Add controlled coding agent automation

src/lai_automation/policy.py

@@ -0,0 +1,65 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path, PurePosixPath
+
+from .config import Settings
+from .git import ChangeSummary
+
+_ALWAYS_DENIED = (
+    ".env",
+    "vendor/",
+    "storage/",
+    "bootstrap/cache/",
+    "docker/",
+    "docker-compose",
+    ".gitea/",
+    ".github/",
+)
+
+_DIRECT_MAIN_DENIED = (
+    "database/migrations/",
+    "app/Http/Middleware/",
+    "app/Models/User.php",
+    "app/Services/PermissionService.php",
+    "app/Services/SQLValidatorService.php",
+    "config/auth.php",
+    "config/database.php",
+    "routes/",
+)
+
+
+@dataclass(frozen=True)
+class PolicyResult:
+    allowed: bool
+    errors: tuple[str, ...]
+
+
+def evaluate_changes(
+    summary: ChangeSummary,
+    settings: Settings,
+    workspace: Path | None = None,
+) -> PolicyResult:
+    errors: list[str] = []
+    if not summary.files:
+        errors.append("Agent produced no file changes")
+    if len(summary.files) > settings.max_changed_files:
+        errors.append(f"Changed {len(summary.files)} files; limit is {settings.max_changed_files}")
+    if summary.changed_lines > settings.max_changed_lines:
+        errors.append(f"Changed {summary.changed_lines} lines; limit is {settings.max_changed_lines}")
+
+    for filename in summary.files:
+        if PurePosixPath(filename).is_absolute() or ".." in PurePosixPath(filename).parts:
+            errors.append(f"Invalid changed path: {filename}")
+            continue
+        if workspace and (workspace / filename).is_symlink():
+            errors.append(f"Symbolic links are not allowed: {filename}")
+            continue
+        if any(filename == prefix or filename.startswith(prefix) for prefix in _ALWAYS_DENIED):
+            errors.append(f"Denied path changed: {filename}")
+        if settings.mode == "direct-main" and any(
+            filename == prefix or filename.startswith(prefix) for prefix in _DIRECT_MAIN_DENIED
+        ):
+            errors.append(f"Direct-main denied path changed: {filename}")
+
+    return PolicyResult(not errors, tuple(errors))