v0.5.1

Fixed

• MCP tool handlers no longer return empty text content blocks. Anthropic's API rejects empty content, and LiteLLM masks the failure by substituting [System: Empty message content sanitised to satisfy protocol]. A new toolResultJSON helper marshals responses to indented JSON and substitutes an explicit success message when the output is empty, null, {}, or []. All tool handlers route through it.
• TestRunner now exits play mode before running tests. Previously a test run requested while the editor was playing never started, and the caller waited for a reply that never came, wedging the editor. If a domain reload interrupts leaving play mode, the caller receives an interrupted response instead of hanging.

MCP context size

=== MCP context size (fixed tools only) ===
tool                        bytes  ~tokens
-------------------------------------------
screenshot                    234       58
help                          205       51
set_project                   138       34
-------------------------------------------
TOTAL (3 tools)               577      144
note: dynamic core tools from Unity are registered at runtime via the 'core' flag