perf(images): repaint one card on a favorite toggle instead of the collection

stream.updateItem tells onChange which item it patched, and the Images
page then skips the full layout pass (computed style, grid metrics and
layout over every loaded item) because no card changed size or place.

tests/js/workspace-images-state.test.js

@@ -277,12 +277,16 @@ test('updating one item replaces it immutably and later pages append after it',
     const { createImageStream, imageKey } = await source;
     const pages = [page([{...image('a'), favorite:false}, {...image('b'), favorite:true}], 3, 'next'), page([image('c')], 3)];
     const states = [];
-    const stream = createImageStream({api:{get:async () => pages.shift()}, onChange:s => states.push(s), batchSize:2});
+    const hints = [];
+    const stream = createImageStream({api:{get:async () => pages.shift()}, onChange:(s, hint) => { states.push(s); hints.push(hint); }, batchSize:2});
     await stream.reset({});
     const before = stream.state, notified = states.length;
+    // Page loads carry no hint; a patch says so, so the page can repaint one card instead of laying out the collection.
+    assert.ok(hints.every(hint => hint === undefined));
     assert.equal(stream.updateItem('0:a', {favorite:true}), true);
     const after = stream.state;
     assert.equal(states.length, notified + 1); assert.equal(states.at(-1), after);
+    assert.deepEqual(hints.at(-1), {patch:'0:a'});
     assert.notEqual(after.items, before.items); assert.ok(Object.isFrozen(after.items)); assert.ok(Object.isFrozen(after.items[0]));
     assert.equal(after.items[0].favorite, true); assert.equal(before.items[0].favorite, false);
     assert.equal(after.items[1], before.items[1]);

web/js/workspace/images-state.mjs

@@ -165,7 +165,8 @@ export function createImageStream({ api, onChange = () => {}, batchSize = 40, re
             const next = withItem(state, key, patch);
             if (disposed || next === state) return false;
             state = next;
-            onChange(state);
+            // The hint names the one patched item, so a page can repaint it without laying out the collection again.
+            onChange(state, {patch:key});
             return true;
         },
         dispose() {

web/js/workspace/images.mjs

@@ -435,9 +435,10 @@ export function mountImages(main, api, parentScope, {embedded = false, fetchPage
         // The concept's end of the collection (app.js updateImageContinuation).
         return `${next.loaded ? 'You’re all caught up' : 'No matching images'} · ${next.total.toLocaleString('en-US')} ${noun(next.total, 'image')}`;
     }
-    function renderState(next) {
+    function renderState(next, {patch} = {}) {
         const previous = state;
-        const changed = state?.items !== next.items;
+        // A patched item (a favorite) keeps every card's size and place; setFavorite repaints its card.
+        const changed = !patch && state?.items !== next.items;
         if (changed) {
             if (!next.items.length) itemIndexes.clear();
             for (let index = state?.items.length || 0; index < next.items.length; index++) itemIndexes.set(imageKey(next.items[index]), index);