feat(maestro): wire sidebar drawer into MainActivity

ModalNavigationDrawer opened by a hamburger button in the top bar,
holding SidebarContent bound to the app's DaemonLink.catalog.

android/app/src/main/java/pt/naps/maestro/MainActivity.kt

@@ -8,25 +8,37 @@ import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.width
+import androidx.compose.material3.DrawerValue
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.ModalDrawerSheet
+import androidx.compose.material3.ModalNavigationDrawer
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.material3.rememberDrawerState
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.launch
 import pt.naps.maestro.connection.DaemonLink
 import pt.naps.maestro.connection.DaemonPrefs
 import pt.naps.maestro.connection.LinkState
+import pt.naps.maestro.ui.sidebar.SidebarContent
 import pt.naps.maestro.ui.theme.MaestroTheme
 
 class MainActivity : ComponentActivity() {
     private lateinit var daemonLink: DaemonLink
 
+    @OptIn(ExperimentalMaterial3Api::class)
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
@@ -38,8 +50,35 @@ class MainActivity : ComponentActivity() {
         setContent {
             MaestroTheme {
                 val linkState by daemonLink.state.collectAsState()
-                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
+                val drawerState = rememberDrawerState(DrawerValue.Closed)
-                    PlaceholderScreen(modifier = Modifier.padding(innerPadding), linkState = linkState)
+                val scope = rememberCoroutineScope()
+
+                ModalNavigationDrawer(
+                    drawerState = drawerState,
+                    drawerContent = {
+                        ModalDrawerSheet(modifier = Modifier.width(320.dp)) {
+                            SidebarContent(
+                                catalogStore = daemonLink.catalog,
+                                onOpenSession = { scope.launch { drawerState.close() } },
+                            )
+                        }
+                    },
+                ) {
+                    Scaffold(
+                        modifier = Modifier.fillMaxSize(),
+                        topBar = {
+                            TopAppBar(
+                                title = { Text("Maestro") },
+                                navigationIcon = {
+                                    IconButton(onClick = { scope.launch { drawerState.open() } }) {
+                                        Text("☰")
+                                    }
+                                },
+                            )
+                        },
+                    ) { innerPadding ->
+                        PlaceholderScreen(modifier = Modifier.padding(innerPadding), linkState = linkState)
+                    }
                 }
             }
         }

