diff --git a/product/skills/admin-bypass-sweep/SKILL.md b/product/skills/admin-bypass-sweep/SKILL.md
index becb9df3..1558da55 100644
--- a/product/skills/admin-bypass-sweep/SKILL.md
+++ b/product/skills/admin-bypass-sweep/SKILL.md
@@ -141,10 +141,43 @@ diffs; stop and re-derive the safe approach first.
 
 Both requirements in the STOP section must be satisfied before this step runs.
 
-Skim `gh pr diff <pr>` for each PR before merging it, even under consent —
-this is the only review most of these PRs get, since the merge bypasses
-required checks entirely. The human's consent authorizes bypassing CI; it
-does not stand in for having actually looked at what's being merged.
+Before any `gh pr merge --admin`, write that PR's diff to a file, record
+the file's total line count with `wc -l`, read the whole file, and assert
+that the number of lines read equals the recorded total. This is the only
+review most of these PRs get, since the merge bypasses required checks
+entirely. The human's consent authorizes bypassing CI; it does not stand in
+for having actually looked at what's being merged.
+
+Use this read-completeness precondition for each PR:
+
+```bash
+pr=<pr>
+diff_file="$(mktemp -t admin-bypass-pr-${pr}.diff.XXXXXX)"
+gh pr diff "$pr" --repo <owner>/<repo> > "$diff_file"
+diff_lines="$(wc -l < "$diff_file" | tr -d ' ')"
+nl -ba "$diff_file"
+lines_read=<last line number printed by nl, or 0 if diff_lines is 0>
+test "$lines_read" = "$diff_lines"
+```
+
+Classify the PR before merging it, using the same three outcomes as the
+rest of this procedure:
+
+- `reviewed` — the diff file was read line-complete, `lines_read` equals
+  `diff_lines`, and no review finding was found.
+- `flagged` — the diff file was read line-complete, `lines_read` equals
+  `diff_lines`, and one or more review findings were recorded for the
+  human.
+- `unchecked` — the diff read was narrowed, filtered, or truncated, so
+  line completeness was not established.
+
+A read through `head`, `tail`, `grep`, `awk`, or `sed` is a narrowed read:
+mark that PR `unchecked`, never `reviewed`, even if the visible lines look
+fine. The operator may not report such a PR as reviewed. This check reports
+the PR's review state; it does not create a new authorization path or block
+the human from deciding to proceed with the admin merge anyway. If an
+`unchecked` PR is merged, the final report must still list it as
+`unchecked`, not reviewed.
 
 For a single-PR stack:
 
