diff --git a/.gitattributes b/.gitattributes
index 6cd6285821..27961f90ea 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1,6 @@
 # Preserve the immutable archive's bytes even with core.autocrlf=true.
 benchmark/deepswe-gptxhigh-v1/** text eol=lf
+
+# Published study archives bind sha256 of their own LF bytes in index.json, so
+# a CRLF checkout must not rewrite them either.
+benchmark/edgebench/studies/**/data/** text eol=lf
diff --git a/benchmark/edgebench/export_report.py b/benchmark/edgebench/export_report.py
index d8be072b56..75138263ae 100644
--- a/benchmark/edgebench/export_report.py
+++ b/benchmark/edgebench/export_report.py
@@ -39,7 +39,8 @@ def read(path: Path):
 
 def write(path: Path, value):
     path.write_text(
-        json.dumps(value, indent=2, ensure_ascii=False, allow_nan=False) + "\n"
+        json.dumps(value, indent=2, ensure_ascii=False, allow_nan=False) + "\n",
+        newline="\n",
     )
 
 
diff --git a/benchmark/edgebench/feedback_hook.py b/benchmark/edgebench/feedback_hook.py
index 99e656f665..cbbe1b76a0 100644
--- a/benchmark/edgebench/feedback_hook.py
+++ b/benchmark/edgebench/feedback_hook.py
@@ -5,13 +5,19 @@
 """
 from __future__ import annotations
 
-import fcntl
 import hashlib
+import importlib
 import json
 import re
 import shlex
 import sys
 from pathlib import Path
+from typing import Any
+
+try:  # POSIX-only: the installed hook serializes delivery with flock.
+    fcntl: Any = importlib.import_module("fcntl")
+except ImportError:  # imported on hosts that only read the report adapter chain
+    fcntl = None
 
 ROOT = Path('/opt/edgebench-feedback')
 EVENTS = ('PostToolUse', 'SessionStart', 'UserPromptSubmit')
@@ -20,6 +26,8 @@
 
