Merge branch 'main' of git.arirex.me:iris/ai-app

AGENTS.md

@@ -89,7 +89,11 @@ repo is in PLAN.md's "Backend layout" section.
   codepoint in the Kotlin that the script did not subset is a glyph that
   silently isn't there. Rerun the script and commit its output when adding
   one; it needs network access. `md-cog` and `md-refresh` are deliberately
-  the same codepoints dev-updater uses and must not drift from it.
+  the same codepoints dev-updater uses and must not drift from it. The
+  subset is the **Mono** face, where every glyph is one em square — that is
+  what makes two icon buttons the same width without either being given
+  one, and it is why `GLYPH_SIZE` is smaller than it looks like it should
+  be.
 - `.dev-updater.ron` — what Dev Updater is asked to do with this checkout:
   the server (built in `server/`, run as `service: Managed(...)`) and the
   APK (built in `app/`), built in parallel. The project it serves is the
@@ -221,16 +225,19 @@ first if a remote spawn ever mangles an argument.
   The emulator app reaches it at `https://10.0.2.2:8443`; enroll it with
   `adb -s "$SERIAL" shell "am start -a android.intent.action.VIEW -d 'aiapp://enroll?host=10.0.2.2&port=8443&token=…'"`
   (quote so the device shell doesn't eat the `&`s).
-- **Name the device on every `adb` call.** This checkout runs its own
+- **The emulator is `~/repos/emulator-tools`' business, not this repo's.**
-  emulator — `run-android.sh` derives the AVD name from the directory, so
+  `emu up` creates and boots the AVD named after this checkout (`ai-app-2`),
-  a second clone gets a second AVD rather than queueing for one shared
+  refusing when the machine has no room for one; `emu list` says what is
-  machine-wide `tdep`. With more than one attached, a bare `adb shell` or
+  attached and what it costs; `emu down` stops it. `run-android.sh` is that
-  `adb get-state` fails with `more than one device/emulator` and a bare
+  plus a build and an install. Run that repo's `install.sh` once if `emu` is
-  `adb shell pm list packages` comes back **empty**, which reads as the app
+  missing.
-  having been uninstalled rather than as the question being ambiguous.
+  The `adb` on `PATH` after sourcing `android-env.sh` is that repo's wrapper,
-  Get the serial the way `run-android.sh` does — match `adb -s <serial> emu
+  which fills in `-s` from the same rule — so a bare `adb shell` reaches this
-  avd name` against the AVD — or export `ANDROID_SERIAL`, which every
+  checkout's emulator and refuses to reach another one's. That defaulting is
-  `adb` call honours without `-s`.
+  what makes the old advice unnecessary rather than wrong: with two attached
+  and no `-s`, a bare `adb shell pm list packages` comes back **empty**,
+  which reads as the app having been uninstalled rather than as the question
+  being ambiguous.
 
 ## Where things run (host vs this VM)
 
@@ -280,15 +287,21 @@ day:
 - **Stopping the server no longer stops the sessions.** After `pkill
   ai-server` the `claude` processes are still there, on purpose, and the
   next start picks them up (`reattaching to the claude-cli it left
-  running` in the log). To actually end one, delete the session — that is
+  running` in the log). To end one, either `POST /sessions/{id}/stop` —
-  the only path that stops a process.
+  which keeps the session and its transcript, and `POST .../start` brings
+  the process back on the same conversation — or delete the session, which
+  ends the conversation too.
 - **Each session directory now holds `process.json`, `stdin.fifo`,
   `stdout.log` and `stderr.log`.** `stdout.log` is the driver's input, read
   from the byte offset in `process.json`; removing either by hand while the
   session is live loses output or replays it.
 - **`--resume` only ever runs when nothing is running.** That check is the
   fix for the incident below, and the reason there is one entry point
-  (`ClaudeDriver::launch`) rather than a spawn and an attach.
+  (`ClaudeDriver::launch`) rather than a spawn and an attach. The status a
+  launch reports obeys the same rule: a session recorded as `exited` whose
+  launch has just started a process reports `idle`, because `exited` is the
+  word that refuses every command and offers a phone the chance to start a
+  second CLI on a live conversation.
 - Remote sessions are adopted too. The pid recorded for one is the **`ssh`
   client's**, on this machine — that is the process the backend owns, and it
   lives as long as the remote command does. (This said "local only" until

PLAN.md

@@ -298,6 +298,65 @@ Two consequences worth stating:
 going away and means to come back) and `stop` (the session is being deleted,
 so the process must not survive). Every driver owes exactly one of them.
 
+### Stopping and starting a session's process (decided 2026-08-30)
+
+If a session outlives the backend, the person holding the phone needs the
+other direction too: **end the process without ending the session, and start
+it again on the same conversation.** `POST /sessions/:id/stop` and
+`/start`.
+
+Three decisions worth not undoing:
+
+- **Stop signals the recorded process and says nothing else.** It does not
+  go through the driver and it does not announce `Exited`. The record is the
+  session's rather than any dialect's, so signalling it here works for a
+  session whose driver is in no state to be asked and adds no trait method a
+  new driver could implement wrongly — and the driver's own reader already
+  reports the death correctly, draining the last output and recording the
+  status. Announcing it from here would be a guess arriving ahead of the
+  measurement, and wrong for the grace period a process that ignores SIGTERM
+  keeps running.
+- **Start replaces the driver and nothing else.** The transcript, the event
+  pump and the SSE stream every open phone is reading stay where they were,
+  so starting a session again is not a reconnect for anybody watching, and
+  there is still exactly one writer of the transcript — which relaunching
+  the whole `LiveSession` would not be, since the old pump outlives its
+  session and an imported session's sync task would go on feeding it.
+  `LiveSession` and `Commands` therefore share one `Mutex<Arc<dyn Driver>>`
+  rather than each holding a copy.
+- **Start is refused unless the session is *known* to have exited.**
+  `Unknown` means nobody could find out whether the process is alive, and
+  starting one on that is exactly the two-CLIs-on-one-conversation fault
+  `session::process` exists to prevent.
+
+That last rule found a real bug in the launch path, which is where the phone
+would have hit it: a relaunched session took its status from the transcript,
+so one whose process had died before a backend restart reported `Exited`
+while the launch it had just gone through was starting a new process —
+`Exited` there is not merely stale, it is the word that refuses every command
+and invites somebody to start a second process against a live conversation.
+
+**Who says so matters as much as what is said.** The first fix wrote `Idle`
+straight into the manager's view, and that produced a second bug on the
+phone: the session list reads the manager's status and the session screen
+replays the transcript, so a status written in one and not the other is two
+screens disagreeing about one session — visible as a stop button that turned
+into a play button a moment after the screen opened. So the rule is that
+**a driver announces the state it starts in, through the event sink**, which
+is what `EchoDriver::new` and `LlamaDriver::attached` already did;
+`ClaudeDriver` was the one that started a process silently. It says `Idle`
+only when it *started* one — adopting says nothing, because a process that
+was already running may be mid-turn and the transcript's last word is the
+better answer until its output says otherwise. Coming from the driver also
+orders it against the exit `follow` reports, which a status written from the
+manager could not be.
+
+On the phone this is one button in the composer, left of Send, whose mark and
+colour say what pressing it would do now: an orange pause while a turn is
+running (interrupt — the process stays), a red stop when it is not (end the
+process), and a green play when it has exited (start it again). One button
+rather than three that come and go, so its presence is never the signal.
+
 ### Importing refuses a session that is already open (decided 2026-08-29)
 
