docs(gfx): animated-compositor design spec + Phase 1 plan + animation RE

engine-re.md: the gfx animation/effects subsystem (gfx_anim_start/0x234, 0x1fd, 0x238 non-blocking anim clock, render model — the fades are host-loop-drivable, no VM/host lockstep). Design spec: retained per-frame animated compositor, 4-phase. Phase 1 plan (TDD): retained DrawLayer model + per-frame clear/recomposite. Ghidra handlers/workers annotated (0x234/0x1fd/0x238/gfx_anim_start). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-07 19:41:13 -04:00
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+# Animated Compositor — Phase 1: Retained Compositor Implementation Plan (TDD)
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax.
+
+**Goal:** Replace the immediate-mode permanent canvas with a **retained-object compositor** — `draw-texture` records/updates a persistent layer keyed by its object handle; the Godot host clears + re-composites all active layers each frame; `0x1f7` erase removes them. This is the foundation for alpha (Phase 2) and time-animation (Phase 3).
+
+**Architecture:** The retained layer set lives in **`GfxState`** (VM-owned, version-neutral, thread-safe): the VM's `draw-texture` updates it (additive — engine parity preserved), `EraseRange` removes from it. The Godot host stops immediate-blitting; `Main._Process` snapshots the layers each frame and composites them (in execution order = current correct paint order) using the host's slot→image map. Design: `docs/superpowers/specs/2026-07-07-animated-compositor-design.md`.
+
+**Tech Stack:** C# / .NET 8 (`engine/`, xUnit); Godot 4.7 .NET (`godot/`).
+
+## Global Constraints
+
+- **Composite order = execution order, handle-keyed update-in-place** (matches the current, correct immediate-mode render — the guardrail is "booted SC0000 CGs must not regress"). Erase removes by handle. This ordering policy is the Phase-1 design choice; validate by screenshot no-regression.
+- **Engine parity:** `draw-texture` gains a `GfxState` update but stays one step / `pc+1`; non-Godot hosts are unaffected (they read nothing new). `dotnet test engine/AgeEngine.sln` must stay green; Godot `--selftest` (synthetic, no gfx) must stay green.
+- **Thread-safety:** `GfxState` layers are mutated on the VM thread and read on the Godot main thread → all layer access is `lock`-guarded; the host reads via an immutable `SnapshotLayers()`.
+- **No auto-screenshot:** per the user, do NOT screenshot-and-quit for validation; the user drives the live window. Provide the numeric `Age.Cli gfx` oracle for headless checks.
+- **Seam:** `GfxState` is `Age.Engine/Model`; the VM references `Model`. `DrawLayer` lives with `GfxState`.
+
+## File structure
+
+| File | Responsibility | Task |
+|---|---|---|
+| `engine/Age.Engine/Model/GfxState.cs` | `DrawLayer` + retained layer list (add/update, remove, snapshot; lock-guarded); `EraseRange` also drops layers | 1.1 |
+| `engine/Age.Engine.Tests/GfxStateTests.cs` | Layer add/update-in-place/order/erase unit tests | 1.1 |
+| `engine/Age.Engine/Vm/VirtualMachine.cs` | `draw-texture` records a `DrawLayer` in `GfxState` | 1.2 |
+| `engine/Age.Engine.Tests/GfxCommandBufferTests.cs` | Synthetic scene: draws → layer list; erase → removed | 1.2 |
+| `engine/Age.Cli/Program.cs` (`gfx` cmd) | Dump the retained layer list (headless oracle) | 1.3 |
+| `godot/GodotAdvHost.cs` | `DrawTexture` no longer blits (retained loop composites); keep slot→BMP map | 1.4 |
+| `godot/Main.cs` | `_Process` snapshots `GfxState` layers → clear + composite each frame | 1.4 |
+
+---
+
+### Task 1.1 — `DrawLayer` + retained layer list in `GfxState` (pure data)
+
+**Files:** Modify `engine/Age.Engine/Model/GfxState.cs`; Test `engine/Age.Engine.Tests/GfxStateTests.cs`.