android/app/src/main/java/pt/naps/maestro/ui/sidebar/ActivityRail.kt

@@ -0,0 +1,91 @@
+package pt.naps.maestro.ui.sidebar
+
+import androidx.compose.animation.animateColorAsState
+import androidx.compose.animation.core.InfiniteTransition
+import androidx.compose.animation.core.LinearEasing
+import androidx.compose.animation.core.RepeatMode
+import androidx.compose.animation.core.animateFloat
+import androidx.compose.animation.core.infiniteRepeatable
+import androidx.compose.animation.core.rememberInfiniteTransition
+import androidx.compose.animation.core.tween
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.width
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.unit.dp
+import pt.naps.maestro.data.ActivityState
+
+/** docs/SIDEBAR.md: the rail's width in the web client. Android mirrors it in
+ * density-independent pixels rather than raw pixels. */
+val ACTIVITY_RAIL_WIDTH = 7.dp
+
+private val RAIL_ACTIVE = Color(0xFF3DDC84)
+private val RAIL_IDLE = Color(0xFF9AA0A6)
+private val RAIL_AWAITING = Color(0xFFF5A623)
+private val RAIL_ERROR = Color(0xFFE5484D)
+
+/** Colour per activity state (docs/SIDEBAR.md's colour table): `Starting`
+ * shares `Idle`'s colour, and an unrecognised state degrades to `Idle` so
+ * rendering never fails (Precedence). */
+fun activityColor(activity: ActivityState): Color =
+    when (activity) {
+        ActivityState.Active -> RAIL_ACTIVE
+        ActivityState.AwaitingInput -> RAIL_AWAITING
+        ActivityState.Error -> RAIL_ERROR
+        ActivityState.Idle, ActivityState.Starting -> RAIL_IDLE
+    }
+
+/** The accessible name the rail carries, since colour is never the only
+ * signal (docs/SIDEBAR.md). */
+fun activityStateWord(activity: ActivityState): String =
+    when (activity) {
+        ActivityState.Active -> "Active"
+        ActivityState.Idle -> "Idle"
+        ActivityState.Starting -> "Starting"
+        ActivityState.AwaitingInput -> "Awaiting input"
+        ActivityState.Error -> "Error"
+    }
+
+/** A held bar that pulses its alpha between 1 and [minAlpha] every
+ * [periodMs] — the blink/flash motion `AwaitingInput`/`Error` earn. */
+@Composable
+private fun InfiniteTransition.pulsingAlpha(minAlpha: Float, periodMs: Int): Float {
+    val alpha by animateFloat(
+        initialValue = 1f,
+        targetValue = minAlpha,
+        animationSpec = infiniteRepeatable(
+            animation = tween(durationMillis = periodMs, easing = LinearEasing),
+            repeatMode = RepeatMode.Reverse,
+        ),
+        label = "activity-rail-alpha",
+    )
+    return alpha
+}
+
+/** The card's rail: a coloured bar in the gutter, full card height. It paints
+ * for every card, `Idle` included, and carries motion only for states that
+ * need attention — a hard blink for `AwaitingInput`, a fast flash for
+ * `Error`. `Active` and `Idle` stay solid; colour alone is their signal. */
+@Composable
+fun ActivityRail(activity: ActivityState, modifier: Modifier = Modifier) {
+    val color by animateColorAsState(targetValue = activityColor(activity), label = "activity-rail-color")
+    val infinite = rememberInfiniteTransition(label = "activity-rail-motion")
+    val alpha = when (activity) {
+        ActivityState.AwaitingInput -> infinite.pulsingAlpha(minAlpha = 0.35f, periodMs = 600)
+        ActivityState.Error -> infinite.pulsingAlpha(minAlpha = 0.25f, periodMs = 220)
+        else -> 1f
+    }
+    Box(
+        modifier = modifier
+            .fillMaxHeight()
+            .width(ACTIVITY_RAIL_WIDTH)
+            .semantics { contentDescription = activityStateWord(activity) }
+            .background(color.copy(alpha = alpha)),
+    )
+}

android/app/src/main/java/pt/naps/maestro/ui/sidebar/FolderNode.kt

@@ -0,0 +1,58 @@
+package pt.naps.maestro.ui.sidebar
+
+import androidx.compose.animation.AnimatedVisibility
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.width
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+
+/** docs/SIDEBAR.md: a collapsible directory in the sidebar tree. An expanded
+ * folder's cards are one row away, so it carries no highlight of its own —
+ * only a collapsed header is ever a keyboard-walk stop, but that distinction
+ * belongs to the caller driving the walk, not this composable. */
+@Composable
+fun FolderNode(
+    label: String,
+    collapsed: Boolean,
+    onToggle: () -> Unit,
+    modifier: Modifier = Modifier,
+    depthPadding: Int = 0,
+    content: @Composable () -> Unit,
+) {
+    Column(modifier = modifier) {
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .clickable(onClick = onToggle)
+                .padding(start = depthPadding.dp, top = 6.dp, bottom = 6.dp, end = 8.dp),
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Text(
+                text = if (collapsed) "▸" else "▾",
+                style = MaterialTheme.typography.labelMedium,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+            Spacer(Modifier.width(6.dp))
+            Text(
+                text = label,
+                style = MaterialTheme.typography.labelMedium,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+            )
+        }
+        AnimatedVisibility(visible = !collapsed) {
+            Column { content() }
+        }
+    }
+}