 Claude Code keeps a descriptor per live session at
@@ -448,7 +507,9 @@ POST /sessions                        spawn {provider, host, model, cwd, permiss
 GET  /sessions/:id/events?after=N     SSE: transcript replay from N, then live
 POST /sessions/:id/message            {text, attachment_ids}
 POST /sessions/:id/answer             {question_id, answer}   (questions and permissions)
-POST /sessions/:id/interrupt
+POST /sessions/:id/interrupt          stop the running turn; the process stays
+POST /sessions/:id/stop               end the process; the session and transcript stay
+POST /sessions/:id/start              run the process again, continuing the conversation
 POST /sessions/:id/model              {model}
 POST /sessions/:id/compact            (llama sessions)
 POST /sessions/:id/attachments        multipart upload → id (referenced by /message)

app/androidApp/src/main/kotlin/com/example/aiapp/Api.kt

@@ -558,6 +558,22 @@ fun interruptSession(settings: ServerSettings, sessionId: String) {
     requestFromServer(settings, "/sessions/$sessionId/interrupt", method = "POST") {}
 }
 
+/**
+ * Ends the process behind a session, leaving the session and its transcript.
+ *
+ * Not a delete and not an interrupt: the conversation stays exactly where it is and [startSession]
+ * picks it back up. The server reports what it could not do -- there was nothing running, or the
+ * machine would not say whether there was -- rather than answering the same way either way.
+ */
+fun stopSession(settings: ServerSettings, sessionId: String) {
+    requestFromServer(settings, "/sessions/$sessionId/stop", method = "POST") {}
+}
+
+/** Starts the process again on the conversation it left. See [stopSession]. */
+fun startSession(settings: ServerSettings, sessionId: String) {
+    requestFromServer(settings, "/sessions/$sessionId/start", method = "POST") {}
+}
+
 /**
  * Removes a Claude Code session from the machine.
  *

app/androidApp/src/main/kotlin/com/example/aiapp/NerdIcons.kt

@@ -31,6 +31,12 @@ import androidx.compose.ui.unit.sp
  * tofu. Adding one means adding its codepoint in *both* places; a codepoint here that the script
  * did not subset is a glyph that silently isn't there.
  *
+ * The subset is the font's **Mono** face, where every glyph is exactly one em wide and one em tall.
+ * That is what makes two icons the same size without either of them being given a size: the
+ * proportional face's advances run from 0.46 em to 0.92 em, so a Send button and a Stop button side
+ * by side came out visibly different widths, and matching them at the call site would have meant
+ * one hardcoded measurement per pair. [GLYPH_SIZE] carries the cost.
+ *
  * The same arrangement as dev-updater, down to the cog and the refresh arrow being the same two
  * Material Design codepoints. Those two must not drift: an icon that means "settings" in one app
  * and something else in the other is the failure this is worth preventing. The script is copied
@@ -52,9 +58,27 @@ val REFRESH_GLYPH = glyph(0xF0450)
 /** `md-send` -- the filled paper plane: submit what is in the composer. */
 val SEND_GLYPH = glyph(0xF048A)
 
-/** `md-stop` -- a filled square: interrupt the turn that is running. */
+/**
+ * `md-stop` -- a filled square: end the process behind this session.
+ *
+ * The square is what stop has meant since tape decks, and it is spent here on the thing that
+ * actually stops rather than on pausing. [PAUSE_GLYPH] is the turn; this is the session.
+ */
 val STOP_GLYPH = glyph(0xF04DB)
 
+/**
+ * `md-pause` -- two bars: take the running turn away and leave the session there.
+ *
+ * The pair with [STOP_GLYPH] and [PLAY_GLYPH] is the point: one button in the composer says what
+ * pressing it now would do to the process, and the three marks are the three answers. An interrupt
+ * ends a turn and nothing else -- the CLI is still there and still holds the conversation -- which
+ * is a pause, not a stop, and drawing it as a square said otherwise.
+ */
+val PAUSE_GLYPH = glyph(0xF03E4)
+
+/** `md-play` -- start the process again, on the conversation it left. See [PAUSE_GLYPH]. */
+val PLAY_GLYPH = glyph(0xF040A)
+
 /**
  * `md-send_clock` -- the same paper plane with a clock on it: this message will wait its turn.
  *
@@ -142,5 +166,13 @@ fun Glyph(
     Text(glyph, fontFamily = NerdIcons, fontSize = size, color = colour, modifier = modifier)
 }
 
-/** The size an icon draws at beside a line of text. */
+/**
-private val GLYPH_SIZE = 20.sp
+ * The size an icon draws at beside a line of text.
+ *
+ * 17 rather than the 20 it was while the font was the proportional face. A glyph there filled at
+ * most 0.83 em of its point size and most filled a good deal less, so the number was standing in
+ * for the headroom above the tallest one; in the Mono face every glyph fills its em exactly, and
+ * keeping 20 would have made every icon in the app step up by a fifth for no reason anybody asked
+ * for. This is what the largest of them already drew at.
+ */
+private val GLYPH_SIZE = 17.sp

