update project docs with grid rewrite, 3d shader, preset system, and key implementation details

AGENTS.md

@@ -17,12 +17,41 @@ V Panel is a Godot Engine project that builds a fancy real-time status monitor.
 - Node names: PascalCase, descriptive (e.g., `CpuPanel`, `NetworkGraph`).
 - Signals: past tense verb (e.g., `value_changed`, `panel_resized`).
 - Scene files: PascalCase matching their main script (e.g., `CpuPanel.tscn`).
+- Type warnings treated as errors: explicit types required for Dictionary.get() returns and Variant-inferred variables (`var x: int = dict.key` not `var x := dict.key`).
+
+### Grid / DashboardGrid
+- `scripts/dashboard_grid.gd` — extends Control, class_name `DashboardGrid`. Uses `gui_input` signal for drag, resize, and double-click events.
+- Modules are direct children of the grid (not cells). Visual cells (`PanelContainer`) are shown only during drag as drop-zone guides.
+- Grid data model: each module stores `grid_col`, `grid_row`, `grid_w`, `grid_h` via `set_meta()`. A 2D `_grid[row][col]` array tracks cell occupancy (supports multi-cell spans).
+- `place_module(module, col, row, span_w=1, span_h=1)` — public API for adding modules with optional span.
+- Drag-and-drop: `_begin_drag` → `_update_drag` → `_end_drag`. Occupancy is cleared during drag and restored on drop. Swaps modules when dropping on occupied cells. Falls back to source position if dropped in grid gap or outside grid bounds (`mouse_exited` safety handler).
+- Resize: `_try_begin_resize` detects clicks within 10px of any module edge. `_update_resize_preview` shows a ghost `ColorRect` at the target span. `_end_resize` commits the new span after overlap check. All 4 edges and corners supported.
+- Double-click: opens `PopupMenu` with shader preset names from `ShaderPresets`. Selection applies all preset params to the module's `ShaderMaterial`.
+- Grid rebuild (`_rebuild_grid`) preserves module metadata (span data lives on modules). Cells are torn down and rebuilt on column/row changes. Orphaned popups cleaned up during rebuild.
 
 ### Shaders
-- `vial_fill.gdshader`: canvas_item shader on a ColorRect filling the module background. Uses rounded-rect SDF (`rr_sdf`), sum-of-sines water surface with edge damping, and layered effects (wave distortion, ripple rings, swirl, HSV shift, top-down lighting, sparkle, foam line).
+- `shaders/vial_fill.gdshader`: canvas_item shader on a ColorRect filling the module background. Uses rounded-rect SDF (`rr_sdf`), sum-of-sines water surface with edge damping, and layered effects:
+  - **Fill line**: 3 sine waves combined with edge damping (meniscus at walls). `wave_amp` and `wave_freq` uniforms control amplitude and base frequency.
+  - **Wave distortion**: UV displacement driven by noise texture + sin.
+  - **Ripple rings**: Concentric circular ripples from module center.
+  - **Swirl**: UV rotation around center with distance falloff.
+  - **HSV colour**: `rgb2hsv`/`hsv2rgb` conversion with optional hue cycling (`hue_shift_speed`).
+  - **Top-down lighting**: Subtle brightening at the top of the liquid column.
+  - **Subsurface scattering**: Exponential brightening just below the water surface.
+  - **Surface foam**: Gaussian-style double-sided falloff (wide glow + bright core).
+  - **Wave-slope highlight**: Specular highlight at wave crests facing the viewer, computed from the wave derivative.
+  - **Pulse/Sparkle**: Subtle animated brightness variation.
+  - Border via `rr_sdf` inset.
 - Noise texture: a static 100×100 PNG (`assets/textures/noise_100.png`) loaded at runtime and passed as `noise_tex` sampler2D uniform. Used for organic distortion modulation.
 - Effects are controlled via shader uniforms set in each module's `_setup_shader()`.
 
+### Shader Presets
+- `scripts/shader_presets.gd` — class_name `ShaderPresets`, static methods only.
+- `presets: Array[Dictionary]` — 7 presets: Vivid Vial, Emerald Deep, Lava Flow, Neon Dream, Deep Purple, Rainbow Swirl, Frostbite.
+- Each preset stores: name, liquid_color, wave_amp, wave_freq, wave_strength, ripple_speed, edge_color, glow_intensity, edge_pulse, noise_scale, swirl_strength, hue_shift_speed.
+- `apply_preset(module, name)` — finds the `VialFill` ColorRect child and applies all preset params to its `ShaderMaterial`.
+- `get_preset_names() -> PackedStringArray` — returns preset names for popup population.
+
 ### Labels / Readability
 - All percentage labels get a 3px black outline (`outline_size` / `font_outline_color`) for legibility against the liquid shader background.
 - Title labels get a 2px outline.
@@ -34,7 +63,7 @@ res://
 ├── assets/          # Fonts, icons, textures, audio
 │   ├── fonts/
 │   ├── icons/
-│   └── textures/
+│   └── textures/   # noise_100.png (static noise for shader distortion)
 ├── autoload/        # Singleton/autoload scripts
 ├── panels/          # Individual status panels (modules)
 │   ├── cpu/
@@ -44,11 +73,24 @@ res://
 │   └── testing/
 ├── scenes/          # Root scenes (dashboard, etc.)
 ├── scripts/         # Shared utility scripts
+│   ├── dashboard_grid.gd   # Responsive grid with drag, resize, preset popup
+│   ├── module_base.gd      # Base class for all modules (mouse_filter IGNORE)
+│   ├── panel_base.gd       # Base class for panels
+│   └── shader_presets.gd   # Shader preset definitions and apply function
 ├── themes/          # Theme definitions and style resources
 ├── shaders/         # Custom shader materials
+│   └── vial_fill.gdshader  # Canvas-item shader with 3D water surface
 └── main.tscn        # Entry point (loads dashboard)
 ```
 
+### Key Implementation Details
+- `mouse_filter = MOUSE_FILTER_IGNORE` is set recursively on all module subtrees in `ModuleBase._ready()`, so clicks pass through to the grid.
+- Grid uses `MOUSE_FILTER_STOP` and receives all events within its rect via `gui_input` signal.
+- `_cell_at_position` clamps position to nearest cell. Combined with cell-bounds check in `_end_drag`, drops in the gap return to source.
+- `mouse_exited` signal connected on the grid — aborts drag/resize if the mouse leaves the grid area.
+- `_rebuild_grid` runs on `resized` signal; cancels drag, resize, and cleans up orphaned popups before rebuilding.
+- Shader `corner_radius` is in UV space (0–0.5) where 0.05 ≈ 12px on a 240px‑tall cell.
+
 ### Git Workflow
 - Main branch: `main`
 - Feature branches: `feature/<short-description>`