hive-claude 0.1.4: the idle watchdog stops claude with SIGINT

hive-claude 0.1.4 (hive-claude #28) sends the idle watchdog's signal as
SIGINT to claude's process group instead of SIGKILL. It then waits for
claude to exit, with no SIGKILL fallback. claude stops the commands its
Bash tool started when it shuts down on SIGINT, and a SIGKILL left them
running. This is the last SIGKILL of a claude process from #4999.

hive-agent's `idle_timeout` -> `Error::IdleTimeout` -> `TurnError::ApiStall`
path is unchanged. The difference is that the error now arrives only
once claude has exited. A claude that ignores the SIGINT keeps the turn
open until it is killed by hand or the unit stops.

The Cargo.lock change is only hive-claude's version and checksum. A plain
`cargo update -p hive-claude --precise 0.1.4` also moved seven crates'
Windows-only `windows-sys` edges from 0.61.2 to 0.52.0, unrelated to this
bump. The minimal lock passes `--locked`.

The turn-loop and web-UI docs, and hive-agent's watchdog docs and stall
note, now say SIGINT instead of "killed". That includes the ACP spots
that the previous commit's `Drop` change made stale.

Cargo.lock

@@ -1835,9 +1835,9 @@ dependencies = [
 
 [[package]]
 name = "hive-claude"
-version = "0.1.2"
+version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1e43e06fd09a7b6d6cca3e70f06d00fa795ceddfe1555121ca0cf4fc578eb9c3"
+checksum = "4d7c5638f8f59e438d6416b3048709c9b3d6a10c23872ecf3825e3fe4c1bd7e8"
 dependencies = [
  "libc",
  "serde",

Cargo.toml

@@ -97,7 +97,7 @@ hive-jobq-metrics = { path = "hive-jobq-metrics" }
 hive-jobq-wire = { path = "hive-jobq-wire" }
 hive-log = { path = "hive-log" }
 hive-core-agent-sock = { path = "hive-core-agent-sock" }
-hive-claude = "0.1.2"
+hive-claude = "0.1.4"
 hive-host-sock = { path = "hive-host-sock" }
 hive-priv-sock = { path = "hive-priv-sock" }
 hive-runtime = { path = "hive-runtime" }

claude-plugins/plugins/base/skills/claude-subagents/SKILL.md

@@ -27,7 +27,7 @@ skill's recipe for you:
 start(name, prompt_file, model?, effort?, trigger?)
 continue(name, prompt, model?, effort?)
 status(name)
-interrupt(name, force?)
+interrupt(name)
 ```
 
 `start` and `continue` return once the turn is under way, not once it
@@ -42,7 +42,8 @@ reports how long since that turn last produced output, so a few seconds
 means it's working and an age climbing into the minutes means it's
 wedged and worth an `interrupt`. Reach for `continue` only once you
 actually have a new instruction for it, since that spends a turn.
-`interrupt` genuinely stops a running turn (`force: true` for SIGKILL).
+`interrupt` genuinely stops a running turn, with SIGINT so claude stops
+the commands it started; `status` says `stopping` until claude has exited.
 
 Model choice, prompt hygiene, splitting big batches, verify-then-report —
 everything else in this skill — applies exactly the same whether you're

docs/tools/subagent.md

@@ -166,6 +166,16 @@ from how the child exited. `continue` clears it and hands the session a
 fresh turn allowance, which is what makes an interrupt a pause you can
 undo rather than a session you have to abandon.
 
+On `claude`, the signal is always SIGINT, and it goes to claude's whole
+process group. The signal doesn't reach a command that moved itself out of
+the group (`setsid`), and claude's Bash tool starts every command that way:
+claude stops those commands itself when it shuts down on SIGINT. A SIGKILL
+would leave them running, so nothing escalates to one. `interrupt` returns
+at once, and the name stays claimed until claude has exited: `status` says
+**stopping**, and the daemon refuses `start` and `continue` on that name
+until then. A claude that ignores the SIGINT stays stopping until someone kills
+it by hand or the unit stops.
+
 When the session knows where its report goes — `start`'s `report_file`,
 or the path the subagent names when it signals — the daemon appends the
 stop reason to that file as well, so the artifact you were going to read
@@ -340,7 +350,7 @@ page applies as written.
 On `acp`:
 
 - each run spawns its own copy of the parent's ACP agent. The end of the
-  run kills it and every command it started. The unit loads
+  run sends SIGINT to it and every command in its process group. The unit loads
   `backendEnvironmentFile` for it. On the `opencode` preset, the daemon
   reads a provider key that file leaves unset from the swarm secret store
   at `swarm/agents/<agent>/acp-provider`, as the harness does.
@@ -349,9 +359,10 @@ On `acp`:
   agent process, and a `continue` with none recorded fails straight away.
 - a role goes in front of the session's first prompt, since ACP has no
   system prompt.
-- `interrupt` sends `session/cancel`, and `force` changes nothing. The
-  runtime kills an agent that ignores the cancel for 10s, with every
-  command it started.
+- `interrupt` sends `session/cancel`. The runtime sends SIGINT to the
+  process group of an agent that ignores the cancel for 10s, and when the
+  run ends. Nothing escalates past that SIGINT. The name is free as soon as
+  `interrupt` sends the cancel.
 - the runtime sets `model` and `effort` on the session when the agent
   offers that value for its `model` or `thought_level` config option. Any
   other value does nothing (`hive_runtime::AcpRuntime`).

docs/turn-loop/README.md

@@ -142,8 +142,8 @@ else a `TurnError`) drives the post-claude branch:
 | `Err(RateLimited)` | sleep `HIVE_RATE_LIMIT_SLEEP_SECS` (default 300), requeue inflight, status back to `online` |
 | `Err(AuthFailed)` | emit `needs_login_idle` sentinel, requeue inflight, park in `wait_for_login` |
 | `Err(SessionNotFound)` | resume + create self-heal both missed ("shouldn't happen"); requeue inflight so the next turn creates fresh — no status park, message not dropped |
-| `Err(ApiStall)` | idle watchdog killed claude after `HIVE_TURN_IDLE_SECS` (default 600) of output silence; sleep `HIVE_STALL_SLEEP_SECS` (default 60), requeue inflight, status back to `online` |
-| `Err(AgentStall(note))` | the same, for an ACP agent: after `HIVE_TURN_IDLE_SECS` with no `session/update` the harness sent the agent `session/cancel`, and killed it if it ignored that; `note` says which |
+| `Err(ApiStall)` | idle watchdog sent claude SIGINT after `HIVE_TURN_IDLE_SECS` (default 600) of output silence and claude exited; sleep `HIVE_STALL_SLEEP_SECS` (default 60), requeue inflight, status back to `online` |
+| `Err(AgentStall(note))` | the same, for an ACP agent: after `HIVE_TURN_IDLE_SECS` with no `session/update` the harness sent the agent `session/cancel`, and SIGINT if it ignored that; `note` says which |
 | `Err(Failed(err))` | route `[system] \`<qualified-label>\` claude turn failed:\n<err>` to `operator` via `send_to_operator` |
 
 `ApiStall` catches an Anthropic API stall — a multi-retry connection storm where
@@ -152,7 +152,11 @@ the stream goes silent for minutes. On `claude` the idle watchdog lives in
 resets on every stdout line, so a large but still-streaming turn is never cut —
 only complete output silence for the window trips it. The harness sets the
 window from `HIVE_TURN_IDLE_SECS` (`0` disables) and maps the driver's
-`Error::IdleTimeout` onto `TurnError::ApiStall`.
