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/constants.py

@@ -19,6 +19,12 @@ UPLOAD_DIR = os.path.join(DATA_DIR, "uploads")
 FEATURES_FILE = os.path.join(DATA_DIR, "features.json")
 SETTINGS_FILE = os.path.join(DATA_DIR, "settings.json")
 
+# Agent tool output limits (single source of truth — imported by tool_execution.py,
+# tool_implementations.py, agent_tools.py, and any other module that needs them)
+MAX_OUTPUT_CHARS = 10_000       # cap for bash/python/web_search/web_fetch output
+MAX_READ_CHARS = 20_000         # cap for read_file / document preview
+MAX_DIFF_LINES = 400            # cap for edit_file unified-diff display
+
 # API Configuration
 MAX_CONTEXT_MESSAGES = 90
 REQUEST_TIMEOUT = 20
@@ -28,7 +34,7 @@ OPENAI_COMPAT_PATH = "/v1/chat/completions"
 DEFAULT_HOST = os.getenv("LLM_HOST", "localhost")
 LLM_HOSTS = [h.strip() for h in os.getenv("LLM_HOSTS", "").split(",") if h.strip()]
 OPENAI_API_KEY = os.getenv("OPENAI_API_KEY")
-SEARXNG_INSTANCE = os.getenv('SEARXNG_INSTANCE', 'http://localhost:8080')
+SEARXNG_INSTANCE = os.getenv("SEARXNG_INSTANCE", "http://localhost:8080")
 
 
 # Cleanup configuration