#790 Stage 0 epic: agentic substrate correctness (pause enforcement, signal wake, route fixes)

Fresh agentic review vs LangGraph/OpenAI SDK/Temporal found substrate-credibility bugs and hygiene items. Epic for Stage 0 of the staged agentic plan: (1) pause is advisory only, (2) signals never wake sleeping runs, (3) make test targets broken, (4) reaction_agent hardcodes model, (5) MCP run_goal cannot pick route. Gates: golden demos v2/disaster/ultimate + eval harness + new pause case.