+`Error::IdleTimeout` onto `TurnError::ApiStall`. The watchdog sends claude's
+process group SIGINT, so claude stops the commands it started, and then
+waits for claude to exit. Nothing escalates to SIGKILL: a claude that
+ignores the SIGINT keeps the turn open until someone kills it or the unit
+stops.
 
 `hive-runtime` applies the same window to an ACP agent's turns. That's
 also how a provider HTTP 429 ends an ACP turn when the agent retries it without

docs/web-ui/agent.md

@@ -227,11 +227,11 @@ Slash commands today:
 
 - `/help` — list commands locally.
 - `/clear` — wipe the local terminal view (server history kept).
-- `/cancel` — `POST /api/cancel` → host shellouts `pkill -INT
-  claude`, emits a Note. On an ACP agent it sends the agent
-  `session/cancel` instead, and kills it if the turn hasn't ended 10s
-  later. Also surfaces as a `■ cancel turn` button in the state row
-  while state=thinking.
+- `/cancel` — `POST /api/cancel` → SIGINT to the turn's claude and every
+  command it started (its process group), emits a Note. On an ACP agent
+  it sends the agent `session/cancel` instead, and SIGINT if the turn
+  hasn't ended 10s later. Also surfaces as a `■ cancel turn` button in
+  the state row while state=thinking.
 - `/compact` — `POST /api/compact` → sets the deferred
   `Bus::request_compact()` flag and returns immediately. The harness
   runs the `/compact` at the next turn boundary (end of the in-flight
@@ -272,8 +272,8 @@ shaped).
 - `POST /login/{start,code,cancel}` — claude OAuth login flow.
   Start/cancel emit `LiveEvent::StatusChanged` to flip the
   badge to/from `needs_login_in_progress`.
-- `POST /api/cancel` — SIGINT the in-flight claude turn. Emits a
-  `LiveEvent::Note`.
+- `POST /api/cancel` — SIGINT the in-flight claude turn and the
+  commands it started. Emits a `LiveEvent::Note`.
 - `POST /api/compact` — run `/compact` on the persistent session
   (same MCP config + system prompt + allowed tools as a normal
   turn — only the stdin payload differs). Flips state to

hive-agent/src/turn.rs

@@ -50,8 +50,8 @@ const DEFAULT_SESSION_TITLE: &str = "hive-session";
 /// capacity limits.
 const DEFAULT_RATE_LIMIT_SLEEP_SECS: u64 = 300;
 
-/// Idle watchdog window: kill claude and surface `ApiStall` if it produces no
-/// stdout for this long. The timer resets on every stdout line, so a large but
+/// Idle watchdog window: send claude SIGINT and surface `ApiStall` once it
+/// exits, if it produces no stdout for this long. The timer resets on every stdout line, so a large but
 /// still-streaming turn is never cut — only a complete silence trips it.
 /// Default is 10 minutes: long enough for legitimate big-context turns, short
 /// enough to cut a multi-retry Anthropic connection storm (atlas telemetry:
@@ -189,14 +189,14 @@ pub enum TurnError {
     /// the wake message, the serve loop requeues it so the next turn retries;
     /// no status park.
     SessionNotFound,
-    /// The harness-side idle watchdog killed claude after `turn_idle_secs()` of
+    /// The harness-side idle watchdog stopped claude after `turn_idle_secs()` of
     /// output silence — indicative of an Anthropic API stall (e.g. a multi-retry
     /// connection storm burning minutes of wall-clock with no stream progress).
     /// The serve loop parks for `stall_sleep_secs()` and requeues, like the
     /// rate-limit path — NOT a crash.
     ApiStall,
     /// The ACP backend's idle watchdog stopped a turn that sent nothing for
-    /// `turn_idle_secs()`: the agent was sent `session/cancel`, and killed if
+    /// `turn_idle_secs()`: the agent was sent `session/cancel`, and SIGINT if
     /// it ignored that. Carries what happened. An ACP agent retrying a failing
     /// provider (e.g. HTTP 429) without reporting it ends up here. Handled
     /// like [`Self::ApiStall`].
@@ -558,11 +558,11 @@ pub fn emit_turn_end(bus: &Bus, outcome: &TurnOutcome) {
             bus.emit(LiveEvent::TurnEnd {
                 ok: false,
                 note: Some(format!(
-                    "claude killed after {}s of output silence — API stall suspected, parking + requeueing",
+                    "claude stopped with SIGINT after {}s of output silence — API stall suspected, parking + requeueing",
                     turn_idle_secs()
                 )),
             });
-            tracing::warn!("turn killed: API stall (idle watchdog)");
+            tracing::warn!("turn stopped: API stall (idle watchdog)");
         }
         Err(TurnError::AgentStall(note)) => {
             bus.emit(LiveEvent::TurnEnd {

hive-agent/src/web_ui/actions.rs

@@ -69,7 +69,7 @@ pub(super) async fn post_cancel_turn(State(state): State<AppState>) -> Response
             .emit(crate::events::LiveEvent::Note { text: note.into() });
         return (axum::http::StatusCode::OK, "ok").into_response();
     }
-    let out = super::sigint_claude().await;
+    let out = super::sigint_claude();
     let note = match out {
         SigintOutcome::Signalled => {
             // A process actually got signalled — the *next* turn's wake

hive-agent/src/web_ui/auth.rs

@@ -84,7 +84,7 @@ pub(super) async fn post_login_cancel(State(state): State<AppState>) -> Response
 /// preservation invariants.
 pub(super) async fn post_logout(State(state): State<AppState>) -> Response {
     // Step 1: SIGINT claude (best-effort, matches `post_cancel_turn`).