 
 def deliver(event, root=ROOT, receipts=Path('/logs/agent/best-feedback-delivery'), *, output=None):
+    if fcntl is None:
+        raise OSError('best-only delivery has no supported session-lock backend on this host')
     output = output or sys.stdout
     name, session = event.get('hook_event_name'), event.get('session_id')
     if name not in EVENTS or not isinstance(session, str) or not session:
diff --git a/benchmark/edgebench/studies/portfolio-ten-arm-20261006/README.md b/benchmark/edgebench/studies/portfolio-ten-arm-20261006/README.md
index ff278804e3..101e04f7ac 100644
--- a/benchmark/edgebench/studies/portfolio-ten-arm-20261006/README.md
+++ b/benchmark/edgebench/studies/portfolio-ten-arm-20261006/README.md
@@ -153,6 +153,19 @@ uv run --extra test python -m benchmark.edgebench.export_report \
   --verify benchmark/edgebench/studies/portfolio-ten-arm-20261006/data
 ```
 
+`.gitattributes` pins this archive to LF line endings, so the recorded digests
+verify even when Git checks out other text files with `core.autocrlf=true`. The
+exporter writes LF bytes on every platform, so a new report binds the same bytes
+Git stores. Git does not rewrite files already materialized in an existing
+checkout and a plain checkout skips them, so delete the stale directory once —
+`rm -rf` below, or `Remove-Item -Recurse -Force` on PowerShell — and restore it
+before verifying:
+
+```sh
+rm -rf benchmark/edgebench/studies/portfolio-ten-arm-20261006/data
+git checkout -- benchmark/edgebench/studies/portfolio-ten-arm-20261006/data
+```
+
 For another terminal collection, supply an explicit JSON list of
 `{"row": <canonical board row>, "settings": <reviewed supplemental settings>}`
 and run the same module with `--runs-root`, `--selection`, `--output` and
diff --git a/benchmark/tests/test_edgebench_feedback_hook.py b/benchmark/tests/test_edgebench_feedback_hook.py
index 94f764e01f..3ca7470f0e 100644
--- a/benchmark/tests/test_edgebench_feedback_hook.py
+++ b/benchmark/tests/test_edgebench_feedback_hook.py
@@ -11,6 +11,14 @@
 from benchmark.edgebench.feedback_hook import deliver, install
 from benchmark.edgebench import feedback_hook
 
+requires_posix_flock = pytest.mark.skipif(
+    feedback_hook.fcntl is None,
+    reason="delivery serializes its session reader with POSIX flock",
+)
+requires_posix_modes = pytest.mark.skipif(
+    os.name != 'posix', reason="the installer asserts POSIX file modes"
+)
+
 
 def packet(root, n=2):
     root.mkdir(exist_ok=True)
@@ -33,6 +41,7 @@ def packet(root, n=2):
     return value
 
 
+@requires_posix_flock
 def test_parallel_tools_resume_and_new_session(tmp_path):
     root, receipts = tmp_path / 'feedback', tmp_path / 'receipts'
     expected = packet(root)
@@ -56,6 +65,7 @@ def call(name='PostToolUse', session='s1'):
     assert call('UserPromptSubmit') and not call()
 
 
+@requires_posix_flock
 @pytest.mark.parametrize('event_name', ['PostToolUse', 'SessionStart', 'UserPromptSubmit'])
 def test_waiting_reader_cannot_rewind_newer_delivery(tmp_path, monkeypatch, event_name):
     root, receipts = tmp_path / 'feedback', tmp_path / 'receipts'
@@ -92,6 +102,7 @@ def call():
     assert not call()  # A later hook must not replay the newest result either.
 
 
+@requires_posix_flock
 def test_empty_and_malformed_do_not_disclose(tmp_path):
     value = packet(tmp_path)
     event = {'session_id': 'test', 'hook_event_name': 'PostToolUse'}
@@ -106,6 +117,7 @@ def test_empty_and_malformed_do_not_disclose(tmp_path):
     assert not output.getvalue()
 
 
+@requires_posix_flock
 @pytest.mark.parametrize('fault', ['digest', 'task', 'submission', 'epoch', 'revision', 'invalid', 'schema'])
 def test_misbound_result_never_advances_session_cursor(tmp_path, fault):
     value = packet(tmp_path)
@@ -136,6 +148,7 @@ def test_misbound_result_never_advances_session_cursor(tmp_path, fault):
     assert stream.getvalue() and len(list(receipts.glob('*.json'))) == 1
 
 
+@requires_posix_modes
 def test_installer_preserves_official_stop_and_is_idempotent(tmp_path):
     settings = {'hooks': {'Stop': [{'hooks': [{'type': 'command', 'command': '/official-stop'}]}]}}
     (tmp_path / 'hooks.json').write_text(json.dumps(settings))
@@ -159,3 +172,11 @@ def test_installer_preserves_official_stop_and_is_idempotent(tmp_path):
     assert tmp_path.stat().st_mode & 0o777 == 0o755
     assert script.stat().st_mode & 0o777 == 0o644
     assert (tmp_path / 'hooks.json').stat().st_mode & 0o777 == 0o644
+
+
