feat: identicons, tap-to-copy fingerprint, recent rooms (Phase 1 backport)

Backport from desktop client to Android:

Identicons:
- New Identicon.kt composable: deterministic 5x5 symmetric Canvas pattern
  from fingerprint hash (same algorithm as desktop identicon.ts)
- Participant list shows identicon + name + tappable fingerprint
- Settings page shows identicon next to fingerprint

CopyableFingerprint:
- Tap any fingerprint text to copy to clipboard with Toast feedback
- Used in participant list and settings page

Recent rooms:
- SettingsRepository: persists last 5 (relay, room) pairs
- CallViewModel: saves on startCall, exposes as StateFlow
- InCallScreen: clickable chips that fill room + select matching server

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/wzp/data/SettingsRepository.kt

@@ -28,6 +28,7 @@ class SettingsRepository(context: Context) {
         private const val KEY_PREFER_IPV6 = "prefer_ipv6"
         private const val KEY_IDENTITY_SEED = "identity_seed_hex"
         private const val KEY_AEC_ENABLED = "aec_enabled"
+        private const val KEY_RECENT_ROOMS = "recent_rooms"
     }
 
     // --- Servers ---
@@ -138,4 +139,33 @@ class SettingsRepository(context: Context) {
     fun saveSeedHex(hex: String) {
         prefs.edit().putString(KEY_IDENTITY_SEED, hex).apply()
     }
+
+    // --- Recent rooms ---
+
+    data class RecentRoom(val relay: String, val room: String)
+
+    fun addRecentRoom(relay: String, room: String) {
+        val rooms = loadRecentRooms().toMutableList()
+        rooms.removeAll { it.relay == relay && it.room == room }
+        rooms.add(0, RecentRoom(relay, room))
+        if (rooms.size > 5) rooms.subList(5, rooms.size).clear()
+        val arr = JSONArray()
+        rooms.forEach { arr.put(JSONObject().apply { put("relay", it.relay); put("room", it.room) }) }
+        prefs.edit().putString(KEY_RECENT_ROOMS, arr.toString()).apply()
+    }
+
+    fun loadRecentRooms(): List<RecentRoom> {
+        val json = prefs.getString(KEY_RECENT_ROOMS, null) ?: return emptyList()
+        return try {
+            val arr = JSONArray(json)
+            (0 until arr.length()).map { i ->
+                val o = arr.getJSONObject(i)
+                RecentRoom(o.getString("relay"), o.getString("room"))
+            }
+        } catch (_: Exception) { emptyList() }
+    }
+
+    fun clearRecentRooms() {
+        prefs.edit().remove(KEY_RECENT_ROOMS).apply()
+    }
 }

android/app/src/main/java/com/wzp/ui/call/CallViewModel.kt

@@ -70,6 +70,9 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _preferIPv6 = MutableStateFlow(false)
     val preferIPv6: StateFlow<Boolean> = _preferIPv6.asStateFlow()
 
+    private val _recentRooms = MutableStateFlow<List<com.wzp.data.SettingsRepository.RecentRoom>>(emptyList())
+    val recentRooms: StateFlow<List<com.wzp.data.SettingsRepository.RecentRoom>> = _recentRooms.asStateFlow()
+
     private val _playoutGainDb = MutableStateFlow(0f)
     val playoutGainDb: StateFlow<Float> = _playoutGainDb.asStateFlow()
 
@@ -139,6 +142,7 @@ class CallViewModel : ViewModel(), WzpCallback {
         _captureGainDb.value = s.loadCaptureGain()
         _seedHex.value = s.getOrCreateSeedHex()
         _aecEnabled.value = s.loadAecEnabled()
+        _recentRooms.value = s.loadRecentRooms()
     }
 
     fun selectServer(index: Int) {
@@ -287,6 +291,8 @@ class CallViewModel : ViewModel(), WzpCallback {
         _debugReportAvailable.value = false
         _debugReportStatus.value = null
         lastCallServer = serverEntry.address
+        settings?.addRecentRoom(serverEntry.address, room)
+        _recentRooms.value = settings?.loadRecentRooms() ?: emptyList()
         debugReporter?.prepareForCall()
         try {
             // Teardown previous call but don't stop the service (we're about to restart it)

android/app/src/main/java/com/wzp/ui/call/InCallScreen.kt

@@ -42,6 +42,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
@@ -200,6 +201,36 @@ fun InCallScreen(
                     modifier = Modifier.fillMaxWidth(0.6f)
                 )
 
