Request: add explicit pre-flight warnings + agent best-practices for complex visual/3D workflows

### Summary
When using agentic coding workflows for complex visual projects (Three.js/Vite, scene-heavy UIs), users need an explicit pre-flight warning and setup checklist before agents begin making scene changes.

### Problem
In ambiguous scene contexts, agents may make valid-but-wrong assumptions (placement, camera/framing, flow mapping, asset control hierarchy). This can cause large time loss and repeated rework, especially when no project-specific guardrails are initialized first.

### Requested product behavior
Please add a default **precautionary warning / best-practices notice** before major scene edits, including:

1. Confirm project intent before coordinate/placement edits.
2. Recommend enabling a dev scene inspector first (object selector, transform/material/animation, keyframe, projection, source-apply).
3. Warn that ambiguous instructions (e.g., "build a 1000m curve camera") require explicit constraints.
4. Encourage diagnostics-first steps (visibility/frustum/material/clip state) before mutation.
5. Suggest setup of explicit logging/functions for fallback behavior.
6. Warn that runtime edits should translate back to source (JS/CSS/HTML), not remain ephemeral.
7. Include a legal/operational disclaimer for potential productivity loss from ambiguous agent assumptions.

### Why this matters
Professional teams often avoid these pitfalls by preconfiguring IDE/engine/pipeline tools. Agentic workflows are different and need first-class safety rails to avoid expensive regressions in real projects.

### Suggested UX
A lightweight "Complex Visual Workflow Detected" prompt with checkboxes:
- Require coordinate-confirmation for spawn/root transform changes
- Enable diagnostics mode first
- Initialize scene inspector utilities
- Enable guarded render-loop integration for tool failures
- Enable one-click source sync for interactive edits

This would materially improve reliability and user trust for complex scene development.

Aucun fichier ni test n’est nommé dans l’issue. Commencez par transformer le prompt et la checklist proposés « Complex Visual Workflow Detected » en critères d’acceptation explicites, puis localisez la surface UX pertinente de Copilot Language Server ; le travail est considéré comme terminé lorsque l’avertissement apparaît avant les modifications majeures de la scène et couvre les mesures de protection et le disclaimer indiqués.

Rédigé par le modèle d'indexation à partir du texte de l'issue.