+
+**Interfaces produced:** `readonly record struct DrawLayer(long Handle, int Slot, int SrcX, int SrcY, int W, int H, int DstX, int DstY)`; on `GfxState`: `void AddOrUpdateLayer(DrawLayer l)` (update-in-place by `Handle`, else append — preserving order), `void RemoveLayers(long handle)`, `IReadOnlyList<DrawLayer> SnapshotLayers()`. `EraseRange` also calls `RemoveLayers` per erased handle.
+
+- [ ] **Step 1: Write the failing tests**
+```csharp
+    [Fact]
+    public void LayersAppendInOrderAndUpdateInPlace()
+    {
+        var g = new GfxState();
+        g.AddOrUpdateLayer(new DrawLayer(0xA, 4, 0, 0, 800, 600, 0, 0));
+        g.AddOrUpdateLayer(new DrawLayer(0xB, 5, 0, 0, 200, 200, 100, 100));
+        g.AddOrUpdateLayer(new DrawLayer(0xA, 4, 0, 0, 800, 600, 0, 50));   // re-draw A -> update in place
+        var s = g.SnapshotLayers();
+        Assert.Equal(2, s.Count);
+        Assert.Equal(0xA, s[0].Handle);           // order preserved (A still first)
+        Assert.Equal(50, s[0].DstY);              // updated
+        Assert.Equal(0xB, s[1].Handle);
+    }
+
+    [Fact]
+    public void EraseRangeAlsoDropsLayers()
+    {
+        var g = new GfxState();
+        g.AddOrUpdateLayer(new DrawLayer(0x10, 4, 0, 0, 10, 10, 0, 0));
+        g.AddOrUpdateLayer(new DrawLayer(0x20, 5, 0, 0, 10, 10, 0, 0));
+        g.EraseRange(0x10, 1);
+        var s = g.SnapshotLayers();
+        Assert.Single(s);
+        Assert.Equal(0x20, s[0].Handle);
+    }
+```
+
+- [ ] **Step 2: Run to verify failure**
+
+Run: `dotnet test engine/AgeEngine.sln --filter FullyQualifiedName~GfxStateTests`
+Expected: FAIL — `DrawLayer`/`AddOrUpdateLayer` don't exist (compile error).
+
+- [ ] **Step 3: Implement**
+
+In `engine/Age.Engine/Model/GfxState.cs`, add the record (top of namespace) and the layer members:
+```csharp
+public readonly record struct DrawLayer(long Handle, int Slot, int SrcX, int SrcY, int W, int H, int DstX, int DstY);
+```
+Inside `GfxState`:
+```csharp
+    private readonly List<DrawLayer> _layers = new();
+    private readonly object _lock = new();
+
+    public void AddOrUpdateLayer(DrawLayer l)
+    {
+        lock (_lock)
+        {
+            for (int i = 0; i < _layers.Count; i++)
+                if (_layers[i].Handle == l.Handle) { _layers[i] = l; return; }
+            _layers.Add(l);
+        }
+    }
+
+    public void RemoveLayers(long handle)
+    {
+        lock (_lock) { _layers.RemoveAll(l => l.Handle == handle); }
+    }
+
+    public IReadOnlyList<DrawLayer> SnapshotLayers()
+    {
+        lock (_lock) { return _layers.ToArray(); }
+    }
+```
+Extend `EraseRange` to also drop layers — change its body to:
+```csharp
+    public void EraseRange(long handle, long count)
+    {
+        if (count > 1) for (long i = handle; i < handle + count; i++) { Release(i); RemoveLayers(i); }
+        else { Release(handle); RemoveLayers(handle); }
+    }
+```
+
+- [ ] **Step 4: Run to verify pass**
+
+Run: `dotnet test engine/AgeEngine.sln --filter FullyQualifiedName~GfxStateTests`
+Expected: PASS (all facts, including the pre-existing ones).
+
+- [ ] **Step 5: Commit**
+```bash
+git add engine/Age.Engine/Model/GfxState.cs engine/Age.Engine.Tests/GfxStateTests.cs
+git commit -m "feat(gfx): retained DrawLayer list in GfxState (thread-safe)
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 1.2 — `draw-texture` records a retained layer
+
+**Files:** Modify `engine/Age.Engine/Vm/VirtualMachine.cs`; Test `engine/Age.Engine.Tests/GfxCommandBufferTests.cs`.
