fix(mcp): offer auto only while the timeline holds one composition, keep the current format writable

Part of #1180

Author: EtienneLescot

electron/ai-edition/editor-settings-tool.test.ts

@@ -123,6 +123,31 @@ describe("setEditorSettings", () => {
 		const vertical = set(document, { aspectRatio: "9:16" });
 		expect(JSON.parse(vertical.resultJson).applied).toEqual(["aspectRatio", "formatFollowCursor"]);
 		expect(getEditorSettings(vertical.document as AxcutDocument).formatFollowCursor).toBe(true);
+		// Two shapes on the timeline: auto is not offered, as in the picker.
+		const mixed = documentSchema.parse({
+			...document,
+			assets: [
+				...document.assets,
+				{ ...document.assets[0], id: "asset_2", video: { width: 1080, height: 1920 } },
+			],
+			timeline: {
+				...document.timeline,
+				clips: [
+					...document.timeline.clips,
+					{
+						...document.timeline.clips[0],
+						id: "clip_2",
+						assetId: "asset_2",
+						timelineStartSec: 30,
+						timelineEndSec: 60,
+					},
+				],
+			},
+		});
+		expect(
+			set(set(mixed, { aspectRatio: "9:16" }).document as AxcutDocument, { aspectRatio: "auto" })
+				.ok,
+		).toBe(false);
 		// The alias takes the same shapes.
 		expect(
 			executeAgentTool(document, "setAspectRatio", JSON.stringify({ aspectRatio: "683:384" })).ok,

electron/ai-edition/editor-settings-tool.ts

@@ -329,11 +329,14 @@ export function editorSettingsSnapshot(
 	};
 }
 
-/** `"auto"`, a preset, or one of the timeline's own shapes: what the format picker offers. */
+/** What the format picker offers: auto (while the timeline holds one composition), a preset, or
+ *  one of the timeline's own shapes. The current value always passes, so a read written back
+ *  as is never fails on it. */
 function aspectRatioError(document: AxcutDocument, value: string): string | null {
 	const original = collectNativeFormats(document).map((f) => f.token);
-	const allowed = ["auto", ...ASPECT_RATIO_PRESETS, ...original];
-	return allowed.includes(value)
+	const auto = isAutoFormatAvailable(document) ? ["auto"] : [];
+	const allowed = [...auto, ...ASPECT_RATIO_PRESETS, ...original];
+	return allowed.includes(value) || value === getEditorSettings(document).aspectRatio
 		? null
 		: `aspectRatio ${JSON.stringify(value)} is not offered for this project. Use one of: ${allowed.join(", ")}.`;
 }