fix: harden journal scanner startup

docs/install/dwh-auth-server.md

@@ -279,18 +279,23 @@ import pathlib, subprocess, sys
 max_journal_bytes = 1_048_576
 max_journal_lines = 10_000
 max_chunk_bytes = 65_536
-actual_keys = {pathlib.Path(path).read_bytes() for path in sys.argv[2:]}
-needles = (b"thtdwh_v1", b"secret_sha256", *actual_keys)
-max_needle_length = max(map(len, needles))
-process = subprocess.Popen(
-    ["journalctl", "-u", "dwh-auth", "--since", sys.argv[1], "--no-pager", "--output=cat"],
-    stdout=subprocess.PIPE,
-    stderr=subprocess.DEVNULL,
-)
+process = None
+try:
+    actual_keys = {pathlib.Path(path).read_bytes() for path in sys.argv[2:]}
+    needles = (b"thtdwh_v1", b"secret_sha256", *actual_keys)
+    max_needle_length = max(map(len, needles))
+    process = subprocess.Popen(
+        ["journalctl", "-u", "dwh-auth", "--since", sys.argv[1], "--no-pager", "--output=cat"],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.DEVNULL,
+    )
+except OSError:
+    raise SystemExit(2)
 def stop_child():
-    if process.poll() is None:
-        process.kill()
-    process.wait()
+    if process is not None:
+        if process.poll() is None:
+            process.kill()
+        process.wait()
 bytes_seen = 0
 line_count = 0
 line_open = False