diff --git a/changelog.d/gst-935-ubi-pack-subdir.md b/changelog.d/gst-935-ubi-pack-subdir.md
new file mode 100644
index 000000000..a62923bbc
--- /dev/null
+++ b/changelog.d/gst-935-ubi-pack-subdir.md
@@ -0,0 +1,8 @@
+**`gstack-ubi sync` and `pack` work on a subdirectory of a git checkout (GST-935).** Packing any folder that sat inside a checkout but was not its root died with "does not appear to be a git repository", after the VM was already up, because pack fetched the checkout's refs from the subdirectory and git only fetches from a repository's root. The gstack-evals launcher syncs `quick/laneb/runner`, so every launch from a git checkout failed at its first sync.
+
+### Fixed
+- **A subdirectory packs its own files.** Pack ships the files git lists under that folder (tracked, edited and untracked, not ignored) with no `.git`. A whole-repository `.git` would show the VM every file outside the folder as deleted. Packing a checkout's root and packing a non-git folder work as before.
+- **A subdirectory git lists no files under is refused.** When the checkout ignores the folder, pack exits with "pack: git lists no files under <dir>" instead of uploading an empty folder, which a run could otherwise pass on.
+
+### Tests
+- `test/ubicloud-runner.test.ts`: packing a subdirectory of a checkout and of a linked worktree ships its tracked, edited and untracked files without a `.git` and leaves out ignored ones, and an ignored subdirectory is refused. This test fails on 1.92.58.0.
diff --git a/scripts/ubicloud/ubi-runner.sh b/scripts/ubicloud/ubi-runner.sh
index 81468387d..fcac57beb 100755
--- a/scripts/ubicloud/ubi-runner.sh
+++ b/scripts/ubicloud/ubi-runner.sh
@@ -1442,11 +1442,31 @@ cmd_down() {
 # options at the first operand and resolves -T names after a -C, so no single
 # tar command line works on both it and GNU tar (#3680). COPYFILE_DISABLE=1
 # keeps Apple's tar from adding ._* AppleDouble entries for files with
-# extended attributes, which the VM would see as untracked files.
+# extended attributes, which the VM would see as untracked files. A
+# subdirectory of a work tree ships the same file set without a .git: git's
+# local transport fetches only from a repository's root, and the whole
+# repository's .git would show the VM every file outside the subdirectory as
+# deleted (GST-935). A subdirectory git lists no files under (one the parent
+# ignores) is refused rather than shipped empty: cmd_run keys the run on the
+# local files and skips the tree check for a subdirectory, so an empty upload
+# would pass on content that never ran.
 cmd_pack() {
   local src tmp gitdir branch head entry
   src=$(cd "${1:-.}" && pwd)
-  if git -C "$src" rev-parse --is-inside-work-tree >/dev/null 2>&1; then
+  if git -C "$src" rev-parse --is-inside-work-tree >/dev/null 2>&1 && [ -n "$(git -C "$src" rev-parse --show-prefix)" ]; then
+    [ -n "$(git -C "$src" ls-files -co --exclude-standard | head -n 1)" ] \
+      || die "pack: git lists no files under $src (ignored by its checkout, or empty); nothing to ship"
+    (
+      cd "$src"
+      export COPYFILE_DISABLE=1
+      git ls-files -z -co --exclude-standard \
+        | while IFS= read -r -d '' f; do
+            if [ -e "$f" ] || [ -L "$f" ]; then printf '%s\0' "$f"; fi
+          done \
+        | tar --null -T - -cf - \
+        | gzip -c
+    )
+  elif git -C "$src" rev-parse --is-inside-work-tree >/dev/null 2>&1; then
     head=$(git -C "$src" rev-parse --verify -q HEAD) || die "pack: $src has no commits; the VM needs a HEAD to fingerprint"
     branch=$(git -C "$src" symbolic-ref -q --short HEAD || true)
     tmp=$(mktemp -d)
@@ -1767,8 +1787,10 @@ cmd_run() {
       for n in ${passes[@]+"${passes[@]}"}; do inherited "$n"; printf 'export %s=%q\n' "$n" "$PASS_VALUE"; done; } \
       | remote "$name" 'umask 077 && cat > ~/.ubirun-env'
     cmd_sync "$name" "$src" "$dest"
-    # A subdirectory of a checkout uploads the whole .git with only its own
-    # files, so its tree is compared VM to VM (tiers) but not to this side.
+    # A subdirectory of a checkout ships without a .git, and its local tree
+    # (a scratch repository, blind to the parent's ignore rules) can count
+    # files pack leaves out, so it is compared VM to VM (tiers) but not to
+    # this side.
