feat(task_step): prompt_agent sets the user-sim's persona (user_system_prompt)

[kaihackney-scale]

A user-sim installed with install_agent, for example co-located on the solver's VM, had no way to get a persona. install_agent sets no system prompt, and prompt_agent sent the user agent only output_format and model. In a prod test with the solver and user on one VM, the uninstructed user just answered as a generic assistant ("I'm ready to help!").

prompt_agent now takes user_system_prompt. It's sent through the user-sim's agent-config extension the same way the solver's system_prompt is, with seed placeholders applied. The step fails before any turn if there's no deployed user-sim, or if the user-sim's agent-config doesn't accept system_prompt. A silently dropped persona would bring back the generic-assistant behaviour unnoticed. The field is keyword-only and serialized only when set, so existing tasks and positional callers are unchanged. The "Configured user-sim" log now lists the fields it set.

Validation: new unit tests cover delivery with the seed applied, the unset case, and both refusals, and I checked that the delivery test fails without the change. The full unit suite passes (7494), except the two test_mcp_cli_builder tests that fail the same way on main. On prod (task-kai-colocate-user-system-prompt, run from this branch), the solver was deployed and the user-sim installed on one VM with user_system_prompt set. The user opened in persona ("Hi! I'm Dana Ortiz, a product manager… write me a two-line poem about coffee") and ended the conversation once it had the poem. The same setup without it got "I'm ready to help!".

🤖 Generated with Claude Code

Confidence Score: 5/5

This PR appears safe to merge; no actionable issues were found.

Summary

Adds user_system_prompt so a deployed user-sim can receive a persona before the conversation starts.

• Prompt steps can give a deployed user-sim its own persona.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A["user_system_prompt set"] --> B{"Deployed user-sim selected?"}
  B -->|No| F["Fail before any turn"]
  B -->|Yes| C["Apply seed values"]
  C --> D{"Card accepts system_prompt?"}
  D -->|No| F
  D -->|Yes| E["Post user-sim configuration"]
  E --> G["Start conversation"]

Loading

_{Reviews (1) · Last reviewed commit: "feat(task_step): prompt_agent sets the u..." · Reviewed by Greptile}