Blocked Participants Screen: Java/XML to Kotlin/Compose migration

[m4pl]

Migrated the Blocked Participants screen from Java + XML to Kotlin + Compose. Partially reused code from the Conversation Settings migration PR to avoid conflicts and code duplication.

Reworked the data layer: the list is now built from a single SQL query that joins blocked participants with existing 1-on-1 conversations. Only blocked participants who currently have a direct chat are shown - after deleting a blocked chat the row disappears, but the participant stays blocked.

Added multi-select mode in the top bar (counter + clear selection + batched delete) and covered the screen with Compose UI tests.

Out of scope (task): the chat screen will surface a "this chat is blocked" indicator so the delete/block flow becomes more transparent to the user.

Screenshots

Before	After

Video

Screen_recording_20260522_171007.webm

[inthewaves]

Let's use shapes based on the the MaterialTheme shapes for this if possible

[inthewaves]

We should use a Box as a parent like the conversation settings PR for cleaner code

[inthewaves]

I think we just have a phone number and no display name, we should vertically center the text

[inthewaves]

filter { it in knownIds } creates an intermediate List

PersistentSet has an APIs for this part like retainAll (renamed to retainingAll in upcoming kotlinx immutable collections 0.5.0): https://kotlin.github.io/kotlinx.collections.immutable/kotlinx-collections-immutable/kotlinx.collections.immutable/-persistent-set/retaining-all.html. This API doesn't exist on ImmutableSet

It might be worth changing selectedParticipantIds to use PersistentSet instead of ImmutableSet so that we can use retainAll directly.

[inthewaves]

ImmutableSet has no ImmutableSet.minus or ImmutableSet.plus operators, so this will use Kotlin's standard Set.minus and Set.plus, hence why val updated can only be typed as a Set. Set.minus and Set.plus are generic so they will do $O(n)$ copies every time

For example, from the Kotlin standard library:

public operator fun <T> Set<T>.minus(element: T): Set<T> {
      val result = LinkedHashSet<T>(mapCapacity(size))
      var removed = false
      return this.filterTo(result) {
          if (!removed && it == element) {
              removed = true
              false
          } else {
              true
          }
      }
  }

It seems it would be better overall to use PersistentSet as the type instead of ImmutableSet in the state data class. If selectedParticipantIds was typed to be a PersistentSet, then these operations would use PersistentSet (copy-on-write) operations for adding and removing elements which looks more efficient:

PersistentCollection.plus and PersistentCollection.minus do exist: https://github.com/Kotlin/kotlinx.collections.immutable/blob/master/core/commonMain/src/extensions.kt#L71

removing calls remove (removing seems to be a new API renaming): https://github.com/Kotlin/kotlinx.collections.immutable/blob/master/core/commonMain/src/ImmutableCollection.kt#L91

PersistentOrderedSet's remove, for example, looks efficient (or at least more specialized than creating a brand-new LinkedHashSet) and reuses PersistentHashMap structure: https://github.com/Kotlin/kotlinx.collections.immutable/blob/master/core/commonMain/src/implementations/persistentOrderedSet/PersistentOrderedSet.kt#L72

[inthewaves]

When in multi-select mode after a long press, for an unselected contact, tapping their avatar will bring up quick actions instead of selecting that contact/number. For a selected contact, tapping their avatar will do nothing. I think quick actions should be disabled when in multi-select mode