manage_scriptable_object: value with JSON object ({guid}/{path}) silently clears ObjectReference instead of setting it

[Art-Zloader]

Description

When using manage_scriptable_object modify action to set an ObjectReference property, passing a JSON object (e.g. {"guid": "..."} or {"path": "..."}) via value silently clears the reference instead of setting it. The response reports success: true, ok: true with the message "Cleared reference.", giving no indication of failure.

This is a silent data loss bug — the caller believes the operation succeeded, but the reference was destroyed.

Two sub-issues

1. Silent data loss: {"value": {"guid": "..."}} and {"value": {"path": "..."}} resolve newRef to null and clear the field without any error or warning.
2. API inconsistency with manage_components: manage_components.set_property uses {"value": {"guid": "..."}} for object references. manage_scriptable_object requires {"ref": {"guid": "..."}} instead. This undocumented inconsistency makes it very easy for AI agents and users to use the wrong format.

Root Cause

In ManageScriptableObject.cs (lines 738–799), the ObjectReference handler reads the "ref" key from the patch object:

var refObj = patchObj["ref"] as JObject;        // ← reads "ref", not "value"
string refGuid = refObj?["guid"]?.ToString();
string refPath = refObj?["path"]?.ToString();

When the caller passes {"value": {"guid": "..."}}:

• patchObj["ref"] is null → refObj is null
• refGuid and refPath are both null
• Falls through to the objRefValue?.Type == JTokenType.String check (line 766)
• But objRefValue is a JObject, not a JTokenType.String → skip
• newRef stays null → reference silently cleared

Reproduction

Environment: unity-mcp v9.6.0, Unity 6000.3.10f1

Setup: EnemyData ScriptableObject with [SerializeField] private GameObject _visualPrefab field.

Step 1: Set a known good value (baseline)

{
  "action": "modify",
  "target": {"path": "Assets/ScriptableObjects/Enemies/SkeletonSoldier_Mid.asset"},
  "patches": [{"path": "_visualPrefab", "ref": {"guid": "a18ddbbe71509274e9c0c45c6285e830"}}]
}

Result: "Set reference (ref.guid)." — File shows guid: a18ddbbe... ✅

Step 2: Overwrite with value object format

{
  "action": "modify",
  "target": {"path": "Assets/ScriptableObjects/Enemies/SkeletonSoldier_Mid.asset"},
  "patches": [{"path": "_visualPrefab", "value": {"guid": "a18ddbbe71509274e9c0c45c6285e830"}}]
}

Response: success: true, ok: true, message: "Cleared reference." — File shows fileID: 0 ❌

Step 3: Same with path format

{
  "patches": [{"path": "_visualPrefab", "value": {"path": "Assets/Prefabs/Enemies/Visuals/Enemy_SkeletonSoldier.prefab"}}]
}

Response: success: true, ok: true, message: "Cleared reference." — File shows fileID: 0 ❌

Step 4: Reproduced on a different SO and field

Tested ProfessionData._projectilePrefab on Archer.asset — same result: value + JSON object silently clears the reference.

Working formats (for reference)

Format	Result
{"ref": {"guid": "xxx"}}	✅ Set reference
{"ref": {"path": "Assets/xxx.prefab"}}	✅ Set reference
{"value": "Assets/xxx.prefab"} (string)	✅ Set reference (path-shorthand)
{"value": "32-char-hex-guid"} (string)	✅ Set reference (guid-shorthand)
{"value": {"guid": "xxx"}} (object)	❌ Silently clears
{"value": {"path": "xxx"}} (object)	❌ Silently clears

Suggestions

1. When value is a JObject containing guid or path keys, treat it as an object reference (same as ref), rather than silently resolving to null.

2. At minimum, return ok: false with an error message like "value contains an object with guid/path keys — did you mean to use 'ref' instead of 'value'?" instead of silently clearing.

3. Consider unifying the API with manage_components, which uses value: {"guid": "..."} for object references. The current inconsistency between tools is a usability trap.

Related

• manage_components / manage_prefabs: Setting Sprite sub-asset references fails with path/guid — undocumented spriteName workaround required #949 — Sprite sub-asset reference documentation issue (different tool, similar category)