diff --git a/setup b/setup
index 87c9573e9..b841efd42 100755
--- a/setup
+++ b/setup
@@ -62,6 +62,65 @@ for _arg in "$@"; do
   esac
 done
 # --status is read-only: no bun, no build, no writes (docs/ADDING_A_HOST.md).
+# _status_install_checks — per registered install (C3): is the router a real
+# file (Codex skips a symlinked SKILL.md), and does every section pointer in an
+# installed SKILL.md resolve? A pointer is "Read `<path>/sections/<f>.md`",
+# optionally "relative to the installed `<skill>` SKILL.md directory". A bare
+# `sections/...` pointer counts in a carved skill (sections/ installed, or a
+# **STOP.** line); prefixed ones ($GSTACK_ROOT, ~, absolute, ../) everywhere.
+_status_install_checks() {
+  local reg="$GSTACK_STATE_ROOT/installs.tsv" host scope project dest root src rest router md dir stop tok names n path checked broken first fix
+  [ -f "$reg" ] || return 0
+  echo "Install checks:"
+  while IFS='	' read -r host scope project dest root src rest; do
+    case "$host" in ''|'#'*) continue ;; esac
+    fix="Fix: cd $src && ./setup --host $host"
+    router="$root/SKILL.md"
+    if [ -L "$router" ]; then router="router is a symlink, which Codex skips. $fix"
+    elif [ -f "$router" ]; then router="router is a real file"
+    else router="router missing at $router. $fix"; fi
+    checked=0 broken=0 first=""
+    for md in "$dest"/*/SKILL.md; do
+      [ -f "$md" ] || continue
+      dir="${md%/SKILL.md}"
+      while IFS='|' read -r stop tok names; do
+        [ -n "$tok" ] || continue
+        path=""
+        case "$tok" in
+          sections/*)
+            if [ -n "$names" ]; then
+              for n in $names; do path="$dest/$n/$tok"; [ -r "$path" ] && break; done
+            elif [ -d "$dir/sections" ] || [ "$stop" = 1 ]; then path="$dir/$tok"
+            else continue; fi ;;
+          '$GSTACK_ROOT/'*) path="$root/${tok#\$GSTACK_ROOT/}" ;;
+          '~/'*) path="$HOME/${tok#\~/}" ;;
+          /*) path="$tok" ;;
+          ../*) path="$dir/$tok" ;;
+          *) continue ;;
+        esac
+        checked=$((checked + 1))
+        [ -r "$path" ] && continue
+        broken=$((broken + 1))
+        [ -n "$first" ] || first="${md#"$dest"/} names $tok"
+      done <<EOF
+$(awk '{
+  line = $0; stop = index(line, "**STOP.**") ? 1 : 0
+  while (match(line, /Read `[^` ]*sections\/[A-Za-z0-9._-]+\.md`( relative to the installed (`[^`]+`\/?)+)?/)) {
+    m = substr(line, RSTART + 6, RLENGTH - 6); line = substr(line, RSTART + RLENGTH)
+    tok = m; sub(/`.*/, "", tok); names = ""
+    if (index(m, " relative to the installed ")) { names = substr(m, index(m, " relative to the installed ") + 27); gsub(/[`\/]+/, " ", names) }
+    print stop "|" tok "|" names
+  }
+}' "$md")
+EOF
+    done
+    if [ "$broken" -eq 0 ]; then
+      printf '  %s %s: %s; section links: %s checked, all resolve\n' "$host" "$scope" "$router" "$checked"
+    else
+      printf '  %s %s: %s; section links: %s of %s broken (first: %s). %s\n' "$host" "$scope" "$router" "$broken" "$checked" "$first" "$fix"
+    fi
+  done < "$reg"
+}
 for _arg in "$@"; do
   case "$_arg" in
     --status)
@@ -69,6 +128,7 @@ for _arg in "$@"; do
       . "$_STATUS_DIR/bin/gstack-state-root.sh" && . "$_STATUS_DIR/bin/gstack-install-registry.sh" || exit 1
       gstack_state_root_select; GSTACK_STATE_ROOT="$_gstack_sr_root"
       gstack_install_status
+      _status_install_checks
       exit 0 ;;
   esac
 done
@@ -511,6 +571,65 @@ _link_runtime_dists() {
   done
 }
 
+# ─── Real-file SKILL.md copies in host runtime roots (C3, #333) ──────────────
+# Codex skips a symlinked SKILL.md file, so the router and the nested SKILL.md
+# files in every host runtime root are real copies, rewritten on every run.
+# setup records the hash of each copy it writes in $GSTACK_STATE_ROOT/
+# skill-copies.tsv (hash<TAB>path); a copy whose bytes no longer match was
+# edited by hand and is saved to a uniquely named backup under the state root
+# before the tree is replaced, so the backup outlives the old tree.