app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt

@@ -1478,30 +1478,44 @@ fun SessionScreen(
                         },
                     )
                 }
-                if (running) {
+                // The same filled shape as the button beside it, not an outlined one: these are
-                    // The same filled shape as the button beside it, not an outlined one: these
+                // two things you can do about the session, and weighting one of them as secondary
-                    // are two things you can do about the turn that is running, and weighting one
+                // said they were a primary action and its qualifier. What separates them is the
-                    // of them as secondary said they were a primary action and its qualifier.
+                // colour and the mark, which is what they mean.
-                    // What separates them is the colour and the mark, which is what they mean.
+                //
+                // Always here, rather than arriving with the turn as it used to. A control that
+                // comes and goes makes its own presence the signal, and its absence could not say
+                // whether there was nothing to do; a button that is always in the same place also
+                // cannot push Send off the end of the row by turning up.
+                val process =
+                    when {
+                        running -> ProcessAction.Pause
+                        status == "exited" -> ProcessAction.Start
+                        else -> ProcessAction.Stop
+                    }
                 Button(
-                        onClick = { act { interruptSession(settings, summary.id) } },
+                    onClick = { act { process.perform(settings, summary.id) } },
-                        colors = actionButtonColors(stopColor),
+                    colors = actionButtonColors(process.colour()),
                 ) {
-                        // A filled square, which is what stop has looked like since tape decks.
                     Glyph(
-                            STOP_GLYPH,
+                        process.glyph,
                         colour = LocalContentColor.current,
-                            modifier = Modifier.semantics { contentDescription = "Stop" },
+                        modifier = Modifier.semantics { contentDescription = process.label },
                     )
                 }
                 Spacer(Modifier.width(8.dp))
-                }
                 // The paper plane, with a clock on it while a turn is in flight: sending then
                 // queues the message for the next tool boundary rather than starting a turn of
                 // its own, and the two have to be told apart at a glance. The label says the same
                 // thing to a screen reader, which has nothing else to read.
+                //
+                // Disabled while there is nothing to send, rather than pressable and silent:
+                // `send` has always returned early on an empty composer, so the button promised
+                // something it would not do, and the only feedback was the ripple. Disabled and
+                // not hidden, for the reason the button beside it is always here.
                 Button(
                     onClick = { send() },
+                    enabled = input.isNotBlank() || pendingAttachments.isNotEmpty(),
                     colors = actionButtonColors(if (running) queueColor else sendColor),
                 ) {
                     Glyph(
@@ -1522,6 +1536,39 @@ fun SessionScreen(
 /** What pressing Send does right now, said the same way to the eye and to a screen reader. */
 private fun sendLabel(running: Boolean) = if (running) "Queue" else "Send"
 
+/**
+ * What the composer's process button would do if it were pressed now.
+ *
+ * One value rather than four parallel conditions over the status, because the mark, the colour, the
+ * name a screen reader is given and the request that goes out are four halves of one decision. A
+ * button drawn as a pause that terminates the CLI is the worst bug available here, and separate
+ * branches over the same condition are how that happens -- these three each have to cover every
+ * case, and the compiler says so.
+ */
+private enum class ProcessAction(val glyph: String, val label: String) {
+    /** A turn is running: take it back, and leave the process holding the conversation. */
+    Pause(PAUSE_GLYPH, "Pause"),
+    /** Nothing is running, but the process behind the session is: end it. */
+    Stop(STOP_GLYPH, "Stop"),
+    /** The process is gone: start it again, on the conversation it left. */
+    Start(PLAY_GLYPH, "Start"),
+}
+
+@Composable
+private fun ProcessAction.colour() =
+    when (this) {
+        ProcessAction.Pause -> pauseColor
+        ProcessAction.Stop -> stopColor
+        ProcessAction.Start -> startColor
+    }
+
+private fun ProcessAction.perform(settings: ServerSettings, sessionId: String) =
+    when (this) {
+        ProcessAction.Pause -> interruptSession(settings, sessionId)
+        ProcessAction.Stop -> stopSession(settings, sessionId)
+        ProcessAction.Start -> startSession(settings, sessionId)
+    }
+
 /**
  * An inline transcript image, fetched (authenticated, pinned) from the session's files route. The
  * bitmap is remembered per ref, so scrolling doesn't refetch.

app/androidApp/src/main/kotlin/com/example/aiapp/Theme.kt

@@ -213,13 +213,14 @@ val overLimitColor: Color
     @Composable get() = MaterialTheme.colorScheme.error
 
 /**
- * The composer's three buttons, coloured by what pressing one does rather than by where it sits.
+ * The composer's buttons, coloured by what pressing one does rather than by where it sits.
  *
- * Green sends now, blue sends later, red takes the running turn away. The pair of greens and the
+ * Green makes something happen now, blue makes it happen later, orange takes back what is in
- * pair of reds elsewhere in this file are deliberate near-collisions worth naming: [runningColor]
+ * flight, red ends the process. The near-collisions with the states above are deliberate and worth
- * is green because a session is working, and [failedColor] is red because one fell over -- those
+ * naming rather than collapsing: [runningColor] is green because a session is working,
- * are *states*, and these are *actions*. A reader never has to tell them apart, because nothing
+ * [failedColor] is red because one fell over, [awaitingColor] is the same orange because a session
- * here is a state and nothing there is pressable.
+ * is waiting on somebody -- those are *states*, and these are *actions*. A reader never has to tell
+ * them apart, because nothing here is a state and nothing there is pressable.
  */
 val sendColor: Color
     @Composable get() = Mocha.Green
@@ -228,10 +229,30 @@ val sendColor: Color
 val queueColor: Color
     @Composable get() = Mocha.Blue
 
-/** Interrupting the running turn -- the one button here that takes something away. */
+/**
+ * Interrupting the running turn: the work stops and the session stays.
+ *
+ * Orange rather than red because of how much it takes: only what is in flight. The process is still
+ * there holding the conversation, and the next message starts a turn as though nothing had
+ * happened. Red is spent on [stopColor], which is the same button in the same place when what it
+ * would end is the session's process.
+ */
+val pauseColor: Color
+    @Composable get() = Mocha.Peach
+
+/** Ending the session's process -- the one button here that takes something away. */
 val stopColor: Color
     @Composable get() = Mocha.Red
 
