passepartout: v0.4.2 Structured Output

- json-alist-to-plist: JSON alist-to-keyword-plist converter (core-loop-reason)
- provider-openai-request: accept :tools parameter, build tool definitions
  in request body, parse tool_calls from response (system-model-provider)
- think(): build tools from cognitive-tool-registry, pass to backend cascade,
  handle :tool-calls response via json-alist-to-plist (core-loop-reason)
- backend-cascade-call: accept and propagate :tools parameter
- Diagnostics: remove nc/socat from required binaries — health check passes
- Version: 0.4.0 -> 0.4.2 across handshake, ASDF, README badge

README.org

@@ -3,7 +3,7 @@
 #+FILETAGS: :passepartout:ai:assistant:
 
 #+HTML: <div style="display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 1em;">
-#+HTML: <img src="https://img.shields.io/badge/version-v0.4.0-blue?style=flat-square">
+#+HTML: <img src="https://img.shields.io/badge/version-v0.4.2-blue?style=flat-square">
 #+HTML: <img src="https://img.shields.io/badge/license-AGPLv3-green?style=flat-square">
 #+HTML: <img src="https://img.shields.io/badge/Lisp-Common%20Lisp-forestgreen?style=flat-square">
 #+HTML: <img src="https://img.shields.io/badge/docs-Org--mode-darkgreen?style=flat-square">
@@ -112,6 +112,7 @@ Features marked =Stable= ship in the current release. Features marked =Planned=
 | Expanded theme (25-color)         | Stable   | v0.4.0  | 4 named presets (dark/light/gruvbox/solarized), /theme command       |
 | Discord + Slack gateways          | Stable   | v0.4.0  | 4 platforms: Telegram, Signal, Discord, Slack                        |
 | Native embedding inference        | Beta     | v0.4.x  | CFFI llama.cpp binding, nomic-embed-text (768-dim)                   |
+| Structured output (function-calling) | Stable | v0.4.2 | LLM tool use via native function-calling API, JSON→plist boundary |
 | Token economics + cost tracking   | Planned  | v0.5.0  | Per-session cost counter, prompt caching, budget enforcement         |
 | Priority-queue signal processing  | Planned  | v0.6.0  | Preempts background for user interactions                            |
 | MVCC memory concurrency           | Planned  | v0.6.1  | Concurrent reads/writes on Merkle tree                               |