fix(setup): Windows re-runs refresh installed skills for codex/factory/opencode hosts

On Windows (Git Bash / MSYS2, no Developer Mode), _link_or_copy installs
REAL directory copies. The install guards in link_codex_skill_dirs,
link_factory_skill_dirs, link_opencode_skill_dirs, and create_agents_sidecar
only ran the copy when the target was a symlink or missing — true on the
first install, never again. Every subsequent ./setup after a git pull
reported 'gstack ready (codex).' and exited 0 while silently refreshing
nothing: users ran stale SKILL.md forever. (link_claude_skill_dirs already
handled this; the other hosts never got the treatment.)

Fix: all five guard sites bypass the symlink-or-missing check when
IS_WINDOWS=1 — _link_or_copy rm -rf's the destination first, so the real-dir
copy refreshes in place. Unix behavior is unchanged (symlinks still pass the
guard via -L and serve updates without re-copying).

The new bash-fixture test drives the REAL extracted functions through the
install → upstream change → re-run cycle under IS_WINDOWS=1 (v1 must become
v2), pins the sidecar-skip behavior, checks the Unix path stayed a symlink,
and statically asserts the bypass at all five sites so factory/opencode
can't regress. Registered in the Windows-safe curated list
(KNOWN_WINDOWS_SAFE) so it actually runs on the windows-latest CI lane —
the 'bin/' pattern hit is a fixture path segment, not a shebang spawn.

Fixes #2444

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

setup

@@ -942,7 +942,11 @@ link_codex_skill_dirs() {
       [ "$skill_name" = "gstack" ] && continue
       target="$skills_dir/$skill_name"
       # Create or update symlink
-      if [ -L "$target" ] || [ ! -e "$target" ]; then
+      # #2444: on Windows the installed target is a REAL directory copy, so
+      # the symlink-or-missing guard skipped every re-run and SKILL.md never
+      # refreshed after `git pull`. IS_WINDOWS bypasses the guard —
+      # _link_or_copy rm -rf's the destination first, refreshing the copy.
+      if [ "$IS_WINDOWS" -eq 1 ] || [ -L "$target" ] || [ ! -e "$target" ]; then
         _link_or_copy "$skill_dir" "$target"
         linked+=("$skill_name")
       fi
@@ -968,7 +972,9 @@ create_agents_sidecar() {
     local src="$SOURCE_GSTACK_DIR/$asset"
     local dst="$agents_gstack/$asset"
     if [ -d "$src" ] || [ -f "$src" ]; then
-      if [ -L "$dst" ] || [ ! -e "$dst" ]; then
+      # #2444: IS_WINDOWS bypass — real-dir copies never match -L, so re-runs
+      # skipped the refresh. _link_or_copy rm -rf's the destination first.
+      if [ "$IS_WINDOWS" -eq 1 ] || [ -L "$dst" ] || [ ! -e "$dst" ]; then
         _link_or_copy "$src" "$dst"
       fi
     fi
@@ -979,7 +985,9 @@ create_agents_sidecar() {
     local src="$SOURCE_GSTACK_DIR/$file"
     local dst="$agents_gstack/$file"
     if [ -f "$src" ]; then
-      if [ -L "$dst" ] || [ ! -e "$dst" ]; then
+      # #2444: IS_WINDOWS bypass — real-dir copies never match -L, so re-runs
+      # skipped the refresh. _link_or_copy rm -rf's the destination first.
+      if [ "$IS_WINDOWS" -eq 1 ] || [ -L "$dst" ] || [ ! -e "$dst" ]; then
         _link_or_copy "$src" "$dst"
       fi
     fi
@@ -1175,7 +1183,11 @@ link_factory_skill_dirs() {
       skill_name="$(basename "$skill_dir")"
       [ "$skill_name" = "gstack" ] && continue
       target="$skills_dir/$skill_name"
-      if [ -L "$target" ] || [ ! -e "$target" ]; then
+      # #2444: on Windows the installed target is a REAL directory copy, so
+      # the symlink-or-missing guard skipped every re-run and SKILL.md never
+      # refreshed after `git pull`. IS_WINDOWS bypasses the guard —
+      # _link_or_copy rm -rf's the destination first, refreshing the copy.
+      if [ "$IS_WINDOWS" -eq 1 ] || [ -L "$target" ] || [ ! -e "$target" ]; then
         _link_or_copy "$skill_dir" "$target"
         linked+=("$skill_name")
       fi
@@ -1207,7 +1219,11 @@ link_opencode_skill_dirs() {
       skill_name="$(basename "$skill_dir")"
       [ "$skill_name" = "gstack" ] && continue
       target="$skills_dir/$skill_name"
-      if [ -L "$target" ] || [ ! -e "$target" ]; then
+      # #2444: on Windows the installed target is a REAL directory copy, so
+      # the symlink-or-missing guard skipped every re-run and SKILL.md never
+      # refreshed after `git pull`. IS_WINDOWS bypasses the guard —
+      # _link_or_copy rm -rf's the destination first, refreshing the copy.
+      if [ "$IS_WINDOWS" -eq 1 ] || [ -L "$target" ] || [ ! -e "$target" ]; then
         _link_or_copy "$skill_dir" "$target"
         linked+=("$skill_name")
       fi