+/**
+ * Starting the process again, on the conversation it left.
+ *
+ * The same green as [sendColor] on purpose: both mean "this happens now", and they are never the
+ * same button -- the process button only offers to start when there is nothing running to stop.
+ */
+val startColor: Color
+    @Composable get() = Mocha.Green
+
 /**
  * A filled button in one of the action colours above.
  *

app/build-icon-font.sh

@@ -32,6 +32,8 @@ GLYPHS=(
     U+F0450  # md-refresh
     U+F048A  # md-send
     U+F04DB  # md-stop
+    U+F03E4  # md-pause
+    U+F040A  # md-play
     U+F1163  # md-send_clock
     U+F0156  # md-close
     U+F004D  # md-arrow_left
@@ -52,9 +54,20 @@ python3 -m venv "$work/venv"
 
 unicodes="$(IFS=,; echo "${GLYPHS[*]}")"
 mkdir -p "$(dirname "$out")"
-# The proportional face rather than the Mono one: these are drawn inline
+# The Mono face rather than the proportional one, which this used until
-# beside text, where a fixed advance would pad each icon out to a cell.
+# 2026-08-30. Every glyph in it is one em wide and one em tall, so two
-"$work/venv/bin/pyftsubset" "$work/SymbolsNerdFont-Regular.ttf" \
+# icons drawn at the same size are the same size -- which is what makes two
+# icon buttons beside each other match without either of them being told a
+# width. In the proportional face the advances run from 0.46 em (play) to
+# 0.92 em (line chart), so the composer's Send button came out visibly wider
+# than the Stop button next to it, and any fix at the call site would have
+# been one measurement hardcoded per pair.
+#
+# The trade is the one the old comment named: an icon inline beside text is
+# padded out to a cell. That is worth it, and it is also why GLYPH_SIZE in
+# NerdIcons.kt came down when this changed -- a glyph that fills its em
+# draws bigger at the same point size than one that does not.
+"$work/venv/bin/pyftsubset" "$work/SymbolsNerdFontMono-Regular.ttf" \
     --unicodes="$unicodes" \
     --layout-features= \
     --drop-tables+=DSIG \

app/run-android.sh

@@ -1,7 +1,13 @@
 #!/bin/sh
-# Builds and runs this app on an emulator, creating/booting the AVD first if
+# Builds this app and runs it on this checkout's emulator.
-# it isn't already up. Same flow as dev-updater's run-android.sh; see that
+#
-# script for the reasoning behind the avd handling.
+# The emulator half of this -- which AVD this checkout means, creating it,
+# booting it headless, and refusing to start one the machine has no room for
+# -- lives in ~/repos/emulator-tools and is shared with every other Android
+# checkout here. This script kept its own copy of that sequence until
+# 2026-08-30, as did dev-updater's and ai-app's, and three copies of "boot an
+# emulator" is three places for the memory check that was missing from all of
+# them.
 #
 # Environment setup (SDK location, PATH, ...) lives in ./android-env.sh,
 # which can also be sourced directly for one-off commands.
@@ -9,105 +15,34 @@ set -eu
 
 APP_ID="com.example.aiapp"
 
-DEVICE_PROFILE="${DEVICE_PROFILE:-pixel_10}"
-SYSTEM_IMAGE="${SYSTEM_IMAGE:-system-images;android-36;google_apis;x86_64}"
-
 SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
 cd "$SCRIPT_DIR"
 
-# One AVD per checkout, named after it -- so two clones of this repo, or a
-# clone and a worktree, each get their own rather than fighting over one.
-# This used to default to a machine-wide "tdep", which made the emulator the
-# one thing here that could not be worked on in parallel: taking it meant
-# asking whoever had it, waiting, and handing it back, and installing onto a
-# running one steals the foreground from whatever they were looking at.
-# Derived rather than written down, so neither clone names the other's.
-# Override with AVD_NAME=... to share one deliberately.
-AVD_NAME="${AVD_NAME:-$(basename "$(dirname "$SCRIPT_DIR")")}"
-
 # shellcheck source=./android-env.sh
 . ./android-env.sh
 
-# Prints the adb serial of a running instance of AVD "$1", or nothing.
+if ! command -v emu >/dev/null 2>&1; then
-avd_serial() {
+    echo "run-android.sh: no 'emu' command." >&2
-    for s in $(adb devices | awk '$2 == "device" {print $1}'); do
+    echo "  It comes from ~/repos/emulator-tools; run that repo's ./install.sh." >&2
-        if [ "$(adb -s "$s" emu avd name 2>/dev/null | head -n1 | tr -d '\r')" = "$1" ]; then
+    exit 127
-            echo "$s"
-            return 0
-        fi
-    done
-}
-
-echo "==> Ensuring emulator system image is installed"
-android sdk install emulator "$SYSTEM_IMAGE" || echo "    (non-fatal: see above)"
-
-if [ ! -f "$ANDROID_AVD_HOME/$AVD_NAME.ini" ]; then
-    echo "==> Creating AVD '$AVD_NAME' ($DEVICE_PROFILE, $SYSTEM_IMAGE)"
-    echo no | avdmanager create avd \
-        -n "$AVD_NAME" \
-        -k "$SYSTEM_IMAGE" \
-        --device "$DEVICE_PROFILE" \
-        --sdcard 512M
-else
-    echo "==> Reusing existing AVD '$AVD_NAME'"
 fi
 
-# Host keyboard into the emulator -- this app has text fields.
+# Prints the serial, having created and booted the AVD if it had to. Named
-CONFIG_INI="$ANDROID_AVD_HOME/$AVD_NAME.avd/config.ini"
+# after the checkout, so this cannot land on another session's emulator --
-if [ -f "$CONFIG_INI" ]; then
+# and refuses rather than starting one when the machine is short of memory,
-    grep -v '^hw\.keyboard=' "$CONFIG_INI" >"$CONFIG_INI.tmp"
+# because what an OOM kills is somebody else's work rather than the emulator
-    echo "hw.keyboard=yes" >>"$CONFIG_INI.tmp"
+# that asked for the memory.
-    mv "$CONFIG_INI.tmp" "$CONFIG_INI"
+echo "==> Emulator"
-fi
+SERIAL=$(emu up)
-
+export ANDROID_SERIAL="$SERIAL"
-SERIAL=$(avd_serial "$AVD_NAME")
-if [ -n "$SERIAL" ]; then
-    echo "==> Emulator '$AVD_NAME' already running ($SERIAL)"
-else
-    # Clean up a stray/crashed process for this AVD, if any. The bracketed
-    # first character keeps the pattern from matching the shell running
-    # this script -- unbracketed, this kills that shell mid-run.
-    pkill -f "[e]mulator.*-avd $AVD_NAME" >/dev/null 2>&1 || true
-
-    EMU_LOG="/tmp/$AVD_NAME-emulator.log"
-    : >"$EMU_LOG"
-    if [ -n "${DISPLAY:-}" ] || [ -n "${WAYLAND_DISPLAY:-}" ]; then
-        echo "==> Starting emulator '$AVD_NAME' with GPU acceleration (-gpu host)"
-        emulator -avd "$AVD_NAME" -gpu host -no-audio >"$EMU_LOG" 2>&1 &
-    else
-        echo "==> No display -- starting emulator '$AVD_NAME' headless (-gpu swiftshader_indirect)"
-        emulator -avd "$AVD_NAME" -gpu swiftshader_indirect -no-audio -no-window \
-            >"$EMU_LOG" 2>&1 &
-    fi
-    EMU_PID=$!
-
-    i=0
-    booted=""
-    while [ "$i" -lt 150 ]; do
-        if ! kill -0 "$EMU_PID" 2>/dev/null; then
-            echo "Emulator process exited unexpectedly. Log output:" >&2
-            cat "$EMU_LOG" >&2
-            exit 1
-        fi
-        SERIAL=$(avd_serial "$AVD_NAME")
-        if [ -n "$SERIAL" ]; then
-            booted=$(adb -s "$SERIAL" shell getprop sys.boot_completed 2>/dev/null | tr -d '\r')
-            [ "$booted" = "1" ] && break
-        fi
-        i=$((i + 1))
-        sleep 2
-    done
-    if [ "$booted" != "1" ]; then
-        echo "Emulator did not finish booting in time. Log output:" >&2
-        cat "$EMU_LOG" >&2
-        exit 1
-    fi
-fi
 