-    let _ = super::sigint_claude().await;
+    let _ = super::sigint_claude();
     // Step 2: delete OAuth credential files only — login::clear_session owns
     // the file set and preserves session-history files alongside them.
     let dir = crate::paths::claude_dir();

hive-agent/src/web_ui/mod.rs

@@ -340,21 +340,40 @@ fn find_claude_child() -> Option<u32> {
 /// (best-effort). See [`find_claude_child`] for how it's identified —
 /// **not** a name-based `pkill claude`, which would also hit an unrelated
 /// `claude` process someone is running interactively in the container.
-async fn sigint_claude() -> SigintOutcome {
+fn sigint_claude() -> SigintOutcome {
     let Some(pid) = find_claude_child() else {
         return SigintOutcome::NoProcess;
     };
-    match tokio::process::Command::new("kill")
-        .args(["-INT", &pid.to_string()])
-        .status()
-        .await
-    {
-        Ok(status) if status.success() => SigintOutcome::Signalled,
-        // Non-zero from `kill` means "no such process" (ESRCH) — it already
-        // exited between the check above and the signal. Same as never
-        // having found it.
-        Ok(_) => SigintOutcome::NoProcess,
-        Err(e) => SigintOutcome::Failed(e),
+    sigint_turn(pid)
+}
+
+/// SIGINT `pid`, and its whole process group when it leads one, so the
+/// commands a turn's claude started stop with it. `hive-claude` spawns the
+/// turn's claude as the leader of its own group. A `claude` child that
+/// leads none (`plugins.rs`'s `claude plugin` calls) shares the harness's
+/// group, so it is signalled alone.
+fn sigint_turn(pid: u32) -> SigintOutcome {
+    // A child is never pid 0 or 1, and `-0` / `-1` would reach the
+    // harness's own group or every process it may signal.
+    let Some(pid) = i32::try_from(pid).ok().filter(|&pid| pid > 1) else {
+        return SigintOutcome::NoProcess;
+    };
+    // SAFETY: `getpgid(2)` only reads; a gone pid returns -1, never `pid`.
+    let target = if unsafe { libc::getpgid(pid) } == pid {
+        -pid
+    } else {
+        pid
+    };
+    // SAFETY: plain `kill(2)` on the child or the group it leads.
+    if unsafe { libc::kill(target, libc::SIGINT) } == 0 {
+        return SigintOutcome::Signalled;
+    }
+    let err = std::io::Error::last_os_error();
+    if err.raw_os_error() == Some(libc::ESRCH) {
+        // It exited between the scan and the signal: same as never found.
+        SigintOutcome::NoProcess
+    } else {
+        SigintOutcome::Failed(err)
     }
 }
 
@@ -419,3 +438,105 @@ fn broker_error_response(err: &BrokerError, action: &str) -> Response {
         ),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::os::unix::process::CommandExt as _;
+    use std::path::Path;
+    use std::process::{Command, Stdio};
+    use std::time::Duration;
+
+    use super::{SigintOutcome, sigint_turn};
+
+    /// Poll `path` until it holds a complete, newline-terminated pid.
+    fn read_pid(path: &Path) -> i32 {
+        for _ in 0..250 {
+            if let Ok(text) = std::fs::read_to_string(path)
+                && text.ends_with('\n')
+            {
+                return text.trim().parse().expect("pid file holds a pid");
+            }
+            std::thread::sleep(Duration::from_millis(20));
+        }
+        unreachable!("no pid in {} within 5s", path.display());
+    }
+
+    /// Whether `pid` is still running. A zombie counts as gone: it has
+    /// exited, and `kill(pid, 0)` only keeps finding it until it is reaped.
+    fn is_running(pid: i32) -> bool {
+        // SAFETY: signal 0 delivers nothing; it only checks that `pid` exists.
+        if unsafe { libc::kill(pid, 0) } != 0 {
+            return false;
+        }
+        !std::fs::read_to_string(format!("/proc/{pid}/stat")).is_ok_and(|stat| {
+            stat.rsplit_once(") ")
+                .is_some_and(|(_, rest)| rest.starts_with('Z'))
+        })
+    }
+
+    #[test]
+    fn a_cancel_stops_the_commands_a_turn_started() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let pidfile = dir.path().join("grandchild.pid");
+        // A turn's claude as hive-claude spawns it: leading its own group,
+        // with a command of its own running in the foreground (a
+        // non-interactive shell starts `&` jobs with SIGINT ignored). The
+        // trailing `exit` keeps `sh -c` from exec'ing into that command.
+        let mut turn = Command::new("/bin/sh")
+            .args([
+                "-c",
+                r#"sh -c 'echo $$ >"$1"; exec sleep 300' sh "$1"; exit"#,
+                "sh",
+            ])
+            .arg(&pidfile)
+            .stdout(Stdio::null())
+            .stderr(Stdio::null())
+            .process_group(0)
+            .spawn()
+            .expect("spawn the stand-in turn");
+        let grandchild = read_pid(&pidfile);
+        assert_ne!(
+            i32::try_from(turn.id()).ok(),
+            Some(grandchild),
+            "the command must be a child of the turn, not the turn itself"
+        );
+
+        assert!(matches!(sigint_turn(turn.id()), SigintOutcome::Signalled));
+
+        let mut alive = is_running(grandchild);
+        for _ in 0..250 {
+            if !alive {
+                break;
+            }
+            std::thread::sleep(Duration::from_millis(20));
+            alive = is_running(grandchild);
+        }
+        if alive {
+            // SAFETY: `kill(2)` on a pid this test started; keeps a failed
+            // run from leaving a 300s `sleep` behind.
+            unsafe {
+                libc::kill(grandchild, libc::SIGKILL);
+            }
+        }
+        let _ = turn.wait();
+        assert!(!alive, "grandchild {grandchild} outlived the cancel");
+    }
+
+    #[test]
+    fn a_claude_sharing_the_harness_group_is_signalled_alone() {
+        // In this test process's own group, as `claude plugin` runs. A group
+        // signal here would SIGINT the test binary itself.
+        let mut child = Command::new("sleep")
+            .arg("300")
+            .spawn()
+            .expect("spawn sleep");
+
+        assert!(matches!(sigint_turn(child.id()), SigintOutcome::Signalled));
+
+        let status = child.wait().expect("reap sleep");
+        assert_eq!(
+            std::os::unix::process::ExitStatusExt::signal(&status),
+            Some(libc::SIGINT)
+        );
+    }
+}

hive-runtime/README.md

@@ -35,13 +35,15 @@ The crate depends on no hyperhive binary crate, so `hive-agent` and
 A turn is stopped with `session/cancel`: by the `Canceller` handle, or by the
 idle watchdog once no `session/update` has arrived for
 `Config::idle_timeout`. An agent that has not answered the prompt 10s later
-is killed, and the next turn respawns it. A watchdog stop fails the turn
-with `AcpError::IdleTimeout` (`IdleKilled` if the agent was killed). This is
+is sent SIGINT, and the next turn respawns it. A watchdog stop fails the turn
+with `AcpError::IdleTimeout` (`IdleKilled` if the agent was sent SIGINT). This is
 the only way a provider error the agent retries without reporting it, such as
 an HTTP 429, ends the turn.