     if [ -z "$(git -C "$src" rev-parse --show-prefix 2>/dev/null)" ]; then
       vmt=$(vm_tree "$name" "$qdest") || vmt=unavailable
       if [ "$vmt" != "$TREE" ]; then
diff --git a/test/ubicloud-runner.test.ts b/test/ubicloud-runner.test.ts
index 66f6605bf..bd9fe4844 100644
--- a/test/ubicloud-runner.test.ts
+++ b/test/ubicloud-runner.test.ts
@@ -380,6 +380,29 @@ test('pack ships a linked worktree with a self-contained .git on the checked-out
     } finally { rmSync(d, { recursive: true, force: true }); }
   }, 60_000);
 
+  // Value: protects=sync and pack of a subdirectory of a git checkout (gstack-evals' launch.sh syncs quick/laneb/runner) ship that subdirectory's working files; fails_when=pack fetches refs from a path below the work tree's root, which git's local transport refuses, or ships the whole repository's .git so the VM sees every file outside the subdirectory as deleted; why_new=every pack test packs a work tree's root or a plain directory; seam=none
+  test('pack of a subdirectory of a checkout or a linked worktree ships its tracked, edited and untracked files without a .git', () => {
+    const d = mkdtempSync(join(tmpdir(), 'ubi-pack-subdir-'));
+    try {
+      const sh = (cmd: string, cwd: string) => { const r = Bun.spawnSync(['bash', '-c', cmd], { cwd, timeout: 30_000, env: { ...process.env, GIT_AUTHOR_NAME: 't', GIT_AUTHOR_EMAIL: 't@t', GIT_COMMITTER_NAME: 't', GIT_COMMITTER_EMAIL: 't@t' } }); expect(r.exitCode, `${cmd}\n${r.stderr.toString()}`).toBe(0); return r.stdout.toString(); };
+      sh('git init -q repo && cd repo && echo top > top && mkdir -p sub/nested && echo a > sub/a && echo b > sub/nested/b && echo g > sub/gone && echo "*.log" > sub/.gitignore && git add -A && git commit -qm one && git worktree add -q ../wt', d);
+      const tree = (dir: string) => sh('find . -type f | sort', dir).split('\n').filter(Boolean);
+      for (const checkout of ['repo', 'wt']) {
+        const sub = join(d, checkout, 'sub');
+        sh('echo edited > a && rm gone && echo n > new && echo x > x.log', sub);
+        const vm = join(d, `vm-${checkout}`);
+        sh(`mkdir ${JSON.stringify(vm)} && bash ${JSON.stringify(join(DIR, 'ubi-runner.sh'))} pack sub | tar -xzf - -C ${JSON.stringify(vm)}`, join(d, checkout));
+        expect(tree(vm)).toEqual(['./.gitignore', './a', './nested/b', './new']);
+        expect(readFileSync(join(vm, 'a'), 'utf8')).toBe('edited\n');
+      }
+      // A subdirectory the checkout ignores lists no files; pack refuses it instead of shipping an empty archive.
+      sh('echo scratch/ > .gitignore && mkdir -p scratch/job && echo s > scratch/job/f', join(d, 'repo'));
+      const ignored = Bun.spawnSync(['bash', join(DIR, 'ubi-runner.sh'), 'pack', 'scratch/job'], { cwd: join(d, 'repo'), timeout: 30_000 });
+      expect(ignored.exitCode).toBe(1);
+      expect(ignored.stderr.toString()).toContain('pack: git lists no files under');
+    } finally { rmSync(d, { recursive: true, force: true }); }
+  }, 60_000);
+
   test('pack snapshots a plain checkout without reading its live .git: remotes resolve, a detached HEAD gets a branch, and git running beside it cannot fail the tar', () => {
     const d = mkdtempSync(join(tmpdir(), 'ubi-pack-live-'));
     try {
diff --git a/ubicloud/SKILL.md b/ubicloud/SKILL.md
index 00e06d577..5bc7ab60b 100644
--- a/ubicloud/SKILL.md
+++ b/ubicloud/SKILL.md
@@ -184,8 +184,9 @@ UBI_TTL_HOURS=3 $U run --setup scripts/ubicloud/bootstrap.sh -- 'make test'
 ```
 
 `run` creates the VM (`-s SIZE`, default `standard-16`; `-l LOCATION`, default
-`eu-central-h1`), streams the checkout (tracked files, untracked files that
-are not ignored, and `.git`, so uncommitted edits are tested), runs the
+`eu-central-h1`), streams the checkout (tracked and non-ignored untracked
+files, and `.git`, so uncommitted edits are tested; a subdirectory skips
+`.git`), runs the
 bootstrap once, runs the command in a login shell with `umask 022`, copies
 `--pull REMOTE_GLOB:LOCAL_DIR` artifacts back and destroys the VM. It exits
 with the command's status. `--env K=V` passes a literal; `--pass NAME` forwards
diff --git a/ubicloud/SKILL.md.tmpl b/ubicloud/SKILL.md.tmpl
index 601d650c2..2b8aa447a 100644
--- a/ubicloud/SKILL.md.tmpl
+++ b/ubicloud/SKILL.md.tmpl
@@ -110,8 +110,9 @@ UBI_TTL_HOURS=3 $U run --setup scripts/ubicloud/bootstrap.sh -- 'make test'
 ```
 
 `run` creates the VM (`-s SIZE`, default `standard-16`; `-l LOCATION`, default
-`eu-central-h1`), streams the checkout (tracked files, untracked files that
-are not ignored, and `.git`, so uncommitted edits are tested), runs the
+`eu-central-h1`), streams the checkout (tracked and non-ignored untracked
+files, and `.git`, so uncommitted edits are tested; a subdirectory skips
+`.git`), runs the
 bootstrap once, runs the command in a login shell with `umask 022`, copies
 `--pull REMOTE_GLOB:LOCAL_DIR` artifacts back and destroys the VM. It exits
 with the command's status. `--env K=V` passes a literal; `--pass NAME` forwards