fix(scripts): check links in tracked files, not everything on disk

The prune list was wrong three times running: it walked the scratch worktrees
under .claude/, then makepkg's vendored cargo registry under
packaging/arch/src/, reporting a dependency's broken README as if it were ours.
Every one of those directories is already git-ignored, so asking git for the
file list makes the exclusion rule the same one the repo already maintains —
and it cannot drift the way a hand-kept prune list did.

It also makes the script do what its header always said it did: check tracked
markdown. Untracked-but-unignored files are included on purpose, so a new doc is
checked before it is committed rather than after. The find(1) path stays as a
fallback for a non-git checkout.

CI was unaffected — a fresh checkout has none of those directories — but the
local gate cried wolf, which is how a gate stops being read.

scripts/check-doc-links.sh

@@ -48,6 +48,9 @@ cd "$(dirname "$0")/.."
 
 # Generated, vendored or build-output trees. Their markdown is not authored here
 # and their link targets are not ours to fix.
+#
+# Only consulted when this is NOT a git checkout — inside one, the tracked-file
+# list does this job and does not need maintaining. Kept for the tarball case.
 EXCLUDES=(
   "./node_modules/*"
   "./.svelte-kit/*"
@@ -81,14 +84,33 @@ is_generated() {
 
 echo "🔎 Checking relative markdown links resolve to files on disk…"
 
-# Build the find(1) prune expression from EXCLUDES.
+# Ask git which markdown files are ours, rather than walking the filesystem.
-find_args=(. )
+#
-for pattern in "${EXCLUDES[@]}"; do
+# This started as a find(1) with a hand-maintained prune list, and that list was
-  find_args+=(-path "$pattern" -prune -o)
+# wrong three times in a row: it walked the scratch worktrees under .claude/,
-done
+# then makepkg's vendored cargo registry under packaging/arch/src/ — each time
-find_args+=(-name "*.md" -type f -print)
+# reporting a dependency's broken README as if it were ours. Every one of those
-
+# directories is already git-ignored, so the tracked-file list is the exclusion
-mapfile -t md_files < <(find "${find_args[@]}" | sort)
+# rule, and it cannot drift out of date the way EXCLUDES did. It also matches
+# what this script always claimed to do.
+#
+# Untracked-but-not-ignored files are deliberately included: a new doc added in
+# a working tree should be checked before it is committed, not after.
+if git rev-parse --git-dir >/dev/null 2>&1; then
+  mapfile -t md_files < <(
+    { git ls-files -z --cached --others --exclude-standard -- '*.md' | tr '\0' '\n'; } \
+      | sed 's|^|./|' | sort -u
+  )
+else
+  # Not a git checkout (an exported tarball, say): fall back to walking, with
+  # the prune list below as the only defence.
+  find_args=(. )
+  for pattern in "${EXCLUDES[@]}"; do
+    find_args+=(-path "$pattern" -prune -o)
+  done
+  find_args+=(-name "*.md" -type f -print)
+  mapfile -t md_files < <(find "${find_args[@]}" | sort)
+fi
 
 echo "   ${#md_files[@]} markdown files"