feat: port engine lib modules (log, sys, tpl, host)

engine/lib/tpl.py

@@ -0,0 +1,37 @@
+# engine/lib/tpl.py
+"""ctx.tpl — stdlib string.Template rendering (envsubst successor, SP2 decision #3).
+
+safe_substitute matches envsubst's forgiving behavior: known $VAR/${VAR} replaced,
+unknown left literal, and shell $(...) command-substitution survives untouched.
+Loops/conditionals live in the python action, never in the template file.
+"""
+from __future__ import annotations
+import os
+from string import Template
+from typing import Dict
+
+
+class Tpl:
+    def __init__(self, configs_dir: str, log):
+        self.configs_dir = configs_dir
+        self.log = log
+
+    def _resolve(self, path: str) -> str:
+        return path if os.path.isabs(path) else os.path.join(self.configs_dir, path)
+
+    def render(self, path: str, vars: Dict[str, str]) -> str:
+        full = self._resolve(path)
+        with open(full) as f:
+            return Template(f.read()).safe_substitute(vars)
+
+    def render_dir(self, rel_dir: str, vars: Dict[str, str]) -> Dict[str, str]:
+        """Render every file under configs/<rel_dir>. Returns {relpath: content}."""
+        base = self._resolve(rel_dir)
+        out: Dict[str, str] = {}
+        for dirpath, _dirs, files in os.walk(base):
+            for fn in sorted(files):
+                full = os.path.join(dirpath, fn)
+                rel = os.path.relpath(full, base).replace(os.sep, "/")
+                with open(full) as f:
+                    out[rel] = Template(f.read()).safe_substitute(vars)
+        return out