 
-The agent leads its own process group. Killing it, and dropping the runtime,
-`SIGKILL`s that group, so the commands the agent started die with it.
+The agent leads its own process group. Stopping it, and dropping the runtime,
+sends that group SIGINT, so the commands the agent started get it too.
+Nothing escalates to SIGKILL: an agent that ignores SIGINT keeps running,
+and the next turn starts a new one beside it.
 
 ## ACP backend: compaction
 

hive-runtime/src/acp/mod.rs

@@ -39,7 +39,7 @@ const SETTLE_QUIET: Duration = Duration::from_millis(500);
 const SETTLE_MAX: Duration = Duration::from_secs(5);
 
 /// How long the agent has to end its turn after `session/cancel` before it is
-/// killed.
+/// sent SIGINT.
 const CANCEL_GRACE: Duration = Duration::from_secs(10);
 
 /// How long a `compact` command may send nothing before it is cancelled and
@@ -120,10 +120,12 @@ pub enum AcpError {
     EmptyEndTurn,
     #[error(
         "ACP agent sent nothing for {silent_secs}s and did not stop within {grace_secs}s of \
-         `session/cancel`, so it was killed"
+         `session/cancel`, so it was sent SIGINT"
     )]
     IdleKilled { silent_secs: u64, grace_secs: u64 },
-    #[error("ACP agent did not stop within {grace_secs}s of `session/cancel`, so it was killed")]
+    #[error(
+        "ACP agent did not stop within {grace_secs}s of `session/cancel`, so it was sent SIGINT"
+    )]
     CancelIgnored { grace_secs: u64 },
 }
 
@@ -141,8 +143,8 @@ struct CancelState {
 impl Canceller {
     /// Ask the turn in flight to stop. The agent is sent `session/cancel`,
     /// and the turn then ends normally with what it produced so far; an
-    /// agent that has not ended it within `CANCEL_GRACE` is killed, and the
-    /// turn fails with [`AcpError::CancelIgnored`]. Returns whether a turn
+    /// agent that has not ended it within `CANCEL_GRACE` is sent SIGINT, and
+    /// the turn fails with [`AcpError::CancelIgnored`]. Returns whether a turn
     /// was in flight; with none, this does nothing.
     #[must_use]
     pub fn cancel(&self) -> bool {
@@ -1062,9 +1064,14 @@ mod tests {
     const AGENT: &str = r#"
 n=0 prompt= model=m/think effort=low
 printf 'start\n' >> "$1.methods"
+# With TRAP_INT set: SIGINT creates <log>.int and exits 0.
+if [ -n "$TRAP_INT" ]; then
+  trap ': > "$1.int"; exit 0' INT
+fi
 # With GRANDCHILD set: a background `sleep`, its pid in <log>.grandchild.
+# `&` starts it with SIGINT ignored; `env` puts the default back.
 if [ -n "$GRANDCHILD" ]; then
-  sh -c 'echo $$ >"$1.grandchild"; exec sleep 300' sh "$1" >/dev/null 2>&1 &
+  sh -c 'echo $$ >"$1.grandchild"; exec env --default-signal=INT sleep 300' sh "$1" >/dev/null 2>&1 &
 fi
 update() {
   printf '{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"%s","update":%s}}\n' "$1" "$2"
@@ -1529,6 +1536,33 @@ done
         assert_gone(grandchild).await;
     }
 
+    /// SIGINT rather than SIGKILL: an agent only stops the commands it
+    /// started itself if it gets to shut down.
+    #[tokio::test]
+    async fn dropping_the_runtime_lets_its_agent_shut_down_on_sigint() {
+        let dir = tempfile::tempdir().unwrap();
+        let runtime = agent(
+            dir.path(),
+            "ok",
+            &[("TRAP_INT", "1")],
+            PercentPolicy::default(),
+        );
+        runtime
+            .run(&config(dir.path()), "one", &NoopSink)
+            .await
+            .unwrap();
+
+        drop(runtime);
+        let marker = dir.path().join("prompts.int");
+        for _ in 0..250 {
+            if marker.exists() {
+                break;
+            }
+            tokio::time::sleep(Duration::from_millis(20)).await;
+        }
+        assert!(marker.exists(), "the agent never got SIGINT");
+    }
+
     fn sent(session: &str, text: &str) -> (String, String) {
         (session.to_owned(), text.to_owned())
     }

hive-runtime/src/acp/rpc.rs

@@ -31,9 +31,10 @@ type Reply = Result<Value, AcpError>;
 type Pending = Arc<Mutex<HashMap<u64, (&'static str, oneshot::Sender<Reply>)>>>;
 
 /// The agent runs as the leader of its own process group; dropping the
-/// connection `SIGKILL`s that group, so the commands the agent started die
-/// with it. A descendant that left the group (`setsid`, `setpgid`) is not
-/// reached.
+/// connection sends that group SIGINT, so the agent can stop the commands
+/// it started, and they get the signal too. Nothing escalates: an agent
+/// that ignores SIGINT keeps running. A descendant that left the group
+/// (`setsid`, `setpgid`) is not reached.
 pub(super) struct Connection {
     child: Child,
     /// The agent's pid, which is its group's id. Read at spawn: a reaped
@@ -66,7 +67,6 @@ impl Connection {
             .stdout(Stdio::piped())
             .stderr(Stdio::piped())
             .process_group(0)
-            .kill_on_drop(true)
             .spawn()
             .map_err(|source| AcpError::Spawn {
                 program: command.command.clone(),
@@ -182,7 +182,7 @@ impl Drop for Connection {
             // SAFETY: plain `kill(2)`; `-pgid` targets the agent's own
             // process group, which `process_group(0)` made it lead.
             unsafe {
-                libc::kill(-pgid, libc::SIGKILL);
+                libc::kill(-pgid, libc::SIGINT);
             }
         }
     }

hive-subagent-mcp/src/mcp.rs

@@ -187,10 +187,6 @@ struct StatusArgs {
 struct InterruptArgs {
     /// The running session's name to signal.
     name: String,
-    /// `true` sends SIGKILL immediately; `false` (default) sends SIGINT,
-    /// letting claude shut down cleanly if it's already mid-response.
-    #[serde(default)]
-    force: bool,
 }
 
 #[derive(Clone)]
@@ -276,11 +272,13 @@ impl SubagentMcp {
             re-prompted toward it afterwards, and `continue` is what restarts it. Only works \
             once it's actually running — a `start`/`continue` still in its brief window before \
             the process is confirmed spawned refuses interrupt too (nothing to signal yet; \
-            retry shortly), same as a name with nothing tracked at all. `force: true` for \
-            SIGKILL, otherwise SIGINT."