android/app/src/main/java/pt/naps/maestro/ui/sidebar/SessionCard.kt

@@ -0,0 +1,242 @@
+package pt.naps.maestro.ui.sidebar
+
+import androidx.compose.foundation.ExperimentalFoundationApi
+import androidx.compose.foundation.combinedClickable
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.input.ImeAction
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+import pt.naps.maestro.data.InTheWay
+import pt.naps.maestro.data.Session
+import pt.naps.maestro.data.SessionStatus
+
+/** docs/SIDEBAR.md: a card is always two lines behind an activity rail —
+ * line 1 the name, line 2 the adaptive meta line. Long-press opens a context
+ * menu (Rename / Kill / Spawn similar); the daemon confirms rename and kill
+ * only through the callbacks the caller supplies. */
+@OptIn(ExperimentalFoundationApi::class)
+@Composable
+fun SessionCard(
+    session: Session,
+    nowMs: Long,
+    modifier: Modifier = Modifier,
+    depthPadding: Int = 0,
+    onOpen: (Session) -> Unit = {},
+    onRename: (Session, String) -> Unit = { _, _ -> },
+    onKill: (Session) -> Unit = {},
+    onSpawnSimilar: (Session) -> Unit = {},
+) {
+    var menuExpanded by remember { mutableStateOf(false) }
+    var renaming by remember { mutableStateOf(false) }
+    var confirmingKill by remember { mutableStateOf(false) }
+
+    val running = session.status == SessionStatus.Running
+    val name = sessionName(session)
+    val muted = isProvisionalName(session)
+
+    Row(
+        modifier = modifier
+            .fillMaxWidth()
+            .combinedClickable(
+                onClick = { onOpen(session) },
+                onLongClick = { menuExpanded = true },
+            )
+            .padding(start = (8 + depthPadding).dp, end = 8.dp, top = 6.dp, bottom = 6.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        ActivityRail(activity = session.activity, modifier = Modifier.height(36.dp))
+        Spacer(Modifier.width(8.dp))
+        Column(modifier = Modifier.fillMaxWidth()) {
+            Text(
+                text = name,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+                color = when {
+                    !running -> MaterialTheme.colorScheme.onSurfaceVariant
+                    muted -> MaterialTheme.colorScheme.onSurfaceVariant
+                    else -> MaterialTheme.colorScheme.onSurface
+                },
+                style = MaterialTheme.typography.bodyMedium,
+            )
+            MetaLine(session = session, nowMs = nowMs)
+        }
+    }
+
+    DropdownMenu(expanded = menuExpanded, onDismissRequest = { menuExpanded = false }) {
+        DropdownMenuItem(
+            text = { Text("Rename") },
+            onClick = {
+                menuExpanded = false
+                renaming = true
+            },
+        )
+        DropdownMenuItem(
+            text = { Text("Spawn similar") },
+            onClick = {
+                menuExpanded = false
+                onSpawnSimilar(session)
+            },
+        )
+        DropdownMenuItem(
+            text = { Text("Kill") },
+            onClick = {
+                menuExpanded = false
+                confirmingKill = true
+            },
+        )
+    }
+
+    if (renaming) {
+        RenameDialog(
+            initial = customSessionName(session) ?: "",
+            onCommit = {
+                renaming = false
+                onRename(session, it)
+            },
+            onCancel = { renaming = false },
+        )
+    }
+
+    if (confirmingKill) {
+        KillConfirmDialog(
+            session = session,
+            onConfirm = {
+                confirmingKill = false
+                onKill(session)
+            },
+            onCancel = { confirmingKill = false },
+        )
+    }
+}
+
+/** Line 2, left to right: `[duration] [detail] command [diff stat | exited]`
+ * — the line itself is unconditional, only its fragments are adaptive. */
+@Composable