+
+**Interfaces:** Consumes `GfxState.AddOrUpdateLayer`. The `draw-texture` case builds a `DrawLayer` from `a[0]`(handle),`a[1]`(slot),`a[2..7]` and records it; it **keeps** the existing `_host.DrawTexture(...)` call (the CLI oracle logs it; the Godot host will no-op-blit in Task 1.4).
+
+- [ ] **Step 1: Write the failing test** (in `GfxCommandBufferTests.cs`)
+```csharp
+    private static (int, Operand[]) DrawTex(int handle, int slot, int w, int h, int dx, int dy)
+        => (0x1fb, new[] { G(handle), G(slot), I(0), I(0), G(w), G(h), G(dx), G(dy) });
+
+    [Fact]
+    public void DrawTextureRecordsARetainedLayer()
+    {
+        var t = T();
+        var scene = ScriptAssembler.Assemble(t, "GFX", new List<(int, Operand[])>
+        {
+            MovGI(1, 0xA), MovGI(2, 4), MovGI(3, 800), MovGI(4, 600), MovGI(5, 0), MovGI(6, 0),
+            DrawTex(1, 2, 3, 4, 5, 6), Exit(),
+        }, System.Array.Empty<string>());
+        var vm = new VirtualMachine(scene, t, new RecordingHost());
+        vm.Run();
+        var layers = vm.Gfx.SnapshotLayers();
+        Assert.Single(layers);
+        Assert.Equal(0xA, layers[0].Handle);
+        Assert.Equal((800, 600, 0, 0), (layers[0].W, layers[0].H, layers[0].DstX, layers[0].DstY));
+    }
+```
+(Note: `draw-texture` reads slot from `a[1]`, dst from `a[6]/a[7]`, w/h from `a[4]/a[5]` — mirror the existing case's operand indices exactly.)
+
+- [ ] **Step 2: Run to verify failure**
+
+Run: `dotnet test engine/AgeEngine.sln --filter FullyQualifiedName~DrawTextureRecords`
+Expected: FAIL — no layer recorded (`Empty` snapshot).
+
+- [ ] **Step 3: Implement** — in `VirtualMachine.Step`, extend the `draw-texture` case:
+```csharp
+            case "draw-texture":   // (handle, slot, srcX, srcY, w, h, dstX, dstY)
+                Gfx.AddOrUpdateLayer(new DrawLayer(Read(a[0]), (int)Read(a[1]), (int)Read(a[2]), (int)Read(a[3]),
+                                     (int)Read(a[4]), (int)Read(a[5]), (int)Read(a[6]), (int)Read(a[7])));
+                _host.DrawTexture((int)Read(a[1]), (int)Read(a[2]), (int)Read(a[3]), (int)Read(a[4]),
+                                  (int)Read(a[5]), (int)Read(a[6]), (int)Read(a[7])); return pc + 1;
+```
+
+- [ ] **Step 4: Run to verify pass + full suite (parity)**
+
+Run: `dotnet test engine/AgeEngine.sln`
+Expected: all green — `draw-texture` still one step; non-Godot hosts unaffected; new test passes.
+
+- [ ] **Step 5: Commit**
+```bash
+git add engine/Age.Engine/Vm/VirtualMachine.cs engine/Age.Engine.Tests/GfxCommandBufferTests.cs
+git commit -m "feat(gfx): draw-texture records a retained layer in GfxState
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 1.3 — CLI `gfx` oracle dumps the retained layer list
+
+**Files:** Modify `engine/Age.Cli/Program.cs` (the `gfx` command, after the run).
+
+- [ ] **Step 1: Add the layer dump** — after the existing `gfx objects` print:
+```csharp
+    var layers = vm.Gfx.SnapshotLayers();
+    Console.WriteLine($"  layers ({layers.Count}, composite order):");
+    foreach (var l in layers)
+        Console.WriteLine($"    h=0x{l.Handle:x} slot={l.Slot} src=({l.SrcX},{l.SrcY} {l.W}x{l.H}) dst=({l.DstX},{l.DstY})");
+```
+
+- [ ] **Step 2: Build + eyeball on the drift scene**
+
+Run: `dotnet run --project engine/Age.Cli -- gfx --boot SC0000.BIN`
+Expected: prints a retained layer list. Sanity: the full-screen CGs appear as layers at `(0,0) 800x600`; erased handles are absent (fewer layers than raw draw-texture calls). This is the headless proof the retained set is built correctly.