+_SKILL_COPIES_FILE="$GSTACK_STATE_ROOT/skill-copies.tsv"
+_copy_skill_md() {
+  rm -f "$2" && cp "$1" "$2"
+}
+_skill_copy_hash() {
+  git hash-object "$1" 2>/dev/null
+}
+# _skill_copy_unmodified FILE — FILE is a copy setup wrote and nobody edited.
+_skill_copy_unmodified() {
+  local h
+  [ -f "$1" ] && [ ! -L "$1" ] && [ -f "$_SKILL_COPIES_FILE" ] || return 1
+  h="$(_skill_copy_hash "$1")" || return 1
+  grep -qxF "$h	$1" "$_SKILL_COPIES_FILE"
+}
+# _preserve_skill_copy_edits ROOT — back up every recorded copy under ROOT
+# whose bytes changed. Non-zero when a backup failed: the caller must then
+# keep the old tree (a failed backup is never a license to overwrite).
+_preserve_skill_copy_edits() {
+  local root="$1" hash path dir=""
+  [ -f "$_SKILL_COPIES_FILE" ] || return 0
+  while IFS='	' read -r hash path; do
+    case "$path" in "$root"/*) ;; *) continue ;; esac
+    { [ -f "$path" ] && [ ! -L "$path" ]; } || continue
+    [ "$(_skill_copy_hash "$path")" = "$hash" ] && continue
+    if [ -z "$dir" ]; then
+      mkdir -p "$GSTACK_STATE_ROOT/backups/skill-copies" || return 1
+      dir="$(mktemp -d "$GSTACK_STATE_ROOT/backups/skill-copies/$(date +%Y%m%dT%H%M%S)-XXXXXX")" || return 1
+    fi
+    mkdir -p "$dir/$(dirname "${path#/}")" && cp -p "$path" "$dir/${path#/}" || return 1
+    echo "  saved your edited $path to $dir/${path#/} (setup rewrites gstack's SKILL.md copies on every run)"
+  done < "$_SKILL_COPIES_FILE"
+}
+# _record_skill_copies ROOT — replace ROOT's rows with the real SKILL.md files
+# now under it (find does not descend into linked directories). Sets
+# _COPIES_REFRESHED and _COPIES_REMOVED (paths relative to ROOT).
+_record_skill_copies() {
+  local root="$1" f tmp old="" new
+  _COPIES_REFRESHED="" _COPIES_REMOVED=""
+  if [ -f "$_SKILL_COPIES_FILE" ]; then
+    old="$(awk -F'\t' -v r="$root/" 'index($2, r) == 1 { print substr($2, length(r) + 1) }' "$_SKILL_COPIES_FILE" | sort)"
+  fi
+  new="$(cd "$root" 2>/dev/null && find . -name SKILL.md -type f | sed 's|^\./||' | sort)"
+  mkdir -p "$GSTACK_STATE_ROOT" || return 1
+  tmp="$_SKILL_COPIES_FILE.tmp.$$"
+  {
+    [ -f "$_SKILL_COPIES_FILE" ] && awk -F'\t' -v r="$root/" 'index($2, r) != 1' "$_SKILL_COPIES_FILE"
+    for f in $new; do printf '%s\t%s\n' "$(_skill_copy_hash "$root/$f")" "$root/$f"; done
+  } > "$tmp" && mv -f "$tmp" "$_SKILL_COPIES_FILE" || { rm -f "$tmp"; return 1; }
+  _COPIES_REFRESHED="$(printf '%s\n' "$new" | tr '\n' ' ' | sed 's/ *$//')"
+  _COPIES_REMOVED="$(printf '%s\n' "$old" | grep -vxF -f <(printf '%s\n' "$new") | tr '\n' ' ' | sed 's/ *$//')"
+}
+
 # ─── Ownership gate for skill entries (#2119) ─────────────────────────────────
 # setup and gstack-relink must never delete or link over a skill they do not
 # own. This is the single rule both use (relink carries the same logic — keep
@@ -2370,6 +2489,11 @@ _activate_runtime_root() {
     echo "  error: could not build the new runtime root for $root (exit $rc); the previous one is unchanged" >&2
     return "$rc"
   fi
+  if ! _preserve_skill_copy_edits "$root"; then
+    rm -rf "$new"
+    echo "  error: could not back up an edited SKILL.md copy under $root; the previous runtime root is unchanged" >&2
+    return 1
+  fi
   if [ -e "$root" ] || [ -L "$root" ]; then
     mv "$root" "$old" || { rm -rf "$new"; return 1; }
   fi
@@ -2379,6 +2503,10 @@ _activate_runtime_root() {
     return 1
   fi
   rm -rf "$old"
+  _record_skill_copies "$root" || echo "  warning: could not record SKILL.md copy hashes in $_SKILL_COPIES_FILE; a later hand edit there may not be backed up" >&2
+  [ -n "$_COPIES_REFRESHED" ] && log "  refreshed SKILL.md copies in $root: $_COPIES_REFRESHED"
+  [ -n "$_COPIES_REMOVED" ] && log "  removed SKILL.md copies from $root: $_COPIES_REMOVED"
+  return 0
 }
 
 # ─── Helper: create a minimal ~/.codex/skills/gstack runtime root ───────────
@@ -2401,7 +2529,7 @@ create_codex_runtime_root() {
   mkdir -p "$codex_gstack" "$codex_gstack/browse" "$codex_gstack/gstack-upgrade" "$codex_gstack/review"
 
   if [ -f "$agents_dir/gstack/SKILL.md" ]; then
-    _link_or_copy "$agents_dir/gstack/SKILL.md" "$codex_gstack/SKILL.md"
+    _copy_skill_md "$agents_dir/gstack/SKILL.md" "$codex_gstack/SKILL.md"
   fi
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$codex_gstack/bin"
@@ -2417,14 +2545,14 @@ create_codex_runtime_root() {
   fi
   _link_runtime_dists "$gstack_dir" "$codex_gstack"
   if [ -f "$agents_dir/gstack-upgrade/SKILL.md" ]; then
-    _link_or_copy "$agents_dir/gstack-upgrade/SKILL.md" "$codex_gstack/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$agents_dir/gstack-upgrade/SKILL.md" "$codex_gstack/gstack-upgrade/SKILL.md"
