[use-effect] Derive effective access during render instead of an Effect

[github-actions]

Effect reviewed

RoomWorkspace (apps/web/src/room-workspace.tsx, previously lines 332-338):

useEffect(() => {
	let editable = canEdit && !archivedAt;
	latestCanEdit.current = editable;
	latestCanManage.current = canManage;
	setEffectiveCanEdit(editable);
	setEffectiveCanManage(canManage);
}, [archivedAt, canEdit, canManage, room]);

Classification

derive-render.

Why the Effect was incorrect

effectiveCanEdit/effectiveCanManage start out equal to a pure function of the canEdit/archivedAt/canManage props (useState(canEdit && !archivedAt) / useState(canManage)). This Effect only re-ran that same pure computation whenever those props changed — it never talked to any external system (no subscription, no DOM, no network). Because it ran in an Effect instead of during render, a prop change was visible for one extra paint with the old authorization values before the Effect fired and corrected them. That is exactly the case the React docs call out: you don't need an Effect for adjusting state that is a pure function of props.

The room dependency was already vestigial — RoomWorkspace is always mounted with key={channel.id} from its callers (document-workspace-host.tsx), so room never changes without remounting the whole component and resetting all state; it did not need to participate in the comparison.

Fix

Replaced the Effect with the React "adjust state during render when a prop changes" pattern: track the previous { archivedAt, canEdit, canManage } in a ref, and if any of them differ from the current render's props, update the ref and call the state setters synchronously in the render body (before any JSX is produced). This keeps the exact same values and the same latestCanEdit/latestCanManage ref side effects that later session:* socket handlers rely on (those still update the same refs/state directly, unaffected by this change), but removes the extra render pass.

Verification

• bun run types — all workspaces (@chopin/web included) type-check cleanly.
• bun test apps/web — 304 pass, 0 fail (no regressions).
• bunx oxlint apps/web/src/room-workspace.tsx — 0 warnings, 0 errors.
• bun run ci could not complete in this sandbox: dprint check fails to download its TypeScript plugin binary because outbound network access to GitHub Releases is blocked here. oxlint (run standalone above) and the token checker were not otherwise affected by this change.

Only this one Effect/file was touched, per the one-violation-per-PR constraint.

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