diff --git a/.github/workflows/no-local-home-paths.yml b/.github/workflows/no-local-home-paths.yml
new file mode 100644
index 000000000..fe13c30b8
--- /dev/null
+++ b/.github/workflows/no-local-home-paths.yml
@@ -0,0 +1,29 @@
+name: No absolute local home paths
+
+'on':
+  pull_request:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  no-local-home-paths:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
+        with:
+          persist-credentials: false
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97
+        with:
+          python-version: '3.11.16'
+      - name: Negative and positive controls
+        run: |
+          python -B -S -m unittest discover -s tests -p 'test_check_no_local_home_paths.py' -v
+          python -B -O -S -m unittest discover -s tests -p 'test_check_no_local_home_paths.py' -v
+      - name: Tracked tree scan
+        run: python -B -S tools/check_no_local_home_paths.py .
+      - run: git diff --exit-code
diff --git a/docs/custody/LOCAL_PATH_MAP.json b/docs/custody/LOCAL_PATH_MAP.json
new file mode 100644
index 000000000..20cb16d69
--- /dev/null
+++ b/docs/custody/LOCAL_PATH_MAP.json
@@ -0,0 +1,143 @@
+{
+ "schema": "local-path-map/v1",
+ "scientific_effect": "NONE",
+ "pinned_head": "6e502c1f8a5632eb90670fd9fc0d52e421c015a2",
+ "purpose": "Owner-side mapping for absolute local home paths retained in hash-pinned historical evidence. Additive only: no pinned file is edited, so no recorded hash changes.",
+ "prefixes": [
+  {
+   "placeholder": "<OWNER_LOCAL_HOME>",
+   "description": "macOS per-user home directory of the repository owner (the prefix up to and including the user name, no trailing slash)",
+   "sha256_of_prefix_utf8": "f42cc646e946c6157467d73f3541203ab2746476c0b6dda88a5baa6358256ef5",
+   "bytes": 15
+  }
+ ],
+ "container_paths": {
+  "pattern": "/root/<workdir>",
+  "status": "N/A: agent-sandbox scratch directories, not a personal home path; not flagged"
+ },
+ "ci_runner_paths": {
+  "pattern": "/home/runner",
+  "status": "N/A: GitHub Actions runner paths; not flagged"
+ },
+ "files": [
+  {
+   "path": "frontiers/lifetime_moment_boundary_20260930/IDENTITY_AND_CONTROL_OBSERVATIONS.json",
+   "lines": [
+    4,
+    10,
+    16,
+    78,
+    84,
+    90
+   ],
+   "hits": 6,
+   "git_blob": "a2aff201bda75aa74b8101d225182ca7731872e3",
+   "sha256": "84164b9ce29f7cc0d0b31a9cd53a870e0ad2c9bd7bb7de271cff877ba96754e5",
+   "bytes": 8495,
+   "disposition": "box-only path remap prepared (obs_paths.patch); not applied here — owner decision"
+  },
+  {
+   "path": "reviews/radial_moment_corollaries_20260930/IDENTITY_AND_CONTROL_OBSERVATIONS.json",
+   "lines": [
+    4,
+    10,
+    16,
+    78,
+    84,
+    90
+   ],
+   "hits": 6,
+   "git_blob": "a2aff201bda75aa74b8101d225182ca7731872e3",
+   "sha256": "84164b9ce29f7cc0d0b31a9cd53a870e0ad2c9bd7bb7de271cff877ba96754e5",
+   "bytes": 8495,
+   "disposition": "box-only path remap prepared (obs_paths.patch); not applied here — owner decision"
+  },
+  {
+   "path": "frontiers/moving_remote_collision_20261003/AUTHOR_CONTROL_RUNS.json",
+   "lines": [
+    6
+   ],
+   "hits": 1,
+   "git_blob": "aeb927abcf637243228d5b3158d7f802763b1928",
+   "sha256": "ee15e53018b87d160a0824c684b0eac8b0b598bd24bd3bf49298a1d3edb79bfe",
+   "bytes": 3214,
+   "disposition": "needs-owner-mapping"
+  },
+  {
+   "path": "frontiers/moving_remote_collision_20261003/review/ENGINEERING_RUNS.json",
+   "lines": [
+    14,
+    17,
+    25,
+    32,
+    43,
+    47,
+    55,
+    63
+   ],
+   "hits": 8,
+   "git_blob": "9bd98bc9df21d39c696335bf949ef3d945ca7d88",
+   "sha256": "ac99011d56f5fdd0674a798bace78de7560c160849c4bce9460b4f047ffbe5fe",
+   "bytes": 8801,
+   "disposition": "historical-evidence+mapping"
+  },
+  {
+   "path": "frontiers/planar_soft_layer_chain_20261003/C102/CHECKER_COMMENT.md",
+   "lines": [
+    510,
+    515,
+    530
+   ],
+   "hits": 3,
+   "git_blob": "7b81b8a5b09b8469441222b1fbf37ea28da60fa5",
