feat(local-agent): ✨ Add dry-run mode and configurable max-diff-bytes parameter for safer agent execution

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/auto_commit_service/tray/local_agent.py

@@ -80,11 +80,15 @@ class LocalCommitAgent:
         cycle_seconds: int = 300,
         co_author: str = "Lilith Autocommit <noreply@atlilith.com>",
         recovery_state_path: Path | None = None,
+        dry_run: bool = False,
+        max_diff_bytes: int = 131072,
     ):
         self.acs_url = acs_url.rstrip("/")
         self.repos_paths = repos_paths
         self.cycle_seconds = cycle_seconds
         self.co_author = co_author
+        self.dry_run = dry_run
+        self.max_diff_bytes = max_diff_bytes
 
         self._client = httpx.Client(base_url=self.acs_url, timeout=30.0)
         self._running = False
@@ -263,11 +267,13 @@ class LocalCommitAgent:
         # stage denied secret paths too).
         _git(repo_path, "add", "--", *allowed)
 
-        # Get the diff of staged changes
+        # Get the diff of staged changes. Size cap comes from self.max_diff_bytes;
+        # the 6000-byte stage-time cap is a sub-cap before the prefilter-level cap.
+        stage_cap = min(6000, self.max_diff_bytes)
         raw_diff = _git(repo_path, "diff", "--cached", "--stat") + "\n" + _git(
-            repo_path, "diff", "--cached", max_bytes=6000
+            repo_path, "diff", "--cached", max_bytes=stage_cap
         )
-        diff, was_truncated = truncate_diff(raw_diff)
+        diff, was_truncated = truncate_diff(raw_diff, max_bytes=self.max_diff_bytes)
         if was_truncated:
             logger.debug(f"{_repo_display_name(repo_path)}: diff truncated for transmission")
         if not diff.strip():
@@ -299,6 +305,15 @@ class LocalCommitAgent:
             _git(repo_path, "reset", "HEAD")
             return False
 
+        # Dry-run gate — log intent, unstage, do not commit or push
+        if self.dry_run:
+            logger.info(
+                f"[DRY-RUN] {repo_name} ({branch}) would commit {len(allowed)} file(s) "
+                f"with message: {message.splitlines()[0] if message else '(empty)'}"
+            )
+            _git(repo_path, "reset", "HEAD")
+            return False
+
         # Commit
         full_message = f"{message}\n\nCo-Authored-By: {self.co_author}"
         _git(repo_path, "commit", "-m", full_message)