Add animation style toggle

docs/window-animations-testing.md

@@ -24,9 +24,24 @@ Relevant internal config hooks:
 
 - `SetAnimationsEnabled`
 - `SetAnimationDurationMs`
+- `SetAnimationStyle`
 - `SetAnimationCurve`
 - `SetAnimationCubicBezier`
 
+TOML example:
+
+```toml
+[animations]
+enabled = true
+duration-ms = 600
+style = "multiphase"
+curve = "ease-out"
+```
+
+Set `style = "plain"` to force ordinary one-step movement interpolation while
+keeping the configured curve. `curve = "linear"` only changes easing; it does
+not select the plain animation style.
+
 Current curve IDs in code:
 
 - `0`: linear
@@ -37,19 +52,20 @@ Current curve IDs in code:
 
 ## Enabling Multiphase Tests
 
-There is currently no separate user-facing multiphase toggle. To exercise the
-multiphase planner:
+To exercise the multiphase planner:
 
 1. Enable animations with `SetAnimationsEnabled`.
 2. Set a slow duration with `SetAnimationDurationMs`, around `400-700ms`.
-3. Use tiled layout commands that are wired through `State::with_layout_animations`.
-4. Use layouts where at least two tiled windows change geometry in the same
+3. Select `style = "multiphase"` in TOML, or call `SetAnimationStyle` with
+   `AnimationStyle::MULTIPHASE`.
+4. Use tiled layout commands that are wired through `State::with_layout_animations`.
+5. Use layouts where at least two tiled windows change geometry in the same
    container layout batch.
 
 The compositor then attempts multiphase planning automatically when the batched
 layout pass completes. If the planner proves a legal no-overlap sequence, that
 group uses phased animation. If it cannot prove one, only that motion group falls
-back to ordinary linear animation.
+back to ordinary plain animation.
 
 Good command families for multiphase testing:
 
@@ -64,7 +80,7 @@ Good command families for multiphase testing:
 
 These paths should not be used as evidence of multiphase behavior:
 
-- tile-to-float and float-to-tile, which deliberately use linear animation
+- tile-to-float and float-to-tile, which deliberately use plain animation
 - command-driven floating move/resize, which may animate but can overlap
 - pointer or tablet drag/resize, which should not animate
 - spawn-in and spawn-out, which are single-phase and use the configured curve
@@ -73,7 +89,7 @@ These paths should not be used as evidence of multiphase behavior:
 
 Useful debug signal:
 
-- `falling back to linear layout animation for group ...` means the group entered
+- `falling back to plain layout animation for group ...` means the group entered
   the multiphase gate but the planner rejected it. That is acceptable for
   unsupported patterns, but unexpected for the supported swap/extraction cases
   below.