   fi
   # plan-eng-review's inline office-hours step reads
   # $GSTACK_ROOT/office-hours/SKILL.md (#2449) — install the codex-rendered
   # variant there so the documented path exists.
   if [ -f "${agents_dir}/gstack-office-hours/SKILL.md" ]; then
     mkdir -p "${codex_gstack}/office-hours"
-    _link_or_copy "${agents_dir}/gstack-office-hours/SKILL.md" "${codex_gstack}/office-hours/SKILL.md"
+    _copy_skill_md "${agents_dir}/gstack-office-hours/SKILL.md" "${codex_gstack}/office-hours/SKILL.md"
   fi
   # Review runtime assets (individual files, NOT the whole review/ dir which has SKILL.md)
   for f in checklist.md design-checklist.md greptile-triage.md TODOS-format.md; do
@@ -2457,7 +2585,7 @@ create_factory_runtime_root() {
   mkdir -p "$factory_gstack" "$factory_gstack/browse" "$factory_gstack/gstack-upgrade" "$factory_gstack/review"
 
   if [ -f "$factory_dir/gstack/SKILL.md" ]; then
-    _link_or_copy "$factory_dir/gstack/SKILL.md" "$factory_gstack/SKILL.md"
+    _copy_skill_md "$factory_dir/gstack/SKILL.md" "$factory_gstack/SKILL.md"
   fi
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$factory_gstack/bin"
@@ -2473,14 +2601,14 @@ create_factory_runtime_root() {
   fi
   _link_runtime_dists "$gstack_dir" "$factory_gstack"
   if [ -f "$factory_dir/gstack-upgrade/SKILL.md" ]; then
-    _link_or_copy "$factory_dir/gstack-upgrade/SKILL.md" "$factory_gstack/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$factory_dir/gstack-upgrade/SKILL.md" "$factory_gstack/gstack-upgrade/SKILL.md"
   fi
   # plan-eng-review's inline office-hours step reads
   # $GSTACK_ROOT/office-hours/SKILL.md (#2449) — install the factory-rendered
   # variant there so the documented path exists.
   if [ -f "${factory_dir}/gstack-office-hours/SKILL.md" ]; then
     mkdir -p "${factory_gstack}/office-hours"
-    _link_or_copy "${factory_dir}/gstack-office-hours/SKILL.md" "${factory_gstack}/office-hours/SKILL.md"
+    _copy_skill_md "${factory_dir}/gstack-office-hours/SKILL.md" "${factory_gstack}/office-hours/SKILL.md"
   fi
   for f in checklist.md design-checklist.md greptile-triage.md TODOS-format.md; do
     if [ -f "$gstack_dir/review/$f" ]; then
@@ -2511,7 +2639,7 @@ create_opencode_runtime_root() {
   mkdir -p "$opencode_gstack" "$opencode_gstack/browse" "$opencode_gstack/gstack-upgrade" "$opencode_gstack/review" "$opencode_gstack/qa" "$opencode_gstack/plan-devex-review"
 
   if [ -f "$opencode_dir/gstack/SKILL.md" ]; then
-    _link_or_copy "$opencode_dir/gstack/SKILL.md" "$opencode_gstack/SKILL.md"
+    _copy_skill_md "$opencode_dir/gstack/SKILL.md" "$opencode_gstack/SKILL.md"
   fi
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$opencode_gstack/bin"
@@ -2527,14 +2655,14 @@ create_opencode_runtime_root() {
   fi
   _link_runtime_dists "$gstack_dir" "$opencode_gstack"
   if [ -f "$opencode_dir/gstack-upgrade/SKILL.md" ]; then
-    _link_or_copy "$opencode_dir/gstack-upgrade/SKILL.md" "$opencode_gstack/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$opencode_dir/gstack-upgrade/SKILL.md" "$opencode_gstack/gstack-upgrade/SKILL.md"