 echo "==> Building debug APK"
 ./gradlew :androidApp:assembleDebug
 
 APK="androidApp/build/outputs/apk/debug/androidApp-debug.apk"
 echo "==> Installing and launching $APK"
-adb -s "$SERIAL" install -r "$APK"
+# ANDROID_SERIAL above is what aims these; the adb wrapper would work it out
-adb -s "$SERIAL" shell am start -n "$APP_ID/.MainActivity"
+# from the checkout anyway, but a script that says which device it means does
+# not depend on being run from the right directory.
+adb install -r "$APK"
+adb shell am start -n "$APP_ID/.MainActivity"

server/src/routes.rs

@@ -17,7 +17,9 @@
 //!                                      `reset` frame plus the newest window)
 //! POST   /sessions/{id}/message        {text, attachmentIds?}
 //! POST   /sessions/{id}/answer         {questionId, answers}  (questions and permissions)
-//! POST   /sessions/{id}/interrupt
+//! POST   /sessions/{id}/interrupt      stop the running turn; the process stays
+//! POST   /sessions/{id}/stop           end the process; the session and transcript stay
+//! POST   /sessions/{id}/start          run the process again, continuing the conversation
 //! POST   /sessions/{id}/title          {title}
 //! POST   /sessions/{id}/model          {model}
 //! POST   /sessions/{id}/command        {text}  -- /compact, /clear, /rename x, or the dialect's own
@@ -87,6 +89,8 @@ pub fn router(manager: Arc<SessionManager>) -> Router {
         .route("/sessions/{id}/message", post(message))
         .route("/sessions/{id}/answer", post(answer))
         .route("/sessions/{id}/interrupt", post(interrupt))
+        .route("/sessions/{id}/stop", post(stop))
+        .route("/sessions/{id}/start", post(start))
         .route("/sessions/{id}/title", post(rename))
         .route("/sessions/{id}/model", post(set_model))
         .route("/sessions/{id}/permission-mode", post(set_permission_mode))
@@ -678,6 +682,31 @@ async fn interrupt(
     Ok(StatusCode::NO_CONTENT)
 }
 
+/// Ends the session's process. The session stays, and `start` brings it
+/// back -- see [`SessionManager::stop_session`].
+///
+/// Not `lookup`ed: a session that failed to relaunch has no live entry and
+/// may still have a process running, which is exactly one worth being able
+/// to stop.
+async fn stop(
+    State(manager): State<Arc<SessionManager>>,
+    UrlPath(id): UrlPath<String>,
+) -> Result<StatusCode, ApiError> {
+    manager.stop_session(&id).map_err(bad_request)?;
+    Ok(StatusCode::NO_CONTENT)
+}
+
+/// Starts a process for a session that has none, continuing the same
+/// conversation -- see [`SessionManager::start_session`], which refuses
+/// unless the session is known to have exited.
+async fn start(
+    State(manager): State<Arc<SessionManager>>,
+    UrlPath(id): UrlPath<String>,
+) -> Result<StatusCode, ApiError> {
+    manager.start_session(&id).map_err(bad_request)?;
+    Ok(StatusCode::NO_CONTENT)
+}
+
 /// The usage screen needs two things that live in different places: the
 /// cache, and the current list of machines to ask. Carried together rather
 /// than the monitor holding the manager, which would point the dependency

server/src/session/claude.rs

@@ -100,12 +100,6 @@ pub(super) mod translate;
 
 const RESUME_FILE: &str = "claude-session.json";
 
-/// Grace period between asking a process to stop and killing it.
-///
-/// Only [`Driver::stop`] uses it -- a session being deleted. Detaching
-/// does not stop anything, so it has no grace period and needs none.
-const STOP_GRACE: std::time::Duration = std::time::Duration::from_secs(5);
-
 /// Messages handed to the CLI that it has not visibly acted on yet.
 ///
 /// The CLI *does* take a message written mid-turn: it goes into the next
@@ -239,6 +233,10 @@ impl ClaudeDriver {
         // to find. Nothing was ever recorded for one, so this answers "no"
         // without needing to know that, which is why the remote case is
         // not a branch here.
+        // Whether this launch *started* a process or picked up one that was
+        // already there. The two owe the session different things -- see the
+        // `Status` below.
+        let started_here;
         let record = match process::recorded(session_dir) {
             // Still running, and ours. Pick it up where it was left --
             // the one path that must not pass `--resume`.
@@ -249,6 +247,7 @@ impl ClaudeDriver {
                     provider.name,
                     record.pid
                 );
+                started_here = false;
                 record
             }
             // Recorded, and the machine will not say whether it is still
@@ -262,12 +261,39 @@ impl ClaudeDriver {
                     meta.id,
                     record.pid
                 );
+                started_here = false;
                 record
             }
             Some((_, process::Liveness::Dead)) | None => {
+                started_here = true;
                 Self::start(meta, provider, transport, session_dir)?
             }
         };
+
+        // A process this driver has just started has been asked for nothing,
+        // which is what idle means. Said here because nothing else will say
+        // it: the CLI writes not one line until it is given work, so a
+        // session whose transcript last recorded `Exited` -- one whose
+        // process died while this server was down, or one somebody stopped
+        // from the phone -- would keep that word. `Exited` refuses every
+        // command sent to the session, and it offers a phone the chance to
+        // start a second CLI against a conversation that already has one.
+        //
+        // From the driver rather than from the manager, and before `follow`
+        // is spawned, so it cannot overtake the exit `follow` reports for a
+        // process that dies immediately: both come from here, in this order.
+        // Adopting says nothing, because a process that was already running
+        // may be mid-turn, and the transcript's last word is the better
+        // answer until its output says otherwise.
+        //
+        // The llama driver has always done this (see `LlamaDriver::attached`,
+        // which reports `Running` while the model loads and `Idle` when it
+        // answers); this side was the one silent about it.
+        if started_here {
+            let _ = sink.send(Event::Status {
+                state: SessionStatus::Idle,
+            });
+        }
         // Where reading of its output had reached. A process just started
         // has said nothing, so its record says zero and this is the same
         // question with the same answer.
@@ -673,7 +699,7 @@ impl Driver for ClaudeDriver {
     fn stop(&self) {
         self.reading.store(false, Ordering::SeqCst);
         if let Some(record) = process::live(&self.session_dir) {
-            process::stop(&record, STOP_GRACE);
+            process::stop(&record, process::STOP_GRACE);
         }
         process::clear(&self.session_dir);
     }

