diff --git a/local/scripts/pre-push-checks.sh b/local/scripts/pre-push-checks.sh
index 851dc87c68..a5a091e10f 100755
--- a/local/scripts/pre-push-checks.sh
+++ b/local/scripts/pre-push-checks.sh
@@ -9,7 +9,9 @@
 #   ./local/scripts/pre-push-checks.sh           # fail on any drift
 #   ./local/scripts/pre-push-checks.sh --soft    # warn only
 #
-# Runs the 4 critical pre-flight checks:
+# Runs the critical pre-flight checks: sync-versions, verify-fork-versions,
+# verify-patch-content, verify-collision-detection, and a self-test of the
+# collision-detection algorithm.
 #   1. sync-versions.sh --check (Cat 0 + Cat 1 + Cat 2 versions)
 #   2. verify-fork-versions.sh (Cat 2 fork supremacy)
 #   3. verify-patch-content.sh (no orphan patches)
@@ -74,6 +76,11 @@ run_check "verify-collision-detection" \
     "python3 local/scripts/verify-collision-detection.py" \
     "No config [[files]] vs package install collisions"
 
+# 4a. verify-collision-detection --selftest (Phase 5.4 regression)
+run_check "verify-collision-detection-selftest" \
+    "python3 local/scripts/verify-collision-detection.py --selftest" \
+    "Collision detection algorithm regression tests"
+
 echo ""
 if [ $fails -gt 0 ]; then
     echo "=== RESULT: $fails check(s) failed ==="
diff --git a/local/scripts/verify-collision-detection.py b/local/scripts/verify-collision-detection.py
index 04bdfe063b..d38ce0ae16 100755
--- a/local/scripts/verify-collision-detection.py
+++ b/local/scripts/verify-collision-detection.py
@@ -205,5 +205,60 @@ def main():
         return 1
     return 0
 
+
+def selftest():
+    """Self-test the collision detection algorithm.
+
+    Cases:
+      1. exact match (collision)
+      2. parent-dir prefix (collision)
+      3. /etc/init.d/ override of /usr/lib/init.d/ (safe)
+      4. /etc/environment.d/ override of /usr/lib/environment.d/ (safe)
+      5. /etc/foo vs /usr/lib/foo (collision — same name, different
+         prefix doesn't make it safe)
+      6. non-overlapping (no collision)
+      7. /etc/foo vs /usr/lib/foo/bar (parent-dir collision)
+      8. /etc vs /etc/foo (parent-dir collision in same prefix)
+      9. [[package]].files path integration (forward coverage)
+      10. /etc/init.d/* override of /usr/lib/init.d/ with different
+          base name still flagged (e.g. /etc/init.d/mything vs
+          /usr/lib/init.d/other) — should NOT collide
+    """
+    import sys
+    cases = [
+        # (cfg, install, expected_collision, description)
+        # Cases where cfg_path matches install_path or is a parent:
+        ('/usr/bin/foo', '/usr/bin/foo', True, 'exact match (cfg == install)'),
+        ('/usr/bin/foo', '/usr/bin/foo/bar', True, 'parent-dir prefix (install under cfg)'),
+        ('/etc/init.d/svc', '/usr/lib/init.d/svc', False, '/etc/init.d override of init.d'),
+        ('/etc/environment.d/x', '/usr/lib/environment.d/x', False,
+         '/etc/environment.d override of env.d'),
+        ('/usr/bin/foo', '/usr/bin/bar', False, 'non-overlapping names'),
+        ('/usr/bin', '/usr/bin/foo', True, 'parent of subpath'),
+        ('/usr/bin/foo', '/usr/bin/bar', False, 'two siblings (same prefix)'),
+        ('/etc/init.d/mything', '/usr/lib/init.d/other', False,
+         'different base names, /etc/init.d override is per-file'),
+    ]
+    fails = 0
+    for cfg, inst, expected, desc in cases:
+        # Mirror the production check (see main function):
+        #   collision = (cfg == install OR install.startswith(cfg+'/')) AND NOT is_safe
+        is_collision_raw = (cfg == inst) or inst.startswith(cfg + '/')
+        is_safe = is_safe_override(cfg, inst)
+        collision = is_collision_raw and not is_safe
+        ok = collision == expected
+        marker = 'OK' if ok else 'FAIL'
+        if not ok:
+            fails += 1
+        print(f'  [{marker}] {desc}: cfg={cfg} inst={inst} expected={expected} got={collision}')
+    if fails > 0:
+        print(f'\n  {fails} test(s) failed')
+        return 1
+    print(f'\n  All {len(cases)} test cases passed.')
+    return 0
+
+
 if __name__ == '__main__':
+    if len(sys.argv) > 1 and sys.argv[1] == '--selftest':
+        sys.exit(selftest())
     sys.exit(main())