   fi
   # plan-eng-review's inline office-hours step reads
   # $GSTACK_ROOT/office-hours/SKILL.md (#2449) — install the opencode-rendered
   # variant there so the documented path exists.
   if [ -f "${opencode_dir}/gstack-office-hours/SKILL.md" ]; then
     mkdir -p "${opencode_gstack}/office-hours"
-    _link_or_copy "${opencode_dir}/gstack-office-hours/SKILL.md" "${opencode_gstack}/office-hours/SKILL.md"
+    _copy_skill_md "${opencode_dir}/gstack-office-hours/SKILL.md" "${opencode_gstack}/office-hours/SKILL.md"
   fi
   for f in checklist.md design-checklist.md greptile-triage.md TODOS-format.md; do
     if [ -f "$gstack_dir/review/$f" ]; then
@@ -2673,7 +2801,7 @@ create_cursor_runtime_root() {
   mkdir -p "$cursor_gstack" "$cursor_gstack/browse" "$cursor_gstack/gstack-upgrade" "$cursor_gstack/review"
 
   if [ -f "$cursor_dir/gstack/SKILL.md" ]; then
-    _link_or_copy "$cursor_dir/gstack/SKILL.md" "$cursor_gstack/SKILL.md"
+    _copy_skill_md "$cursor_dir/gstack/SKILL.md" "$cursor_gstack/SKILL.md"
   fi
   # bin scripts import shared modules via ../lib — bin and lib travel together.
   if [ -d "$gstack_dir/bin" ]; then
@@ -2690,7 +2818,7 @@ create_cursor_runtime_root() {
   fi
   _link_runtime_dists "$gstack_dir" "$cursor_gstack"
   if [ -f "$cursor_dir/gstack-upgrade/SKILL.md" ]; then
-    _link_or_copy "$cursor_dir/gstack-upgrade/SKILL.md" "$cursor_gstack/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$cursor_dir/gstack-upgrade/SKILL.md" "$cursor_gstack/gstack-upgrade/SKILL.md"
   fi
   # Review runtime assets — the cursor host config ships the lean pair.
   for f in checklist.md TODOS-format.md; do
@@ -2850,7 +2978,7 @@ create_copilot_runtime_root() {
   mkdir -p "$copilot_gstack" "$copilot_gstack/browse" "$copilot_gstack/gstack-upgrade" "$copilot_gstack/review"
   printf '%s\n' "$gstack_dir" > "$copilot_gstack/.source-path"
   if [ -f "$copilot_dir/gstack/SKILL.md" ]; then
-    _link_or_copy "$copilot_dir/gstack/SKILL.md" "$copilot_gstack/SKILL.md"
+    _copy_skill_md "$copilot_dir/gstack/SKILL.md" "$copilot_gstack/SKILL.md"
   fi
   for asset in bin lib browse/dist browse/bin; do
     if [ -d "$gstack_dir/$asset" ]; then
@@ -2859,11 +2987,11 @@ create_copilot_runtime_root() {
   done
   _link_runtime_dists "$gstack_dir" "$copilot_gstack"
   if [ -f "$copilot_dir/gstack-upgrade/SKILL.md" ]; then
-    _link_or_copy "$copilot_dir/gstack-upgrade/SKILL.md" "$copilot_gstack/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$copilot_dir/gstack-upgrade/SKILL.md" "$copilot_gstack/gstack-upgrade/SKILL.md"
   fi
   if [ -f "$copilot_dir/gstack-office-hours/SKILL.md" ]; then
     mkdir -p "$copilot_gstack/office-hours"
-    _link_or_copy "$copilot_dir/gstack-office-hours/SKILL.md" "$copilot_gstack/office-hours/SKILL.md"
+    _copy_skill_md "$copilot_dir/gstack-office-hours/SKILL.md" "$copilot_gstack/office-hours/SKILL.md"
   fi
   for f in checklist.md design-checklist.md greptile-triage.md TODOS-format.md; do
     if [ -f "$gstack_dir/review/$f" ]; then
@@ -3150,11 +3278,15 @@ if [ "$INSTALL_KIRO" -eq 1 ]; then
       mkdir -p "$KIRO_GSTACK/supabase"
       _link_or_copy "$SOURCE_GSTACK_DIR/supabase/config.sh" "$KIRO_GSTACK/supabase/config.sh"
     fi
-    _link_or_copy "$KIRO_DIR/gstack-upgrade/SKILL.md" "$KIRO_GSTACK/gstack-upgrade/SKILL.md"
-    _link_or_copy "$KIRO_DIR/gstack/SKILL.md" "$KIRO_GSTACK/SKILL.md"
+    if ! _preserve_skill_copy_edits "$KIRO_GSTACK"; then
+      echo "  error: could not back up an edited SKILL.md copy under $KIRO_GSTACK; Kiro install stopped before overwriting it" >&2
+      exit 1
+    fi
+    _copy_skill_md "$KIRO_DIR/gstack-upgrade/SKILL.md" "$KIRO_GSTACK/gstack-upgrade/SKILL.md"
+    _copy_skill_md "$KIRO_DIR/gstack/SKILL.md" "$KIRO_GSTACK/SKILL.md"
     if [ -f "$KIRO_DIR/gstack-office-hours/SKILL.md" ]; then
       mkdir -p "$KIRO_GSTACK/office-hours"
