Fix embeds intermittently lost until page refresh

[RobbyV2]

Problem

Embeds occasionally never render until the page is refreshed.

Embed resolution is fully async on the backend: a fire-and-forget task fetches the link preview and broadcasts a separate EmbedsResolved ws event, decoupled from the Message event with no ordering guarantee tying the embed to the message being present in the store.

The embeds_resolved handler applied embeds only through patchMessage, which silently no-ops when the target message isn't in any cache at that instant (message merged after the event, or the real id still sitting in the optimistic outbox). Separately, merge gives precedence to incoming messages, so a late duplicate message echo carrying embeds: [] (the POST response / ws echo of a freshly sent message) clobbers embeds already applied. Either path drops the embed until a refresh reloads history with embeds baked in from the DB.

Fix

Buffer resolved embeds in a bounded (256-entry FIFO) map keyed by message id, and enrich every recent-message insertion (drain, ws message merges for channel and thread, openChannel/openDm/openThread fetches, poll refresh) from it via a small applyEmbeds helper. Embeds now survive regardless of EmbedsResolved vs Message ordering. embeds_removed keeps the buffer consistent so a removed embed doesn't reappear on a later insert.

Tests

Added two store_reducer cases: embed resolving before the message is inserted still lands, and a later duplicate message echo does not clobber resolved embeds. Full suite 47/47, eslint clean, tsc --noEmit clean.

🤖 Generated with Claude Code

[gitnotebooks]

Review these changes at https://app.gitnotebooks.com/RobbyV2/RChat/pull/1