feat(maestro): add Android wire-format data types

Kotlin data classes mirroring maestro-protocol's wire types (Session,
CatalogEvent, ClientControl, structured-session projections, etc.),
@Serializable with kotlinx-serialization. ActivityState and NameSource
carry custom lenient deserializers matching the Rust side's forward-
compat behavior: an unknown variant degrades to the neutral default
instead of failing the whole payload.

Verified against fixtures mirrored from maestro-protocol's own test
suite (tag placement, snake_case renames, legacy-payload defaults).

android/app/src/main/java/pt/naps/maestro/data/ActivityState.kt

@@ -0,0 +1,43 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+/**
+ * Session activity, orthogonal to [SessionStatus]. Mirrors
+ * `maestro_protocol::ActivityState`.
+ *
+ * Deserializes leniently: an unknown variant from a newer daemon decodes as
+ * [Idle] instead of failing the whole [Session].
+ */
+@Serializable(with = ActivityStateSerializer::class)
+enum class ActivityState {
+    Active,
+    Idle,
+    AwaitingInput,
+    Error,
+    Starting,
+}
+
+object ActivityStateSerializer : KSerializer<ActivityState> {
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("ActivityState", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: ActivityState) {
+        encoder.encodeString(value.name)
+    }
+
+    override fun deserialize(decoder: Decoder): ActivityState =
+        when (decoder.decodeString()) {
+            "Active" -> ActivityState.Active
+            "AwaitingInput" -> ActivityState.AwaitingInput
+            "Error" -> ActivityState.Error
+            "Starting" -> ActivityState.Starting
+            else -> ActivityState.Idle
+        }
+}

android/app/src/main/java/pt/naps/maestro/data/ApiError.kt

@@ -0,0 +1,19 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** Structured failure body inside an [ApiError] envelope. Mirrors
+ * `maestro_protocol::ErrorInfo`. */
+@Serializable
+data class ErrorInfo(
+    val code: String,
+    val message: String,
+    /** Set only by the kill guard: what blocked an unforced
+     * `DELETE /api/sessions/:id`. */
+    val unsaved_work: InTheWay? = null,
+)
+
+/** The envelope every `/api` failure is wrapped in: `{"error": {...}}`.
+ * Mirrors `maestro_protocol::ApiError`. */
+@Serializable
+data class ApiError(val error: ErrorInfo)

android/app/src/main/java/pt/naps/maestro/data/BranchInfo.kt

@@ -0,0 +1,17 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** One local branch of a repository, from `GET /api/branches`. A client
+ * disables the entry when [is_head] is set or [worktree] is present — git
+ * refuses to check the same branch out in two worktrees at once. Mirrors
+ * `maestro_protocol::BranchInfo`. */
+@Serializable
+data class BranchInfo(
+    /** Short branch name (`main`, `feature/foo`). */
+    val name: String,
+    /** Whether this branch is the main checkout's current HEAD. */
+    val is_head: Boolean,
+    /** Toplevel path of the linked worktree holding this branch, if any. */
+    val worktree: String? = null,
+)

android/app/src/main/java/pt/naps/maestro/data/CatalogEvent.kt

@@ -0,0 +1,37 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * Messages the daemon broadcasts to clients over `WS /api/events`. Mirrors
+ * `maestro_protocol::CatalogEvent`; tagged by a `type` field.
+ *
+ * A subscriber receives a single [Snapshot] immediately on connect, then a
+ * stream of deltas as sessions are created, updated, and killed. Skipped
+ * events (broadcast channel lag) surface as [Lagged].
+ */
+@Serializable
+sealed class CatalogEvent {
+    @Serializable
+    @SerialName("Snapshot")
+    data class Snapshot(val sessions: List<Session>) : CatalogEvent()
+
+    @Serializable
+    @SerialName("SessionAdded")
+    data class SessionAdded(val session: Session) : CatalogEvent()
+
+    @Serializable
+    @SerialName("SessionRemoved")
+    data class SessionRemoved(val id: Uuid) : CatalogEvent()
+
+    @Serializable
+    @SerialName("SessionUpdated")
+    data class SessionUpdated(val session: Session) : CatalogEvent()
+
+    /** Server-issued notification that the broadcast queue dropped frames.
+     * Clients should re-fetch a full snapshot. */
+    @Serializable
+    @SerialName("Lagged")
+    data class Lagged(val skipped: Long) : CatalogEvent()
+}

