feat(wiki-lint): check #4 — top-level docs dangling links

PR #224 fixed two stale references to removed docs by hand. The root
cause: wiki-lint only validated docs/wiki/, never the top-level
docs/*.md — so a doc could link to a removed sibling forever with
nothing to catch it.

Add check #4: scan docs/*.md for two doc-reference patterns and
verify they resolve (relative to docs/ or repo root):

  a) markdown links [label](local.md) — the exact #224 bug class
  b) backtick SHOUTING-CASE .md refs (e.g. `FOO-BAR.md`)

Scoped to doc-to-doc references deliberately. External URLs, anchors,
and cross-repo paths are skipped, and bare lowercase source filenames
(env.sh, build.sh — often runtime/contextual) are out of scope, so
the check has zero false positives on current main (171 pass) and
fail-closes under --strict (which CI already runs).

Calibrated by injecting fake removed-doc links: both the markdown
link and the backtick doc-name ref are detected and exit non-zero.

(Sam & Claude)

scripts/wiki-lint

@@ -1,11 +1,13 @@
 #!/bin/sh
 # wiki-lint — validate the docs/wiki/ knowledge base against the codebase.
 #
-# Three deterministic checks (no LLM, CI-friendly):
+# Four deterministic checks (no LLM, CI-friendly):
 #   1. Dangling references: every path/line cited in wiki pages must exist.
 #   2. Resurrected old names: "Shipped" renames from naming-decisions.md
 #      must not reappear in code (outside the wiki).
 #   3. Orphan pages: every docs/wiki/*.md must be linked from index.md.
+#   4. Top-level docs dangling links: markdown links + doc-name refs in
+#      docs/*.md must resolve (catches links to removed docs, e.g. PR #224).
 #
 # Output: PASS count or FAIL report. Non-zero exit on failure in --strict.
 #
@@ -17,6 +19,7 @@ set -eu
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
 WIKI_DIR="$REPO_ROOT/docs/wiki"
+TOP_DOCS_DIR="$REPO_ROOT/docs"
 FAIL=0
 PASS=0
 STRICT=0
@@ -174,6 +177,52 @@ done
 
 echo ""
 
+# ── 4. top-level docs dangling links ──────────────────────────────────
+#
+# Catches links to removed docs (the PR #224 bug class). Two patterns:
+#   a) markdown links [label](local.md) — resolve relative to docs/ or root
+#   b) backtick SHOUTING-CASE .md refs — doc-name references (e.g. FOO-BAR.md)
+# External URLs, anchors, and cross-repo paths are skipped. Bare lowercase
+# source filenames (env.sh, build.sh) are intentionally out of scope — those
+# are often runtime/contextual, not committed doc references.
+
+echo "=== 4. top-level docs dangling links ==="
+
+for doc_file in "$TOP_DOCS_DIR"/*.md; do
+    base="$(basename "$doc_file")"
+    # index.md (README) and the wiki-split plan doc are meta; still check them.
+
+    # a) markdown links to local .md files
+    _tmp_links=$(mktemp)
+    grep -oE '\]\([^)]+\.md\)' "$doc_file" \
+        | sed 's/^\](//; s/)$//' > "$_tmp_links"
+    while IFS= read -r link; do
+        case "$link" in
+            http*|\#|mailto:*) continue ;;
+        esac
+        if [ -e "${TOP_DOCS_DIR}/$link" ] || [ -e "$REPO_ROOT/$link" ]; then
+            pass
+        else
+            fail "docs/$base → markdown link '$link' (target not found)"
+        fi
+    done < "$_tmp_links"
+    rm -f "$_tmp_links"
+
+    # b) backtick SHOUTING-CASE doc-name references (e.g. `COLIBRI-SKILLS.md`)
+    _tmp_docrefs=$(mktemp)
+    grep -o '`[A-Z][A-Z0-9_-]*\.md`' "$doc_file" | tr -d '`' > "$_tmp_docrefs"
+    while IFS= read -r docref; do
+        if [ -e "${TOP_DOCS_DIR}/$docref" ] || [ -e "$REPO_ROOT/$docref" ]; then
+            pass
+        else
+            fail "docs/$base → doc reference '$docref' (not found)"
+        fi
+    done < "$_tmp_docrefs"
+    rm -f "$_tmp_docrefs"
+done
+
+echo ""
+
 # ── report ────────────────────────────────────────────────────────────
 
 printf "=== PASS: %d  FAIL: %d ===\n" "$PASS" "$FAIL"