docs(execute_code): clarify that scripts run in their own temp dir, not session CWD (#11956)

Weaker models (Gemma-class) repeatedly rediscover and forget that execute_code's
working directory differs from terminal()/read_file()'s, leading to
os.path.exists('.env') returning False even though the file exists in the
session's CWD. They then bounce between 'the file exists' and 'the file is
missing' across tool calls.

Adds a 'Working directory' note to the execute_code schema description
pointing agents at absolute paths (os.path.expanduser) or terminal()/read_file()
for inspecting user files.

Carefully avoids the 'sandbox'/'isolated'/'cloud' language that commit
39b83f34 removed (it caused agents on local backends to refuse networking
tasks and save false sandbox beliefs to persistent memory). Purely factual
CWD guidance — no restriction implications.

tools/code_execution_tool.py

@@ -1367,6 +1367,8 @@ def build_execute_code_schema(enabled_sandbox_tools: set = None) -> dict:
         f"{tool_lines}\n\n"
         "Limits: 5-minute timeout, 50KB stdout cap, max 50 tool calls per script. "
         "terminal() is foreground-only (no background or pty).\n\n"
+        "Scripts run in their own temp dir, not the session's CWD — use absolute paths "
+        "(os.path.expanduser('~/.hermes/.env')) or terminal()/read_file() for user files.\n\n"
         "Print your final result to stdout. Use Python stdlib (json, re, math, csv, "
         "datetime, collections, etc.) for processing between tool calls.\n\n"
         "Also available (no import needed — built into hermes_tools):\n"