+
+- [ ] **Step 3: Commit**
+```bash
+git add engine/Age.Cli/Program.cs
+git commit -m "feat(gfx): gfx oracle dumps the retained layer list
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 1.4 — Godot: per-frame clear + recomposite from the retained layers
+
+**Files:** Modify `godot/GodotAdvHost.cs`, `godot/Main.cs`.
+
+**Interfaces:** Consumes `_vm.Gfx.SnapshotLayers()` + the host's slot→BMP map. Produces a per-frame composite in `Main._Process`.
+
+- [ ] **Step 1: Godot host — stop immediate-blitting; keep slot→BMP**
+
+In `godot/GodotAdvHost.cs`, make `DrawTexture` a no-op for compositing (the retained loop handles it) but keep the slot→BMP map current (still populated by `SetTexture`). Expose the slot→BMP map (e.g. `public string? SlotBmp(int slot)`), since `Main._Process` needs it to composite a layer's slot.
+
+- [ ] **Step 2: Main — per-frame recomposite in `_Process`**
+
+In `godot/Main.cs`, give `Main` access to the VM (`_vm` already a field) and the host. In `_Process`, each frame:
+```csharp
+    // Retained recomposite: clear, then blit each layer (execution order) from its slot's BMP.
+    var layers = _vm.Gfx.SnapshotLayers();
+    _screen.Fill(new Color(0, 0, 0, 0));                 // clear (transparent; the frame is rebuilt)
+    foreach (var l in layers)
+    {
+        var bmp = _host.SlotBmp(l.Slot);
+        if (bmp == null) continue;
+        BlitLayer(bmp, l.SrcX, l.SrcY, l.W, l.H, l.DstX, l.DstY);   // same clamp logic as the old BlitSlot
+    }
+    _screenTex.Update(_screen);
+```
+`BlitLayer` is the old `BlitSlot` body (load BMP, clamp src rect, `BlitRect`) minus the per-call `_screenTex.Update` (do one update after the loop). Cache loaded `Image`s by path to avoid re-reading every frame (a `Dictionary<string, Image>`), since `_Process` runs every frame.
+
+**Guardrail:** the booted opening CGs must render identically to before (same execution-order composite, now rebuilt each frame). If a CG flickers/disappears, the layer set or order is wrong — check the `gfx --boot` oracle layer dump against the expected draws.
+
+- [ ] **Step 3: Build**
+
+Run: `godot --headless --path godot --import && dotnet build godot/Himegari.csproj`
+Expected: builds clean.
+
+- [ ] **Step 4: Selftest parity**
+
+Run: `godot --headless --path godot -- --selftest`
+Expected: `SELFTEST OK …` (synthetic scene, no gfx layers → unaffected).
+
+- [ ] **Step 5: Live check (user-driven, NOT auto-screenshot)**
+
+Launch for the user in the background: `godot --path godot -- --boot`. Ask them to confirm: (a) the opening CGs still render correctly (no regression), and (b) the stuck bottom overlay no longer persists indefinitely across pages (it's now rebuilt per frame from the active layer set; it clears when its handle is erased or no longer drawn). *A still-opaque, non-fading glow while its handle is active is EXPECTED at Phase 1 — alpha is Phase 2, fading is Phase 3.*
+
+- [ ] **Step 6: Commit**
+```bash
+git add godot/GodotAdvHost.cs godot/Main.cs
+git commit -m "feat(gfx): retained per-frame compositor in Godot (clear + recomposite)
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+## Self-review
+
+- **Spec coverage (Phase 1):** retained layer model in `GfxState` → 1.1; `draw-texture` retained → 1.2; per-frame clear + recomposite → 1.4; headless oracle → 1.3. Alpha/animation explicitly NOT here (Phases 2/3). ✓
+- **Parity:** `draw-texture` stays one step + keeps `_host.DrawTexture`; non-Godot hosts read nothing new; engine suite + selftest re-asserted (1.2 Step 4, 1.4 Step 4). ✓
+- **Threading:** all `_layers` access lock-guarded; host reads via immutable `SnapshotLayers()`; the Image cache prevents per-frame disk reads. ✓
+- **Placeholder scan:** 1.1–1.3 have complete code; 1.4 is host glue (concrete approach + key code, validated live) — the honest boundary (no unit oracle for pixels). ✓
+- **Guardrail explicit:** "booted CGs must not regress" stated at 1.4; the Phase-1 layer-order/reset policy (execution-order, handle-keyed, erase-removes) is called out for screenshot validation. ✓
+
+**Next:** Phase 2 (alpha/blend) then Phase 3 (time-animation), per the design spec.
