diff --git a/changelog.d/+ruff-target-version-auto.fixed.md b/changelog.d/+ruff-target-version-auto.fixed.md
new file mode 100644
index 0000000..dccaf20
--- /dev/null
+++ b/changelog.d/+ruff-target-version-auto.fixed.md
@@ -0,0 +1,4 @@
+Generated `ruff.toml` no longer pins `target-version`
+
+Ruff now auto-derives its target from `pyproject.toml`'s `requires-python`, so edits to the
+project's supported Python versions stay in sync with ruff without re-running copier.
diff --git a/mise.lock b/mise.lock
index f3130c3..ca4eaf1 100644
--- a/mise.lock
+++ b/mise.lock
@@ -1,4 +1,4 @@
-# @generated - this file is auto-generated by `mise lock` https://mise.en.dev/dev-tools/mise-lock.html
+# @generated - this file is auto-generated by `mise lock` https://mise.jdx.dev/dev-tools/mise-lock.html
 
 [[tools.python]]
 version = "3.12.11"
diff --git a/ruff.toml b/ruff.toml
index ce9d500..1bd9ff7 100644
--- a/ruff.toml
+++ b/ruff.toml
@@ -74,6 +74,9 @@ ignore = [
 
 [lint.per-file-ignores]
 'tasks/*.py' = ['EXE003']
+# Polyglot sh/python bootstrap: the sh preamble must be the first statement, so imports
+# can't be at the top of the file.  (EXE003 already covered by the tasks/*.py glob above.)
+'tasks/mise-uv-init.py' = ['E402']
 
 
 [lint.flake8-builtins]
diff --git a/src/coppy_extensions.py b/src/coppy_extensions.py
index be33f56..d8a3748 100644
--- a/src/coppy_extensions.py
+++ b/src/coppy_extensions.py
@@ -14,12 +14,6 @@ def git_user_email() -> str:
     return subprocess.getoutput('git config user.email').strip()
 
 
-@jinja2.pass_context
-def ruff_python_version(ctx) -> str:
-    python_version = ctx.get('python_version_min') or ctx.get('python_version')
-    return 'py' + python_version.replace('.', '')
-
-
 def slugify(value, separator='-'):
     value = unicodedata.normalize('NFKD', str(value)).encode('ascii', 'ignore').decode('ascii')
     value = re.sub(r'[^\w\s-]', '', value.lower())
@@ -42,7 +36,6 @@ def __init__(self, environment):
         environment.globals['git_user_name'] = git_user_name
         environment.globals['git_user_email'] = git_user_email
         environment.globals['gh_action_badge'] = gh_action_badge
-        environment.globals['ruff_python_version'] = ruff_python_version
 
         # filters
         environment.filters['slugify'] = slugify
diff --git a/template/ruff.toml.jinja b/template/ruff.toml.jinja
index a3c07a2..4f0524f 100644
--- a/template/ruff.toml.jinja
+++ b/template/ruff.toml.jinja
@@ -1,5 +1,4 @@
 line-length = 100
-target-version = '{{ ruff_python_version() }}'
 output-format = 'concise'
 
 [format]
@@ -74,6 +73,9 @@ ignore = [
 
 [lint.per-file-ignores]
 'tasks/*.py' = ['EXE003']
+# Polyglot sh/python bootstrap: the sh preamble must be the first statement, so imports
+# can't be at the top of the file.  (EXE003 already covered by the tasks/*.py glob above.)
+'tasks/mise-uv-init.py' = ['E402']
 