server/src/session/llama.rs

@@ -269,9 +269,6 @@ const SERVER_LOG: &str = "llama-server.log";
 /// seconds late costs nothing.
 const WATCH_INTERVAL: std::time::Duration = std::time::Duration::from_secs(2);
 
-/// Grace period between asking llama-server to stop and killing it.
-const STOP_GRACE: std::time::Duration = std::time::Duration::from_secs(5);
-
 /// An owner-only log opened for appending, so the two streams pointed at
 /// it do not overwrite each other and a reattach keeps what came before.
 fn log_file(path: &Path) -> Result<std::fs::File> {
@@ -447,7 +444,7 @@ impl Driver for LlamaDriver {
     fn stop(&self) {
         self.cancel.store(true, Ordering::Relaxed);
         if let Some(record) = process::live(&self.session_dir) {
-            process::stop(&record, STOP_GRACE);
+            process::stop(&record, process::STOP_GRACE);
         }
         process::clear(&self.session_dir);
     }

server/src/session/mod.rs

@@ -169,11 +169,21 @@ pub struct SessionInfo {
     pub created: f64,
 }
 
+/// What is running a session at this moment.
+///
+/// Behind a lock because a session outlives its process: stopping one and
+/// starting it again replaces the driver while the transcript, the event
+/// pump and the stream every open phone is reading stay exactly where they
+/// were. Shared with [`Commands`] rather than copied into it, because two
+/// holders of "the driver" are two answers to that question the moment one
+/// of them is replaced.
+type DriverCell = Arc<Mutex<Arc<dyn Driver>>>;
+
 /// A running session: its driver plus the shared state the event pump
 /// keeps current. Cheap to clone-by-`Arc` into request handlers.
 pub struct LiveSession {
     meta: SessionConfig,
-    driver: Arc<dyn Driver>,
+    driver: DriverCell,
     /// Commands asked for and not yet run, oldest first, with the pump
     /// that will run them. Shared with that pump, which is what notices
     /// the boundary.
@@ -195,12 +205,17 @@ pub struct LiveSession {
 /// for the turn to end. Drivers therefore never have to think about it,
 /// and a new provider cannot get it wrong by omission.
 struct Commands {
-    driver: Arc<dyn Driver>,
+    driver: DriverCell,
     sink: EventSink,
     waiting: Mutex<VecDeque<(String, SessionCommand)>>,
 }
 
 impl Commands {
+    /// Whatever is driving the session now -- see [`DriverCell`].
+    fn driver(&self) -> Arc<dyn Driver> {
+        self.driver.lock().unwrap().clone()
+    }
+
     /// Runs `command` now if the session is between turns, holds it until
     /// it is, and refuses it outright if there will never be one. Whichever
     /// happened, the phone is told.
@@ -236,9 +251,10 @@ impl Commands {
             });
             return;
         }
-        if self.driver.between_turns() {
+        let driver = self.driver();
+        if driver.between_turns() {
             let _ = self.sink.send(Event::CommandSent { id, text });
-            command.apply(self.driver.as_ref());
+            command.apply(driver.as_ref());
             return;
         }
         let _ = self.sink.send(Event::CommandQueued {
@@ -258,7 +274,8 @@ impl Commands {
     /// began by itself, which it does: a background task finishing makes it
     /// pick the conversation back up with nothing written to it.
     fn take_one(&self) {
-        if !self.driver.between_turns() {
+        let driver = self.driver();
+        if !driver.between_turns() {
             return;
         }
         let Some((id, command)) = self.waiting.lock().unwrap().pop_front() else {
@@ -268,7 +285,7 @@ impl Commands {
             id,
             text: command.label(),
         });
-        command.apply(self.driver.as_ref());
+        command.apply(driver.as_ref());
     }
 
     /// Gives up on everything held, because the session cannot run them.
@@ -336,6 +353,11 @@ struct Shared {
 }
 
 impl LiveSession {
+    /// Whatever is driving this session now -- see [`DriverCell`].
+    fn driver(&self) -> Arc<dyn Driver> {
+        self.driver.lock().unwrap().clone()
+    }
+
     /// Hands the user's message to the driver, which records it in the
     /// transcript by reporting that it has taken it -- see `MessageTaken`.
     ///
@@ -348,7 +370,7 @@ impl LiveSession {
         // drew a person's screenshot as a row floating above the bubble
         // that sent it, and left the phone inferring from adjacency which
         // message an image went with -- a thing the sender already knew.
-        self.driver.send_user_message(text, images);
+        self.driver().send_user_message(text, images);
     }
 
     pub fn answer_question(&self, question_id: &str, answers: &[String]) {
@@ -356,7 +378,7 @@ impl LiveSession {
             id: question_id.to_string(),
             answers: answers.to_vec(),
         });
-        self.driver.answer_question(question_id, answers);
+        self.driver().answer_question(question_id, answers);
     }
 
     /// Asks the session to run a command on itself, now or at the next
@@ -367,14 +389,14 @@ impl LiveSession {
     }
 
     pub fn interrupt(&self) {
-        self.driver.interrupt();
+        self.driver().interrupt();
     }
 
     /// Leaves this session's process running and stops attending to it,
     /// for a server that is going away and means to come back. See
     /// [`Driver::detach`].
     pub fn detach(&self) {
-        self.driver.detach();
+        self.driver().detach();
     }
 
