fix: assign properties of mutations in withMutation

[michael-small]

Description

Would fix #286

Would fix the following:

// component
readonly myMutation = this.store.myMutation; // Mutation<number, any>

// html
{{ myMutation.isPending() }}

// runtime error:
ERROR TypeError: ctx.myMutation.isPending is not a function

Object.assign will explicitly copy the properties of the mutation so that they are all available

Outstanding before going out of Draft

Tests pending

[michael-small]

@copilot

[Copilot]

Pull request overview

Fixes a runtime mismatch where mutations exposed via withMutations were callable but did not carry the Mutation signal properties (e.g. isPending, status), causing failures when components referenced store.myMutation.isPending().

Changes:

• Wrap mutation methods with Object.assign(...) to attach selected Mutation properties onto the callable method.
• Preserve the existing derived store props (<mutation>IsPending, <mutation>Status, <mutation>Error) behavior.

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[Copilot]

The new Object.assign accesses mutations[key].status/value/... during feature creation. If mutationsFactory accidentally returns an object with an undefined entry, this will now throw a generic Cannot read properties of undefined at store init time, and the explicit Mutation ${key} not found error inside the async wrapper will never run. Consider validating const mutation = mutations[key] once per key (outside the wrapper) and throwing the custom error before reading any properties, or otherwise guarding property reads.

[Copilot]

Only a fixed subset of Mutation properties are copied onto the wrapped function. This means any mutation subtype that adds extra properties (e.g. HttpMutation adds uploadProgress, downloadProgress, headers, statusCode) will still lose those when exposed via the store method. To make this future-proof and fully preserve mutation capabilities, prefer assigning from the mutation object itself (e.g. copy all enumerable properties from mutation) rather than enumerating a hard-coded list.

[Copilot]

This change is intended to make store.<mutation> usable as a full Mutation object (e.g. store.increment.isPending()), but the existing with-mutations.spec.ts suite only asserts the derived <mutation>IsPending/<mutation>Status signals and does not cover property access on the method itself. Add a regression test that calls store.increment.isPending()/status() (and ideally hasValue()), so the runtime shape is verified.

Suggested change

	status: mutations[key].status,
	value: mutations[key].value,
	isPending: mutations[key].isPending,
	isSuccess: mutations[key].isSuccess,
	error: mutations[key].error,
	hasValue: mutations[key].hasValue,
	status: () => mutations[key].status(),
	value: () => mutations[key].value(),
	isPending: () => mutations[key].isPending(),
	isSuccess: () => mutations[key].isSuccess(),
	error: () => mutations[key].error(),
	hasValue: () => mutations[key].hasValue(),