Tool requests carrying an explicit `timeout` kwarg (terminal_execute,
python_action, etc.) were capped at the sandbox hard timeout (default
120s) regardless of the tool-level value, producing a "Tool timed out
after 120s" error on legitimate long-running scans.
- Resolve the wait_for envelope per-request: if the tool kwarg sets a
timeout larger than the default cap, grow the envelope to
`tool_timeout + 30s` so the tool's own timer runs to completion
plus a small buffer for sandbox overhead. Otherwise keep the
sandbox default as the hard cap.
- Make the timeout error actionable — mention
STRIX_SANDBOX_EXECUTION_TIMEOUT and the per-call timeout kwarg so
users can self-discover the knob.
Closes#436
