fix: stop writing wordSpacing on rich-caption clips

src/core/ui/rich-caption-toolbar.ts

@@ -61,7 +61,12 @@ export class RichCaptionToolbar extends RichTextToolbar {
 	}
 
 	protected override createSpacingPanel(): SpacingPanel {
-		return new SpacingPanel({ showWordSpacing: true });
+		// No word-spacing control: RichCaptionStyle deliberately excludes wordSpacing
+		return new SpacingPanel();
+	}
+
+	protected override supportsWordSpacing(): boolean {
+		return false;
 	}
 
 	protected override createFontColorPicker(): FontColorPicker {

src/core/ui/rich-text-toolbar.ts

@@ -375,7 +375,7 @@ export class RichTextToolbar extends BaseToolbar {
 						style: {
 							...(asset.style || {}),
 							letterSpacing: state.letterSpacing,
-							wordSpacing: state.wordSpacing,
+							...(this.supportsWordSpacing() ? { wordSpacing: state.wordSpacing } : {}),
 							lineHeight: state.lineHeight
 						}
 					};
@@ -384,7 +384,11 @@ export class RichTextToolbar extends BaseToolbar {
 				} else {
 					// Discrete update (creates command)
 					this.updateClipProperty({
-						style: { letterSpacing: state.letterSpacing, wordSpacing: state.wordSpacing, lineHeight: state.lineHeight }
+						style: {
+							letterSpacing: state.letterSpacing,
+							...(this.supportsWordSpacing() ? { wordSpacing: state.wordSpacing } : {}),
+							lineHeight: state.lineHeight
+						}
 					});
 				}
 			});
@@ -404,7 +408,9 @@ export class RichTextToolbar extends BaseToolbar {
 				const finalClip = structuredClone(session.initialState);
 				if (finalClip.asset && (finalClip.asset.type === "rich-text" || finalClip.asset.type === "rich-caption") && finalClip.asset.style) {
 					finalClip.asset.style.letterSpacing = finalState.letterSpacing;
-					(finalClip.asset.style as Record<string, unknown>)["wordSpacing"] = finalState.wordSpacing;
+					if (this.supportsWordSpacing()) {
+						(finalClip.asset.style as Record<string, unknown>)["wordSpacing"] = finalState.wordSpacing;
+					}
 					finalClip.asset.style.lineHeight = finalState.lineHeight;
 				}
 
@@ -943,6 +949,14 @@ export class RichTextToolbar extends BaseToolbar {
 		return new SpacingPanel();
 	}
 
+	/**
+	 * Whether this toolbar's asset type accepts `style.wordSpacing`. Rich-caption
+	 * does not — its schema rejects the key, so it must never be written.
+	 */
+	protected supportsWordSpacing(): boolean {
+		return true;
+	}
+
 	protected createFontColorPicker(): FontColorPicker {
 		return new FontColorPicker();
 	}

tests/rich-caption-toolbar.test.ts

@@ -712,3 +712,71 @@ describe("RichCaptionToolbar", () => {
 		});
 	});
 });
+
+// ============================================================================
+// Word spacing exclusion (RichCaptionStyle rejects the key — never render or write it)
+// ============================================================================
+
+describe("RichCaptionToolbar spacing controls", () => {
+	let toolbar: InstanceType<typeof import("../src/core/ui/rich-caption-toolbar").RichCaptionToolbar>;
+	let mockEdit: ReturnType<typeof createMockEdit>;
+	let container: HTMLDivElement;
+
+	beforeEach(async () => {
+		mockEdit = createMockEdit();
+		const { RichCaptionToolbar } = await import("../src/core/ui/rich-caption-toolbar");
+		toolbar = new RichCaptionToolbar(mockEdit as never);
+		container = createTestContainer();
+		setupCaptionClip(mockEdit);
+		toolbar.mount(container);
+	});
+
+	afterEach(() => {
+		toolbar.dispose();
+		cleanupTestContainer(container);
+	});
+
+	it("does not render a word-spacing slider", () => {
+		expect(container.querySelector("[data-word-spacing-slider]")).toBeNull();
+		expect(container.querySelector("[data-letter-spacing-slider]")).not.toBeNull();
+	});
+
+	it("omits wordSpacing from spacing updates", () => {
+		const slider = container.querySelector("[data-letter-spacing-slider]") as HTMLInputElement;
+		expect(slider).not.toBeNull();
+		simulateInput(slider, 5);
+
+		expect(mockEdit.updateClip).toHaveBeenCalled();
+		const lastCall = mockEdit.updateClip.mock.calls.at(-1) as unknown[];
+		const updates = lastCall[2] as { asset: { style: Record<string, unknown> } };
+		expect(updates.asset.style["letterSpacing"]).toBe(5);
+		expect(updates.asset.style).not.toHaveProperty("wordSpacing");
+	});
+});
+
+describe("RichTextToolbar spacing controls (contrast)", () => {
+	it("includes wordSpacing in spacing updates for rich-text", async () => {
+		const mockEdit = createMockEdit();
+		const { RichTextToolbar } = await import("../src/core/ui/rich-text-toolbar");
+		const toolbar = new RichTextToolbar(mockEdit as never);
+		const container = createTestContainer();
+
+		const asset = { type: "rich-text", text: "Hello", font: { family: "Open Sans", size: 48 } };
+		const clip = { asset, start: 0, length: 5 };
+		mockEdit.getPlayerClip.mockReturnValue({ clipConfiguration: clip, getMergeFieldBinding: jest.fn(() => null) } as never);
+		mockEdit.getResolvedClip.mockReturnValue(clip as never);
+		toolbar.mount(container);
+
+		const slider = container.querySelector("[data-letter-spacing-slider]") as HTMLInputElement;
+		expect(slider).not.toBeNull();
+		simulateInput(slider, 5);
+
+		expect(mockEdit.updateClip).toHaveBeenCalled();
+		const lastCall = mockEdit.updateClip.mock.calls.at(-1) as unknown[];
+		const updates = lastCall[2] as { asset: { style: Record<string, unknown> } };
+		expect(updates.asset.style).toHaveProperty("wordSpacing");
+
+		toolbar.dispose();
+		cleanupTestContainer(container);
+	});
+});