Extract dock file and organization handlers

CHANGELOG.md

@@ -39,6 +39,7 @@ The format is based on Keep a Changelog, and this project follows semantic versi
 - **History thumbnails skip GPU readback** when the History section is hidden, and new rows append instead of rebuilding the list.
 
 ### Changed
+- **Dock services are split by responsibility** ([#22](https://github.com/saworbit/hammerforge/issues/22)): file-dialog and import/export callbacks live in `dock_file_handler.gd`, visgroup/group/cordon workflows live in `dock_visgroup_handler.gd`, and settings plus `LevelRoot` signal wiring live in `dock_connections.gd`. `dock.gd` retains thin compatibility delegates.
 - **Exported levels skip editor-only subsystem initialization** ([#21](https://github.com/saworbit/hammerforge/issues/21)): export templates keep the brush, entity, bake, paint, and file core needed to load and run levels, but do not load or construct grid, drag, snap, selection, preview, prefab-authoring, validation, spawn-authoring, displacement, bevel, undo, or other editor services. Editor builds and headless editor tests retain the complete tool graph.
 - **Atlas gutter fill uses `blit_rect` / `fill_rect`** instead of a per-texel `get_pixel` / `set_pixel` loop: 4 * GUTTER + 4 native calls per tile rather than one call per gutter texel. Measured 11x faster on a 128px tile, which matters now that each PBR slot builds its own atlas.
 - **Face paint composites are memoised** ([#39](https://github.com/saworbit/hammerforge/issues/39)): `FaceData.get_painted_albedo()` caches its result against a key covering `max_size`, layer count, each layer's texture identity/size, blend mode, opacity, and a content hash of its weight image. `rebuild_preview()` runs from 27 call sites — including once per surface-paint sample — and previously recomposited every painted face of the brush each time. Measured on Godot 4.7 at 256x256: 61.7 ms cold, 0.077 ms on a cache hit. Call `invalidate_painted_albedo()` after mutating paint layers through any path the key does not cover.

DEVELOPMENT.md

@@ -38,6 +38,9 @@ addons/hammerforge/
   dock_entity_handler.gd Objects-tab property/create/I/O handlers
   dock_manage_handler.gd Test-tab bake/play/spawn/validation handlers
   dock_paint_handler.gd  Paint-tab layer/heightmap/scatter/sculpt handlers
+  dock_visgroup_handler.gd Manage-tab visgroup/group/cordon handlers
+  dock_file_handler.gd   File-dialog and import/export handlers
+  dock_connections.gd    Settings and LevelRoot signal wiring
   shortcut_hud.gd        Context-sensitive shortcut overlay (dynamic per mode) + persistent grid size indicator with flash-on-change
   brush_instance.gd      DraftBrush node
   baker.gd               CSG -> mesh bake pipeline (per-face materials, atlas integration, snapshot-based non-blocking face bakes, convex collision shapes)

README.md

@@ -260,6 +260,7 @@ HammerForge uses a **coordinator + subsystems** pattern:
 
 ```
 plugin.gd            EditorPlugin — input routing, toolbar, viewport overlay
+  ├─ dock.gd         Four-tab UI coordinator with focused handler modules
   └─ level_root.gd   Thin coordinator — owns containers, exports, signals
        ├─ HFBrushSystem     Brush CRUD, hollow, clip, tie, move, UV justify, caching
        ├─ HFDragSystem      Two-stage draw lifecycle + preview management

ROADMAP.md

@@ -392,9 +392,9 @@ channel swizzling — the one operation with no native `Image` equivalent.
 The May 2026 simplification phase 1 landed shared utilities and migrated low-risk call sites. The following items continue that initiative but each requires a dedicated session with interactive UI/bake validation, or a profiling pass, before landing safely.
 
 ### Continued dock.gd decomposition
-The current 6,051-line file is still dominated by `_on_*` signal handlers wired to dock-internal state.
-- Split into per-tab handler files: `dock_brush_handler.gd` (done), `dock_paint_handler.gd` (done), `dock_entity_handler.gd` (done), `dock_manage_handler.gd` (Test-tab bake/play done). Target dock.gd shell at ~1,500 lines. File I/O, visgroups, and cordon still live on dock.gd.
-- Extract signal-wiring into `dock_connections.gd`.
+The current 5,475-line file is still dominated by `_on_*` signal handlers wired to dock-internal state.
+- Split into per-tab handler files: `dock_brush_handler.gd` (done), `dock_paint_handler.gd` (done), `dock_entity_handler.gd` (done), `dock_manage_handler.gd` (Test-tab bake/play done), and `dock_visgroup_handler.gd` (visgroups, grouping, and cordon done). Target dock.gd shell at ~1,500 lines.
+- File dialogs and import/export callbacks delegate to `dock_file_handler.gd`; settings and `LevelRoot` signal lifecycle delegate to `dock_connections.gd`.
 - Consolidate the entity-properties UI builder and the external-tool-settings UI builder (both schema-driven; share ~100 lines of dispatch logic).
 - Migrate `paint_tab_builder.gd` (50 call sites) and `manage_tab_builder.gd` (58 call sites) from `dock._make_*` to direct `HFUIFactory` calls. Mechanical churn — wait until shared with another tab-builder change.