diff --git a/docs/compaction-refresh/probes/p3_d4_focused_run.py b/docs/compaction-refresh/probes/p3_d4_focused_run.py
index 6e5e973..9614aaf 100644
--- a/docs/compaction-refresh/probes/p3_d4_focused_run.py
+++ b/docs/compaction-refresh/probes/p3_d4_focused_run.py
@@ -292,11 +292,17 @@ def resolve_gated_wi_root() -> Path:
     try:
         if not gated_root.is_dir():
             raise RuntimeError("D4 precondition: GATED_WI_ROOT is not a directory")
+        is_worktree = subprocess.check_output(
+            ["git", "-C", str(gated_root), "rev-parse", "--is-inside-work-tree"],
+            text=True,
+        ).strip()
         head = subprocess.check_output(
             ["git", "-C", str(gated_root), "rev-parse", "HEAD"], text=True
         ).strip()
     except (OSError, subprocess.CalledProcessError) as error:
         raise RuntimeError("D4 precondition: GATED_WI_ROOT is not a git worktree") from error
+    if is_worktree != "true":
+        raise RuntimeError("D4 precondition: GATED_WI_ROOT is not a git worktree")
     if head != GATED_WI_HEAD:
         raise RuntimeError(f"D4 precondition: gated WI head mismatch: {head}")
     return gated_root
@@ -353,23 +359,21 @@ def gated_launcher_precondition(
     except UnicodeDecodeError as error:
         raise RuntimeError("D4 precondition: pinned launcher is not UTF-8") from error
 
-    register = launcher_source.find('"action": "register_anchor"')
-    initialize = launcher_source.find("initialize_runtime_generation(generation_file, generation)")
-    execute = launcher_source.find("execute(command[0], command, environment)")
-    fixture_socket = launcher_source.find('source_environment["MOSAIC_LEASE_BROKER_SOCKET"]')
-    fixture_state = launcher_source.find('socket_path.parent / f"generation-{session_id}.state"')
-    exported_state = launcher_source.find('environment["MOSAIC_LEASE_GENERATION_FILE"]')
-    generation_api = (
+    # The exact launcher digest above is the trust anchor. These marker checks
+    # are diagnostic belt-and-suspenders only, never a substitute for the pin.
+    behavior_markers = (
+        '"action": "register_anchor"',
+        "initialize_runtime_generation(generation_file, generation)",
+        "execute(command[0], command, environment)",
+        'source_environment["MOSAIC_LEASE_BROKER_SOCKET"]',
+        'socket_path.parent / f"generation-{session_id}.state"',
+        'environment["MOSAIC_LEASE_GENERATION_FILE"]',
+    )
+    if not all(marker in launcher_source for marker in behavior_markers) or not (
         "def read_runtime_generation" in generation_source
         and "def bump_runtime_generation" in generation_source
-    )
-    if (
-        min(register, initialize, execute, fixture_socket, fixture_state, exported_state) < 0
-        or register >= initialize
-        or initialize >= execute
-        or not generation_api
     ):
-        raise RuntimeError("D4 precondition: launcher is not file-generation fixture-bound")
+        raise RuntimeError("D4 precondition: pinned launcher lacks file-generation markers")
 
     fixture_launcher_dir = root / "pinned-lease-broker"
     fixture_launcher_dir.mkdir(mode=0o700)