fix: untrack does not exempt owned-scope writes — correct the docs, name the owner in the throw (#3157)

CHEATSHEET listed untrack/untracked blocks as an escape hatch for
REACTIVE_WRITE_IN_OWNED_SCOPE, but the guard fires on the ambient owner
and untrack only toggles tracking/strictRead — the documented fix throws
the identical error. The docs were the wrong side, by construction:
component bodies already run untracked and are exactly the scope the
guard most needs to cover. Both lines now say so explicitly.

Also lands the reporter's enhancement: the thrown message appends the
owning scope's name, which previously reached only the diagnostics
channel apps don't subscribe to by default.

Reported by @antoinevanwel with the correct root-cause analysis.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ryansolid

.changeset/fix-owned-write-guard-docs.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/signals": patch
+---
+
+The owned-scope write guard's thrown message now names the owning scope (previously only the diagnostics channel carried it); CHEATSHEET no longer claims `untrack` exempts owned-scope writes — the guard is owner-based and untrack only stops tracking (#3157)

packages/signals/src/core/core.ts

@@ -1256,10 +1256,19 @@ export function devGuardStoreSetterWrite(): void {
       ownerName: (context as any)._name,
       data: { operation: "setStore" }
     });
-    throw new Error(REACTIVE_WRITE_IN_OWNED_SCOPE_SIGNAL_MESSAGE);
+    // the owner name reaches the THROWN message too, not just the
+    // diagnostics channel apps don't subscribe to by default (#3157)
+    throw new Error(ownedScopeWriteMessage(context));
   }
 }
 
+function ownedScopeWriteMessage(owner: Owner) {
+  const name = (owner as any)._name;
+  return name
+    ? `${REACTIVE_WRITE_IN_OWNED_SCOPE_SIGNAL_MESSAGE} (in ${name})`
+    : REACTIVE_WRITE_IN_OWNED_SCOPE_SIGNAL_MESSAGE;
+}
+
 export function setSignal<T>(el: Signal<T> | Computed<T>, v: T | ((prev: T) => T)): T {
   if (
     __DEV__ &&
@@ -1278,7 +1287,7 @@ export function setSignal<T>(el: Signal<T> | Computed<T>, v: T | ((prev: T) => T
       nodeName: (el as any)._name,
       data: { operation: "setSignal" }
     });
-    throw new Error(REACTIVE_WRITE_IN_OWNED_SCOPE_SIGNAL_MESSAGE);
+    throw new Error(ownedScopeWriteMessage(context));
   }
 
   if (el._transition && activeTransition !== el._transition)

packages/solid/CHEATSHEET.md

@@ -512,7 +512,7 @@ import { renderToString, renderToStream, isServer, isDev } from "@solidjs/web";
 Common dev-mode warnings/errors you may hit:
 
 - **Top-level reactive read in component body** — read inside JSX or wrap in `untrack`/`createMemo`.
-- **Write under owned scope** — move setters into event handlers / `onSettled` / `untrack`, or opt in with `{ ownedWrite: true }`.
+- **Write under owned scope** — move setters into event handlers / `onSettled` (`untrack` does NOT exempt writes: the guard is owner-based, and untrack only stops tracking), or opt in with `{ ownedWrite: true }`.
 - **Strict read untracked** — extract values in the compute phase; don't read store proxies inside the effect callback.
 - **Multiple Solid instances** — single `solid-js` install required.
 
@@ -645,7 +645,7 @@ If your training data is 1.x, these are the corrections. **Read this before gene
 
 - **`createEffect` takes two arguments now**: `(compute, apply)`. The single-arg form is gone — using it is an error.
 - **Setters don't update reads immediately** — values become visible after the microtask flushes (or via `flush()`).
-- **No writes inside owned scope** — writing a signal/store from inside a memo, effect compute, or component body throws in dev. Move writes to event handlers, `onSettled`, or untracked blocks. Opt in narrowly with `{ ownedWrite: true }` for internal state.
+- **No writes inside owned scope** — writing a signal/store from inside a memo, effect compute, or component body throws in dev. Move writes to event handlers or `onSettled`. (`untrack` does not help: the guard fires on the ambient OWNER, which untrack never touches — component bodies already run untracked and are exactly where the guard fires.) Opt in narrowly with `{ ownedWrite: true }` for internal state.
 - **No top-level reactive reads in component body** — reading signals/props directly at the top of a component warns. Read inside JSX, a memo, or `untrack`.
 - **Props are values, not accessors** — at the call site call accessors (`<X v={count()} />`, not `<X v={count} />`). The single most common AI-generated bug.
 - **Don't destructure props** — `function Comp({ name })` warns; use `props.name` to keep reactivity. (Same root cause as above; see the Props section.)