 
 [lint.flake8-builtins]
diff --git a/template/tasks/mise-uv-init.py b/template/tasks/mise-uv-init.py
index 592d9f6..25d1100 100755
--- a/template/tasks/mise-uv-init.py
+++ b/template/tasks/mise-uv-init.py
@@ -1,4 +1,18 @@
-#!/usr/bin/env python3
+#!/bin/sh
+# Polyglot bootstrap (valid as both /bin/sh and python).  This runs during mise's env
+# evaluation, before any venv/tool exists, so it must use a real *system* python3 and never
+# a mise/uv shim.  `#!/usr/bin/env python3` can't be used: env resolves `python3` to mise's
+# shim, which re-enters mise and exhausts process limits (os error 11).  The sh preamble
+# below re-execs this file under the first real python3 it finds (covers Linux + macOS);
+# to python the whole preamble is just an ignored string literal.
+""":"
+for _py in /usr/bin/python3 /opt/homebrew/bin/python3 /usr/local/bin/python3; do
+    [ -x "$_py" ] && exec "$_py" "$0" "$@"
+done
+echo 'mise-uv-init: no system python3 found (checked /usr/bin, Homebrew, /usr/local)' >&2
+exit 1
+":"""
+
 """
 #MISE hide=true
 
diff --git a/tests/coppy_tests/test_template.py b/tests/coppy_tests/test_template.py
index fa3cb1e..80db846 100644
--- a/tests/coppy_tests/test_template.py
+++ b/tests/coppy_tests/test_template.py
@@ -1,5 +1,6 @@
 import datetime
 from pathlib import Path
+import subprocess
 
 import pytest
 
@@ -49,12 +50,14 @@ def test_pyproject_python_version_min(self, package: Package):
         assert config.project['requires-python'] == '>=3.12'
         assert package.read_text('.python-version').strip() == '3.13'
 
-    def test_ruff_tracks_python_version_min(self, gen_pkg: Package, package: Package):
-        assert gen_pkg.toml_config('ruff.toml')['target-version'] == 'py313'
+    def test_ruff_target_version_unset(self, gen_pkg: Package, package: Package):
+        # Omit `target-version` from ruff.toml so ruff auto-derives it from `requires-python`
+        # in pyproject.toml.  Otherwise the two pins drift whenever a user later edits
+        # `requires-python` without re-running copier.
+        assert 'target-version' not in gen_pkg.toml_config('ruff.toml')
 
         package.generate(python_version='3.13', python_version_min='3.12')
-
-        assert package.toml_config('ruff.toml')['target-version'] == 'py312'
+        assert 'target-version' not in package.toml_config('ruff.toml')
 
     def test_hatch_uv(self, gen_pkg: Package):
         hatch = gen_pkg.toml_config('hatch.toml')
@@ -145,6 +148,39 @@ def test_scripts(self, gen_pkg: Package, package: Package):
         assert snippet in package.read_text('pyproject.toml')
 
 
+class TestMiseUvInitPolyglot:
+    """`template/tasks/mise-uv-init.py` is a polyglot that must parse as both /bin/sh and Python.
+
+    Mise runs the script's sh preamble before any python3 shim exists, so the preamble must
+    re-exec under a real system python3 without sh choking on the trailing terminator.
+    """
+
+    @pytest.fixture(scope='class')
+    def script_fpath(self) -> Path:
+        return utils.pkg_dpath / 'template' / 'tasks' / 'mise-uv-init.py'
+
+    def test_python_compiles(self, script_fpath: Path):
+        compile(script_fpath.read_text(), str(script_fpath), 'exec')
+
+    def test_sh_preamble_syntax(self, script_fpath: Path):
+        # The preamble is delimited by the polyglot opener/closer.  An invalid closer (e.g. a
+        # bare `"""`) leaves an unterminated sh quote and fails `sh -n`.
+        lines = script_fpath.read_text().splitlines()
+        start = next(i for i, line in enumerate(lines) if line.startswith('""":"'))
+        end = next(
+            i for i, line in enumerate(lines[start + 1 :], start + 1) if line.startswith('":"""')
+        )
+        preamble = '\n'.join(lines[start : end + 1])
+
+        result = subprocess.run(
+            ['/bin/sh', '-n'],
+            input=preamble,
+            capture_output=True,
+            text=True,
+        )
+        assert result.returncode == 0, result.stderr
+
+
 class TestTemplateWithSandbox:
     """
     Sandbox tests take longer.  Separate them out for easier targeting of quicker tests.