android/app/src/main/java/pt/naps/maestro/data/ClientControl.kt

@@ -0,0 +1,30 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/** Text-frame control messages on a `WS /api/attach/:id` connection. PTY
+ * bytes travel in binary frames and are not modeled here. Mirrors
+ * `maestro_protocol::ClientControl`; tagged by a `type` field. */
+@Serializable
+sealed class ClientControl {
+    @Serializable
+    @SerialName("Resize")
+    data class Resize(val cols: Int, val rows: Int) : ClientControl()
+
+    @Serializable
+    @SerialName("Ping")
+    object Ping : ClientControl()
+
+    @Serializable
+    @SerialName("Pong")
+    object Pong : ClientControl()
+
+    @Serializable
+    @SerialName("Error")
+    data class Error(
+        val code: String,
+        val message: String,
+        val unsaved_work: InTheWay? = null,
+    ) : ClientControl()
+}

android/app/src/main/java/pt/naps/maestro/data/DaemonInfo.kt

@@ -0,0 +1,41 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** `GET /api/info` — the daemon's identity plus its spawn presets. Mirrors
+ * `maestro_protocol::DaemonInfo`. */
+@Serializable
+data class DaemonInfo(
+    val hostname: String = "",
+    /** The protocol version the daemon implements. */
+    val version: String = "",
+    /** Home dir of the user the daemon runs as; empty for older daemons. */
+    val home_dir: String = "",
+    val presets: List<SpawnPreset> = emptyList(),
+    val build: BuildInfo = BuildInfo(),
+    /** Identity of the daemon *process*, regenerated on every start — a
+     * changed value across a reconnect means the daemon restarted. */
+    val instance: String = "",
+    /** Canonical leader key the operator configured (`[tui].leader`), so a
+     * client binds the same chord the TUI does. Empty means "use your
+     * default". */
+    val leader: String = "",
+)
+
+/** A spawn-form command preset advertised by the daemon. */
+@Serializable
+data class SpawnPreset(
+    val id: String,
+    val label: String,
+    val command: String,
+    val auto_approve: Boolean = false,
+)
+
+/** Build provenance of the running daemon. Every field is empty when the
+ * binary was built outside a git checkout. */
+@Serializable
+data class BuildInfo(
+    val commit: String = "",
+    val commit_date: String = "",
+    val dirty: Boolean = false,
+)

android/app/src/main/java/pt/naps/maestro/data/Dirs.kt

@@ -0,0 +1,33 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** `GET /api/dirs?path=` — one directory's immediate subdirectories. Mirrors
+ * `maestro_protocol::DirListing`. */
+@Serializable
+data class DirListing(
+    /** Resolved absolute directory that was listed (after ~/relative
+     * expansion). */
+    val path: String,
+    /** Immediate subdirectory names, sorted case-insensitively. */
+    val entries: List<String> = emptyList(),
+    /** True when the listing was capped server-side. */
+    val truncated: Boolean = false,
+)
+
+/** One deduplicated recent working dir for the spawn form's recents picker.
+ * Mirrors `maestro_protocol::RecentDir`. */
+@Serializable
+data class RecentDir(
+    val cwd: String,
+    val last_command: String,
+    val last_used: IsoTimestamp,
+)
+
+/** `GET /api/recent-dirs` — the daemon's recent working dirs, newest-first
+ * and deduped by `cwd`. */
+@Serializable
+data class RecentDirs(
+    val dirs: List<RecentDir> = emptyList(),
+    val truncated: Boolean = false,
+)

android/app/src/main/java/pt/naps/maestro/data/GitRoot.kt

@@ -0,0 +1,9 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** `GET /api/gitroot?path=` — the enclosing repo toplevel of a path, or
+ * `null` when the path isn't inside a repo. Mirrors
+ * `maestro_protocol::GitRoot`. */
+@Serializable
+data class GitRoot(val root: String? = null)

android/app/src/main/java/pt/naps/maestro/data/Ids.kt

@@ -0,0 +1,7 @@
+package pt.naps.maestro.data
+
+/** A session id. Mirrors `uuid::Uuid` on the wire — a plain UUID string. */
+typealias Uuid = String
+
+/** An RFC 3339 timestamp, as the daemon serializes `chrono::DateTime<Utc>`. */
+typealias IsoTimestamp = String

