feat(blueprint): make User Defined Structs editable after creation

CHANGELOG.md

@@ -6,6 +6,28 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Added
+
+- **User Defined Structs are editable after creation.** `create_user_defined_struct` authors a struct once, and there was no way to change or even *read* one afterwards — adding a single field to a struct that shipping Blueprints already break had to be done by hand in the editor, and its schema could only be recovered by dumping raw T3D through `project export_asset_text`. Five actions close that: `get_struct_fields`, `add_struct_field`, `remove_struct_field`, `rename_struct_field`, `set_struct_field_type`.
+
+  No new engine surface was needed — `FStructureEditorUtils` was already included and already driving `create_user_defined_struct`; it was simply unreachable for an existing asset. Fields are targeted by display name (`Mobility`) rather than the serialized `VarName` (`Mobility_36_31089BED…`), though either resolves, and a miss lists the names that do exist. `get_struct_fields` reports types through `PinTypeToString`, the same grammar the writers parse, so its output feeds straight back into `add_struct_field`.
+
+  Three behaviours are deliberate rather than incidental. `RemoveVariable` hardcodes `bAllowToMakeEmpty = false` and returns `false` for *both* "would empty the struct" and "no such field", distinguishing them only in a log line — so `remove_struct_field` pre-checks the count and says which happened. `RenameVariable` preserves `VarGuid`, which is why a rename does not disconnect existing Break/Make pins, whereas `set_struct_field_type` does and is documented as a migration. And every engine writer opens its own `FScopedTransaction`, so these actions open none; nesting would only widen the undo scope.
+
+  `add_struct_field` takes an optional `after` to position the new member, resolving the anchor's GUID *before* mutating because `AddVariable` reallocates the description array.
+
+  Tests lock the engine contract the handlers depend on (empty-struct refusal, GUID survival across rename, append ordering, `MoveVariable(PositionBelow)`, and a type-grammar round-trip across eight types) plus the action-level validation paths.
+
+- **`project search` gains an `asset_class` filter.** Takes a bare string (`"Blueprint"`) or an array (`["Blueprint","WidgetBlueprint"]`), matches case-insensitively, de-duplicates, and is capped at 32 entries. Searching a common token in a project with a large third-party content folder previously buried the target: a real `E_` search over this project returned 16 `UserDefinedEnum` rows under 21 `Texture2D`, 10 `NiagaraEmitter` and 3 `StaticMesh` — the data needed to filter was already on every result row, but there was no way to ask for it.
+
+  The predicate is applied **inside the SQL**, not as a pass over the returned array. `LIMIT` is applied by the query, so a post-hoc filter would return fewer rows than the caller asked for — frequently zero — while matching assets sat below the cut; `limit` now counts *matching* rows. Both FTS statements already `JOIN assets`, so no extra join was needed and a graph-node text hit inside a Blueprint still survives a `Blueprint` filter. Only the placeholder count is interpolated into the SQL; every class name stays bound.
+
+  The parameter is type-checked against `EJson` rather than read through `TryGetStringField`, which coerces — a numeric `7` would otherwise arrive as the string `"7"` and become a filter for a class of that name, i.e. zero results presented as a valid search instead of a `-32602`. Whitespace-only input is likewise a caller error rather than a silent widening to unfiltered. A class no asset uses is a successful empty result.
+
+  Mirrored into `monolith_query.exe` and `monolith_offline.py`, whose search path `verify_offline_parity.py` does not gate (`SPEC_MonolithIndex` asks for these three to be kept in step by hand). `Args::options` in the C++ tool is single-valued, so both CLIs take the list comma-separated; the Python tool additionally accepts a repeated `--asset-class`.
+
+  Two automation tests: `Monolith.ProjectSearch.AssetClassFilter` locks the in-SQL behaviour with a deliberately lopsided fixture (10 noise assets, 3 wanted) that a post-hoc implementation cannot pass by luck, and covers case-insensitivity, multi-class union and unknown classes; `Monolith.ProjectSearch.AssetClassValidation` covers the `-32602` paths.
+
 ## [0.22.0] - 2026-08-01
 
 ### Internal

Skills/unreal-blueprints/unreal-blueprints.md

@@ -150,7 +150,7 @@ Also works on: Level Blueprints (map path or `$current`), Widget Blueprints.
 | `add_timeline_track` | `asset_path`, `timeline_name`, `track_name`, `track_type`? | float/vector/event/color track |
 | `set_timeline_keys` | `asset_path`, `timeline_name`, `track_name`, `keys` | `[{time, value, interp_mode?}]` |
 
-### Struct, Enum & DataTable (6)
+### Struct, Enum & DataTable (11)
 
 | Action | Key Params | Purpose |
 |--------|-----------|---------|
@@ -161,6 +161,23 @@ Also works on: Level Blueprints (map path or `$current`), Widget Blueprints.
 | `add_data_table_row` | `asset_path`, `row_name`, `values` | `{column: value}` |
 | `get_data_table_rows` | `asset_path`, `row_name`? | Read rows |
 
+**Editing an existing struct.** `create_user_defined_struct` authors a struct once;
+these change one afterwards. Target fields by their **display name** (`Mobility`),
+not the serialized `VarName` (`Mobility_36_31089BED...`), though either resolves.
+
+| Action | Key Params | Purpose |
+|--------|-----------|---------|
+| `get_struct_fields` | `asset_path` | Read the field schema in declaration order. Types come back in the same grammar the writers accept, so `get` -> `add` round-trips |
+| `add_struct_field` | `asset_path`, `name`, `type`, `default_value`?, `after`?, `skip_save`? | Append a field, optionally positioned after an existing one |
+| `remove_struct_field` | `asset_path`, `name`, `skip_save`? | Remove a field. **A struct cannot be left empty** -- removing the last one is refused |
+| `rename_struct_field` | `asset_path`, `name`, `new_name`, `skip_save`? | Rename. The GUID is preserved, so existing Break/Make pins keep their connections |
+| `set_struct_field_type` | `asset_path`, `name`, `type`, `skip_save`? | Retype a field. Pins of the old type **are disconnected** by the recompile -- a migration, not a rename |
+
+Each writer recompiles the struct, which propagates the change to every Blueprint
+that breaks it. Audit references before removing or retyping: a removed member
+takes its pins with it, and a green compile afterwards is not evidence the
+callers still do the right thing.
+
 ### Build from Spec (1)
 
 | Action | Key Params | Purpose |