main.rs
+++ b/pyre/pyre-wasm-runner/src/main.rs
@@ -376,6 +376,20 @@ fn run(module_path: &PathBuf, source: &str, script: &Path) -> Result<i32> {
         set_force.call(&mut store, selector)?;
     }
 
+    // `-P` / PYTHONSAFEPATH, resolved host-side: the guest's environment is
+    // permanently empty, so the variable has to be handed over explicitly or it
+    // would read as unset there while working natively. A presence flag, matching
+    // `pyrex::resolve_safe_path` — any non-empty value enables it, `"0"`
+    // included, and an empty value counts as unset. Absent on a module predating
+    // the export, leaving the guest on its default of seeding `sys.path[0]`.
+    if std::env::var_os("PYTHONSAFEPATH").is_some_and(|value| !value.is_empty()) {
+        if let Ok(set_safe_path) =
+            instance.get_typed_func::<u32, ()>(&mut store, "pyre_set_safe_path")
+        {
+            set_safe_path.call(&mut store, 1)?;
+        }
+    }
+
     // Name the script so the guest compiles it under its real path: that is
     // what a traceback prints, what its source-line lookup reads back through
     // `pyre_host.host_read`, and the directory that heads `sys.path`. Absent
diff --git a/pyre/pyre-wasm/src/lib.rs b/pyre/pyre-wasm/src/lib.rs
index edbbf4b2f01..b9a9625ab52 100644
--- a/pyre/pyre-wasm/src/lib.rs
+++ b/pyre/pyre-wasm/src/lib.rs
@@ -516,6 +516,13 @@ thread_local! {
     /// compiles as `<string>` and a traceback can name neither the file nor
     /// the offending line.
     static SCRIPT_PATH: RefCell<Option<String>> = const { RefCell::new(None) };
+    /// `-P` / PYTHONSAFEPATH, which suppresses the `sys.path[0]` entry. The
+    /// guest has no environment, so the embedder passes the resolved flag in
+    /// through `pyre_set_safe_path` rather than the variable being read here.
+    /// Only the native-host binding seeds that entry — the browser build has no
+    /// filesystem to seed it from.
+    #[cfg(feature = "wasm-host")]
+    static SAFE_PATH: std::cell::Cell<bool> = const { std::cell::Cell::new(false) };
 }
 
 #[cfg(any(feature = "web", feature = "wasm-host"))]
@@ -558,9 +565,11 @@ fn run_python_impl(source: &str) -> String {
     {
         // `pymain_sys_path_add_path0`: the script's directory heads
         // `sys.path`, ahead of the stdlib root `install` appends, so a module
-        // beside the script shadows one of the same name in the stdlib.
+        // beside the script shadows one of the same name in the stdlib. `-P`
+        // (safe_path) suppresses it entirely, as it does natively.
         if let Some(dir) = SCRIPT_PATH
             .with(|p| p.borrow().clone())
+            .filter(|_| !SAFE_PATH.with(|f| f.get()))
             .and_then(|p| std::path::Path::new(&p).parent().map(|d| d.to_path_buf()))
         {
             pyre_interpreter::importing::add_sys_path(&dir);
@@ -801,6 +810,15 @@ mod host_abi {
         super::SCRIPT_PATH.with(|p| *p.borrow_mut() = path);
     }
 
+    /// Set `-P` / PYTHONSAFEPATH for the next `pyre_run_python`, suppressing the
+    /// `sys.path[0]` entry `pyre_set_script_path` would otherwise seed. Passed in
+    /// rather than read from the environment because the guest's is permanently
+    /// empty, so the flag would silently read as unset there.
+    #[unsafe(no_mangle)]
+    pub extern "C" fn pyre_set_safe_path(enabled: u32) {
+        super::SAFE_PATH.with(|f| f.set(enabled != 0));
+    }
+
     /// Copy `[ptr, ptr+len)` out of linear memory as UTF-8. The embedder
     /// supplies the pair raw, so a range escaping linear memory is rejected
     /// (`None`) before a slice is formed rather than being undefined