+fun MetaLine(session: Session, nowMs: Long, modifier: Modifier = Modifier) {
+    val heldMs = activityHeldMs(session.activity_since, nowMs)
+    val duration = if (heldMs != null && heldMs >= META_LINE_MIN_HOLD_MS) {
+        activityDurationLabel(heldMs)
+    } else {
+        null
+    }
+    val blockers = sessionBlockers(session)
+
+    Row(modifier = modifier.fillMaxWidth(), verticalAlignment = Alignment.CenterVertically) {
+        if (duration != null) {
+            Text(
+                text = duration,
+                color = activityColor(session.activity),
+                style = MaterialTheme.typography.labelSmall,
+            )
+            Spacer(Modifier.width(6.dp))
+        }
+        if (session.activity_detail != null) {
+            Text(
+                text = session.activity_detail,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+                style = MaterialTheme.typography.labelSmall,
+                modifier = Modifier.weight(1f, fill = false),
+            )
+            Spacer(Modifier.width(6.dp))
+        }
+        Text(
+            text = programName(session.command),
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            maxLines = 1,
+            overflow = TextOverflow.Ellipsis,
+            style = MaterialTheme.typography.labelSmall,
+        )
+        if (blockers != null) {
+            Spacer(Modifier.width(6.dp))
+            BlockedFragment(blockers)
+        }
+        if (session.status == SessionStatus.Dead) {
+            Spacer(Modifier.width(6.dp))
+            Text(
+                text = "exited",
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                style = MaterialTheme.typography.labelSmall,
+            )
+        }
+    }
+}
+
+@Composable
+private fun BlockedFragment(blockers: InTheWay) {
+    Row(verticalAlignment = Alignment.CenterVertically) {
+        blockerStats(blockers).forEachIndexed { index, stat ->
+            if (index > 0) Spacer(Modifier.width(4.dp))
+            Text(
+                text = stat.text,
+                style = MaterialTheme.typography.labelSmall,
+                color = when (stat.kind) {
+                    "add" -> MaterialTheme.colorScheme.primary
+                    "del" -> MaterialTheme.colorScheme.error
+                    else -> MaterialTheme.colorScheme.onSurfaceVariant
+                },
+            )
+        }
+    }
+}
+
+@Composable
+private fun RenameDialog(initial: String, onCommit: (String) -> Unit, onCancel: () -> Unit) {
+    var text by remember { mutableStateOf(initial) }
+    AlertDialog(
+        onDismissRequest = onCancel,
+        title = { Text("Rename session") },
+        text = {
+            OutlinedTextField(
+                value = text,
+                onValueChange = { text = it },
+                singleLine = true,
+                keyboardOptions = KeyboardOptions(imeAction = ImeAction.Done),
+            )
+        },
+        confirmButton = { TextButton(onClick = { onCommit(text.trim()) }) { Text("Rename") } },
+        dismissButton = { TextButton(onClick = onCancel) { Text("Cancel") } },
+    )
+}
+
+@Composable
+private fun KillConfirmDialog(session: Session, onConfirm: () -> Unit, onCancel: () -> Unit) {
+    val blockers = sessionBlockers(session)
+    AlertDialog(
+        onDismissRequest = onCancel,
+        title = { Text("Kill “${sessionName(session)}”?") },
+        text = {
+            Text(
+                if (blockers != null) {
+                    "This worktree has unsaved work: ${formatInTheWay(blockers)}. Killing may be refused unless forced."
+                } else {
+                    "This ends the session's process. This can't be undone."
+                },
+            )
+        },
+        confirmButton = { TextButton(onClick = onConfirm) { Text("Kill") } },
+        dismissButton = { TextButton(onClick = onCancel) { Text("Cancel") } },
+    )
+}

