perf(mobile): load only the directory when search opens - #9466

Opening search on a list that is already loaded refreshed the whole channel list to get the open-channel directory: the membership rosters (kind 39002), member channel metadata, hidden DMs, Huddle starts, DM names and the latest messages of every joined channel, then the directory pages. Only the directory was what search needed; everything else was already in the list and kept current by live updates.

Search now reads only the directory pages and merges them into the current list: every channel you are not a member of is rebuilt from the fresh directory (latest revision per channel, open and non-DM only, the same rules as a full refresh), and joined channels keep their entries untouched. When the list has not loaded yet, the full refresh runs as before.

Races:

• A directory-only load is fenced by scope alone (community, identity, disposal), not by the list-refresh generation, so it neither retires an in-flight membership refresh nor is retired by one. A community or identity switch retires it: its response is discarded and it no longer owns its loading status, so returning to the first community (before or after the old request ends) lets search load the directory again.
• Directory loads are ordered among themselves: only the newest one writes the directory and its load status, so an older full refresh cannot overwrite a newer search load and vice versa.
• A list refresh that merged an older directory and then installs after a search load landed re-merges the newer directory, so the open channel search just found does not disappear.
• A list refresh no longer resets a live directory-only load's status to idle (that reset existed because a refresh used to discard the in-flight directory, which it no longer does for this kind of load). A load retired by a scope switch is not live, so the reset still applies to the status it left behind.

Results

iPhone 12 mini, profile build, Builderlab account. Typing a query into search on a loaded list, more than 30 seconds after the last directory load (two runs each, same numbers both times):

Unjoined open channels still appear in results with their Open badge.

Regressions

The tradeoff we accept: on a search open, joined channels' member counts, unread badges and latest-message times are not re-read; they show what the last full refresh found, as updated by live events since. Live join and leave notices, metadata changes and new messages still apply as they arrive, and the next ordinary refresh (launch, reconnect, resume, pull to refresh) re-reads everything. The case that differs is a change that live delivery missed on a healthy connection (for example a roster change made while a live chunk was briefly refused): before, opening search happened to repair it; now the next ordinary refresh does.

Nothing else changes: open channels are listed under the same visibility rules, a failed directory load still reports its error to search and keeps the cached discovery, and the first load is unchanged.

Testing

• Full mobile suite passes; flutter analyze clean.
• New tests: a search load on a loaded list issues only directory queries (no roster, member metadata, hidden-DM, Huddle or message reads), lists the new open channel, drops one that became private and keeps the joined channel object unchanged; a membership refresh during the load is kept and does not reset its status; a list refresh that merged the directory before a search load landed keeps the newer directory; a community switch discards the response; returning to the first community, both while the old request is in flight and after it ended, loads the directory again.
• Automated device run on the iPhone 12 mini: launch, two search sessions typing a query, results list joined and unjoined open channels, close and reopen search. Rerun on f216dd6 (after the scope-switch fix) with the same results: 1.26 MB HTTP per query, unjoined open channels marked Open.