From da87e9b38427edb930904760fef76e319e7b3eba Mon Sep 17 00:00:00 2001
From: Gabriel Valfridsson <gabriel.valfridsson@gmail.com>
Date: Thu, 3 Sep 2026 23:25:37 +0200
Subject: [PATCH] refactor(signals): preserve supplied store types

---
 .changeset/remove-store-readonly.md           |  6 ++++
 packages/signals/src/store/store.ts           |  4 +--
 .../signals/tests/store/createStore.test.ts   |  1 -
 .../signals/tests/store/store.type-tests.ts   | 36 +++++++++++++++++--
 4 files changed, 42 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/remove-store-readonly.md

diff --git a/.changeset/remove-store-readonly.md b/.changeset/remove-store-readonly.md
new file mode 100644
index 000000000..1d40f278e
--- /dev/null
+++ b/.changeset/remove-store-readonly.md
@@ -0,0 +1,6 @@
+---
+"@solidjs/signals": patch
+"solid-js": patch
+---
+
+Preserve the supplied type in `Store<T>` instead of adding a shallow readonly mapping.
diff --git a/packages/signals/src/store/store.ts b/packages/signals/src/store/store.ts
index 2451f60e4..14ed794bd 100644
--- a/packages/signals/src/store/store.ts
+++ b/packages/signals/src/store/store.ts
@@ -4,8 +4,8 @@ import type { Refreshable } from "../core/index.js";
 import { GlobalQueue } from "../core/scheduler.js";
 import { storeNextLookup } from "./next/target.js";
 
-/** A read-only view of a store's value as seen by consumers. Mutate it via the paired `StoreSetter`. */
-export type Store<T> = Readonly<T>;
+/** A reactive view of a store's value. Update it through the paired `StoreSetter`. */
+export type Store<T> = T;
 /**
  * A store setter. The callback receives a writable **draft** of the store.
  *
diff --git a/packages/signals/tests/store/createStore.test.ts b/packages/signals/tests/store/createStore.test.ts
index 7daa0c031..34099a3bd 100644
--- a/packages/signals/tests/store/createStore.test.ts
+++ b/packages/signals/tests/store/createStore.test.ts
@@ -25,7 +25,6 @@ describe("State immutability", () => {
   test("Setting a property", () => {
     const [state] = createStore({ name: "John" });
     expect(state.name).toBe("John");
-    // @ts-expect-error can't write readonly property
     state.name = "Jake";
     expect(state.name).toBe("John");
   });
diff --git a/packages/signals/tests/store/store.type-tests.ts b/packages/signals/tests/store/store.type-tests.ts
index 9befde120..56d83015b 100644
--- a/packages/signals/tests/store/store.type-tests.ts
+++ b/packages/signals/tests/store/store.type-tests.ts
@@ -12,8 +12,40 @@ import {
   const [store, setStore] = createStore({ name: "John", age: 30 });
   store.name satisfies string;
   store.age satisfies number;
-  // @ts-expect-error readonly
-  store.name = "Jake";
+}
+
+// ── stores preserve the supplied type ────────────────────────────────
+
+{
+  const [source] = createStore([{ id: 1 }]);
+  const [store, setStore] = createStore(source);
+  setStore(draft => {
+    draft.push({ id: 2 });
+  });
+  store satisfies { id: number }[];
+}
+
+{
+  type List = { readonly id: string; items: { title: string }[] };
+  const [list] = createStore<List>({ id: "todos", items: [] });
+  const [store, setStore] = createStore({ list });
+  setStore(draft => {
+    draft.list.items = [{ title: "Review PR" }];
+    // @ts-expect-error User-authored readonly remains readonly through nesting.
+    draft.list.id = "done";
+  });
+  store satisfies { list: List };
+}
+
+{
+  type State = { readonly id: number; name: string };
+  const [store, setStore] = createStore<State>({ id: 1, name: "John" });
+  store satisfies State;
+  setStore(draft => {
+    draft.name = "Jane";
+    // @ts-expect-error User-authored readonly properties remain readonly.
+    draft.id = 2;
+  });
 }
 
 // ── createStore (projection) — seed matches return type ───────────────