android/app/src/main/java/pt/naps/maestro/ui/sidebar/SessionFormatting.kt

@@ -0,0 +1,161 @@
+package pt.naps.maestro.ui.sidebar
+
+import java.time.Instant
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonPrimitive
+import pt.naps.maestro.data.InTheWay
+import pt.naps.maestro.data.NameSource
+import pt.naps.maestro.data.Session
+
+/** docs/SIDEBAR.md: a state held shorter than this has no duration fragment. */
+const val META_LINE_MIN_HOLD_MS: Long = 30_000L
+
+/** Payloads predating #102 default `activity_since` to the Unix epoch;
+ * anything implausibly old is "never observed" rather than a huge duration. */
+private val PLAUSIBLE_EPOCH_MS = Instant.parse("2010-01-01T00:00:00Z").toEpochMilli()
+
+/** Milliseconds held in the current activity state, or `null` when `since` is
+ * missing/unparsable/implausible. Mirrors the web's `activityHeldMs`. */
+fun activityHeldMs(since: String?, nowMs: Long): Long? {
+    if (since.isNullOrEmpty()) return null
+    val t = runCatching { Instant.parse(since).toEpochMilli() }.getOrNull() ?: return null
+    if (t < PLAUSIBLE_EPOCH_MS) return null
+    return (nowMs - t).coerceAtLeast(0L)
+}
+
+/** `<60s` whole seconds, `<60m` whole minutes, else whole hours — floored
+ * everywhere so the counter never shows a duration the state hasn't reached. */
+fun activityDurationLabel(heldMs: Long): String {
+    val seconds = heldMs / 1000
+    if (seconds < 60) return "${seconds}s"
+    val minutes = seconds / 60
+    if (minutes < 60) return "${minutes}m"
+    return "${minutes / 60}h"
+}
+
+/** The session's own name (#125), without the command fallback: `null` for a
+ * session that was never given one. */
+fun customSessionName(session: Session): String? {
+    val element = session.metadata["name"] ?: return null
+    val primitive = element as? JsonPrimitive ?: return null
+    if (!primitive.isString) return null
+    return primitive.content.takeIf { it.isNotEmpty() }
+}
+
+/** Line 1's name: `metadata.name` if present, else the command line. */
+fun sessionName(session: Session): String = customSessionName(session) ?: session.command
+
+/** Where the session's name came from (#131), read leniently: anything
+ * unrecognised — including a session named before the field existed — reads
+ * as [NameSource.User], so an existing name is never dimmed or overwritten. */
+fun sessionNameSource(session: Session): NameSource {
+    val element = session.metadata["name_source"] as? JsonPrimitive ?: return NameSource.User
+    return when (element.jsonPrimitive.content) {
+        "Generated" -> NameSource.Generated
+        "Haiku" -> NameSource.Haiku
+        else -> NameSource.User
+    }
+}
+
+/** Whether line 1 renders the name muted (#131): a handle the daemon
+ * generated at spawn and may still replace with one derived from the first
+ * prompt. */
+fun isProvisionalName(session: Session): Boolean =
+    customSessionName(session) != null && sessionNameSource(session) == NameSource.Generated
+
+/** One fragment of the compact blocked-work stat (docs/SIDEBAR.md). `kind`
+ * picks the colour; `text` is what the card prints. */
+data class BlockerStat(val kind: String, val text: String)
+
+/** #83: this session's blocked-work breakdown when something actually blocks
+ * an unforced kill; `null` while clear or not yet probed. */
+fun sessionBlockers(session: Session): InTheWay? {
+    val w = session.blocked_work ?: return null
+    val blocked = w.uncommitted_files > 0 || w.untracked_files > 0 || w.unpushed_commits > 0
+    return if (blocked) w else null
+}
+
+/** The blocked-work breakdown as diff notation: `+124 -18 ?3 ↑2`. A tree whose
+ * only tracked change carries no line delta falls back to the file count
