Phase 1: consolidate tool output constants into src/constants.py (#2989)

MAX_OUTPUT_CHARS, MAX_READ_CHARS, and MAX_DIFF_LINES are now
defined once in src/constants.py and imported by the three files
that previously duplicated them (tool_execution.py,
tool_implementations.py, agent_tools.py). agent_tools.py re-exports
them for backward compatibility.

Co-authored-by: mcnoliveira <mcnoliveira@gmail.com>

src/tool_execution.py

@@ -19,6 +19,7 @@ import time
 from typing import Any, Awaitable, Callable, Dict, Optional, Tuple
 
 from src.tool_security import is_public_blocked_tool, owner_is_admin_or_single_user
+from src.constants import MAX_OUTPUT_CHARS, MAX_READ_CHARS, MAX_DIFF_LINES
 
 # Persistent working directory for agent subprocesses.
 # Resolves to <repo_root>/data, which is the bind-mounted volume in Docker
@@ -27,10 +28,6 @@ from src.tool_security import is_public_blocked_tool, owner_is_admin_or_single_u
 # in ephemeral container layers that are lost on the next rebuild.
 _AGENT_WORKDIR = str(pathlib.Path(__file__).parent.parent / "data")
 
-MAX_OUTPUT_CHARS = 10_000
-MAX_READ_CHARS = 20_000
-MAX_DIFF_LINES = 400  # cap unified-diff size returned to the UI
-
 
 def _unified_diff(old: str, new: str, path: str) -> Optional[Dict[str, Any]]:
     """Build a unified diff of a file write for display in the chat.