+                // Recent rooms
+                val recentRooms by viewModel.recentRooms.collectAsState()
+                if (recentRooms.isNotEmpty()) {
+                    Spacer(modifier = Modifier.height(8.dp))
+                    FlowRow(
+                        modifier = Modifier.fillMaxWidth(),
+                        horizontalArrangement = Arrangement.Center
+                    ) {
+                        recentRooms.forEach { recent ->
+                            Surface(
+                                onClick = {
+                                    viewModel.setRoomName(recent.room)
+                                    // Select matching server
+                                    val idx = servers.indexOfFirst { it.address == recent.relay }
+                                    if (idx >= 0) viewModel.selectServer(idx)
+                                },
+                                shape = RoundedCornerShape(16.dp),
+                                color = MaterialTheme.colorScheme.surfaceVariant,
+                                modifier = Modifier.padding(2.dp)
+                            ) {
+                                Text(
+                                    text = recent.room,
+                                    style = MaterialTheme.typography.labelSmall,
+                                    modifier = Modifier.padding(horizontal = 12.dp, vertical = 4.dp)
+                                )
+                            }
+                        }
+                    }
+                }
+
                 Spacer(modifier = Modifier.height(24.dp))
 
                 Button(
@@ -262,11 +293,33 @@ fun InCallScreen(
                         color = MaterialTheme.colorScheme.onSurfaceVariant
                     )
                     unique.forEach { member ->
-                        Text(
-                            text = member.displayName,
-                            style = MaterialTheme.typography.labelSmall,
-                            color = MaterialTheme.colorScheme.onSurfaceVariant
-                        )
+                        Row(
+                            verticalAlignment = Alignment.CenterVertically,
+                            modifier = Modifier.padding(vertical = 2.dp)
+                        ) {
+                            com.wzp.ui.components.Identicon(
+                                fingerprint = member.fingerprint.ifEmpty { member.displayName },
+                                size = 28.dp,
+                            )
+                            Spacer(modifier = Modifier.width(8.dp))
+                            Column {
+                                Text(
+                                    text = member.displayName,
+                                    style = MaterialTheme.typography.labelSmall,
+                                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                                )
+                                if (member.fingerprint.isNotEmpty()) {
+                                    com.wzp.ui.components.CopyableFingerprint(
+                                        fingerprint = member.fingerprint.take(16),
+                                        style = MaterialTheme.typography.labelSmall.copy(
+                                            fontSize = 9.sp,
+                                            fontFamily = FontFamily.Monospace,
+                                        ),
+                                        color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.6f),
+                                    )
+                                }
+                            }
+                        }
                     }
                 }
 