+ * (`~2`) rather than claiming `+0 -0`. */
+fun blockerStats(w: InTheWay): List<BlockerStat> {
+    val stats = mutableListOf<BlockerStat>()
+    if (w.insertions > 0 || w.deletions > 0) {
+        if (w.insertions > 0) stats += BlockerStat("add", "+${w.insertions}")
+        if (w.deletions > 0) stats += BlockerStat("del", "-${w.deletions}")
+    } else if (w.uncommitted_files > 0) {
+        stats += BlockerStat("files", "~${w.uncommitted_files}")
+    }
+    if (w.untracked_files > 0) stats += BlockerStat("untracked", "?${w.untracked_files}")
+    if (w.unpushed_commits > 0) stats += BlockerStat("unpushed", "↑${w.unpushed_commits}")
+    return stats
+}
+
+/** The spelled-out phrasing shared by the kill refusal and every client's
+ * tooltip, so no two describe the same tree differently. */
+fun formatInTheWay(w: InTheWay): String {
+    val parts = mutableListOf<String>()
+    fun push(n: Int, unit: String) {
+        if (n <= 0) return
+        parts += if (n == 1) "1 $unit" else "$n ${unit}s"
+    }
+    push(w.uncommitted_files, "uncommitted file")
+    push(w.untracked_files, "untracked file")
+    push(w.unpushed_commits, "unpushed commit")
+    return if (parts.isNotEmpty()) parts.joinToString(", ") else "no unsaved work"
+}
+
+private val ENV_ASSIGNMENT = Regex("^[A-Za-z_][A-Za-z0-9_]*=.*$")
+private val PLAIN_WRAPPERS = setOf("sudo", "env")
+private val DLX_CAPABLE = setOf("pnpm", "yarn")
+
+/** The program a command line runs — never its arguments (docs/SIDEBAR.md).
+ * Looks through leading `FOO=bar` assignments, `sudo`/`env` wrappers (and
+ * their own flags), and JS-toolchain launchers (`npx`, `bunx`, `pnpm`/`yarn
+ * dlx`), then basenames what is left. A command that is nothing but wrappers
+ * is returned as written rather than as an empty string. */
+fun programName(command: String): String {
+    val trimmed = command.trim()
+    val words = trimmed.split(Regex("\\s+")).filter { it.isNotEmpty() }
+    if (words.isEmpty()) return trimmed
+
+    var i = 0
+    while (i < words.size && ENV_ASSIGNMENT.matches(words[i])) i++
+    while (i < words.size && words[i] in PLAIN_WRAPPERS) {
+        i++
+        while (i < words.size && (ENV_ASSIGNMENT.matches(words[i]) || words[i].startsWith("-"))) i++
+    }
+    if (i >= words.size) return basename(words.last())
+
+    when {
+        words[i] in DLX_CAPABLE && words.getOrNull(i + 1) == "dlx" -> i += 2
+        words[i] == "npx" || words[i] == "bunx" -> i += 1
+        words[i] == "bun" && words.getOrNull(i + 1) == "x" -> i += 2
+    }
+    val program = words.getOrNull(i) ?: return basename(words.last())
+    return basename(program)
+}
+
+private fun basename(path: String): String = path.substringAfterLast('/')
+
+/** Sessions are grouped by the repository they belong to (#265): a
+ * worktree's `base_repo`, or the session's own `cwd` when it owns none. */
+fun sessionGroupKey(session: Session): String = session.worktree?.base_repo ?: session.cwd
+
+/** One folder in the sidebar tree: a repo/cwd group and the sessions in it,
+ * sorted by name. */
+data class SessionGroup(val key: String, val label: String, val sessions: List<Session>)
+
+/** Group sessions by [sessionGroupKey], each group sorted by name and the
+ * groups themselves sorted by label. */
+fun groupSessions(sessions: Collection<Session>): List<SessionGroup> =
+    sessions
+        .groupBy(::sessionGroupKey)
+        .map { (key, members) ->
+            SessionGroup(
+                key = key,
+                label = key.trimEnd('/').substringAfterLast('/').ifEmpty { key },
+                sessions = members.sortedBy { sessionName(it).lowercase() },
+            )
+        }
+        .sortedBy { it.label.lowercase() }