android/app/src/main/java/pt/naps/maestro/data/InTheWay.kt

@@ -0,0 +1,17 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** What currently blocks an unforced kill of a session's worktree,
+ * recomputed by the daemon on every read. Mirrors
+ * `maestro_protocol::InTheWay`. */
+@Serializable
+data class InTheWay(
+    val uncommitted_files: Int = 0,
+    val untracked_files: Int = 0,
+    val unpushed_commits: Int = 0,
+    /** Lines added across the tracked changes, staged and unstaged together. */
+    val insertions: Int = 0,
+    /** Lines removed across the same tracked changes. */
+    val deletions: Int = 0,
+)

android/app/src/main/java/pt/naps/maestro/data/NameBatch.kt

@@ -0,0 +1,8 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** `GET /api/names?count=N` — a batch of fresh session handles. Mirrors
+ * `maestro_protocol::NameBatch`. */
+@Serializable
+data class NameBatch(val names: List<String>)

android/app/src/main/java/pt/naps/maestro/data/NameSource.kt

@@ -0,0 +1,40 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+/**
+ * Where a session's stored name (`metadata["name"]`) came from. Mirrors
+ * `maestro_protocol::NameSource`.
+ *
+ * Deserializes leniently: an unknown spelling decodes as [User], the settled
+ * variant — a name wrongly painted as settled is only a missed dimming; one
+ * wrongly painted as provisional invites overwriting a name a person chose.
+ */
+@Serializable(with = NameSourceSerializer::class)
+enum class NameSource {
+    User,
+    Generated,
+    Haiku,
+}
+
+object NameSourceSerializer : KSerializer<NameSource> {
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("NameSource", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: NameSource) {
+        encoder.encodeString(value.name)
+    }
+
+    override fun deserialize(decoder: Decoder): NameSource =
+        when (decoder.decodeString()) {
+            "Generated" -> NameSource.Generated
+            "Haiku" -> NameSource.Haiku
+            else -> NameSource.User
+        }
+}

android/app/src/main/java/pt/naps/maestro/data/Project.kt

@@ -0,0 +1,21 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+
+/** One discovered git repository (or linked worktree) for `GET
+ * /api/projects`. Mirrors `maestro_protocol::Project`. */
+@Serializable
+data class Project(
+    /** Absolute path of the repository/worktree toplevel. */
+    val path: String,
+    /** Basename of [path]. */
+    val name: String,
+    val is_worktree: Boolean = false,
+    /** The main checkout this worktree belongs to; `null` on plain repos. */
+    val base_repo: String? = null,
+    /** Later of the repo's git HEAD mtime and the newest spawn-history use of
+     * any directory inside it; `null` when neither is known. */
+    val last_activity: IsoTimestamp? = null,
+    /** Command last spawned in this project, from spawn history. */
+    val last_command: String? = null,
+)

android/app/src/main/java/pt/naps/maestro/data/Session.kt

@@ -0,0 +1,71 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
+
+/** Default for [Session.last_activity_at] / [Session.activity_since] when an
+ * older payload omits them — mirrors the daemon's Unix-epoch default. */
+const val EPOCH: IsoTimestamp = "1970-01-01T00:00:00Z"
+
+/** A live or recently-dead tmux session managed by the daemon. Mirrors
+ * `maestro_protocol::Session`. */
+@Serializable
+data class Session(
+    val id: Uuid,
+    val cwd: String,
+    val command: String,
+    val env: Map<String, String> = emptyMap(),
+    val metadata: Map<String, JsonElement> = emptyMap(),
+    /** The worktree this session owns, when it was spawned with one. */
+    val worktree: SessionWorktree? = null,
+    val status: SessionStatus,
+    val created_at: IsoTimestamp,
+    /** Current foreground command in the pane (e.g. `claude`, `bash`), as the
+     * daemon's activity watcher observed it. `null` until observed. */
+    val foreground: String? = null,
+    /** Inferred activity dimension, orthogonal to [status]. */
+    val activity: ActivityState = ActivityState.Idle,
+    /** Short human string an agent reported alongside its activity — e.g. why
+     * it is in [ActivityState.Error]. `null` unless an agent reported one. */
+    val activity_detail: String? = null,
+    val last_activity_at: IsoTimestamp = EPOCH,
+    val activity_since: IsoTimestamp = EPOCH,
+    /** The pane's *current* working directory, distinct from [cwd] (the spawn
+     * dir). `null` until first observed. */
+    val current_cwd: String? = null,
+    /** What currently blocks an unforced kill of this session, as the
+     * daemon's watcher last probed it. `null` while clear or not yet probed. */
+    val blocked_work: InTheWay? = null,
+    /** When this session last became the pane a client was showing. `null`
+     * until the session has been focused at least once. */
+    val last_focused_at: IsoTimestamp? = null,
+    /** Terminal (PTY bytes) or structured (ACP rows). Fixed at spawn and
+     * immutable for the session's life. */
+    val view: SessionView = SessionView.Terminal,
+    /** The ACP session id the selected provider adapter returned from
+     * `session/new`. Only a [SessionView.Structured] session whose handshake
+     * succeeded has one. */
+    val acp_session_id: String? = null,
+    /** When `true`, the daemon auto-approves every ACP permission request for
+     * this session instead of surfacing them to the client. */
+    val auto_approve: Boolean = false,
+    /** Prompts queued on the daemon while a turn was in flight or the adapter
+     * was still booting. */
+    val queued_prompts: List<String> = emptyList(),
+)
+
+@Serializable
+enum class SessionStatus { Running, Dead }
+
+/** A session's process shape: mirrors `maestro_protocol::SessionView`.
+ * `Terminal` is the default. */
+@Serializable
+enum class SessionView { Terminal, Structured }
+
+/** A session's daemon-created worktree. `base_repo` is the repository's main
+ * checkout, which is what the session tree groups by. */
+@Serializable
+data class SessionWorktree(
+    val path: String,
+    val base_repo: String,
+)