+   "sha256": "68e847b5e74fa734923a31cc0fe6c452c7e183223dbc24d08f0872504402655e",
+   "bytes": 28098,
+   "disposition": "historical-evidence"
+  },
+  {
+   "path": "frontiers/planar_soft_layer_chain_20261003/C124/AUTHOR_CONTROLS_COMMENT.md",
+   "lines": [
+    344
+   ],
+   "hits": 1,
+   "git_blob": "447c317461e10d088672c04ad4fb412543e8c031",
+   "sha256": "c8387191a6b11b2e9a1f67e7f22a5ad58b667cc11d29b90fded1c0b33e459dc4",
+   "bytes": 23018,
+   "disposition": "historical-evidence"
+  },
+  {
+   "path": "frontiers/planar_soft_layer_chain_20261003/C124/CONTROLS.md",
+   "lines": [
+    61
+   ],
+   "hits": 1,
+   "git_blob": "7b5c77b4d359d93c023aeb4a4c8b77831084806f",
+   "sha256": "400a043d664f2ad894bbc669c38203d9809a14743522c031cc86bdbef923e399",
+   "bytes": 10113,
+   "disposition": "needs-owner-mapping"
+  },
+  {
+   "path": "frontiers/planar_soft_layer_chain_20261003/C124/REVIEW.md",
+   "lines": [
+    139
+   ],
+   "hits": 1,
+   "git_blob": "5cd4095e16bad897641254e6f2b2089f8d8e7db0",
+   "sha256": "19c405c68a93c3f5506629f0ebf1ffa78d5c25ad92f17fc4fd04ef0066deb6cf",
+   "bytes": 22542,
+   "disposition": "historical-evidence"
+  },
+  {
+   "path": "frontiers/qs_d3_soft_layer_chain_20261005/A3_2/REVIEW_C135_Q4.md",
+   "lines": [
+    140
+   ],
+   "hits": 1,
+   "git_blob": "d00fec057c73e1ba3a63efce7688832c40d4f647",
+   "sha256": "0724c5b9fd84c689bd52be84c67b0f0ad047065b5cf57b1c9ec8de19f92c5daa",
+   "bytes": 20565,
+   "disposition": "historical-evidence"
+  }
+ ],
+ "rule": "tools/check_no_local_home_paths.py fails on any absolute local home path in a tracked text file, except a file listed here whose git_blob is unchanged."
+}
diff --git a/tests/test_check_no_local_home_paths.py b/tests/test_check_no_local_home_paths.py
new file mode 100644
index 000000000..c2b93d350
--- /dev/null
+++ b/tests/test_check_no_local_home_paths.py
@@ -0,0 +1,72 @@
+import json, pathlib, subprocess, sys, tempfile, unittest
+
+ROOT = pathlib.Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT / 'tools'))
+import check_no_local_home_paths as chk
+
+S = '/'
+MAC_HOME = S + 'Us' + 'ers' + S + 'synthetic' + 'user'
+LIN_HOME = S + 'ho' + 'me' + S + 'synthetic' + 'user'
+WIN_HOME = 'C:' + '\\' + 'Us' + 'ers' + '\\' + 'synthetic' + 'user'
+RUN_HOME = S + 'ho' + 'me' + S + 'run' + 'ner' + S + 'work'
+ROOT_SCRATCH = S + 'root' + S + 'scratch_dir'
+
+
+def repo(files, allow=None):
+    d = tempfile.TemporaryDirectory()
+    r = pathlib.Path(d.name)
+    subprocess.run(['git', 'init', '-q', str(r)], check=True)
+    for k, v in files.items():
+        (r / k).parent.mkdir(parents=True, exist_ok=True)
+        (r / k).write_text(v, encoding='utf-8')
+    if allow is not None:
+        (r / 'docs/custody').mkdir(parents=True, exist_ok=True)
+        (r / chk.MAP).write_text(json.dumps({'schema': 'local-path-map/v1', 'files': allow}))
+    subprocess.run(['git', '-C', str(r), 'add', '-A'], check=True)
+    return d, r
+
+
+class NegativeControls(unittest.TestCase):
+    def test_each_synthetic_home_fails(self):
+        for home in (MAC_HOME, LIN_HOME, WIN_HOME, WIN_HOME.replace('\\', '/')):
+            d, r = repo({'a.md': 'ran ' + home + '/venv/bin/python\n'})
+            with d:
+                self.assertEqual(len(chk.scan(r)), 1, home)
+
+    def test_runner_and_root_scratch_pass(self):
+        d, r = repo({'a.log': RUN_HOME + '\n' + ROOT_SCRATCH + '\n'})
+        with d:
+            self.assertEqual(chk.scan(r), [])
+
+    def test_allowlisted_unchanged_passes_and_changed_fails(self):
+        body = 'x ' + MAC_HOME + '/p\n'
+        d, r = repo({'e.json': body})
+        with d:
+            b = chk.blob(body.encode())
+            (r / 'docs/custody').mkdir(parents=True)
+            (r / chk.MAP).write_text(json.dumps({'schema': 'local-path-map/v1', 'files': [{'path': 'e.json', 'git_blob': b}]}))
+            subprocess.run(['git', '-C', str(r), 'add', '-A'], check=True)
