refactor(terminal): remove check_interval parameter (#8001)

The check_interval parameter on terminal_tool sent periodic output
updates to the gateway chat, but these were display-only — the agent
couldn't see or act on them. This added schema bloat and introduced
a bug where notify_on_complete=True was silently dropped when
check_interval was also set (the not-check_interval guard skipped
fast-watcher registration, and the check_interval watcher dict
was missing the notify_on_complete key).

Removing check_interval entirely:
- Eliminates the notify_on_complete interaction bug
- Reduces tool schema size (one fewer parameter for the model)
- Simplifies the watcher registration path
- notify_on_complete (agent wake-on-completion) still works
- watch_patterns (output alerting) still works
- process(action='poll') covers manual status checking

Closes #7947 (root cause eliminated rather than patched).

tools/code_execution_tool.py

@@ -301,7 +301,7 @@ def _call(tool_name, args):
 # ---------------------------------------------------------------------------
 
 # Terminal parameters that must not be used from ephemeral sandbox scripts
-_TERMINAL_BLOCKED_PARAMS = {"background", "check_interval", "pty", "notify_on_complete", "watch_patterns"}
+_TERMINAL_BLOCKED_PARAMS = {"background", "pty", "notify_on_complete", "watch_patterns"}
 
 
 def _rpc_server_loop(