android/app/src/main/java/pt/naps/maestro/data/SessionRequests.kt

@@ -0,0 +1,43 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
+
+/** `POST /api/sessions` body. Mirrors
+ * `maestro_protocol::CreateSessionRequest`. */
+@Serializable
+data class CreateSessionRequest(
+    val cwd: String,
+    val command: String,
+    val env: Map<String, String> = emptyMap(),
+    val metadata: Map<String, JsonElement> = emptyMap(),
+    val worktree: WorktreeSpec? = null,
+    /** The process shape to spawn. Defaults to a `Terminal` session. */
+    val view: SessionView = SessionView.Terminal,
+    /** When `true`, the daemon auto-approves every ACP permission request for
+     * this structured session. */
+    val auto_approve: Boolean = false,
+)
+
+/** Optional worktree request attached to a [CreateSessionRequest]. Mirrors
+ * `maestro_protocol::WorktreeSpec`. */
+@Serializable
+data class WorktreeSpec(
+    val base_repo: String,
+    val branch: String,
+    /** When `false`, [branch] already exists and is checked out as-is.
+     * Defaults to `true` (create a new branch). */
+    val create_branch: Boolean = true,
+)
+
+/** `PATCH /api/sessions/:id` body: rename a live session. An empty [name]
+ * clears the custom one, so the card falls back to the command. Mirrors
+ * `maestro_protocol::RenameSessionRequest`. */
+@Serializable
+data class RenameSessionRequest(val name: String)
+
+/** `POST /api/sessions/:id/focus` body: a client reports whether its pane is
+ * the one currently showing this session. Mirrors
+ * `maestro_protocol::SetFocusRequest`. */
+@Serializable
+data class SetFocusRequest(val focused: Boolean)