--- a/docs/superpowers/specs/2026-07-07-animated-compositor-design.md
+++ b/docs/superpowers/specs/2026-07-07-animated-compositor-design.md
@@ -0,0 +1,119 @@
+# Design: Retained Animated Compositor (the AE* fades / gfx effects)
+
+Status: **approved (design)** · Date: 2026-07-07
+RE source: `docs/engine-re.md` (op `0x215` + "The gfx animation/effects subsystem"). Builds on the gfx
+command-buffer work (`docs/phase-a-slice-plan.md` A2b; `docs/superpowers/specs/2026-07-07-gfx-command-buffer-design.md`).
+Touches: `engine/Age.Engine/Model/GfxState.cs`, `engine/Age.Engine/Vm/VirtualMachine.cs`,
+`engine/Age.Cli/Program.cs` (`GfxTraceHost`), `godot/{Main,GodotAdvHost}.cs`.
+
+## Problem / goal
+
+SC0000's opening event CGs now render (gfx command-buffer + system boot), but the `AE*` flash/glow effects
+draw **opaque and never clear** — a white "explosion" glow stays at the bottom of the screen. Root cause
+(RE, `engine-re.md`): those effects are a **native time-animated retained render loop** — objects carry
+animation state (progress/duration/target), op `0x238` sets a non-blocking global animation clock, and the
+engine's per-frame loop interpolates + composites. Our **immediate-mode permanent canvas** can neither
+animate (fade) nor clear (remove the overlay). **Goal:** replace it with a **retained, host-driven,
+per-frame animated compositor** so effects fade and clear correctly — completing SC0000's rendering, which
+proves the ADV effectful-op layer for all ADV scenes.
+
+## Key architectural shift: immediate → retained
+
+Today `draw-texture` (and `BlitSlot`) blit **immediately and permanently** onto one canvas. The real engine
+is **retained**: the VM configures object/layer state; a per-frame render loop clears, advances animations,
+and re-composites the active set. We adopt that:
+
+- **The VM's gfx ops update retained `GfxState`** (they already do for geometry; extend to alpha + animation
+  + a draw/layer list). They do **not** paint pixels.
+- **The host owns a per-frame render loop** (`godot/_Process`): advance time, interpolate, clear, composite.
+- **No VM/host frame-lockstep** — the VM parks at `wait-for-input` and the host animates during the park;
+  the bytecode's `configure → wait` structure gives the timing (RE-confirmed: `0x238` is non-blocking).
+
+## The model — `GfxState` extensions
+
+`GfxState` (VM-owned execution state) gains, per object, the reversed animation fields and a compositor-
+facing draw list:
+
+```
+GfxObject (additions)
+  int  Alpha            // 0..255, from 0x202/0x203 (default 255)
+  bool Animating        // native flag bit 4
+  long AnimDuration     // obj+0x228 (from gfx_anim_start / 0x234)
+  long AnimProgress     // obj+0x214 (advanced by the host clock)
+  (long X,Y,Z) AnimTarget   // obj+0x244/248/24c
+  // (existing: Slot, V18/V24/V16c, Field64/68/6c, Color)
+
+GfxState (additions)
+  long AnimClockElapsed, AnimClockDuration   // op 0x238 global clock (ctx+0x51b78/7c)
+  IReadOnlyList<DrawLayer> Layers            // retained composite list (order = paint order)
+```
+
+`DrawLayer` = a resolved draw command (slot/source-rect/dst/alpha) captured when the VM executes
+`draw-texture`/`0x202`/`0x203`, **replacing** the immediate blit. The host composites `Layers` each frame.