android/app/src/main/java/pt/naps/maestro/ui/sidebar/SidebarContent.kt

@@ -0,0 +1,123 @@
+package pt.naps.maestro.ui.sidebar
+
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateMapOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.delay
+import pt.naps.maestro.connection.CatalogStore
+import pt.naps.maestro.data.Session
+import pt.naps.maestro.data.Uuid
+
+/** A clock that advances at least once every 30s (docs/SIDEBAR.md), ticked
+ * faster than that so a duration's cutover lands within one visible frame. */
+@Composable
+fun rememberTickingNowMs(periodMs: Long = 5_000L): Long {
+    var now by remember { mutableStateOf(System.currentTimeMillis()) }
+    LaunchedEffect(periodMs) {
+        while (true) {
+            delay(periodMs)
+            now = System.currentTimeMillis()
+        }
+    }
+    return now
+}
+
+/** Assembles the full sidebar from the [CatalogStore] built in #264: sessions
+ * grouped into collapsible folders by repository, each rendered as a
+ * two-line [SessionCard] behind its [ActivityRail]. */
+@Composable
+fun SidebarContent(
+    catalogStore: CatalogStore,
+    onOpenSession: (Session) -> Unit,
+    modifier: Modifier = Modifier,
+    onRenameSession: (Uuid, String) -> Unit = { _, _ -> },
+    onKillSession: (Uuid) -> Unit = {},
+    onSpawnSimilar: (Session) -> Unit = {},
+) {
+    val sessions by catalogStore.sessions.collectAsState()
+    SidebarContent(
+        sessions = sessions.values.toList(),
+        onOpenSession = onOpenSession,
+        modifier = modifier,
+        onRenameSession = onRenameSession,
+        onKillSession = onKillSession,
+        onSpawnSimilar = onSpawnSimilar,
+    )
+}
+
+/** Same as the [CatalogStore]-driven overload, but takes the session list
+ * directly — the shape used by tests and previews. */
+@Composable
+fun SidebarContent(
+    sessions: List<Session>,
+    onOpenSession: (Session) -> Unit,
+    modifier: Modifier = Modifier,
+    onRenameSession: (Uuid, String) -> Unit = { _, _ -> },
+    onKillSession: (Uuid) -> Unit = {},
+    onSpawnSimilar: (Session) -> Unit = {},
+) {
+    val nowMs = rememberTickingNowMs()
+    val groups = remember(sessions) { groupSessions(sessions) }
+    val collapsed = remember { mutableStateMapOf<String, Boolean>() }
+
+    Column(modifier = modifier.fillMaxSize()) {
+        Text(
+            text = "Sessions",
+            style = MaterialTheme.typography.titleMedium,
+            modifier = Modifier.padding(16.dp),
+        )
+        if (groups.isEmpty()) {
+            Box(modifier = Modifier.fillMaxSize().padding(16.dp)) {
+                Text(
+                    text = "No sessions",
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+            return
+        }
+        LazyColumn(modifier = Modifier.fillMaxSize()) {
+            for (group in groups) {
+                val isCollapsed = collapsed[group.key] == true
+                item(key = "folder:${group.key}") {
+                    FolderNode(
+                        label = group.label,
+                        collapsed = isCollapsed,
+                        onToggle = { collapsed[group.key] = !isCollapsed },
+                        depthPadding = 8,
+                    ) {
+                        Column {
+                            for (session in group.sessions) {
+                                SessionCard(
+                                    session = session,
+                                    nowMs = nowMs,
+                                    depthPadding = 16,
+                                    onOpen = onOpenSession,
+                                    onRename = { s, name -> onRenameSession(s.id, name) },
+                                    onKill = { s -> onKillSession(s.id) },
+                                    onSpawnSimilar = onSpawnSimilar,
+                                )
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