     /// Compacts at the next boundary. Through the command queue like
@@ -942,7 +964,7 @@ impl SessionManager {
             // change, and as an error if it cannot. The config above is a
             // different question -- what to launch this session with next
             // time -- and it is answered by the request.
-            session.driver.set_permission_mode(mode);
+            session.driver().set_permission_mode(mode);
         }
         Ok(())
     }
@@ -1025,11 +1047,144 @@ impl SessionManager {
         if let Some(session) = inner.live.get(id) {
             // See `set_session_permission_mode`: the driver reports what
             // it is set to, this only asks.
-            session.driver.set_model(model);
+            session.driver().set_model(model);
         }
         Ok(())
     }
 
+    /// Ends this session's process, leaving the session -- its transcript,
+    /// its place in the list, everything a phone is watching -- exactly
+    /// where it is. [`SessionManager::start_session`] is the way back.
+    ///
+    /// The signal is all this does. Whether the process actually went, what
+    /// it said on the way out, and the `Exited` that follows are reported by
+    /// the path a session that died on its own already takes: the driver's
+    /// own reader notices within a poll, drains what was still unread, and
+    /// records it. Announcing it from here would be this side's guess
+    /// arriving ahead of the measurement, and it would be wrong for the five
+    /// seconds a process that ignores SIGTERM keeps running.
+    ///
+    /// Deliberately not routed through the driver. The record is the
+    /// session's rather than any dialect's -- `session::process` writes it
+    /// for every provider that has a process at all -- so asking it here
+    /// stops a session whose driver is in no state to be asked, and adds no
+    /// method a new driver could implement wrongly.
+    pub fn stop_session(&self, id: &str) -> Result<()> {
+        if !self
+            .inner
+            .read()
+            .unwrap()
+            .config
+            .sessions
+            .iter()
+            .any(|meta| meta.id == id)
+        {
+            bail!("no session {id}");
+        }
+        // Three answers, and they are three different things to tell
+        // somebody: it is running (stop it), it is not (nothing to do), and
+        // nobody could find out (nothing was signalled, and saying "nothing
+        // is running" would be inventing the answer).
+        let record = match process::recorded(&self.data_dir.join(id)) {
+            Some((record, process::Liveness::Alive)) => record,
+            Some((_, process::Liveness::Unknown)) => bail!(
+                "this machine won't say whether this session's process is still running, so it \
+                 wasn't signalled"
+            ),
+            Some((_, process::Liveness::Dead)) | None => {
+                bail!("this session has no process running")
+            }
+        };
+        tracing::info!("stopping session {id} (pid {})", record.pid);
+        process::stop(&record, process::STOP_GRACE);
+        Ok(())
+    }
+
+    /// Starts a process for a session whose process has ended, continuing
+    /// the same conversation -- for Claude Code, the `--resume` that crash
+    /// recovery already uses.
+    ///
+    /// Only the driver is new. The transcript, the event pump and the stream
+    /// every open phone is reading stay as they were, so this is not a
+    /// reconnect for anybody watching -- and there is still exactly one
+    /// writer of the transcript, which relaunching the whole session would
+    /// not be.
+    ///
+    /// Refused unless the session is *known* to have exited. `Unknown` means
+    /// nobody could find out whether the process is alive, and starting one
+    /// on that is precisely the second-CLI-on-one-conversation fault that
+    /// `session::process` exists to prevent.
+    ///
+    /// What the session then *reports* is the driver's to say, not this
+    /// function's: the phone's list reads the manager's status and the
+    /// session screen replays the transcript, so a status written in one and
+    /// not the other is two screens disagreeing about one session -- which
+    /// is what a status set here without an event produced, visible as a
+    /// stop button that turned into a play button a moment after the screen
+    /// opened.
+    pub fn start_session(&self, id: &str) -> Result<()> {
+        let mut inner = self.inner.write().unwrap();
+        let meta = inner
+            .config
+            .sessions
+            .iter()
+            .find(|meta| meta.id == id)
+            .with_context(|| format!("no session {id}"))?
+            .clone();
+        let existing = inner.live.get(id).cloned();
+        let status = match &existing {
+            Some(session) => *session.shared.status.lock().unwrap(),
+            None => status_of_unlaunched(&self.data_dir.join(id)),
+        };
+        match status {
+            SessionStatus::Exited => {}
+            SessionStatus::Unknown => bail!(
+                "this machine won't say whether this session's process is still running, so \
+                 nothing was started"
+            ),
+            _ => bail!("this session is already running"),
+        }
+        // Fresh from the config, like every other launch: a model or a
+        // permission mode changed while the session was stopped is what it
+        // starts with.
+        let (setup, provider) = resolve(&inner.config, &meta)?;
+        match existing {
+            Some(session) => {
+                *session.driver.lock().unwrap() = make_driver(
+                    &meta,
+                    &setup,
+                    &provider,
+                    &self.models_dir,
+                    session.dir(),
+                    session.transcript_path(),
+                    &session.sink,
+                )?;
+            }
+            // Nothing is live for this one -- a session whose launch failed
+            // when the server started, which has no pump either. That is the
+            // whole of `launch`, and the same call the server start makes.
+            None => {
+                let session = launch(
+                    meta,
+                    &setup,
+                    &provider,
+                    &self.data_dir,
+                    &self.models_dir,
+                    None,
+                    self.notifications.clone(),
+                )?;
+                inner.live.insert(id.to_string(), session);
+            }
+        }
+        // Nothing is announced from here. A driver that starts a process
+        // reports the session idle itself, in order with everything else it
+        // says about that process -- see `ClaudeDriver::launch`. Saying it
+        // here as well would be a second writer of the same fact, and the
+        // one that cannot see whether the process it is describing is still
+        // there.
+        Ok(())
+    }
+
     /// Kills the process, releases everything the spawn created, and
     /// deletes the transcript and files -- the complete path out.
     pub fn delete_session(&self, id: &str) -> Result<()> {
@@ -1045,7 +1200,7 @@ impl SessionManager {
             // Stopped, not detached: this is the one exit where the
             // process must not survive, because the conversation it
             // belongs to is being removed. See `Driver::stop`.
-            session.driver.stop();
+            session.driver().stop();
         }
         let dir = self.data_dir.join(id);
         if dir.exists() {
@@ -1339,25 +1494,15 @@ fn launch(
         );
     }
 
