Fix gnDownload reducer mutating previous state on DOWNLOAD_METADATA_COMPLETE

[Valyrian-Code]

Problem

In reducers/gnDownload, the DOWNLOAD_METADATA_COMPLETE case mutates the previous state:

const newState = { ...state };                 // shallow copy
const downloads = newState.downloads[linkType]; // same reference as state.downloads[linkType]
delete downloads[action.pk];                    // mutates the incoming state!

{ ...state } is shallow, so newState.downloads[linkType] is the same object as the incoming state.downloads[linkType]. The delete removes the key from the previous state before the immutable spread runs. Reducers must be pure — mutating prior state can break referential-equality checks, memoized selectors, and time-travel debugging.

Fix

Copy the link bucket before deleting, so the previous state is untouched:

const linkType = action?.link?.split(' ').join('');
const remaining = { ...(state.downloads[linkType] || {}) };
delete remaining[action.pk];
return { ...state, downloads: { ...state.downloads, [linkType]: remaining } };

Test

Added to reducers/__tests__/gndownload-test.js: captures the previous link bucket and asserts it is unchanged after dispatch. Fails on master (Expected {} to equal { 1: true }), passes with the fix. Output value is unchanged. Full suite green.

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[gemini-code-assist]

Code Review

This pull request fixes a state mutation bug in the gndownload reducer during the DOWNLOAD_METADATA_COMPLETE action by copying the target downloads object before deleting the action's primary key. A corresponding unit test was also added to verify that the previous state is not mutated. The reviewer suggested a cleaner, more idiomatic approach using object destructuring with rest syntax to immutably omit the key instead of copying and using the delete operator.

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[Valyrian-Code]

Done — switched to object rest destructuring (const { [action.pk]: removed, ...remaining } = ...) to omit the key immutably without delete. Lint and the non-mutation test pass.