[2.0 rc.15 – rc.19 / next] createOptimisticStore: a reorder inside an action is visible to direct reads but not to <For> when rows have no id #4344

Describe the bug

Since 2.0.0-rc.15, reordering a plain createOptimisticStore array inside an action (setter returning a new array) shows up in direct store reads but not in <For>. While the action is pending, items.map(r => r.name) already gives c,b,a, but <For> (keyed or not) keeps rendering a,b,c. This happens only when the rows have no id field. With an id on every row, both <For> modes show the new order at once.

Your Example Website or App

Inline below: a self-contained vitest + jsdom test, solid-js / @solidjs/web only.

Steps to Reproduce the Bug or Issue

repro.test.jsx:

import { render } from "@solidjs/web";
import { action, createOptimisticStore, flush, For } from "solid-js";
import { expect, it } from "vitest";

const tick = () => new Promise((r) => setTimeout(r, 0));

for (const withId of [false, true])
  for (const keyed of [true, false])
    it(`optimistic reorder inside an action reaches <For> (keyed: ${keyed}, rows have id: ${withId})`, async () => {
      const row = (n) => (withId ? { id: n, name: n } : { name: n });
      const el = document.createElement("div");
      let release;
      const server = new Promise((r) => (release = r));
      let items, reorder;
      render(() => {
        const [store, setItems] = createOptimisticStore([row("a"), row("b"), row("c")]);
        items = store;
        reorder = action(function* () {
          setItems(() => [row("c"), row("b"), row("a")]);
          yield server;
        });
        return <ul><For each={store} keyed={keyed}>{(r) => <li>{(keyed ? r : r()).name}</li>}</For></ul>;
      }, el);
      const rows = () => [...el.querySelectorAll("li")].map((li) => li.textContent).join(",");
      expect(rows()).toBe("a,b,c");
      const done = reorder();
      flush(); await tick(); flush();
      expect(items.map((r) => r.name).join(",")).toBe("c,b,a"); // store already reordered
      expect(rows()).toBe("c,b,a"); // DOM is not, when rows have no `id`
      release();
      await done;
    });

{
  "private": true,
  "type": "module",
  "dependencies": {
    "solid-js": "2.0.0-rc.19", "@solidjs/web": "2.0.0-rc.19", "@solidjs/signals": "2.0.0-rc.19",
    "@solidjs/babel-plugin": "2.0.0-rc.19", "@babel/core": "7.28.5",
    "vitest": "3.2.4", "vite": "7.1.12", "jsdom": "26.1.0"
  },
  "pnpm": { "overrides": { "solid-js": "2.0.0-rc.19", "@solidjs/web": "2.0.0-rc.19", "@solidjs/signals": "2.0.0-rc.19" } }
}

// vitest.config.mjs
import { transformAsync } from "@babel/core";
import solid from "@solidjs/babel-plugin";
const conditions = ["browser", "development"];
export default {
  plugins: [{
    name: "solid-jsx", enforce: "pre",
    async transform(code, id) {
      if (!id.endsWith(".jsx")) return null;
      const r = await transformAsync(code, { filename: id, babelrc: false, configFile: false, sourceMaps: true,
        plugins: [[solid, { generate: "dom", hydratable: false }]] });
      return { code: r.code, map: r.map };
    },
  }],
  resolve: { conditions },
  ssr: { resolve: { conditions, externalConditions: conditions }, noExternal: [/solid-js/, /@solidjs\//] },
  test: { environment: "jsdom", server: { deps: { inline: [/solid-js/, /@solidjs\//] } } },
};

Expected behavior

While the action is pending, <For> renders c,b,a, matching what the store returns when read directly. That is what rc.13 and rc.14 do, and what rc.19 does when the rows carry an id.

Actual on rc.15 – rc.19 and on next@17d4d1b, for rows without id (keyed: true and keyed: false): the DOM stays a,b,c while items.map(...) is c,b,a.

Screenshots or Videos

No response

Platform

• OS: macOS
• Runtime: Node 25.8.2, vitest 3.2.4, jsdom 26.1.0, @solidjs/babel-plugin (generate dom)
• Version: solid-js / @solidjs/web / @solidjs/signals 2.0.0-rc.19. Also reproduces on next@17d4d1b (signals built from source, which includes fix(signals): optimistic store guesses survive re-asks, answer latest() and stay per-action (#4329) #4330).

Additional context

Bisect. I built packages/signals from source between the rc.14 and rc.15 release commits (c421e199fa … ea4438b1a5), with solid-js and @solidjs/web at rc.15:

• first bad: 1c14992 fix(signals): an external source echo satisfies until after await (#3898) (#3937);
• last good signals commit: f6905dc8f7.

Usage. The createOptimisticStore reference shows exactly this return form inside an action (setTodos((t) => t.filter((x) => x.id !== id))). The stores guide says a returned array is written by index: "The callback may return a replacement value instead of mutating. For an array, Solid writes the returned entries by index and adjusts the length." The plain form takes no key option, so nothing documents that an id field is required.