Base: Look up display name ambiguity under the name a member is shown with

[SamuraiF0x]

The ambiguity index is keyed by the name a member set themselves, which is also what RoomMember::name renders: own profile, then the latest member event, then the localpart. But the lookup behind RoomMember::name_ambiguous used the latest member event's name. The two differ for a kicked member: the kick event carries no display name, and the profile writer deliberately keeps the member's own profile, so the member is still shown under their old name while the lookup asked about their localpart and always came back unambiguous.

Concretely, with three members sharing a display name and one of them kicked, the kicked member's messages render under the shared name without disambiguation while the two remaining members are disambiguated.

The fix resolves the name once, through a helper that RoomMember::display_name now shares so the two cannot drift, and uses it for the lookup in members, get_member and from_parts. No public API changes. The new test drives the scenario through sync and the real profile writer; it fails on name_ambiguous() without the fix.

This touches the same lines as #7004, whichever merges second rebases trivially.

• I've documented the public API changes in the appropriate changelog files (see Writing changelog entries).
• This PR was made with the help of AI.

Signed-off-by: Šimun Kordiš kordis.simun@gmail.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.27%. Comparing base (2e2f867) to head (ed0ae9c).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7010      +/-   ##
==========================================
+ Coverage   90.26%   90.27%   +0.01%     
==========================================
  Files         408      408              
  Lines      117566   117612      +46     
  Branches   117566   117612      +46     
==========================================
+ Hits       106121   106175      +54     
+ Misses       7491     7483       -8     
  Partials     3954     3954              

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[codspeed]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing SamuraiF0x:base/ambiguity-rendered-name (ed0ae9c) with main (2e2f867)}