+
+- **Layer lifecycle:** a full-screen opaque draw resets the layer set (it covers everything, matching the
+  engine's frame); `0x1f7` erase / animation-complete removes layers; a new frame's draws append. Exact
+  reset policy is a Phase-1 decision, validated by the oracle/screenshot (see Phase 1 plan).
+- **Native workers still NOT modelled** — only the retained data the render loop needs.
+
+## Data flow (per frame, host)
+
+```
+VM thread:  gfx ops → mutate GfxState (layers, alpha, anim target/duration/clock) → park at wait-for-input
+Host _Process(delta):
+  1. advance AnimClockElapsed += delta-scaled; per-object AnimProgress += ...            (Phase 3)
+  2. interpolate each Animating object's current props toward AnimTarget by progress/dur (Phase 3)
+  3. clear screen; composite Layers in order, each blended by its Alpha                  (Phase 1–2)
+  4. present (update the TextureRect)
+```
+
+## Phasing (each a runnable, screenshot-checkable checkpoint)
+
+- **Phase 1 — Retained compositor + clear.** `draw-texture` registers a `DrawLayer` instead of blitting;
+  Godot `_Process` clears + composites the layer set each frame. No alpha/anim yet (layers opaque). Fixes
+  the *never-clears* half — stuck overlays disappear when the frame resets. **Check:** opening CGs still
+  render; the stuck bottom glow no longer persists across pages.
+- **Phase 2 — Alpha/blend.** `0x202/0x203` set per-object/layer `Alpha`; the composite blends by alpha.
+  **Check:** the glow renders translucent, not solid white.
+- **Phase 3 — Time-animation.** Host clock + per-object interpolation (`0x234`/`0x1fd`/`0x238`) advance in
+  `_Process`. **Check:** the explosion/glow **fades** over its duration.
+- **Phase 4 — Remaining effect ops + polish.** RE + fold in the render/present family
+  (`0x243/0x20c/0x21c/0x224`), green chromakey for sprites, residual effect ops. **Check:** opening correct
+  end-to-end by-eye.
+
+## Parity & testing
+
+- **Engine tests stay host-agnostic.** `GfxState` additions are pure data → unit-testable (layer list built
+  by the ops; alpha/anim fields set; clock advance is a pure function). No Godot needed.
+- **`Age.Cli gfx` oracle** dumps the resolved layer list (slot/dst/alpha) + anim state — the headless
+  numeric check that the VM builds the right retained state.
+- **Godot `--selftest`** stays green (synthetic scene, no gfx) — the compositor rewrite must not perturb it.
+- **Screenshot / by-eye** on `SC0000 --boot` is the human oracle per phase (the user drives it live — do
+  **not** auto-screenshot-and-quit).
+- **Guardrail:** the existing booted CG render (event CGs at `(0,0)`) must not regress at any phase.
+
+## Deferrals (explicit)
+
+- **SRPG rendering ops** (map/sprite `RENDERMAP`/`DRAWOBJ` family) — a separate surface SC0000 doesn't
+  exercise; out of scope.
+- **Exact easing curve** of the interpolation (linear vs the engine's curve) — start linear; refine if
+  by-eye shows it matters.
+- **The render/present family internals** (`0x243/0x20c/0x21c/0x224`) — RE in Phase 4 as needed; Phases 1–3
+  don't require them (the host loop is our present).
+
+## Risks / open questions
+
+1. **Layer-reset policy** (when does the frame clear / which layers persist): the main Phase-1 design risk.
+   Fallback: reset on each full-screen opaque draw + on `0x1f7` erase; validated by the oracle + screenshot,
+   iterate if wrong.
+2. **VM-runs-ahead** vs animation timing: mitigated by the bytecode's `setup → wait-for-input` structure
+   (the VM parks after each animation setup). If a sequence sets up an animation without a following wait,
+   the retained state still animates from its configured values — acceptable.
+3. **Time base** for the clock (`delta` seconds vs the engine's unit): calibrate the elapsed→progress scale
+   against a known-duration effect (e.g. the `9000` explosion) by-eye in Phase 3.
+
+## Success criteria (design done)
+
+- This spec approved; the retained/host-loop architecture + 4-phase split committed.
+- Phase 1 expanded into a TDD plan (`docs/superpowers/plans/2026-07-07-animated-compositor-phase1.md`).
+- RE findings recorded in `engine-re.md` (done).