android/app/src/main/java/pt/naps/maestro/data/Structured.kt

@@ -0,0 +1,136 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
+
+/** The semantic shape of a [TranscriptRow]. Mirrors
+ * `maestro_protocol::TranscriptRowKind`, snake_case on the wire. */
+@Serializable
+enum class TranscriptRowKind {
+    @SerialName("user") User,
+    @SerialName("agent_text") AgentText,
+    @SerialName("agent_thought") AgentThought,
+    @SerialName("tool_call") ToolCall,
+    @SerialName("tool_diff") ToolDiff,
+    @SerialName("approval") Approval,
+    @SerialName("plan") Plan,
+    @SerialName("notice") Notice,
+}
+
+/** One client-neutral item in a structured session transcript. [data]
+ * preserves the ACP payload verbatim without committing to an ACP
+ * dependency. Mirrors `maestro_protocol::TranscriptRow`. */
+@Serializable
+data class TranscriptRow(
+    /** Stable within one session, so later deltas can address this row. */
+    val id: String,
+    val kind: TranscriptRowKind,
+    val data: JsonElement,
+)
+
+/** The complete transcript at a durable event-log position — a structured
+ * session's first `WS /api/structured/:id` message. Mirrors
+ * `maestro_protocol::TranscriptSnapshot`. */
+@Serializable
+data class TranscriptSnapshot(
+    val cursor: Long,
+    val rows: List<TranscriptRow> = emptyList(),
+)
+
+/** A change to one transcript row, addressed by [id]. Mirrors
+ * `maestro_protocol::TranscriptDelta`; tagged by a snake_case `type` field. */
+@Serializable
+sealed class TranscriptDelta {
+    @Serializable
+    @SerialName("append")
+    data class Append(val row: TranscriptRow) : TranscriptDelta()
+
+    @Serializable
+    @SerialName("patch")
+    data class Patch(val row: TranscriptRow) : TranscriptDelta()
+
+    @Serializable
+    @SerialName("remove")
+    data class Remove(val id: String) : TranscriptDelta()
+}
+
+/** Per-turn indicators derived from the ACP stream — read verbatim, never
+ * re-derived client-side. Mirrors `maestro_protocol::TurnState`. */
+@Serializable
+data class TurnState(
+    val responding: Boolean = false,
+    val thinking: Boolean = false,
+    val active_tool_calls: List<String> = emptyList(),
+    /** Wall-clock start of the active prompt, so a reconnecting client keeps
+     * one continuous elapsed-time display instead of restarting at zero. */
+    val started_at: IsoTimestamp? = null,
+    val started_context_tokens: Long? = null,
+)
+
+/**
+ * A whole-session view derived from ACP notifications. Mirrors
+ * `maestro_protocol::ReducedState`.
+ *
+ * [pending_approval], [plan], [usage], [context] and [config_options] carry
+ * opaque ACP JSON — their shape is ACP's, not covered by this crate's own
+ * compatibility guarantee, so they are kept as [JsonElement] rather than
+ * modeled strongly.
+ */
+@Serializable
+data class ReducedState(
+    val turn: TurnState = TurnState(),
+    val pending_approval: JsonElement? = null,
+    val plan: JsonElement? = null,
+    val usage: JsonElement? = null,
+    val context: JsonElement? = null,
+    val model: String? = null,
+    val mode: String? = null,
+    val config_options: JsonElement? = null,
+    /** Prompts queued on the daemon while a turn is in flight. */
+    val queued_prompts: List<String> = emptyList(),
+)
+
+/** Server messages on `WS /api/structured/:id`. Mirrors
+ * `maestro_protocol::StructuredEvent`; tagged by a snake_case `type` field. */
+@Serializable
+sealed class StructuredEvent {
+    @Serializable
+    @SerialName("transcript_snapshot")
+    data class TranscriptSnapshotEvent(val snapshot: TranscriptSnapshot) : StructuredEvent()
+
+    @Serializable
+    @SerialName("reduced_state")
+    data class ReducedStateEvent(val state: ReducedState) : StructuredEvent()
+
+    @Serializable
+    @SerialName("projection_update")
+    data class ProjectionUpdate(
+        val transcript: TranscriptDelta? = null,
+        val state: ReducedState,
+    ) : StructuredEvent()
+}
+
+/** `POST /api/sessions/:id/structured/prompt` body. */
+@Serializable
+data class StructuredPromptRequest(val prompt: String)
+
+/** `POST /api/sessions/:id/structured/config` body: change one option
+ * advertised by a live ACP session. */
+@Serializable
+data class StructuredConfigRequest(val config_id: String, val value: JsonElement)
+
+/** Operator decision for a pending ACP permission request
+ * (`POST /api/sessions/:id/structured/approvals/:nonce` body) — a bare JSON
+ * string on the wire, not `{decision: ...}`. Mirrors
+ * `maestro_protocol::StructuredApprovalDecision`. */
+@Serializable
+enum class StructuredApprovalDecision {
+    @SerialName("allow_once") AllowOnce,
+    @SerialName("allow_for_session") AllowForSession,
+    @SerialName("deny") Deny,
+}
+
+/** Response of `POST /api/sessions/:id/structured/attachments`. */
+@Serializable
+data class StructuredAttachmentResponse(val path: String)