+            retry shortly), same as a name with nothing tracked at all. On claude it sends \
+            SIGINT, which claude answers by stopping the commands it started and exiting; \
+            nothing escalates past it. Returns at once; the name stays claimed until claude \
+            has exited, and `status` says `stopping` until then."
     )]
     fn interrupt(&self, Parameters(args): Parameters<InterruptArgs>) -> String {
-        match session::interrupt(&self.state, &args.name, args.force) {
+        match session::interrupt(&self.state, &args.name) {
             Ok(msg) => msg,
             Err(e) => format!("interrupt error: {e:#}"),
         }

hive-subagent-mcp/src/session.rs

@@ -5,8 +5,8 @@
 //! continuation loop records.
 //!
 //! **No task files, no restart recovery.** The daemon's only state is an
-//! in-memory `name -> Option<Stopper>` map (see `State`'s own doc for the
-//! rest of the maps and for what the `None`/`Some` split is for) — all of
+//! in-memory `name -> Slot` map (see `State`'s own doc for the rest of the
+//! maps, and `Slot`'s for what each state of a claimed name means) — all of
 //! it living for exactly as long as the process is. A daemon restart means
 //! whatever was running gets killed
 //! with it (`tokio`'s own child-process drop semantics), not adopted, and
@@ -230,11 +230,33 @@ enum SubagentRuntime {
 enum Stopper {
     /// Signals the turn's `claude` process.
     Claude(Cancel),
-    /// Sends the ACP agent `session/cancel`; one that ignores it is killed
-    /// by the runtime after its own grace period.
+    /// Sends the ACP agent `session/cancel`; the runtime sends SIGINT to one
+    /// that ignores it for its own grace period.
     Acp(Canceller),
 }
 
+/// What `running` holds for a claimed name.
+enum Slot {
+    /// Claimed, with no process confirmed under it: a `start`/`continue`
+    /// that hasn't spawned yet, or a goal run between turns.
+    Starting,
+    /// A turn is in flight, and this is how `interrupt` reaches it.
+    Running(Stopper),
+    /// `interrupt` has signalled a claude turn and its process hasn't exited
+    /// yet. Nothing escalates past that SIGINT, so a claude that ignores it
+    /// stays here until it exits; the turn's own `finish_turn` frees the
+    /// name.
+    Stopping,
+}
+
+/// Which [`Slot`] a claimed name is in, without its cancel handle.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Occupancy {
+    Starting,
+    Running,
+    Stopping,
+}
+
 /// What settled a resumed turn's bounded wait — the one thing `continue`
 /// blocks on before it answers.
 enum ResumeVerdict {
@@ -333,13 +355,13 @@ fn searched_location(config: &Config) -> Option<String> {
 /// and where to push the completion todo. `Arc`-wrapped so the background
 /// task driving a run outlives the tool call that started it.
 ///
-/// The map value is `Option<Stopper>`: `None` means `name` is reserved for
-/// an in-flight `start`/`continue` that hasn't reached a confirmed
-/// spawn yet; `Some(stopper)` means a real turn is tracked and
-/// interruptible. The `None` state exists to close a real TOCTOU window a
-/// reviewer caught in the original check-then-insert version: checking "is
-/// `name` free" and committing to it are two different lock acquisitions
-/// unless the check *is* the reservation — see `reserve`.
+/// The map value is a `Slot`: `Starting` means `name` is reserved for an
+/// in-flight `start`/`continue` that hasn't reached a confirmed spawn yet;
+/// `Running` means a real turn is tracked and interruptible; `Stopping`
+/// means it was interrupted and its process is still winding down. Each
+/// claims the name. `Starting` closes a TOCTOU window: checking "is `name`
+/// free" and committing to it are two different lock acquisitions unless
+/// the check *is* the reservation — see `reserve`.
 ///
 /// `killed` is the other half of that map's story: `running` says what is in
 /// flight *now*, `killed` remembers the names whose last turn ended on a
@@ -359,7 +381,7 @@ fn searched_location(config: &Config) -> Option<String> {
 /// name across directories at your own risk, the tool doesn't disambiguate
 /// it (flagged in review when `dir` was added).
 pub struct State {
-    running: Mutex<HashMap<String, Option<Stopper>>>,
+    running: Mutex<HashMap<String, Slot>>,
     dirs: Mutex<HashMap<String, String>>,
     killed: Mutex<HashMap<String, i32>>,
     last_event: Mutex<HashMap<String, Instant>>,
@@ -547,17 +569,17 @@ impl State {
         }
     }
 
-    /// `Some(true)` — a live process is tracked, interruptible. `Some(false)`
-    /// — the name is claimed but no process is confirmed under it: an
-    /// in-flight start/continue that hasn't spawned yet, or the gap between
-    /// one continued turn's child exiting and the next one spawning (see
-    /// `between_turns`). `None` — nothing tracked under `name` at all.
-    fn occupancy(&self, name: &str) -> Option<bool> {
+    /// Which [`Slot`] `name` is in; `None` with nothing tracked under it.
+    fn occupancy(&self, name: &str) -> Option<Occupancy> {
         self.running
             .lock()
             .unwrap_or_else(PoisonError::into_inner)
             .get(name)
-            .map(Option::is_some)
+            .map(|slot| match slot {
+                Slot::Starting => Occupancy::Starting,
+                Slot::Running(_) => Occupancy::Running,
+                Slot::Stopping => Occupancy::Stopping,
+            })
     }
 
     /// Atomically claim `name` for an in-flight start/continue: check
@@ -572,21 +594,21 @@ impl State {
         if running.contains_key(name) {
             return false;
         }
-        running.insert(name.to_owned(), None);
+        running.insert(name.to_owned(), Slot::Starting);
         true
     }
 
     /// Release a reservation that never made it to a real spawn (an error
     /// on the slow path between `reserve` and `Claude::spawn` succeeding).
-    /// A no-op if the entry was already upgraded to `Some` — this only ever
-    /// clears a still-`None` placeholder, never a live process.
+    /// A no-op if the entry was already upgraded to `Running` — this only
+    /// ever clears a still-`Starting` placeholder, never a live process.
     ///
     /// The signal token the failed call minted goes with it: no process ever
     /// read that URL, and a token outliving the call that minted it is the
     /// one way a route could resolve to a session that isn't there.
     fn release_reservation(&self, name: &str) {
         let mut running = self.running.lock().unwrap_or_else(PoisonError::into_inner);
-        let released = matches!(running.get(name), Some(None));
+        let released = matches!(running.get(name), Some(Slot::Starting));
         if released {
             running.remove(name);
         }
@@ -742,14 +764,14 @@ impl State {
         }
     }
 
-    /// Upgrade `name`'s `None` reservation to a real, interruptible process.