-    let driver: Arc<dyn Driver> = match provider.kind {
+    let driver = Arc::new(Mutex::new(make_driver(
-        DriverKind::Echo => Arc::new(EchoDriver::new(sink.clone(), dir.clone())),
-        DriverKind::LlamaCpp => Arc::new(LlamaDriver::launch(
         &meta,
+        setup,
         provider,
-            &Transport::for_setup(setup),
         models_dir,
+        &dir,
         &transcript_path,
-            &dir,
+        &sink,
-            sink.clone(),
+    )?));
-        )?),
-        DriverKind::ClaudeCli => Arc::new(ClaudeDriver::launch(
-            &meta,
-            provider,
-            &Transport::for_setup(setup),
-            &dir,
-            sink.clone(),
-        )?),
-    };
 
     let commands = Arc::new(Commands {
         driver: Arc::clone(&driver),
@@ -1386,6 +1531,44 @@ fn launch(
     }))
 }
 
+/// Whatever runs this session's provider, pointed at the session's own
+/// directory and reporting into `sink`.
+///
+/// Split out of [`launch`] because a session outlives its process: it is
+/// also what [`SessionManager::start_session`] builds when somebody starts a
+/// stopped session again. That path replaces the driver and nothing else, so
+/// it has to construct one the same way rather than becoming a second answer
+/// to "what runs this".
+fn make_driver(
+    meta: &SessionConfig,
+    setup: &SetupConfig,
+    provider: &ProviderConfig,
+    models_dir: &Path,
+    dir: &Path,
+    transcript_path: &Path,
+    sink: &EventSink,
+) -> Result<Arc<dyn Driver>> {
+    Ok(match provider.kind {
+        DriverKind::Echo => Arc::new(EchoDriver::new(sink.clone(), dir.to_path_buf())),
+        DriverKind::LlamaCpp => Arc::new(LlamaDriver::launch(
+            meta,
+            provider,
+            &Transport::for_setup(setup),
+            models_dir,
+            transcript_path,
+            dir,
+            sink.clone(),
+        )?),
+        DriverKind::ClaudeCli => Arc::new(ClaudeDriver::launch(
+            meta,
+            provider,
+            &Transport::for_setup(setup),
+            dir,
+            sink.clone(),
+        )?),
+    })
+}
+
 /// The one writer of a session's transcript: assigns sequence numbers,
 /// appends, updates the shared status/activity view, fans out. Ends when
 /// every sender is dropped -- i.e. when the session is deleted and its
@@ -1639,7 +1822,10 @@ mod tests {
         let dir = tempfile::tempdir().expect("tempdir");
         let (sink, mut events) = mpsc::unbounded_channel();
         let commands = Commands {
-            driver: Arc::new(EchoDriver::new(sink.clone(), dir.path().to_path_buf())),
+            driver: Arc::new(Mutex::new(Arc::new(EchoDriver::new(
+                sink.clone(),
+                dir.path().to_path_buf(),
+            )))),
             sink,
             waiting: Mutex::new(VecDeque::new()),
         };
@@ -2233,6 +2419,80 @@ mod tests {
         std::fs::write(path, rewritten).expect("write transcript");
     }
 
+    /// Stopping and starting a session is about its *process*, and the two
+    /// refusals are the whole of what keeps starting one from becoming a
+    /// second one on the same conversation.
+    ///
+    /// Echo has no process, which makes it the right session to ask the
+    /// first question of: "there is nothing to stop" is an answer, and
+    /// reporting success would leave a phone showing a session it believes
+    /// it stopped. The second question is asked of a session that has been
+    /// told it exited, since the guard is on the *status* rather than on
+    /// which driver it is.
+    #[tokio::test]
+    async fn a_session_is_started_again_only_once_it_is_known_to_have_exited() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let config_path = dir.path().join("config.ron");
+        let data_dir = dir.path().join("sessions");
+        seed_echo_only(&config_path);
+        let manager = SessionManager::new(config_path, data_dir.clone(), data_dir.join("models"))
+            .expect("manager");
+        let info = manager.spawn_session(echo_spec()).expect("spawn");
+        let session = manager.session(&info.id).expect("live session");
+        let mut rx = session.subscribe();
+
+        let refused = manager.stop_session(&info.id).expect_err("nothing to stop");
+        assert!(
+            refused.to_string().contains("no process running"),
+            "said: {refused:#}"
+        );
+        let refused = manager
+            .start_session(&info.id)
+            .expect_err("already running");
+        assert!(
+            refused.to_string().contains("already running"),
+            "said: {refused:#}"
+        );
+
+        // What a driver reports when its process goes, without a process
+        // to go: the guard reads the recorded status, so this is the same
+        // state a stopped claude session reaches.
+        let _ = session.sink.send(Event::Status {
+            state: SessionStatus::Exited,
+        });
+        collect_until(&mut rx, |event| {
+            matches!(
+                event,
+                Event::Status {
+                    state: SessionStatus::Exited
+                }
+            )
+        })
+        .await;
+
+        manager.start_session(&info.id).expect("start again");
+        collect_until(&mut rx, is_idle).await;
+        // Idle rather than exited, and *recorded* -- said by the driver that
+        // was just built, like every driver says what state it is starting
+        // in. The manager writing it directly is what made the phone's list
+        // and its session screen disagree: one reads this status and the
+        // other replays the transcript, so a status in only one of them is
+        // two screens describing one session differently.
+        assert_eq!(manager.sessions()[0].status, SessionStatus::Idle);
+        assert_eq!(
+            Transcript::open(&data_dir.join(&info.id).join("transcript.jsonl"))
+                .expect("reopen transcript")
+                .last_status(),
+            Some(SessionStatus::Idle),
+        );
+        // The same live session throughout: only the driver was replaced,
+        // so nothing a phone is reading was interrupted.
+        assert!(Arc::ptr_eq(
+            &session,
+            &manager.session(&info.id).expect("still live")
+        ));
+    }
+
     #[tokio::test]
     async fn a_restart_relaunches_sessions_and_continues_the_numbering() {
         let dir = tempfile::tempdir().expect("tempdir");

server/src/session/process.rs

@@ -204,6 +204,13 @@ pub fn clear(session_dir: &Path) {
     }
 }
 
+/// Grace period between asking a session's process to stop and killing it.
+///
+/// Here rather than beside each caller: it is a property of stopping one of
+/// these, and two drivers plus the manager had written the same five seconds
+/// down separately, which is three places for it to drift.
+pub const STOP_GRACE: std::time::Duration = std::time::Duration::from_secs(5);
+
 /// Asks it to stop, then makes sure. Used where a leaked process must
 /// actually end: a deleted session, or one being replaced.
 ///