ask_user tool, prompt-JSON CLI repair loop, tool-loop research archive

- New ask_user core tool: mid-turn user question with option picking,
  refusing cleanly in autonomous mode, for background workers, and
  without a tty; system prompt points at it instead of prose questions.
- Structural loop control for prompt-JSON CLI backends (opencode,
  grok, claude, codex, gemini): shared cli_json_turn repairs a
  missing JSON envelope exactly once, then accepts prose; prompt
  contract hardened against narrate-without-calling.
- research/agentic-tool-loop-design: 74 sources plus 2 conclusions
  backing the loop-control decisions; INDEX updated to 6 subjects.

research/agentic-tool-loop-design/mattbusel-llm-agent-cpp-header.md

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+# mattbusel/llm-agent
+
+## Metadata
+
+| Field | Value |
+|---|---|
+| Institute | Molodetz Institute — Research & Retrieval Division |
+| Subject | agentic-tool-loop-design |
+| Document type | Source Citation Card |
+| Tier | 2 |
+| Source title | mattbusel/llm-agent |
+| Source URL | https://github.com/mattbusel/llm-agent |
+| Source type | repository |
+| Date researched | 2026-10-11 |
+| Researched by | tai (agent), model: Muse Spark, on behalf of retoor |
+| Research method | Search aggregator result listing (not independently opened or quoted) |
+| Confidence | Not independently verified |
+| Status | Active |
+
+## Why it's here
+
+Surfaced by the OpenAI function-calling loop search; looked relevant as a minimal single-header tool-calling loop with step-trace output.
+
+## Changelog
+
+| Date | Change |
+|---|---|
+| 2026-10-11 | Logged as consulted-but-not-analyzed. |