-      _link_or_copy "$KIRO_DIR/gstack-office-hours/SKILL.md" "$KIRO_GSTACK/office-hours/SKILL.md"
+      _copy_skill_md "$KIRO_DIR/gstack-office-hours/SKILL.md" "$KIRO_GSTACK/office-hours/SKILL.md"
     fi
     for f in checklist.md design-checklist.md greptile-triage.md TODOS-format.md; do
       if [ -f "$SOURCE_GSTACK_DIR/review/$f" ]; then
@@ -3176,13 +3308,15 @@ if [ "$INSTALL_KIRO" -eq 1 ]; then
       mkdir -p "$target_dir"
       if [ -f "$target_dir/SKILL.md" ] && [ ! -L "$target_dir/SKILL.md" ] \
          && ! _claude_entry_owned_strongly "$target_dir" "$SOURCE_GSTACK_DIR" \
+         && ! _skill_copy_unmodified "$target_dir/SKILL.md" \
          && ! cmp -s "$target_dir/SKILL.md" "$skill_dir/SKILL.md"; then
         if ! _backup_skill_md "$target_dir/SKILL.md" "$skill_name"; then
           echo "  skipped $skill_name: could not back up its customized SKILL.md — left untouched" >&2
           continue
         fi
       fi
-      _link_or_copy "$skill_dir/SKILL.md" "$target_dir/SKILL.md"
+      _copy_skill_md "$skill_dir/SKILL.md" "$target_dir/SKILL.md"
+      _record_skill_copies "$target_dir" || true
       # Native sections already contain Kiro paths/provider markers. Refresh
       # generated files individually so user assets next to them survive.
       if [ -d "$skill_dir/sections" ]; then
@@ -3236,6 +3370,8 @@ if [ "$INSTALL_KIRO" -eq 1 ]; then
       fi
     done
     _prune_stale_generated "$SOURCE_GSTACK_DIR" "$KIRO_DIR" "$KIRO_SKILLS"
+    _record_skill_copies "$KIRO_GSTACK" || echo "  warning: could not record SKILL.md copy hashes in $_SKILL_COPIES_FILE" >&2
+    [ -n "$_COPIES_REFRESHED" ] && log "  refreshed SKILL.md copies in $KIRO_GSTACK: $_COPIES_REFRESHED"
     _setup_arm_publish kiro global - "$KIRO_SKILLS" "$KIRO_GSTACK" -
     echo "gstack ready (kiro)."
     echo "  browse: $BROWSE_BIN"
diff --git a/test/host-conformance.test.ts b/test/host-conformance.test.ts
index 793488a5e..60aebbd98 100644
--- a/test/host-conformance.test.ts
+++ b/test/host-conformance.test.ts
@@ -11,7 +11,7 @@
  * namespace (#2879). Instruction-only hosts must change nothing.
  */
 import { afterEach, describe, expect, test } from 'bun:test';
-import { chmodSync, existsSync, mkdirSync, mkdtempSync, readFileSync, readdirSync, realpathSync, rmSync } from 'node:fs';
+import { chmodSync, existsSync, lstatSync, mkdirSync, mkdtempSync, readFileSync, readdirSync, realpathSync, rmSync, symlinkSync, writeFileSync } from 'node:fs';
 import { join } from 'node:path';
 import { ALL_HOST_CONFIGS } from '../hosts/index';
 import { cleanupFixtures, makeFixture, makeSource, put, registryRows, runSetup, setVersion, tree } from './helpers/install-fixture';
@@ -45,6 +45,18 @@ function skillNames(dir: string): string[] {
   return names;
 }
 
+/** Every SKILL.md under dir that is itself a symlink; linked directories are not entered (INV-3). */
+function symlinkedSkillMds(dir: string): string[] {
+  const found: string[] = [];
+  for (const name of readdirSync(dir)) {
+    const p = join(dir, name);
+    const st = lstatSync(p);
+    if (st.isSymbolicLink()) { if (name === 'SKILL.md') found.push(p); continue; }
+    if (st.isDirectory()) found.push(...symlinkedSkillMds(p));
+  }
+  return found;
+}
+
 describe.skipIf(process.platform === 'win32')('host conformance kit', () => {
   test('the kit covers every installable host', () => {
     expect(Object.keys(DISCOVERY).sort()).toEqual([...installable].sort());
@@ -84,6 +96,12 @@ describe.skipIf(process.platform === 'win32')('host conformance kit', () => {
       const status = runSetup(f, join(src, 'setup'), ['--status']);
       expect(status.status).toBe(0);
       expect(status.stdout).toMatch(new RegExp(`\\b${host}\\s+${ALL_HOST_CONFIGS.find(c => c.name === host)!.tier}\\s+global\\s+current`));
+
+      // C3: Codex skips a symlinked SKILL.md file; directory links are fine.
