Feature: Room aliases — view & manage room aliases from Room Settings

[ZhangHanDong]

Issue 012: Room aliases can be read but not managed from the client

Date: 2026-07-23
Type: Feature
Status: Open
Driven by spec: specs/task-room-aliases.spec.md (agent-spec, estimate 2d)
Affected components: src/home/room_settings_modal.rs, src/sliding_sync.rs, src/app.rs, src/i18n.rs, resources/i18n/**

Summary

Robrix already reads room aliases end-to-end but offers no way to manage them.
RoomsList populates canonical_alias: Option<OwnedRoomAliasId> and
alt_aliases: Vec<OwnedRoomAliasId> from matrix-sdk (room.canonical_alias() /
room.alt_aliases()), and the Room Settings modal is even handed the canonical alias
today — but only as a read-only string. Users cannot publish a new alias, remove one,
or choose which alias is canonical.

This issue adds a "Room Aliases" section to the Room Settings modal so users with the
right power level can view and manage a room's aliases.

Current behavior (evidence)

• src/home/rooms_list.rs:307-309 / :389-391 — canonical_alias + alt_aliases are
  already tracked in the room model.
• src/sliding_sync.rs:7378-7384 / :7487-7491 — both are read from
  room.canonical_alias() / room.alt_aliases().
• src/app.rs:1927-1931 — on RoomSettingsAction::Open, the canonical alias is fetched
  (get_room_canonical_alias) and passed into show_settings(...) as a plain string.
• src/home/room_settings_modal.rs — renders room settings but has no alias
  add/remove/set-canonical controls.
• Joining a room by alias already works (src/home/add_room.rs::parse_address); this
  issue is strictly about managing an existing room's aliases, not joining.

Proposed scope

1. View: show canonical alias + all alt aliases in the Room Settings modal.
2. Publish: register a new alias (#localpart:server, or bare localpart resolved
   against the current homeserver) into the room directory.
3. Remove: unbind an alias from the room directory.
4. Set canonical: write the m.room.canonical_alias state event (alias + alt_aliases),
   or clear it.
5. Permission-gated: edit controls appear only when the user can send the
   m.room.canonical_alias state event; otherwise the section is read-only.
6. Pure, unit-testable core: alias normalization/validation
   (normalize_and_validate_alias) and canonical/alt reconciliation
   (reconcile_canonical_alias), plus i18n key presence — all covered by the spec's
   Completion Criteria scenarios.

Out of scope

• Join-by-alias flow (already covered by add_room.rs).
• Space canonical alias management (space_service_sync.rs).
• Directory visibility / history-visibility toggles.
• Cross-homeserver alias migration or bulk import.

Development contract

Development is driven by the agent-spec Task Contract at
specs/task-room-aliases.spec.md. Verify with:

agent-spec lint   specs/task-room-aliases.spec.md
agent-spec verify specs/task-room-aliases.spec.md

Acceptance is bound to pure-function unit tests (alias validation + canonical
reconciliation + i18n key presence); platform behavior (macOS/Android) is confirmed
manually in the implementation PR.