-    /// Same key as the reservation, so there is no window in which `name`
-    /// reads as unoccupied between the two.
+    /// Upgrade `name`'s `Starting` reservation to a real, interruptible
+    /// process. Same key as the reservation, so there is no window in which
+    /// `name` reads as unoccupied between the two.
     fn track(&self, name: &str, stopper: Stopper) {
         self.running
             .lock()
             .unwrap_or_else(PoisonError::into_inner)
-            .insert(name.to_owned(), Some(stopper));
+            .insert(name.to_owned(), Slot::Running(stopper));
     }
 
     /// Drop `name`'s cancel handle but keep the name claimed — the moment
@@ -763,7 +785,7 @@ impl State {
         self.running
             .lock()
             .unwrap_or_else(PoisonError::into_inner)
-            .insert(name.to_owned(), None);
+            .insert(name.to_owned(), Slot::Starting);
     }
 
     /// Set (or clear) `name`'s goal and start its turn budget over at turn
@@ -1286,7 +1308,7 @@ pub async fn start(state: &Arc<State>, req: StartRequest) -> anyhow::Result<Stri
     // process spawned.
     let role = req.role.as_deref().map(crate::role::load).transpose()?;
     if !state.reserve(name) {
-        anyhow::bail!("subagent `{name}` is already running — use `continue` or `interrupt`");
+        return Err(name_taken(state, name, "use `continue` or `interrupt`"));
     }
     // Only commit the remembered `dir` now that `reserve` has actually
     // claimed `name` — see `resolve_dir`'s doc for why the order matters,
@@ -1460,9 +1482,11 @@ pub async fn continue_(
     validate_name(name)?;
     state.allow_model(model.as_deref()).await?;
     if !state.reserve(name) {
-        anyhow::bail!(
-            "subagent `{name}` is already running — use `interrupt` first if you meant to redirect it"
-        );
+        return Err(name_taken(
+            state,
+            name,
+            "use `interrupt` first if you meant to redirect it",
+        ));
     }
     // Read before the spawn, which clears the record as soon as the new turn
     // is confirmed — this reply is the last chance to mention it.
@@ -2179,7 +2203,7 @@ fn describe_turns(turns: Option<(u32, u32)>) -> String {
 /// them is a fact about the same session.
 struct StatusFacts<'a> {
     name: &'a str,
-    occupancy: Option<bool>,
+    occupancy: Option<Occupancy>,
     killed: Option<i32>,
     session_exists: bool,
     last_event_age: Option<Duration>,
@@ -2224,7 +2248,7 @@ fn describe_status(facts: &StatusFacts<'_>) -> anyhow::Result<String> {
     let name = facts.name;
     let turns = describe_turns(facts.turns);
     match facts.occupancy {
-        Some(true) => {
+        Some(Occupancy::Running) => {
             return Ok(format!(
                 "subagent `{name}` is running — its turn is still in flight, so there's nothing \
                  to do but let it work: the daemon pushes a todo when the run ends, or \
@@ -2233,7 +2257,7 @@ fn describe_status(facts: &StatusFacts<'_>) -> anyhow::Result<String> {
                 describe_pending_signal(facts.stop.as_ref()),
             ));
         }
-        Some(false) => {
+        Some(Occupancy::Starting) => {
             return Ok(format!(
                 "subagent `{name}` is starting — the name is claimed but no process is confirmed \
                  under it yet, either because a `start`/`continue` hasn't spawned one or because \
@@ -2241,6 +2265,15 @@ fn describe_status(facts: &StatusFacts<'_>) -> anyhow::Result<String> {
                  shortly rather than starting anything else under this name.{turns}"
             ));
         }
+        Some(Occupancy::Stopping) => {
+            return Ok(format!(
+                "subagent `{name}` is stopping — `interrupt` sent it SIGINT and its process \
+                 hasn't exited yet. The name stays claimed until it does, so `start` and \
+                 `continue` are refused meanwhile. Nothing escalates past that SIGINT: one that \
+                 never exits needs killing by hand.{turns}{}",
+                describe_liveness(facts.last_event_age),
+            ));
+        }
         None => {}
     }
     if let Some(signal) = facts.killed {
@@ -2327,57 +2360,60 @@ fn describe_stopped(name: &str, stop: &StopReason, turns: &str) -> String {
     }
 }
 
-/// Signal `name`'s running process — `force` picks SIGKILL over SIGINT (see
-/// `hive_claude::Cancel::cancel`). Refuses a name with nothing running: no
-/// entry at all, or one still in the brief not-yet-spawned window (nothing
-/// to signal yet — the reservation is put back so a concurrent
-/// `start`/`continue` for the same name still gets refused).
+/// Stop `name`'s running turn: SIGINT to claude's process group (see
+/// `hive_claude::Cancel::cancel`), or `session/cancel` on ACP. Nothing
+/// escalates to SIGKILL: each command claude's Bash tool starts leads its
+/// own session, and only claude shutting down on SIGINT stops it.
 ///
-/// This stops a goal run, not just the turn in it — and it does so by
-/// **recording `StopReason::Cancelled`**, not by relying on how the child
-/// dies.
+/// Returns without waiting. A claude turn's name stays claimed as
+/// `Slot::Stopping` until the turn's own `finish_turn` clears it, so no
+/// second claude starts on the session while the first is winding down.
 ///
-/// That distinction is the entire fix. The signal alone is not enough: the
-/// default is SIGINT, claude handles SIGINT by emitting its terminal
-/// `result` event and exiting 0, and a zero exit is `TurnEnd::Complete` —
-/// so `spawn_and_track`'s killed-turn early return never fires and the loop
-/// goes straight on to spawn turn three of five. The recorded reason is what
-/// `plan_after_turn` reads, and it is checked before the goal, so the run
-/// stops whichever way the child ends up exiting. `force`'s SIGKILL does
-/// produce a `TurnEnd::Killed`; recording the reason anyway costs nothing
-/// and keeps one path, and `status` still prefers the kill record it
-/// already had.
-///
-/// The reason is written while the `running` lock is still held, so there is
-/// no instant in which the name has lost its cancel handle but not yet
-/// gained its stop reason — a turn ending of its own accord in that gap
-/// would find nothing to stop it and start the next one.
+/// It stops the goal run, not just the turn, by **recording
+/// `StopReason::Cancelled`**: claude answers SIGINT by emitting its
+/// terminal `result` event and exiting 0, which is `TurnEnd::Complete`, so
+/// only the recorded reason, which `plan_after_turn` checks before the
+/// goal, keeps the loop from re-prompting. It is written while the
+/// `running` lock is held, so a turn that ends on its own in between still
+/// finds it.