+      if (host !== 'claude') {
+        expect(symlinkedSkillMds(dest), `${host}: symlinked SKILL.md files (Codex skips them)`).toEqual([]);
+        expect(status.stdout).toContain(`\n  ${host} global: router is a real file; section links: `);
+      }
     }, 60_000);
   }
 
@@ -128,6 +146,20 @@ describe.skipIf(process.platform === 'win32')('host conformance kit', () => {
     expect(status.stdout).toContain(`register it: cd ${realpathSync(src)} && ./setup --host codex`);
   }, 60_000);
 
+  test('--status names a symlinked router and a broken section link per host (C3)', () => {
+    const f = makeFixture();
+    const src = makeSource(f, join(f.dir, 'gstack'));
+    expect(runSetup(f, join(src, 'setup'), ['--host', 'codex']).status).toBe(0);
+    const router = join(f.home, '.codex/skills/gstack/SKILL.md');
+    rmSync(router);
+    symlinkSync(join(src, '.agents/skills/gstack/SKILL.md'), router);
+    const qa = join(src, '.agents/skills/gstack-qa/sections');
+    rmSync(join(qa, readdirSync(qa).find(n => n.endsWith('.md'))!));
+    const status = runSetup(f, join(src, 'setup'), ['--status']);
+    expect(status.status).toBe(0);
+    expect(status.stdout).toMatch(/codex global: router is a symlink, which Codex skips\. Fix: cd \S+ && \.\/setup --host codex; section links: [1-9]\d* of \d+ broken \(first: [^)]*\)\. Fix: cd /);
+  }, 60_000);
+
   test('upgrade from the previous release layout refreshes every installed host (#1925)', () => {
     const f = makeFixture();
     const src = makeSource(f, join(f.home, '.claude/skills/gstack'), '1.91.12.0');
@@ -135,6 +167,11 @@ describe.skipIf(process.platform === 'win32')('host conformance kit', () => {
     // v1.91.13.0 and earlier: same links, no registry, marker in ~/.gstack.
     rmSync(join(f.home, '.gstack/installs.tsv'));
     setVersion(src, '1.91.14.0');
+    // C3: a hand edit to the router copy is saved under the state root before
+    // the runtime root is replaced, and the refresh rewrites the copy.
+    const router = join(f.home, '.codex/skills/gstack/SKILL.md');
+    expect(lstatSync(router).isSymbolicLink()).toBe(false);
+    writeFileSync(router, readFileSync(router, 'utf8') + '\nmy local note\n');
 
     const oldUpgrade = runSetup(f, join(src, 'setup'), []);
     expect(oldUpgrade.status).toBe(0);
@@ -147,6 +184,13 @@ describe.skipIf(process.platform === 'win32')('host conformance kit', () => {
     expect(registryRows(f).map(r => [r[0], r[6]]).sort()).toEqual([['claude', '1.91.14.0'], ['codex', '1.91.14.0']]);
     // The refreshed Codex install runs the new checkout's render.
     expect(realpathSync(join(f.home, '.codex/skills/gstack-review/SKILL.md'))).toBe(join(realpathSync(src), '.agents/skills/gstack-review/SKILL.md'));
+    expect(readFileSync(router, 'utf8')).toBe(readFileSync(join(src, '.agents/skills/gstack/SKILL.md'), 'utf8'));
+    const saved = upgrade.stdout.match(/saved your edited (\S+) to (\S+) /);
+    expect(saved, upgrade.stdout).not.toBeNull();
+    expect(saved![1]).toBe(router);
+    expect(saved![2].startsWith(join(f.home, '.gstack/backups/skill-copies/'))).toBe(true);
+    expect(readFileSync(saved![2], 'utf8')).toEndWith('\nmy local note\n');
+    expect(upgrade.stdout).toContain(`refreshed SKILL.md copies in ${join(f.home, '.codex/skills/gstack')}: SKILL.md gstack-upgrade/SKILL.md office-hours/SKILL.md`);
   }, 90_000);
 
   test('a Codex namespace captured by a vendored project copy is reported, never repointed (#2879)', () => {
diff --git a/test/setup-codex-design-pdf-runtime.test.ts b/test/setup-codex-design-pdf-runtime.test.ts
index 86a1a4416..55ef99449 100644
--- a/test/setup-codex-design-pdf-runtime.test.ts
+++ b/test/setup-codex-design-pdf-runtime.test.ts
@@ -100,7 +100,7 @@ const BUILDERS: Record<string, (sandbox: string, src: string) => Built> = {
   },
 };
 
-const FUNCTIONS = ['_link_or_copy', '_link_runtime_dists', '_sidecar_root_user_owned', '_gstack_generated_header', 'create_agents_sidecar', 'create_codex_runtime_root']
