fix: reuse cached scene definition on LSD reload instead of full re-discovery

[dalkia]

Pull Request Description

What does this PR change?

Cuts ~1.8s off every Local Scene Development (LSD) scene reload by reusing the scene definition already cached in ECS instead of re-running the full static-pointer discovery pipeline.

Problem. On every LSD reload (/reload-scene chat command or CLI websocket trigger), the client destroyed the scene definition entity and nulled StaticScenePointers.Promise, forcing a complete re-discovery: entities/active POST → deferred-loading queue wait → definition deserialization → scene entity re-creation. Measured on Genesis Plaza 2025 via LSD, this discovery round-trip costs ~1.8s of an ~4.9s reload (~6.1s with local asset bundles, where the pipeline additionally re-fetches the AB manifest twice — see follow-ups).

Why the re-fetch buys nothing. The LSD dev server derives content hashes from file paths, not content (entity id = b64 of the project path; every content entry hash = b64 of the file path). Editing code or models changes nothing in the definition — the same JSON is returned byte-for-byte. The client re-fetches the JS bundle and re-loads assets on reload anyway.

Fix. Two deletions, reusing the mechanism regular scenes already have:

• UnloadSceneSystem: stop excluding LSD from the "keep definition entity = cache in ECS itself" path (the localSceneDevelopment ctor param is now unused and removed).
• ECSReloadScene: stop nulling StaticScenePointers.Promise on LSD reload.

On reload, ResolveStaticPointersSystem recreates the facade promise from the kept entity (it queries for definition entities with no ISceneFacade/promise). Realm teardown still destroys the kept entities via RealmController.CLEAR_QUERY, same as regular scenes.

Reload timing (Genesis Plaza 2025, measured before / expected after):

Step	Before	After
Dispose + cache drain	~0.5s	~0.5s
Definition re-discovery	~1.8s	~0s
Facade creation (JS fetch + V8 + ECS world)	~1.3s	~1.3s
Total (to Running + loading concluded signal)	~4.9s	~3.1s

Known limitation. Adding or removing files changes the definition's content list and is no longer picked up by a reload — re-entering the realm (or restarting the preview) is required. Edits to existing files (code, models, scene.json metadata — the overwhelmingly common case) are unaffected: scene.json is re-fetched during facade creation, and JS/assets are re-fetched by path. A follow-up can restore added-file support with an inline entities/active refresh (~0.3s) that patches the kept definition.

Follow-ups identified while profiling (not in this PR):

• With --local-asset-bundles, the definition flow fetches the same AB manifest twice (AssetBundleManifestFallbackHelper + SceneAssetBundleDigestsLoader) at ~2.5s each — the manifest system uses NoCache, so the "deduped via the promise cache" assumption doesn't hold.
• GatherGltfAssetsSystem concludes immediately on reload (no readiness report queued → assets 0/N), so SceneLoadingConcluded fires before any GLTF is loaded, defeating the collider-protection wait in ECSReloadScene and unfreezing the character early.
• The LSD websocket reload timeout (5s) is shorter than a real reload, so ws-triggered reloads always "time out".

Test Instructions

Steps (LSD reload):

# In a scene project (e.g. Genesis-Plaza-2025):
npm run start  # CLI preview server on :8000
# Launch Explorer with local scene development pointing at the local realm,
# teleport into the scene, then trigger a reload:
#   - chat command: /reload-scene
#   - or save a source file so the CLI ws message triggers the reload

Expected result:

• Scene reloads visibly faster (definition re-discovery step gone; no entities/active POST between reloads in the CLI server logs).
• Code edits are reflected after reload; edits to existing GLB/assets are reflected after reload.
• Known limitation (expected): a newly added file is not picked up until the realm is re-entered.
• Regular (non-LSD) realm scene loading/unloading behavior is unchanged.

Automation (if applicable):

metaforge explorer test XXXX

🤖 Generated with Claude Code

[github-actions]

Build skipped — no changes detected under Explorer/.