build: add reproducible markdown link gate

scripts/check-doc-links.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+# Verify that local Markdown links resolve inside the repository.
+set -eu
+
+TASK_ROOT=${ORBIT_ROOT_DIR:-.}
+python3 - "$TASK_ROOT" <<'PY'
+import re
+import sys
+from pathlib import Path
+
+root = Path(sys.argv[1]).resolve()
+missing = []
+files = 0
+for path in root.rglob("*.md"):
+    if ".git" in path.parts or "bin" in path.parts:
+        continue
+    files += 1
+    text = path.read_text(encoding="utf-8")
+    for raw in re.findall(r"\]\(([^)]+)\)", text):
+        target = raw.strip()
+        if target.startswith("<") and target.endswith(">"):
+            target = target[1:-1]
+        target = target.split("#", 1)[0].split("?", 1)[0]
+        if not target or "://" in target or target.startswith(("mailto:", "/")):
+            continue
+        if not (path.parent / target).exists():
+            missing.append(f"{path.relative_to(root)}: {raw}")
+
+if missing:
+    print("unresolved local Markdown links:", file=sys.stderr)
+    print("\n".join(missing), file=sys.stderr)
+    raise SystemExit(1)
+print(f'{{"markdown_files":{files},"local_links":"resolved"}}')
+PY