 ///
 /// # Errors
 ///
-/// An invalid name, nothing tracked under `name`, or nothing to signal right
-/// now (a spawn or ACP turn not yet live, or a goal run between turns).
-pub fn interrupt(state: &State, name: &str, force: bool) -> anyhow::Result<String> {
+/// An invalid name, nothing tracked under `name`, nothing to signal right
+/// now (a spawn or ACP turn not yet live, or a goal run between turns; the
+/// reservation is put back, so a concurrent `start`/`continue` is still
+/// refused), or a claude already signalled and not yet exited.
+pub fn interrupt(state: &State, name: &str) -> anyhow::Result<String> {
     validate_name(name)?;
     let mut running = state.running.lock().unwrap_or_else(PoisonError::into_inner);
+    let mut claimed = "";
     match running.remove(name) {
         None => anyhow::bail!("no subagent named `{name}` is currently running"),
-        Some(None) => {
-            running.insert(name.to_owned(), None);
+        Some(Slot::Starting) => {
+            running.insert(name.to_owned(), Slot::Starting);
             return Err(still_starting(name));
         }
-        Some(Some(Stopper::Claude(cancel))) => {
-            state.record_stop(name, StopReason::Cancelled);
-            drop(running);
-            cancel.cancel(force);
+        Some(Slot::Stopping) => {
+            running.insert(name.to_owned(), Slot::Stopping);
+            anyhow::bail!(
+                "subagent `{name}` was already interrupted and its process hasn't exited yet — \
+                 `status` says when it has"
+            );
         }
-        // `force` has no stronger form on ACP: the runtime already kills an
-        // agent that ignores `session/cancel`. `cancel()` is `false` when no
-        // turn is in flight (the agent not prompted yet, or a turn just
-        // ended), and then nothing was cancelled. The stop goes in before the
-        // cancel and comes out under the same `stops` lock, so
-        // `plan_after_turn` never reads a cancel that didn't happen.
-        Some(Some(Stopper::Acp(canceller))) => {
+        Some(Slot::Running(Stopper::Claude(cancel))) => {
+            state.record_stop(name, StopReason::Cancelled);
+            running.insert(name.to_owned(), Slot::Stopping);
+            drop(running);
+            cancel.cancel(false);
+            claimed = " The name stays claimed until claude has exited; `status` says `stopping` \
+                       until then.";
+        }
+        // `cancel()` is `false` when no turn is in flight (the agent not
+        // prompted yet, or a turn just ended), and then nothing was
+        // cancelled. The stop goes in before the cancel and comes out under
+        // the same `stops` lock, so `plan_after_turn` never reads a cancel
+        // that didn't happen.
+        Some(Slot::Running(Stopper::Acp(canceller))) => {
             let mut stops = state.stops.lock().unwrap_or_else(PoisonError::into_inner);
             let prior = stops.insert(name.to_owned(), StopReason::Cancelled);
             if !canceller.cancel() {
@@ -2386,7 +2422,7 @@ pub fn interrupt(state: &State, name: &str, force: bool) -> anyhow::Result<Strin
                     None => stops.remove(name),
                 };
                 drop(stops);
-                running.insert(name.to_owned(), Some(Stopper::Acp(canceller)));
+                running.insert(name.to_owned(), Slot::Running(Stopper::Acp(canceller)));
                 return Err(still_starting(name));
             }
         }
@@ -2394,10 +2430,24 @@ pub fn interrupt(state: &State, name: &str, force: bool) -> anyhow::Result<Strin
     Ok(format!(
         "interrupt sent to subagent `{name}` — the run is cancelled, not just the turn that was \
          in flight, so no further goal turn will start. `continue` is what restarts it, with a \
-         fresh turn allowance."
+         fresh turn allowance.{claimed}"
     ))
 }
 
+/// `start`'s and `continue`'s refusal for a name `reserve` found claimed:
+/// `hint` says what to do about a live session, and an interrupted one that
+/// hasn't exited yet gets its own answer.
+fn name_taken(state: &State, name: &str, hint: &str) -> anyhow::Error {
+    if state.occupancy(name) == Some(Occupancy::Stopping) {
+        anyhow::anyhow!(
+            "subagent `{name}` is stopping — it was interrupted and its process hasn't exited \
+             yet; the name is free once it has (`status` says when)"
+        )
+    } else {
+        anyhow::anyhow!("subagent `{name}` is already running — {hint}")
+    }
+}
+
 /// `interrupt`'s refusal for a name that is claimed but has nothing to
 /// signal yet.
 fn still_starting(name: &str) -> anyhow::Error {
@@ -2539,7 +2589,7 @@ mod tests {
         state.reserve("n");
         assert_eq!(
             state.occupancy("n"),
-            Some(false),
+            Some(Occupancy::Starting),
             "reserved-but-not-yet-spawned must read as occupied-but-not-running"
         );
     }
@@ -2984,7 +3034,7 @@ mod tests {
         // has to carry its own explanation — checked one state at a time,
         // which is all a caller ever gets back.
         let running = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             ..StatusFacts::new("n")
         })
         .expect("running status");
@@ -2993,7 +3043,7 @@ mod tests {
             "a running answer must say the turn is in flight and how to stop it: {running}"
         );
         let starting = describe_status(&StatusFacts {
-            occupancy: Some(false),
+            occupancy: Some(Occupancy::Starting),
             ..StatusFacts::new("n")
         })
         .expect("starting status");
@@ -3238,7 +3288,7 @@ mod tests {
     #[test]
     fn a_running_status_reports_the_age_and_an_idle_one_does_not() {
         let running = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             last_event_age: Some(Duration::from_secs(4)),
             ..StatusFacts::new("n")
         })
@@ -3249,7 +3299,7 @@ mod tests {
              {running}"
         );
         let wedged = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             last_event_age: Some(Duration::from_mins(15)),
             ..StatusFacts::new("n")
         })
@@ -3281,7 +3331,7 @@ mod tests {
         // turn can finish between the two. The answer drops the age rather
         // than inventing one.
         let raced = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             ..StatusFacts::new("n")
         })
         .expect("running status");
@@ -3710,9 +3760,7 @@ mod tests {
         }
         assert_eq!(turns_spawned(&log), 1, "the first turn never started");
 
-        // An operator's plain `interrupt`, not `force` — SIGINT is the
-        // default and the case that was broken.
-        interrupt(&state, "n", false).expect("a running turn is interruptible");
+        interrupt(&state, "n").expect("a running turn is interruptible");
 
         // Generous: the fake logs its invocation as its first act, so a
         // re-prompt shows up here almost immediately once the loop decides
@@ -3731,6 +3779,178 @@ mod tests {
         std::fs::remove_dir_all(&dir).ok();
     }
 
+    /// A stand-in for claude with a command of its own still running: an
+    /// inner `sh` writes its pid to `pidfile` and execs `sleep`. It runs in
+    /// the foreground because a non-interactive shell starts `&` jobs with
+    /// SIGINT ignored, and its output goes to /dev/null so it cannot hold the
+    /// driver's pipes open.
