AND-1180

Goal

The channel header has three accessibility gaps that prevent TalkBack users from interacting with it:

1. The trailing avatar and the title Column are clickable with Role.Button but expose no readable name. TalkBack treats them as malformed buttons and skips them during swipe navigation.
2. The channel name announces only when focus lands on it. There is no heading semantic, so TalkBack heading-navigation can't jump to it.
3. On group channels with overflow members, the avatar's +N CountBadge and the channel formatter's +N more text both announce — TalkBack hears the count twice.

Implementation

• Name the trailing avatar. Add Modifier.semantics(mergeDescendants = true) { contentDescription = avatarLabel } on the clickable, where avatarLabel comes from ChatTheme.channelNameFormatter.formatChannelName(channel, currentUser) — the same source the header title uses. TalkBack announces the avatar as "<channel name>, button. Double-tap to <onClickLabel>.".
• Name the title Column when clickable. Add Modifier.semantics(mergeDescendants = true) {} after the clickable. The merge folds the title + subtitle Text content into the button's label, so TalkBack announces the column as one node.
• Mark the title as a heading. Add Modifier.semantics { heading() } to the channel-name Text. TalkBack heading-navigation can now jump to the channel name.
• Hide the overflow count badge. Add Modifier.semantics { hideFromAccessibility() } to the +N CountBadge inside StackedGroupAvatar. The badge is visual emphasis; the formatter's +N more text already conveys the count to TalkBack.

🎨 UI Changes

None. All changes live in the accessibility tree only.

Testing

Enable TalkBack on a physical device. Run the Compose sample.

1. 1:1 DM — Open a 1:1 channel (e.g. the Padmé Amidala DM) and swipe through the header:
   • Back button: "Back".
   • Title: "<channel name>, heading". Heading-navigation jumps to it.
   • Avatar: "<channel name>, button. Double-tap to open conversation info." (the verb comes from onChannelAvatarClickLabel).
2. Double-tap the avatar — the conversation info screen opens.
3. Group with overflow — Open a group channel with 5+ members so the avatar renders the +N overflow badge. Confirm the avatar's announcement includes +N more once, not twice.
4. Group with image — Open a group channel with a channel.image set (uses SimpleGroupAvatar, no CountBadge). Avatar still names itself correctly.
5. Title click — If a downstream integration wires onHeaderTitleClick + onHeaderTitleClickLabel, TalkBack focuses the title Column as one node and announces "<title>. <subtitle>. Button. Double-tap to <label>.".

Summary by CodeRabbit

• Accessibility
  • Enhanced screen reader support in channel headers with improved semantic descriptions
  • Better accessibility labels for channel avatars to help users navigate more effectively