android/app/src/main/java/com/wzp/ui/components/Identicon.kt

@@ -0,0 +1,141 @@
+package com.wzp.ui.components
+
+import android.widget.Toast
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalClipboardManager
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.text.AnnotatedString
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import kotlin.math.min
+
+/**
+ * Deterministic identicon — generates a unique 5x5 symmetric pattern
+ * from a hex fingerprint string. Identical algorithm to the desktop
+ * TypeScript implementation in identicon.ts.
+ */
+@Composable
+fun Identicon(
+    fingerprint: String,
+    size: Dp = 36.dp,
+    clickToCopy: Boolean = true,
+    modifier: Modifier = Modifier,
+) {
+    val clipboard = LocalClipboardManager.current
+    val context = LocalContext.current
+    val bytes = hashBytes(fingerprint)
+    val (bg, fg) = deriveColors(bytes)
+    val grid = buildGrid(bytes)
+
+    Canvas(
+        modifier = modifier
+            .size(size)
+            .clip(RoundedCornerShape(size * 0.12f))
+            .then(
+                if (clickToCopy && fingerprint.isNotEmpty()) {
+                    Modifier.clickable {
+                        clipboard.setText(AnnotatedString(fingerprint))
+                        Toast.makeText(context, "Copied", Toast.LENGTH_SHORT).show()
+                    }
+                } else Modifier
+            )
+    ) {
+        val cellW = this.size.width / 5f
+        val cellH = this.size.height / 5f
+
+        // Background
+        drawRect(color = bg, size = this.size)
+
+        // Foreground cells
+        for (y in 0 until 5) {
+            for (x in 0 until 5) {
+                if (grid[y][x]) {
+                    drawRect(
+                        color = fg,
+                        topLeft = Offset(x * cellW, y * cellH),
+                        size = Size(cellW, cellH),
+                    )
+                }
+            }
+        }
+    }
+}
+
+/**
+ * Fingerprint text that copies to clipboard on tap.
+ */
+@Composable
+fun CopyableFingerprint(
+    fingerprint: String,
+    modifier: Modifier = Modifier,
+    style: androidx.compose.ui.text.TextStyle = androidx.compose.material3.MaterialTheme.typography.bodySmall,
+    color: Color = Color.Unspecified,
+) {
+    val clipboard = LocalClipboardManager.current
+    val context = LocalContext.current
+
+    androidx.compose.material3.Text(
+        text = fingerprint,
+        style = style,
+        color = color,
+        modifier = modifier.clickable {
+            if (fingerprint.isNotEmpty()) {
+                clipboard.setText(AnnotatedString(fingerprint))
+                Toast.makeText(context, "Fingerprint copied", Toast.LENGTH_SHORT).show()
+            }
+        }
+    )
+}
+
+// --- Internal helpers (matching desktop identicon.ts) ---
+
+private fun hashBytes(hex: String): List<Int> {
+    val clean = hex.filter { it.isLetterOrDigit() }
+    val bytes = mutableListOf<Int>()
+    var i = 0
+    while (i + 1 < clean.length) {
+        val b = clean.substring(i, i + 2).toIntOrNull(16) ?: 0
+        bytes.add(b)
+        i += 2
+    }
+    // Pad to at least 16 bytes
+    while (bytes.size < 16) bytes.add(0)
+    return bytes
+}
+
+private fun deriveColors(bytes: List<Int>): Pair<Color, Color> {
+    val hue1 = bytes[0] * 360f / 256f
+    val hue2 = (bytes[1] * 360f / 256f + 120f) % 360f
+    val bg = hslToColor(hue1, 0.65f, 0.35f)
+    val fg = hslToColor(hue2, 0.70f, 0.55f)
+    return bg to fg
+}
+
+private fun buildGrid(bytes: List<Int>): List<List<Boolean>> {
+    return (0 until 5).map { y ->
+        val left = (0 until 3).map { x ->
+            val idx = 2 + y * 3 + x
+            bytes[idx % bytes.size] > 128
+        }
+        // Mirror: col3 = col1, col4 = col0
+        listOf(left[0], left[1], left[2], left[1], left[0])
+    }
+}
+
+private fun hslToColor(h: Float, s: Float, l: Float): Color {
+    val k = { n: Float -> (n + h / 30f) % 12f }
+    val a = s * min(l, 1f - l)
+    val f = { n: Float ->
+        l - a * maxOf(-1f, minOf(k(n) - 3f, minOf(9f - k(n), 1f)))
+    }
+    return Color(f(0f), f(8f), f(4f))
+}

android/app/src/main/java/com/wzp/ui/settings/SettingsScreen.kt

@@ -158,20 +158,30 @@ fun SettingsScreen(
 
             Spacer(modifier = Modifier.height(16.dp))
 
-            // Fingerprint display
+            // Fingerprint display with identicon
             val fingerprint = if (draftSeedHex.length >= 16) draftSeedHex.take(16).uppercase() else "Not generated"
             Text(
                 text = "Fingerprint",
                 style = MaterialTheme.typography.labelSmall,
                 color = MaterialTheme.colorScheme.onSurfaceVariant
             )
-            Text(
-                text = fingerprint.chunked(4).joinToString(" "),
-                style = MaterialTheme.typography.bodyMedium.copy(
-                    fontFamily = FontFamily.Monospace
-                ),
-                color = MaterialTheme.colorScheme.onSurface
-            )
+            Row(
+                verticalAlignment = Alignment.CenterVertically,
+                modifier = Modifier.padding(vertical = 4.dp)
+            ) {
+                com.wzp.ui.components.Identicon(
+                    fingerprint = draftSeedHex,
+                    size = 40.dp,
+                )
+                Spacer(modifier = Modifier.width(12.dp))
+                com.wzp.ui.components.CopyableFingerprint(
+                    fingerprint = fingerprint.chunked(4).joinToString(" "),
+                    style = MaterialTheme.typography.bodyMedium.copy(
+                        fontFamily = FontFamily.Monospace
+                    ),
+                    color = MaterialTheme.colorScheme.onSurface,
+                )
+            }
 
             Spacer(modifier = Modifier.height(12.dp))