docs: add NestProgressForm redesign spec

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-03-15-nest-progress-redesign.md

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+# NestProgressForm Redesign
+
+## Problem
+
+The current `NestProgressForm` is a flat list of label/value pairs with no visual hierarchy, no progress indicator, and default WinForms styling. It's functional but looks basic and gives no sense of where the engine is in its process.
+
+## Solution
+
+Redesign the form with three changes:
+1. A custom-drawn **phase stepper** control showing which nesting phase is active
+2. **Grouped sections** separating results from status information
+3. **Modern styling** — Segoe UI fonts, subtle background contrast, better spacing
+
+## Phase Stepper Control
+
+**New file: `OpenNest/Controls/PhaseStepperControl.cs`**
+
+A custom `UserControl` that draws 4 connected circles with labels beneath:
+
+```
+  ●━━━━━━━●━━━━━━━○━━━━━━━○
+Linear   BestFit   Pairs   Remainder
+```
+
+### Visual States
+
+- **Completed:** Filled circle with accent color, bold label
+- **Active:** Filled circle with accent color and slightly larger radius, bold label
+- **Pending:** Hollow circle with border only, dimmed label text
+- **All complete:** All 4 circles filled (used when `ShowCompleted()` is called)
+
+### Implementation
+
+- Single `OnPaint` override. Circles evenly spaced across control width. Connecting lines drawn between circle centers — completed segments use accent color, pending segments use a light gray.
+- Colors defined as `static readonly Color` fields at the top of the class for easy tweaking.
+- Exposes a `CurrentPhase` property (type `NestPhase?`). Setting it calls `Invalidate()`. A `null` value means no phase is active yet. An additional `bool IsComplete` property marks all phases as done.
+- `DoubleBuffered = true` to prevent flicker on repaint.
+- Fixed height (~60px), docks to fill width.
+
+## Form Layout
+
+Three vertical zones using `DockStyle.Top` stacking:
+
+```
+┌─────────────────────────────────────┐
+│  ●━━━━━━━●━━━━━━━○━━━━━━━○          │  Phase stepper
+│ Linear  BestFit  Pairs  Remainder   │
+├─────────────────────────────────────┤
+│  Results                            │  Results group
+│  Parts:    156                      │
+│  Density:  68.3%                    │
+│  Nested:   24.1 x 36.0 (867.6 sq in)│
+│  Unused:   43.2 sq in              │
+├─────────────────────────────────────┤
+│  Status                            │  Status group
+│  Plate:    2                        │
+│  Elapsed:  1:24                     │
+│  Detail:   Trying 45° rotation...   │
+├─────────────────────────────────────┤
+│                           [ Stop ]  │  Button bar
+└─────────────────────────────────────┘
+```
+
+### Group Panels
+
+Each group is a `Panel` containing:
+- A header label (Segoe UI 9pt bold) at the top
+- A `TableLayoutPanel` with label/value rows beneath
+
+Group panels use `Color.White` (or very light gray) `BackColor` against the form's `SystemColors.Control` background to create visual separation without borders. Small padding/margins between groups.
+
+### Typography
+
+- All fonts: Segoe UI (replaces MS Sans Serif)
+- Group headers: 9pt bold
+- Row labels: 8.25pt bold
+- Row values: 8.25pt regular
+- Value labels use `ForeColor = SystemColors.ControlText`
+
+### Sizing
+
+- Width: ~450px (slightly wider than current 425px for breathing room)
+- Height: auto-sizes to content via `AutoSize = true` on the table panels
+- `FormBorderStyle.FixedToolWindow`, `StartPosition.CenterParent`, `ShowInTaskbar = false`
+
+### Plate Row Visibility
+
+The Plate row in the Status group is hidden when `showPlateRow: false` is passed to the constructor (same as current behavior).
+
+## Public API
+
+No signature changes. The form remains a drop-in replacement.
+
+### Constructor
+
+`NestProgressForm(CancellationTokenSource cts, bool showPlateRow = true)` — unchanged.
+
+### UpdateProgress(NestProgress progress)
+
+Same as today, plus sets `phaseStepperControl.CurrentPhase = progress.Phase` to advance the stepper visual.
+
+### ShowCompleted()
+
+Same as today (stops timer, changes button to "Close"), plus sets `phaseStepperControl.IsComplete = true` to fill all circles.
+
+## No External Changes
+
+- `NestProgress` and `NestPhase` are unchanged.
+- All callers (`MainForm`, `PlateView.FillWithProgress`) continue calling `UpdateProgress` and `ShowCompleted` with no code changes.
+- The form file paths remain the same — this is a modification, not a new form.
+
+## Files Touched
+
+| File | Change |
+|------|--------|
+| `OpenNest/Controls/PhaseStepperControl.cs` | New — custom-drawn phase stepper control |
+| `OpenNest/Forms/NestProgressForm.cs` | Rewritten — grouped layout, stepper integration |
+| `OpenNest/Forms/NestProgressForm.Designer.cs` | Rewritten — new control layout |