+const FUNCTIONS = ['_link_or_copy', '_link_runtime_dists', '_copy_skill_md', '_sidecar_root_user_owned', '_gstack_generated_header', 'create_agents_sidecar', 'create_codex_runtime_root']
   .filter(name => SETUP_SRC.includes(`\n${name}() {`))
   .map(extractFunction)
   .join('\n');
diff --git a/test/setup-codex-model.test.ts b/test/setup-codex-model.test.ts
index ab2a24ccb..b7d6db21f 100644
--- a/test/setup-codex-model.test.ts
+++ b/test/setup-codex-model.test.ts
@@ -78,8 +78,8 @@ describe('setup Codex model activation', () => {
     const kiroStart = setup.indexOf('# 6. Install for Kiro CLI');
     const kiroEnd = setup.indexOf('# 6b.', kiroStart);
     const block = setup.slice(kiroStart, kiroEnd);
-    expect(block).toContain('_link_or_copy "$KIRO_DIR/gstack-upgrade/SKILL.md"');
-    expect(block).toContain('_link_or_copy "$KIRO_DIR/gstack/SKILL.md"');
+    expect(block).toContain('_copy_skill_md "$KIRO_DIR/gstack-upgrade/SKILL.md"');
+    expect(block).toContain('_copy_skill_md "$KIRO_DIR/gstack/SKILL.md"');
     expect(block).toContain('_link_or_copy "$SOURCE_GSTACK_DIR/bin" "$KIRO_GSTACK/bin"');
     expect(block).toContain('_link_or_copy "$SOURCE_GSTACK_DIR/lib" "$KIRO_GSTACK/lib"');
     expect(block).not.toContain('$AGENTS_DIR');
diff --git a/test/setup-kiro-native.test.ts b/test/setup-kiro-native.test.ts
index 229a37529..ddfd1eb57 100644
--- a/test/setup-kiro-native.test.ts
+++ b/test/setup-kiro-native.test.ts
@@ -21,6 +21,7 @@ const helpers = [
   '_claude_entry_owned_strongly', '_gstack_link_target_abs', '_gstack_target_is_ours',
   '_gstack_generated_header', '_backup_skill_md', '_prune_stale_generated',
   '_skill_source_exists', '_owned_for_windows_refresh', '_cleanup_weak_dir',
+  '_copy_skill_md', '_skill_copy_hash', '_skill_copy_unmodified', '_preserve_skill_copy_edits', '_record_skill_copies',
 ].map(fn).join('\n');
 
 describe.skipIf(process.platform === 'win32')('native Kiro setup installation', () => {
@@ -51,6 +52,7 @@ describe.skipIf(process.platform === 'win32')('native Kiro setup installation',
           'bun_cmd() { printf "%s\\n" "$*" >> "$BUN_LOG"; }',
           'INSTALL_KIRO=1', `IS_WINDOWS=${windowsCopy}`, 'BROWSE_BIN=unused',
           '_BACKED_UP_SKILL_MDS=()', '_SKILL_BACKUP_ROOT="$HOME/backups"',
+          'GSTACK_STATE_ROOT="$HOME/.gstack"', '_SKILL_COPIES_FILE="$GSTACK_STATE_ROOT/skill-copies.tsv"',
           'KIRO_SKILLS="$HOME/.kiro/skills"', block,
         ].join('\n'), {
           env: { ...process.env, HOME: home, SOURCE_GSTACK_DIR: root, BUN_LOG: log }, timeout: 30_000,
diff --git a/test/setup-skill-copies.test.ts b/test/setup-skill-copies.test.ts
new file mode 100644
index 000000000..549586267
--- /dev/null
+++ b/test/setup-skill-copies.test.ts
@@ -0,0 +1,97 @@
+import { afterEach, describe, expect, test } from 'bun:test';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import { runBashScript } from './helpers/bash-script';
+
+// C3 (#333): host runtime roots hold real SKILL.md copies. setup records each
+// copy's hash under the state root; an edited copy is saved to a uniquely
+// named backup before the tree is replaced, and a failed backup stops the
+// replacement.
+const setup = fs.readFileSync(path.resolve(import.meta.dir, '../setup'), 'utf8');
+const fn = (name: string) => {
+  const start = setup.indexOf(`\n${name}() {`);
+  const end = setup.indexOf('\n}\n', start);
+  if (start < 0 || end < 0) throw new Error(`missing setup helper: ${name}`);
+  return setup.slice(start + 1, end + 2);
+};
+const helpers = ['_copy_skill_md', '_skill_copy_hash', '_skill_copy_unmodified', '_preserve_skill_copy_edits', '_record_skill_copies', '_activate_runtime_root'].map(fn).join('\n');
+
+const tmps: string[] = [];
+afterEach(() => { for (const t of tmps.splice(0)) { fs.chmodSync(t, 0o755); fs.rmSync(t, { recursive: true, force: true }); } });
+
+function run(tmp: string, body: string) {
+  return runBashScript([
+    'set -e', 'log() { echo "$@"; }', `GSTACK_STATE_ROOT="${tmp}/state"`, '_SKILL_COPIES_FILE="$GSTACK_STATE_ROOT/skill-copies.tsv"',
+    helpers,
+    // A runtime root build: router plus one nested copy, from $SRC.
