Make WP Codebox a thin Homeboy execution target

Related: Extra-Chill/homeboy#8282, Extra-Chill/homeboy#7530, Extra-Chill/homeboy-extensions#2154

## Problem

WP Codebox GitHub agent-task execution and Homeboy Extensions both own task translation, workspace snapshotting, patch application, verification, publication, result projection, and terminal status. This creates two orchestration authorities and extensive path/artifact compatibility handling.

## Desired outcome

Extend the existing Homeboy runner workload/execution envelope and WP Codebox runtime contracts so Codebox owns WordPress sandbox materialization, execution, and native artifact emission only. Homeboy owns lifecycle, retries, application, verification policy, promotion, publication, and final projection. Extensions becomes a thin provider selector/adapter.

## Acceptance criteria

- One typed request enters Codebox and one canonical typed result returns.
- Codebox emits typed artifacts and workspace delta without filename inference or host-path leakage.
- Homeboy applies, verifies, promotes, and publishes exactly once.
- GitHub workflow-side apply/publication/result projection is removed after migration.
- End-to-end tests cover success, no-op, malformed artifacts, verification failure, retry, and expired source materialization.

## AI assistance
- **AI assistance:** Yes
- **Tool(s):** OpenCode with openai/gpt-5.6-sol
- **Used for:** Traced the WP Codebox and Homeboy Extensions agent-task execution paths and drafted the ownership consolidation.

Inizia tracciando i percorsi di esecuzione degli agent-task di WP Codebox e Homeboy Extensions citati negli issue correlati, quindi esamina l’envelope esistente di workload/esecuzione di Homeboy runner e i contratti di runtime di WP Codebox. Il lavoro è completato quando sono presenti una richiesta e un risultato tipizzati, artefatti tipizzati senza fuoriuscita di percorsi dell’host, una gestione centralizzata del ciclo di vita e una copertura end-to-end per successo, no-op, artefatti malformati, fallimento della verifica, retry e materializzazione scaduta del materiale sorgente.

Scritto dal modello di indicizzazione a partire dal testo della issue.