fix(uninstall): remove real-directory skill installs, gated on provenance

On Windows, setup installs skills as REAL directory copies (cp -R via
_link_or_copy). gstack-uninstall's per-skill loop filtered on [ -L ], so
every copy was skipped: --force exited 0 and printed 'gstack uninstalled.'
while leaving ~52 gstack-* directories plus _gstack-command/ behind in
~/.claude/skills. The same filter also missed the standard Unix shape (real
dir + symlinked SKILL.md), which was left as a dangling-symlink husk.

Fix: the loop now handles all three install shapes. Symlink entries keep
the existing readlink check. Real dirs with a SYMLINKED SKILL.md are removed
when the link points into gstack (same semantics as setup's cleanup
helpers). Real dirs with a REAL-FILE SKILL.md — the Windows copy shape — are
removed ONLY when both provenance gates pass (F8): (a) the directory name is
in gstack's skill inventory (source dir names, frontmatter names, gstack-
prefixed variants, and the alias dirs), and (b) the SKILL.md carries the
existing generated banner '<!-- AUTO-GENERATED from' (ENG-OV10: every
pre-v1.67 copy already carries it; a NEW marker would refuse to delete
legitimate old installs, recreating the bug). Anything failing a gate is
listed to stderr and never deleted — a user's own skill that happens to
share a name with a gstack skill survives.

Tests: a fake-tree fixture covers removed/kept/listed for every shape
(including the F8 name-collision row), and a census test asserts every
installable skill's generated SKILL.md carries the banner so the gate can't
strand a bannerless skill. Registered in the Windows-safe curated list —
the copy shape is exactly what windows-latest exercises.

Fixes #2563

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/gstack-uninstall

@@ -130,22 +130,78 @@ fi
 
 # ─── Remove global Claude skills ────────────────────────────
 CLAUDE_SKILLS="$HOME/.claude/skills"
+
+# Skill-name inventory (#2563 gate a): every name setup could have installed —
+# each source skill's directory name, its frontmatter name, their gstack-
+# prefixed variants, and the alias dirs. Built BEFORE the install root is
+# removed. A real directory in ~/.claude/skills is only deletable when its
+# name is in this inventory AND its SKILL.md carries the generated banner.
+_INVENTORY=" _gstack-command connect-chrome gstack-connect-chrome "
+if [ -d "$GSTACK_DIR" ]; then
+  for _SRC in "$GSTACK_DIR"/*/; do
+    [ -f "$_SRC/SKILL.md" ] || continue
+    _SRC_NAME="$(basename "$_SRC")"
+    _FM_NAME=$(grep -m1 '^name:' "$_SRC/SKILL.md" 2>/dev/null | sed 's/^name:[[:space:]]*//' | tr -d '[:space:]' || true)
+    for _N in "$_SRC_NAME" "$_FM_NAME"; do
+      [ -n "$_N" ] || continue
+      case "$_INVENTORY" in *" $_N "*) ;; *) _INVENTORY="$_INVENTORY$_N gstack-$_N " ;; esac
+    done
+  done
+fi
+_in_skill_inventory() { case "$_INVENTORY" in *" $1 "*) return 0 ;; *) return 1 ;; esac; }
+
+_SKIPPED_DIRS=()
 if [ -d "$CLAUDE_SKILLS/gstack" ] || [ -L "$CLAUDE_SKILLS/gstack" ]; then
-  # Remove per-skill symlinks that point into gstack/
-  for _LINK in "$CLAUDE_SKILLS"/*; do
-    [ -L "$_LINK" ] || continue
-    _NAME="$(basename "$_LINK")"
+  # Remove per-skill entries created by setup. Three install shapes exist:
+  #   1. symlink entry                      (oldest installs)
+  #   2. real dir + SYMLINKED SKILL.md      (standard Unix install)
+  #   3. real dir + REAL-FILE SKILL.md      (Windows copy install, #2563)
+  # Shape 3 was skipped entirely — gstack-uninstall exited 0 and reported
+  # success while leaving ~52 gstack-* directories behind on Windows.
+  for _ENTRY in "$CLAUDE_SKILLS"/*; do
+    _NAME="$(basename "$_ENTRY")"
     [ "$_NAME" = "gstack" ] && continue
-    _TARGET="$(readlink "$_LINK" 2>/dev/null || true)"
-    case "$_TARGET" in
-      gstack/*|*/gstack/*) rm -f "$_LINK"; REMOVED+=("claude/$_NAME") ;;
-    esac
+    if [ -L "$_ENTRY" ]; then
+      _TARGET="$(readlink "$_ENTRY" 2>/dev/null || true)"
+      case "$_TARGET" in
+        gstack/*|*/gstack/*) rm -f "$_ENTRY"; REMOVED+=("claude/$_NAME") ;;
+      esac
+    elif [ -d "$_ENTRY" ] && { [ -f "$_ENTRY/SKILL.md" ] || [ -L "$_ENTRY/SKILL.md" ]; }; then
+      if [ -L "$_ENTRY/SKILL.md" ]; then
+        # Shape 2: provenance readable from the symlink target itself
+        # (mirrors setup's cleanup_old_claude_symlinks semantics).
+        _TARGET="$(readlink "$_ENTRY/SKILL.md" 2>/dev/null || true)"
+        case "$_TARGET" in
+          *gstack*) rm -rf "$_ENTRY"; REMOVED+=("claude/$_NAME") ;;
+          *) _SKIPPED_DIRS+=("$_ENTRY") ;;
+        esac
+      elif _in_skill_inventory "$_NAME" && grep -q '<!-- AUTO-GENERATED from' "$_ENTRY/SKILL.md" 2>/dev/null; then
+        # Shape 3: delete ONLY when BOTH gates pass (F8) — the name is in
+        # gstack's skill inventory AND the SKILL.md carries the existing
+        # generated banner. ENG-OV10: the banner IS the provenance marker —
+        # every pre-v1.67 copy already carries it; inventing a new marker
+        # would refuse to delete legitimate old installs, recreating #2563.
+        rm -rf "$_ENTRY"
+        REMOVED+=("claude/$_NAME")
+      else
+        # A real dir we cannot prove is gstack-managed (name collision with a
+        # user's own skill, or a hand-written SKILL.md): NEVER delete — list.
+        _SKIPPED_DIRS+=("$_ENTRY")
+      fi
+    fi
   done
 
   rm -rf "$CLAUDE_SKILLS/gstack"
   REMOVED+=("~/.claude/skills/gstack")
 fi
 
+if [ ${#_SKIPPED_DIRS[@]} -gt 0 ]; then
+  echo "left in place (not provably gstack-managed — remove by hand if they are yours):" >&2
+  for _D in "${_SKIPPED_DIRS[@]}"; do
+    echo "  $_D" >&2
+  done
+fi
+
 # ─── Remove project-local Claude skills (--local installs) ──
 if [ -n "$_GIT_ROOT" ] && [ -d "$_GIT_ROOT/.claude/skills" ]; then
   for _LINK in "$_GIT_ROOT/.claude/skills"/*; do