+    'build() { mkdir -p "$2/gstack-upgrade"; _copy_skill_md "$SRC/router.md" "$2/SKILL.md"; [ -f "$SRC/upgrade.md" ] && _copy_skill_md "$SRC/upgrade.md" "$2/gstack-upgrade/SKILL.md"; return 0; }',
+    `SRC="${tmp}/src"; ROOT="${tmp}/home/.codex/skills/gstack"`,
+    body,
+  ].join('\n'), { timeout: 30_000 });
+}
+
+describe.skipIf(process.platform === 'win32')('setup: real-file SKILL.md copies (C3)', () => {
+  test('copies, refreshes, saves hand edits uniquely, and reports removals', () => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-skill-copies-'));
+    tmps.push(tmp);
+    fs.mkdirSync(path.join(tmp, 'src'));
+    fs.writeFileSync(path.join(tmp, 'src/router.md'), 'router v1\n');
+    fs.writeFileSync(path.join(tmp, 'src/upgrade.md'), 'upgrade v1\n');
+    const root = path.join(tmp, 'home/.codex/skills/gstack');
+
+    let r = run(tmp, '_activate_runtime_root build "$SRC" "$ROOT"');
+    expect(r.status, r.stderr).toBe(0);
+    expect(r.stdout).toContain(`refreshed SKILL.md copies in ${root}: SKILL.md gstack-upgrade/SKILL.md`);
+    expect(fs.lstatSync(path.join(root, 'SKILL.md')).isSymbolicLink()).toBe(false);
+
+    // An unedited copy is refreshed with no backup.
+    fs.writeFileSync(path.join(tmp, 'src/router.md'), 'router v2\n');
+    r = run(tmp, '_activate_runtime_root build "$SRC" "$ROOT"');
+    expect(r.status, r.stderr).toBe(0);
+    expect(r.stdout).not.toContain('saved your edited');
+    expect(fs.readFileSync(path.join(root, 'SKILL.md'), 'utf8')).toBe('router v2\n');
+
+    // Two runs with hand edits keep two separate backups.
+    const backups: string[] = [];
+    for (const note of ['edit one', 'edit two']) {
+      fs.appendFileSync(path.join(root, 'SKILL.md'), `${note}\n`);
+      r = run(tmp, '_activate_runtime_root build "$SRC" "$ROOT"');
+      expect(r.status, r.stderr).toBe(0);
+      const m = r.stdout.match(/saved your edited (\S+) to (\S+) /);
+      expect(m, r.stdout).not.toBeNull();
+      expect(m![1]).toBe(path.join(root, 'SKILL.md'));
+      expect(m![2].startsWith(path.join(tmp, 'state/backups/skill-copies/'))).toBe(true);
+      expect(fs.readFileSync(m![2], 'utf8')).toBe(`router v2\n${note}\n`);
+      backups.push(m![2]);
+      expect(fs.readFileSync(path.join(root, 'SKILL.md'), 'utf8')).toBe('router v2\n');
+    }
+    expect(new Set(backups).size).toBe(2);
+    expect(fs.readFileSync(backups[0], 'utf8')).toBe('router v2\nedit one\n');
+
+    // A copy setup no longer writes is reported as removed.
+    fs.rmSync(path.join(tmp, 'src/upgrade.md'));
+    r = run(tmp, '_activate_runtime_root build "$SRC" "$ROOT"');
+    expect(r.stdout).toContain(`removed SKILL.md copies from ${root}: gstack-upgrade/SKILL.md`);
+  });
+
+  test('a backup that cannot be written keeps the old tree', () => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-skill-copies-'));
+    tmps.push(tmp);
+    fs.mkdirSync(path.join(tmp, 'src'));
+    fs.writeFileSync(path.join(tmp, 'src/router.md'), 'router v1\n');
+    const root = path.join(tmp, 'home/.codex/skills/gstack');
+    expect(run(tmp, '_activate_runtime_root build "$SRC" "$ROOT"').status).toBe(0);
+    fs.appendFileSync(path.join(root, 'SKILL.md'), 'mine\n');
+    fs.mkdirSync(path.join(tmp, 'state/backups'), { recursive: true });
+    fs.chmodSync(path.join(tmp, 'state/backups'), 0o555);
+    try {
+      const r = run(tmp, '_activate_runtime_root build "$SRC" "$ROOT" || echo "rc=$?"');
+      expect(r.stdout).toContain('rc=1');
+      expect(r.stderr).toContain('could not back up an edited SKILL.md copy');
+      expect(fs.readFileSync(path.join(root, 'SKILL.md'), 'utf8')).toBe('router v1\nmine\n');
+    } finally {
+      fs.chmodSync(path.join(tmp, 'state/backups'), 0o755);
+    }
+  });
+});