android/app/src/test/java/pt/naps/maestro/ui/sidebar/SessionFormattingTest.kt

@@ -0,0 +1,190 @@
+package pt.naps.maestro.ui.sidebar
+
+import kotlinx.serialization.json.JsonPrimitive
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import pt.naps.maestro.data.InTheWay
+import pt.naps.maestro.data.Session
+import pt.naps.maestro.data.SessionStatus
+import pt.naps.maestro.data.SessionWorktree
+
+private fun session(
+    command: String = "claude",
+    cwd: String = "/home/user/project",
+    metadata: Map<String, JsonPrimitive> = emptyMap(),
+    worktree: SessionWorktree? = null,
+    blockedWork: InTheWay? = null,
+    activitySince: String = "1970-01-01T00:00:00Z",
+) = Session(
+    id = "s1",
+    cwd = cwd,
+    command = command,
+    metadata = metadata,
+    worktree = worktree,
+    status = SessionStatus.Running,
+    created_at = "2026-01-01T00:00:00Z",
+    blocked_work = blockedWork,
+    activity_since = activitySince,
+)
+
+class DurationFormattingTest {
+    @Test
+    fun `floors seconds under a minute`() {
+        assertEquals("30s", activityDurationLabel(30_000))
+        assertEquals("59s", activityDurationLabel(59_999))
+    }
+
+    @Test
+    fun `floors minutes under an hour`() {
+        assertEquals("4m", activityDurationLabel(4 * 60_000 + 59_000))
+    }
+
+    @Test
+    fun `floors hours with no days unit`() {
+        assertEquals("2h", activityDurationLabel(2 * 3_600_000 + 59 * 60_000))
+    }
+
+    @Test
+    fun `held ms is null for missing or implausible since`() {
+        assertNull(activityHeldMs(null, 1_000))
+        assertNull(activityHeldMs("", 1_000))
+        assertNull(activityHeldMs("1970-01-01T00:00:00Z", 1_000))
+        assertNull(activityHeldMs("not-a-timestamp", 1_000))
+    }
+
+    @Test
+    fun `held ms is the gap to now for a plausible timestamp`() {
+        val since = "2026-01-01T00:00:00Z"
+        val nowMs = java.time.Instant.parse("2026-01-01T00:00:31Z").toEpochMilli()
+        assertEquals(31_000L, activityHeldMs(since, nowMs))
+    }
+}
+
+class SessionNameTest {
+    @Test
+    fun `falls back to the command when no name is set`() {
+        assertEquals("claude --resume", sessionName(session(command = "claude --resume")))
+    }
+
+    @Test
+    fun `uses the custom name when set`() {
+        val s = session(metadata = mapOf("name" to JsonPrimitive("api-work")))
+        assertEquals("api-work", sessionName(s))
+    }
+
+    @Test
+    fun `an empty stored name is treated as unset`() {
+        val s = session(metadata = mapOf("name" to JsonPrimitive("")))
+        assertNull(customSessionName(s))
+    }
+
+    @Test
+    fun `generated name is provisional, user and haiku are not`() {
+        val generated = session(
+            metadata = mapOf(
+                "name" to JsonPrimitive("brave-otter"),
+                "name_source" to JsonPrimitive("Generated"),
+            ),
+        )
+        val user = session(
+            metadata = mapOf(
+                "name" to JsonPrimitive("api-work"),
+                "name_source" to JsonPrimitive("User"),
+            ),
+        )
+        val unknownSource = session(
+            metadata = mapOf(
+                "name" to JsonPrimitive("api-work"),
+                "name_source" to JsonPrimitive("something-new"),
+            ),
+        )
+        assertTrue(isProvisionalName(generated))
+        assertFalse(isProvisionalName(user))
+        assertFalse(isProvisionalName(unknownSource))
+    }
+}
+
+class BlockerStatsTest {
+    @Test
+    fun `renders insertions and deletions in diff notation`() {
+        val w = InTheWay(uncommitted_files = 2, untracked_files = 3, unpushed_commits = 2, insertions = 124, deletions = 18)
+        val stats = blockerStats(w).associate { it.kind to it.text }
+        assertEquals("+124", stats["add"])
+        assertEquals("-18", stats["del"])
+        assertEquals("?3", stats["untracked"])
+        assertEquals("↑2", stats["unpushed"])
+        assertNull(stats["files"])
+    }
+
+    @Test
+    fun `falls back to a file count when a tracked change carries no line delta`() {
+        val w = InTheWay(uncommitted_files = 2, insertions = 0, deletions = 0)
+        val stats = blockerStats(w)
+        assertEquals(listOf(BlockerStat("files", "~2")), stats)
+    }
+
+    @Test
+    fun `session blockers are null when nothing blocks a kill`() {
+        assertNull(sessionBlockers(session(blockedWork = null)))
+        assertNull(sessionBlockers(session(blockedWork = InTheWay())))
+    }
+
+    @Test
+    fun `format in the way spells out zero as no unsaved work`() {
+        assertEquals("no unsaved work", formatInTheWay(InTheWay()))
+        assertEquals("1 uncommitted file, 2 untracked files", formatInTheWay(InTheWay(uncommitted_files = 1, untracked_files = 2)))
+    }
+}
+
+class ProgramNameTest {
+    @Test
+    fun `drops arguments and basenames the path`() {
+        assertEquals("claude", programName("/usr/local/bin/claude -p hi"))
+        assertEquals("claude", programName("claude --dangerously-skip-permissions"))
+    }
+
+    @Test
+    fun `looks through leading env assignments`() {
+        assertEquals("claude", programName("FOO=bar BAZ=qux claude --resume"))
+    }
+
+    @Test
+    fun `looks through sudo and env wrappers with their own flags`() {
+        assertEquals("claude", programName("sudo claude"))
+        assertEquals("claude", programName("env -i FOO=bar claude"))
+    }
+
+    @Test
+    fun `looks through js-toolchain launchers`() {
+        assertEquals("claude-code", programName("npx claude-code"))
+        assertEquals("claude", programName("pnpm dlx claude"))
+        assertEquals("claude", programName("bunx claude"))
+    }
+
+    @Test
+    fun `a command that is nothing but wrappers is shown as written`() {
+        assertEquals("sudo", programName("sudo"))
+    }
+}
+
+class GroupingTest {
+    @Test
+    fun `groups by worktree base_repo when present`() {
+        val a = session(cwd = "/wt/a", worktree = SessionWorktree(path = "/wt/a", base_repo = "/home/user/maestro"))
+        val b = session(cwd = "/wt/b", worktree = SessionWorktree(path = "/wt/b", base_repo = "/home/user/maestro"))
+        val groups = groupSessions(listOf(a, b))
+        assertEquals(1, groups.size)
+        assertEquals("maestro", groups.single().label)
+        assertEquals(2, groups.single().sessions.size)
+    }
+
+    @Test
+    fun `falls back to cwd with no worktree`() {
+        val a = session(cwd = "/home/user/scratch")
+        val groups = groupSessions(listOf(a))
+        assertEquals("scratch", groups.single().label)
+    }
+}