Fix Unity 6000.6 InstanceIDToObjectCompat NotImplementedException

[yuseres]

Summary

Fixes #1398.

On Unity 6000.6.0f1, UnityObjectIdCompat.InstanceIDToObjectCompat(int) throws NotImplementedException for every call. This breaks manage_components (set_property/add) whenever GameObjectLookup resolves a target — including search_method="by_name", since FindByTarget round-trips through an instance ID internally — and breaks the gameobject/{id} and gameobject/{id}/components resources entirely.

Root cause

Verified via reflection against a live 6000.6.0f1 Editor: both EditorUtility.InstanceIDToObject(int) and EntityId's implicit int→EntityId conversion are unimplemented stubs at runtime on 6000.6.0f1 — not merely obsolete-marked. The existing CS0619-avoidance reflection shim successfully resolves the MethodInfo, but invoking it always throws.

The only reverse-resolution path that actually works on 6000.6 is:

EditorUtility.EntityIdToObject(EntityId.FromULong(fullUlong))

...which needs the full 64-bit id. GetInstanceIDCompat (forward direction) already discards the high 32 bits by truncating to int for wire compatibility, so by the time InstanceIDToObjectCompat receives the int, there's no way to reconstruct a valid EntityId from it alone.

Fix

Cache the full 64-bit value behind the truncated int at mint time (in GetInstanceIDCompat), and use that cache to resolve in InstanceIDToObjectCompat instead of trying to rebuild the EntityId from the int. This:

• Keeps the existing int wire format and the already-documented session-scoped id contract (a static Dictionary naturally resets on domain reload, matching that scope)
• Requires no changes to the ~30 call sites across the package or to the Python-side protocol
• Only touches UnityObjectIdCompat.cs

Testing

Verified end-to-end against a live Unity 6000.6.0f1 project:

• manage_components set_property targeting a GameObject by name (previously threw TargetInvocationException → NotImplementedException) — now succeeds
• manage_components set_property targeting by a cross-call instance ID (obtained from an earlier find_gameobjects call) — now succeeds and actually writes the value
• mcpforunity://scene/gameobject/{id}/components resource read — now returns data instead of erroring
• No new console errors after the fix; clean recompile

🤖 Generated with Claude Code

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