Search results screen is completely blank when a search finds no messages

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

Development build from current main (commit adb64adc5b). The affected code path (LegacyMessageListFragment.updateFooterText, which sets the footer to null for manual searches) is unchanged in released versions.

Where did you get the app from?

Other (self-built from source)

Android version

Android 15 (emulator, API 35)

Device model

Android Emulator (Pixel)

Steps to reproduce

1. Set up an IMAP account
2. Open a folder (e.g. Inbox) and tap the search icon
3. Search for a term that matches no locally synced message (e.g. a message that only exists on the server outside the sync window, or a random word)

Expected behavior

Some feedback about the outcome: a "no results" message, ideally with a hint that only locally synced messages were searched and that a server search is available (the remote search action is otherwise hard to discover: a small toolbar icon / pull-to-refresh, only in single-folder searches on IMAP).

Actual behavior

The search results screen is completely blank. No empty-state text, no hint about the server search. A failed remote search only shows a short toast; a remote search with zero hits also ends on the blank screen, indistinguishable from "nothing happened".

Logs

Not applicable (no crash). Screenshots of the behavior before/after a proposed fix are available in the preview release on my fork: https://github.com/JustNotesa/thunderbird-android/releases/tag/search-preview-1

Start in LegacyMessageListFragment.updateFooterText, the affected code path named in the report, and reproduce an empty local or remote search on Android. Trace why manual searches set the footer to null, then make the empty results state provide the expected feedback and verify the behavior on the listed search paths.