+            self.assertEqual(chk.scan(r), [])
+            (r / 'e.json').write_text(body + 'y ' + LIN_HOME + '/q\n')
+            self.assertEqual(len(chk.scan(r)), 2)
+
+    def test_cli_exit_code(self):
+        d, r = repo({'a.txt': MAC_HOME + '\n'})
+        with d:
+            p = subprocess.run([sys.executable, str(ROOT / 'tools/check_no_local_home_paths.py'), str(r)], capture_output=True)
+            self.assertEqual(p.returncode, 1)
+
+    def test_own_sources_have_no_literal_home_path(self):
+        for f in ('tools/check_no_local_home_paths.py', 'tests/test_check_no_local_home_paths.py', '.github/workflows/no-local-home-paths.yml', chk.MAP):
+            p = ROOT / f
+            if p.exists():
+                self.assertFalse(chk.PATTERN.search(p.read_text(encoding='utf-8')), f)
+
+
+class PositiveControl(unittest.TestCase):
+    def test_current_tree_passes(self):
+        self.assertEqual(chk.scan(ROOT), [])
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/tools/check_no_local_home_paths.py b/tools/check_no_local_home_paths.py
new file mode 100644
index 000000000..946d58e68
--- /dev/null
+++ b/tools/check_no_local_home_paths.py
@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+"""Fail if a tracked text file contains an absolute local home path.
+
+Flagged: macOS per-user homes, Linux /home/<user> (except the GitHub Actions
+runner), and Windows C:/Users or C:\\Users homes.  Agent-container scratch
+paths under /root are not personal homes and are not flagged.  Files listed in
+docs/custody/LOCAL_PATH_MAP.json are allowed only while their git blob is
+unchanged, so any edit to such a file that keeps or adds a home path fails.
+
+Patterns are assembled from fragments so this file never contains a literal
+home path itself.
+"""
+import hashlib, json, pathlib, re, subprocess, sys
+
+SEP = '/'
+MAC = SEP + 'Us' + 'ers' + SEP
+LINUX = SEP + 'ho' + 'me' + SEP
+WIN = 'C:' + '[\\\\/]+' + 'Us' + 'ers' + '[\\\\/]+'
+RUNNER = 'run' + 'ner'
+NAME = r'[A-Za-z0-9._-]+'
+PATTERN = re.compile(
+    '(?:' + re.escape(MAC) + NAME + ')'
+    + '|(?:' + re.escape(LINUX) + '(?!' + RUNNER + r'(?![A-Za-z0-9._-]))' + NAME + ')'
+    + '|(?:' + WIN + NAME + ')',
+    re.IGNORECASE)
+MAP = 'docs/custody/LOCAL_PATH_MAP.json'
+
+
+def blob(data):
+    return hashlib.sha1(b'blob %d\0' % len(data) + data).hexdigest()
+
+
+def tracked(root):
+    out = subprocess.run(['git', '-C', str(root), 'ls-files', '-z'],
+                         check=True, capture_output=True).stdout
+    return [p for p in out.decode('utf-8', 'surrogateescape').split('\0') if p]
+
+
+def load_allow(root):
+    path = pathlib.Path(root) / MAP
+    if not path.is_file():
+        return {}
+    doc = json.loads(path.read_text(encoding='utf-8'))
+    if doc.get('schema') != 'local-path-map/v1':
+        raise SystemExit('unexpected schema in ' + MAP)
+    return {e['path']: e['git_blob'] for e in doc['files']}
+
+
+def scan(root, files=None):
+    root = pathlib.Path(root)
+    allow = load_allow(root)
+    findings = []
+    for rel in (files if files is not None else tracked(root)):
+        p = root / rel
+        if p.is_symlink() or not p.is_file():
+            continue
+        data = p.read_bytes()
+        if b'\0' in data[:8192]:
+            continue
+        if allow.get(rel) == blob(data):
+            continue
+        text = data.decode('utf-8', 'replace')
+        for n, line in enumerate(text.split('\n'), 1):
+            if PATTERN.search(line):
+                note = ' (allowlisted file changed)' if rel in allow else ''
+                findings.append(f'{rel}:{n}: absolute local home path{note}')
+    return findings
+
+
+def main(argv):
+    root = argv[1] if len(argv) > 1 else '.'
+    findings = scan(root)
+    for f in findings:
+        print(f)
+    print(json.dumps({'findings': len(findings), 'scientific_effect': 'NONE'}))
+    return 1 if findings else 0
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv))