diff --git a/scripts/check_plugin.py b/scripts/check_plugin.py
index 9fc42e2..22c706b 100755
--- a/scripts/check_plugin.py
+++ b/scripts/check_plugin.py
@@ -181,13 +181,25 @@ def check_shellcheck() -> None:
 # pinning: the bug and the healthy no-results case look identical from outside.
 # Pinning it does NOT make the failure visible; it makes sure the fail-open
 # behaviour is deliberate rather than accidental.
+# A symbol that exists nowhere, ASSEMBLED rather than written literally.
+# The prior-art hook's local arm (#2280) fires with no credentials, so the
+# silence assertion below needs a name the repo genuinely lacks. Two traps,
+# both hit while writing this:
+#   - `def f` matched real code, so the hook spoke and "silent" was asserting
+#     the wrong thing;
+#   - spelling the replacement out in full put `def <name>(` INTO this file,
+#     so the smoke event defined the very symbol it claimed was absent.
+# Concatenating keeps the contiguous string out of the source.
+_ABSENT_SYM = "zz" + "_absent_" + "9f3a2b"
+
 SMOKE_EVENTS: dict[str, str] = {
     "scribe_autoinject.sh": json.dumps(
         {"session_id": "smoke", "cwd": ".", "prompt": "a multi-line\nprompt\nhere"}
     ),
     "scribe_prior_art.sh": json.dumps(
         {"session_id": "smoke", "cwd": ".", "tool_name": "Edit",
-         "tool_input": {"file_path": "src/x.py", "new_string": "def f():\n    pass\n"}}
+         "tool_input": {"file_path": "src/x.py",
+                        "new_string": f"def {_ABSENT_SYM}():\n    pass\n"}}
     ),
     "scribe_sync_processes.sh": json.dumps({"source": "startup"}),
     "scribe_session_context.sh": json.dumps({"source": "startup"}),
@@ -253,6 +265,48 @@ def check_fail_open() -> None:
                 ok(f"{rel} [{label}]: exit 0, silent")
 
 
+def check_local_prior_art_needs_no_instance() -> None:
+    """The prior-art hook's local arm must answer with no credentials (#2280).
+
+    The other arms ask Scribe what was RECORDED. This one asks the repo what
+    EXISTS, which needs no instance — and that is the whole reason it catches
+    the case the recorded arms structurally cannot: a helper nobody thought to
+    record. If it ever silently starts depending on configuration, it stops
+    covering that case and nothing else would notice.
+
+    Paired with the silence assertion in check_fail_open, which uses a symbol
+    that cannot exist. Together they pin both halves: silent when there is
+    nothing to say, and speaking when there is — both with no instance at all.
+    """
+    script = HOOKS_DIR / "scribe_prior_art.sh"
+    if not script.is_file() or not shutil.which("jq"):
+        skip("prior-art local arm: hook or jq missing")
+        return
+
+    # A definition this repo really does contain, written into a DIFFERENT file
+    # so the self-match exclusion doesn't suppress it.
+    event = json.dumps({
+        "session_id": "smoke", "cwd": ".", "tool_name": "Write",
+        "tool_input": {
+            "file_path": "scripts/_probe_not_real.py",
+            "content": "def check_local_prior_art_needs_no_instance():\n    pass\n",
+        },
+    })
+    try:
+        proc = _run_hook(script, event, {})       # NO credentials, on purpose
+    except subprocess.TimeoutExpired:
+        fail("prior-art local arm: hung")
+        return
+    if proc.returncode != 0:
+        fail(f"prior-art local arm: exited {proc.returncode}, must be 0")
+    elif "already defined" not in proc.stdout:
+        fail("prior-art local arm: found nothing for a symbol this repo "
+             "defines, with no credentials — the arm that needs no instance "
+             "has stopped working, and the recorded arms cannot cover for it")
+    else:
+        ok("prior-art local arm: answers with no instance configured")
+
+
 def _git(*args: str) -> tuple[int, str]:
     proc = subprocess.run(
         ["git", *args], capture_output=True, text=True, cwd=ROOT
@@ -344,6 +398,7 @@ def main() -> int:
     check_patterns()
     check_shellcheck()
     check_fail_open()
+    check_local_prior_art_needs_no_instance()
     if not args.no_version:
         check_version_bump(args.base)