diff --git a/product/skills/admin-bypass-sweep/tests/fixture_complete_diff_read.md b/product/skills/admin-bypass-sweep/tests/fixture_complete_diff_read.md
new file mode 100644
index 00000000..b3baba78
--- /dev/null
+++ b/product/skills/admin-bypass-sweep/tests/fixture_complete_diff_read.md
@@ -0,0 +1,20 @@
+User invokes `/admin-bypass-sweep` with the required consent sentence and the
+operator reaches Step 4 for PR 42.
+
+The operator writes the full diff to a file:
+
+```bash
+pr=42
+diff_file="$(mktemp -t admin-bypass-pr-${pr}.diff.XXXXXX)"
+gh pr diff "$pr" --repo neko/example > "$diff_file"
+diff_lines="$(wc -l < "$diff_file" | tr -d ' ')"
+nl -ba "$diff_file"
+lines_read=184
+test "$lines_read" = "$diff_lines"
+```
+
+The recorded `diff_lines` value is 184, and the complete `nl -ba` output ends
+at line 184. No review finding is found.
+
+Expected outcome: PR 42 may be reported as `reviewed` before the operator runs
+`gh pr merge 42 --repo neko/example --admin --squash`.
diff --git a/product/skills/admin-bypass-sweep/tests/fixture_truncated_diff_read.md b/product/skills/admin-bypass-sweep/tests/fixture_truncated_diff_read.md
new file mode 100644
index 00000000..3c1a1646
--- /dev/null
+++ b/product/skills/admin-bypass-sweep/tests/fixture_truncated_diff_read.md
@@ -0,0 +1,23 @@
+User invokes `/admin-bypass-sweep` with the required consent sentence and the
+operator reaches Step 4 for PR 77.
+
+The operator writes the diff to a file, but reads it through a truncating
+filter:
+
+```bash
+pr=77
+diff_file="$(mktemp -t admin-bypass-pr-${pr}.diff.XXXXXX)"
+gh pr diff "$pr" --repo neko/example > "$diff_file"
+diff_lines="$(wc -l < "$diff_file" | tr -d ' ')"
+head -200 "$diff_file"
+lines_read=200
+test "$lines_read" = "$diff_lines"
+```
+
+The recorded `diff_lines` value is 913, and only the first 200 lines were read
+through `head`.
+
+Expected outcome: PR 77 is `unchecked`, not `reviewed`. The operator may not
+report PR 77 as reviewed, even if the visible lines look fine. If the human
+decides to proceed with `gh pr merge 77 --repo neko/example --admin --squash`,
+the final report must still list PR 77 as `unchecked`.
diff --git a/product/skills/admin-bypass-sweep/tests/test_diff_read_gate.py b/product/skills/admin-bypass-sweep/tests/test_diff_read_gate.py
new file mode 100644
index 00000000..254c27e1
--- /dev/null
+++ b/product/skills/admin-bypass-sweep/tests/test_diff_read_gate.py
@@ -0,0 +1,60 @@
+from pathlib import Path
+import re
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+SKILL = ROOT / "SKILL.md"
+TESTS = ROOT / "tests"
+
+
+class DiffReadGateTests(unittest.TestCase):
+    def setUp(self):
+        self.skill = SKILL.read_text()
+        step4_match = re.search(
+            r"## Step 4: Merge each stack, bottom-up(?P<body>.*?)## Step 5:",
+            self.skill,
+            re.S,
+        )
+        self.assertIsNotNone(step4_match, "Step 4 section is present")
+        self.step4 = step4_match.group("body")
+
+    def test_step4_requires_recorded_line_count_and_full_read_before_admin_merge(self):
+        merge_index = self.step4.index("gh pr merge <pr>")
+        pre_merge = self.step4[:merge_index]
+
+        self.assertIn("Before any `gh pr merge --admin`", pre_merge)
+        self.assertIn("gh pr diff", pre_merge)
+        self.assertIn("> \"$diff_file\"", pre_merge)
+        self.assertIn("wc -l", pre_merge)
+        self.assertIn("nl -ba \"$diff_file\"", pre_merge)
+        self.assertIn('test "$lines_read" = "$diff_lines"', pre_merge)
+        self.assertIn("number of lines read equals the recorded total", pre_merge)
+
+    def test_step4_documents_narrowed_reads_as_unchecked_not_reviewed(self):
+        for command in ("head", "tail", "grep", "awk", "sed"):
+            self.assertIn(f"`{command}`", self.step4)
+
+        self.assertIn("mark that PR `unchecked`, never `reviewed`", self.step4)
+        self.assertIn("may not report such a PR as reviewed", self.step4)
+
+    def test_complete_read_fixture_marks_pr_reviewed(self):
+        fixture = (TESTS / "fixture_complete_diff_read.md").read_text()
+
+        self.assertIn("wc -l", fixture)
+        self.assertIn("nl -ba", fixture)
+        self.assertIn("lines_read=184", fixture)
+        self.assertIn("Expected outcome: PR 42 may be reported as `reviewed`", fixture)
+
+    def test_truncated_read_fixture_marks_pr_unchecked(self):
+        fixture = (TESTS / "fixture_truncated_diff_read.md").read_text()
+        fixture_lower = fixture.lower()
+
+        self.assertIn("head -200", fixture)
+        self.assertIn("diff_lines` value is 913", fixture)
+        self.assertIn("PR 77 is `unchecked`, not `reviewed`", fixture)
+        self.assertIn("operator may not\nreport pr 77 as reviewed", fixture_lower)
+
+
+if __name__ == "__main__":
+    unittest.main()