android/app/src/test/java/pt/naps/maestro/data/WireSerializationTest.kt

@@ -0,0 +1,114 @@
+package pt.naps.maestro.data
+
+import kotlinx.serialization.decodeFromString
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/** Wire-format checks against fixtures mirrored from
+ * `crates/maestro-protocol/src/lib.rs`'s own test suite, so a Kotlin type
+ * that drifts from the Rust source of truth fails here first. */
+class WireSerializationTest {
+    private val json = Json { ignoreUnknownKeys = true; isLenient = true }
+
+    private fun legacySessionJson(extra: String = "") = """
+        {"id":"00000000-0000-0000-0000-000000000001","cwd":"/tmp","command":"bash",
+         "status":"Running","created_at":"2026-05-24T12:00:00Z"$extra}
+    """.trimIndent()
+
+    @Test
+    fun `legacy session payload defaults new fields`() {
+        val s = json.decodeFromString<Session>(legacySessionJson())
+        assertEquals(ActivityState.Idle, s.activity)
+        assertEquals(SessionView.Terminal, s.view)
+        assertNull(s.foreground)
+        assertNull(s.blocked_work)
+        assertEquals(EPOCH, s.last_activity_at)
+    }
+
+    @Test
+    fun `unknown activity state degrades to Idle`() {
+        val s = json.decodeFromString<Session>(legacySessionJson(""","activity":"QuantumEntangled""""))
+        assertEquals(ActivityState.Idle, s.activity)
+    }
+
+    @Test
+    fun `unknown name source degrades to User`() {
+        assertEquals(NameSource.User, json.decodeFromString<NameSource>("\"Rolled\""))
+        assertEquals(NameSource.Haiku, json.decodeFromString<NameSource>("\"Haiku\""))
+    }
+
+    @Test
+    fun `catalog event tags by type`() {
+        assertEquals(
+            """{"type":"Lagged","skipped":3}""",
+            json.encodeToString<CatalogEvent>(CatalogEvent.Lagged(3)),
+        )
+        val removed = CatalogEvent.SessionRemoved("00000000-0000-0000-0000-000000000001")
+        assertEquals(removed, json.decodeFromString<CatalogEvent>(json.encodeToString<CatalogEvent>(removed)))
+    }
+
+    @Test
+    fun `client control tags by type`() {
+        assertEquals(
+            """{"type":"Resize","cols":120,"rows":40}""",
+            json.encodeToString<ClientControl>(ClientControl.Resize(120, 40)),
+        )
+        assertEquals(ClientControl.Ping, json.decodeFromString<ClientControl>("""{"type":"Ping"}"""))
+    }
+
+    @Test
+    fun `structured approval decision is a bare string`() {
+        assertEquals(
+            StructuredApprovalDecision.AllowOnce,
+            json.decodeFromString<StructuredApprovalDecision>("\"allow_once\""),
+        )
+        assertEquals(
+            "\"allow_for_session\"",
+            json.encodeToString(StructuredApprovalDecision.AllowForSession),
+        )
+    }
+
+    @Test
+    fun `structured event tags snake_case`() {
+        val event = json.decodeFromString<StructuredEvent>(
+            """{"type":"transcript_snapshot","snapshot":{"cursor":7,"rows":[]}}""",
+        )
+        assertTrue(event is StructuredEvent.TranscriptSnapshotEvent)
+        assertEquals(7L, (event as StructuredEvent.TranscriptSnapshotEvent).snapshot.cursor)
+    }
+
+    @Test
+    fun `transcript delta tags snake_case and round trips`() {
+        val row = TranscriptRow(
+            id = "tool:read-1",
+            kind = TranscriptRowKind.ToolCall,
+            data = json.parseToJsonElement("""{"name":"vendor.read"}"""),
+        )
+        val patch = TranscriptDelta.Patch(row)
+        val encoded = json.encodeToString<TranscriptDelta>(patch)
+        assertTrue(encoded.startsWith("""{"type":"patch","row":"""))
+        assertEquals(patch, json.decodeFromString<TranscriptDelta>(encoded))
+        assertEquals("\"agent_thought\"", json.encodeToString(TranscriptRowKind.AgentThought))
+    }
+
+    @Test
+    fun `rename request encodes plainly`() {
+        assertEquals(
+            """{"name":"amber-falcon"}""",
+            json.encodeToString(RenameSessionRequest("amber-falcon")),
+        )
+    }
+
+    @Test
+    fun `api error decodes nested unsaved work with defaults`() {
+        val apiError = json.decodeFromString<ApiError>(
+            """{"error":{"code":"unsaved_work","message":"nope","unsaved_work":{"uncommitted_files":3}}}""",
+        )
+        assertEquals(3, apiError.error.unsaved_work?.uncommitted_files)
+        assertEquals(0, apiError.error.unsaved_work?.unpushed_commits)
+    }
+}