feat(templates): add py: lines to command templates' scripts frontmatter (#3403)

* feat(templates): add py: lines to command templates' scripts frontmatter

Every templates/commands/*.md with a scripts: block now declares a py:
variant so --script py renders a Python invocation via the existing
interpreter-prefixing in process_template.

Fixes #3283

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: install scripts/python for the py script type

install_shared_infra mapped every non-sh script type to powershell, so
--script py rendered invocations pointing at files that were never
installed. Map py to the python variant dir and skip __pycache__
artifacts during the copy.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* test: read templates with explicit utf-8 encoding

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: keep py: lines standalone, enforce script existence in tests

Drop the plan/tasks py: lines that referenced scripts shipping in the
core port (#3280); they move to that PR. Tests now assert every py:
line points at a script the repo ships, so a dangling reference can
never merge green.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/test_command_template_py_scripts.py

@@ -0,0 +1,96 @@
+"""Command templates with a py: script line must render for --script py.
+
+Covers #3283: ``py:`` lines in the ``scripts:`` frontmatter of
+``templates/commands/*.md`` reference Python scripts that exist in the repo,
+and ``process_template`` turns them into a valid Python invocation
+(interpreter-prefixed, path rewritten to the ``.specify`` tree).
+
+``plan.md`` and ``tasks.md`` gain their ``py:`` lines together with
+``setup_plan.py``/``setup_tasks.py`` in the core-scripts port (#3280); the
+existence check below enforces that ordering.
+"""
+
+import re
+from pathlib import Path
+
+import pytest
+
+from specify_cli.integrations.base import IntegrationBase
+
+REPO_ROOT = Path(__file__).parent.parent
+TEMPLATES_DIR = REPO_ROOT / "templates" / "commands"
+
+_PY_LINE = re.compile(r"^\s*py: (scripts/python/\S+\.py)", re.MULTILINE)
+
+
+def _py_script(name: str) -> str | None:
+    match = _PY_LINE.search((TEMPLATES_DIR / name).read_text(encoding="utf-8"))
+    return match.group(1) if match else None
+
+
+PY_TEMPLATES = sorted(
+    p.name for p in TEMPLATES_DIR.glob("*.md") if _py_script(p.name)
+)
+
+
+@pytest.fixture(autouse=True)
+def _pin_interpreter(monkeypatch):
+    monkeypatch.setattr(
+        "specify_cli.integrations.base.shutil.which",
+        lambda name: "/usr/bin/python3" if name == "python3" else None,
+    )
+
+
+def test_py_templates_discovered():
+    # Guard: the glob must find the known py-scripted templates, otherwise
+    # the parametrized tests below would silently pass on an empty set.
+    assert "implement.md" in PY_TEMPLATES
+    assert "clarify.md" in PY_TEMPLATES
+
+
+@pytest.mark.parametrize("name", PY_TEMPLATES)
+def test_referenced_python_script_exists(name: str):
+    # A py: line must never point at a script the repo does not ship —
+    # rendering would produce a broken invocation at runtime.
+    script = _py_script(name)
+    assert (REPO_ROOT / script).is_file(), f"{name} references missing {script}"
+
+
+@pytest.mark.parametrize("name", PY_TEMPLATES)
+def test_template_renders_python_invocation(name: str):
+    content = (TEMPLATES_DIR / name).read_text(encoding="utf-8")
+    result = IntegrationBase.process_template(content, "agent", "py")
+    assert "{SCRIPT}" not in result
+    assert re.search(
+        r"python3 \.specify/scripts/python/\w+\.py(?: --[\w-]+)*", result
+    ), f"{name} did not render a Python invocation"
+
+
+@pytest.mark.parametrize("name", PY_TEMPLATES)
+def test_sh_rendering_unchanged(name: str):
+    # Negative: adding py: lines must not leak into sh rendering.
+    content = (TEMPLATES_DIR / name).read_text(encoding="utf-8")
+    result = IntegrationBase.process_template(content, "agent", "sh")
+    assert "{SCRIPT}" not in result
+    assert "scripts/python" not in result
+
+
+def test_install_shared_infra_copies_python_scripts(tmp_path):
+    # --script py must install scripts/python/ into .specify/scripts/python/
+    # so the rendered invocations point at files that exist.
+    from rich.console import Console
+
+    from specify_cli.shared_infra import install_shared_infra
+
+    install_shared_infra(
+        tmp_path,
+        "py",
+        version="0.0.0",
+        core_pack=None,
+        repo_root=REPO_ROOT,
+        console=Console(quiet=True),
+        force=False,
+    )
+    dest = tmp_path / ".specify" / "scripts" / "python"
+    assert (dest / "check_prerequisites.py").is_file()
+    assert not (tmp_path / ".specify" / "scripts" / "powershell").exists()