+def test_delivery_refuses_a_host_without_the_posix_session_lock(tmp_path, monkeypatch):
+    monkeypatch.setattr(feedback_hook, 'fcntl', None)
+    receipts = tmp_path / 'receipts'
+    with pytest.raises(OSError, match='session-lock backend'):
+        deliver({'session_id': 'test', 'hook_event_name': 'PostToolUse'}, tmp_path, receipts)
+    assert not receipts.exists()
diff --git a/benchmark/tests/test_edgebench_report.py b/benchmark/tests/test_edgebench_report.py
index d0b7993210..984995ae9f 100644
--- a/benchmark/tests/test_edgebench_report.py
+++ b/benchmark/tests/test_edgebench_report.py
@@ -3,14 +3,20 @@
 import copy
 import csv
 import json
+import shutil
 import subprocess
 import sys
+from pathlib import Path
 
 import pytest
 
 from benchmark.edgebench.export_report import digest, export, verify, write
 
 
+ROOT = Path(__file__).resolve().parents[2]
+PUBLISHED_DATA = Path("benchmark/edgebench/studies/portfolio-ten-arm-20261006/data")
+
+
 @pytest.mark.parametrize("strategy", [None, "off", "evidence_conditioned_v1"])
 def test_report_preserves_observed_stride_version_and_absence(trial, strategy):
     runs, selection, output, task = trial
@@ -394,3 +400,79 @@ def test_cli_rejects_inconsistent_reports(trial, operation):
     assert '"verified": true' not in result.stdout
     if operation == "export":
         assert not trial[2].exists()
+
+
+def _windows_text_writes(monkeypatch):
+    """Mirror the os.linesep translation CPython applies to Windows text writes."""
+    real_open = Path.open
+
+    def windows_text_write(self, mode="r", *args, **kwargs):
+        if "b" not in mode and any(flag in mode for flag in "wax"):
+            if kwargs.get("newline") is None:
+                kwargs["newline"] = "\r\n"
+        return real_open(self, mode, *args, **kwargs)
+
+    monkeypatch.setattr(Path, "open", windows_text_write)
+
+
+def _publish_and_recheck(tmp_path, build_data):
+    """Publish files through Git with text conversion forced on, then verify."""
+    repository = tmp_path / "repository"
+    repository.mkdir()
+    subprocess.run(["git", "init", "-q", str(repository)], check=True)
+    shutil.copyfile(ROOT / ".gitattributes", repository / ".gitattributes")
+    data = build_data(repository)
+    (repository / "control.txt").write_bytes(b"control\n")
+
+    def git(*args):
+        return subprocess.run(
+            ["git", "-C", str(repository), "-c", "core.autocrlf=true", *args],
+            check=True, capture_output=True, text=True,
+        )
+
+    relative = data.relative_to(repository).as_posix()
+    pin = git("check-attr", "eol", f"{relative}/index.json").stdout
+    assert pin.strip().endswith("eol: lf"), "the LF pin must apply to this path"
+    git("add", "--", ".gitattributes", relative, "control.txt")
+    checkout = tmp_path / "checkout"
+    checkout.mkdir()
+    git("checkout-index", "--all", f"--prefix={checkout.as_posix()}/")
+    assert (checkout / "control.txt").read_bytes() == b"control\r\n", "conversion must be active"
+    restored = checkout / relative
+    assert verify(restored)["verified"] is True
+    for path in data.rglob("*"):
+        if path.is_file():
+            assert (restored / path.relative_to(data)).read_bytes() == path.read_bytes()
+    return restored
+
+
+def test_json_writer_ignores_host_text_newline_translation(tmp_path, monkeypatch):
+    _windows_text_writes(monkeypatch)
+    value = {"best_score": 2, "note": "first line\nsecond line"}
+    path = tmp_path / "value.json"
+    write(path, value)
+    expected = json.dumps(value, indent=2, ensure_ascii=False, allow_nan=False) + "\n"
+    assert path.read_bytes() == expected.encode("utf-8")
+
+
+def test_published_archive_materializes_byte_exact_under_autocrlf(tmp_path):
+    def build(repository):
+        data = repository / PUBLISHED_DATA
+        shutil.copytree(ROOT / PUBLISHED_DATA, data)
+        return data
+
+    _publish_and_recheck(tmp_path, build)
+
+
+def test_exported_report_survives_autocrlf_publication(tmp_path, trial, monkeypatch):
+    """A Windows host writes CRLF for default text writes, but this export binds
+    its own bytes, so Git must store and restore exactly what was written."""
+    _windows_text_writes(monkeypatch)
+
+    def build(repository):
+        data = repository / "benchmark/edgebench/studies/review-roundtrip/data"
+        runs, selection, _unused, _task = trial
+        export(runs, selection, data, observed_at="2026-01-02T00:00:00+00:00")
+        return data
+
+    _publish_and_recheck(tmp_path, build)