+    fn busy_claude(dir: &Path, pidfile: &Path) -> PathBuf {
+        let script = dir.join("busy-claude");
+        write_executable(
+            &script,
+            &format!(
+                "#!/bin/sh\nsh -c 'echo $$ >\"$1\"; exec sleep 300' sh '{}' >/dev/null 2>&1\n",
+                pidfile.display()
+            ),
+        );
+        script
+    }
+
+    /// Poll `path` until it holds a complete, newline-terminated pid.
+    async fn read_pid(path: &Path) -> i32 {
+        for _ in 0..250 {
+            if let Ok(text) = std::fs::read_to_string(path)
+                && text.ends_with('\n')
+            {
+                return text.trim().parse().expect("pid file holds a pid");
+            }
+            tokio::time::sleep(Duration::from_millis(20)).await;
+        }
+        unreachable!("no pid in {} within 5s", path.display());
+    }
+
+    /// Whether `pid` is still running. A zombie counts as gone: it has
+    /// exited, and `kill(pid, 0)` only keeps finding it until it is reaped.
+    fn is_running(pid: i32) -> bool {
+        // SAFETY: signal 0 delivers nothing; it only checks that `pid` exists.
+        if unsafe { libc::kill(pid, 0) } != 0 {
+            return false;
+        }
+        !std::fs::read_to_string(format!("/proc/{pid}/stat")).is_ok_and(|stat| {
+            stat.rsplit_once(") ")
+                .is_some_and(|(_, rest)| rest.starts_with('Z'))
+        })
+    }
+
+    #[tokio::test]
+    async fn an_interrupt_stops_the_commands_the_subagent_started() {
+        let dir = scratch_dir("group");
+        let pidfile = dir.join("grandchild.pid");
+        let state = Arc::new(mid_run("n", "carry on indefinitely", 5));
+        let config = Config {
+            program: Some(busy_claude(&dir, &pidfile)),
+            ..Config::default()
+        };
+        spawn_and_track(
+            &state,
+            "n",
+            &config,
+            &Attach::Create("n".to_owned()),
+            "turn one".to_owned(),
+            None,
+        )
+        .expect("the fake claude spawns");
+        let grandchild = read_pid(&pidfile).await;
+
+        interrupt(&state, "n").expect("a running turn is interruptible");
+
+        let mut alive = is_running(grandchild);
+        for _ in 0..250 {
+            if !alive {
+                break;
+            }
+            tokio::time::sleep(Duration::from_millis(20)).await;
+            alive = is_running(grandchild);
+        }
+        if alive {
+            // SAFETY: `kill(2)` on a pid this test started; keeps a failed
+            // run from leaving a 300s `sleep` behind.
+            unsafe {
+                libc::kill(grandchild, libc::SIGKILL);
+            }
+        }
+        std::fs::remove_dir_all(&dir).ok();
+        assert!(!alive, "grandchild {grandchild} outlived the interrupt");
+    }
+
+    /// A stand-in for claude that shuts down on SIGINT the way claude does:
+    /// it writes `interrupted` once the signal arrives, then exits 0 as soon
+    /// as `release` exists, or after 10s. It writes `ready` once its trap is
+    /// set. A SIGKILL leaves no `interrupted` behind.
+    fn graceful_claude(dir: &Path) -> PathBuf {
+        let script = dir.join("graceful-claude");
+        write_executable(
+            &script,
+            &format!(
+                "#!/bin/sh\ncd '{}'\ntrap ': > interrupted; i=0; until [ -e release ] || \
+                 [ $i -ge 200 ]; do sleep 0.05; i=$((i+1)); done; kill $!; exit 0' INT\n\
+                 sleep 300 >/dev/null 2>&1 &\n: > ready\nwait\n",
+                dir.display()
+            ),
+        );
+        script
+    }
+
+    /// Spawn [`graceful_claude`] as `n`'s turn and wait until its trap is set.
+    async fn spawn_graceful(state: &Arc<State>, dir: &Path) {
+        let config = Config {
+            program: Some(graceful_claude(dir)),
+            ..Config::default()
+        };
+        spawn_and_track(
+            state,
+            "n",
+            &config,
+            &Attach::Create("n".to_owned()),
+            "turn one".to_owned(),
+            None,
+        )
+        .expect("the fake claude spawns");
+        until("the fake claude sets its trap", || {
+            dir.join("ready").exists()
+        })
+        .await;
+    }
+
+    #[tokio::test]
+    async fn an_interrupt_lets_claude_shut_down_on_sigint() {
+        let dir = scratch_dir("sigint");
+        std::fs::write(dir.join("release"), "").expect("release file");
+        let state = Arc::new(mid_run("n", "carry on indefinitely", 5));
+        spawn_graceful(&state, &dir).await;
+
+        interrupt(&state, "n").expect("a running turn is interruptible");
+
+        until("the run ends", || state.occupancy("n").is_none()).await;
+        let interrupted = dir.join("interrupted").exists();
+        std::fs::remove_dir_all(&dir).ok();
+        assert!(
+            interrupted,
+            "claude must get SIGINT, which it shuts its tool commands down on, never SIGKILL"
+        );
+        assert_eq!(state.killed_by("n"), None, "it exited on its own");
+    }
+
+    #[tokio::test]
+    async fn an_interrupted_name_stays_claimed_until_claude_has_exited() {
+        let dir = scratch_dir("stopping");
+        let state = Arc::new(mid_run("n", "carry on indefinitely", 5));
+        spawn_graceful(&state, &dir).await;
+
+        interrupt(&state, "n").expect("a running turn is interruptible");
+        until("the fake claude gets the SIGINT", || {
+            dir.join("interrupted").exists()
+        })
+        .await;
+
+        assert_eq!(state.occupancy("n"), Some(Occupancy::Stopping));
+        let status = status(&state, "n", None).expect("status");
+        assert!(status.contains("is stopping"), "{status}");
+        let refused = continue_(&state, "n", "more".to_owned(), None, None, None)
+            .await
+            .expect_err("a second claude must not start on the session");
+        assert!(refused.to_string().contains("is stopping"), "{refused}");
+        assert!(interrupt(&state, "n").is_err(), "it was already signalled");
+
+        std::fs::write(dir.join("release"), "").expect("release file");
+        until("the run ends", || state.occupancy("n").is_none()).await;
+        std::fs::remove_dir_all(&dir).ok();
+        assert!(
+            state.reserve("n"),
+            "the name is free once claude has exited"
+        );
+    }
+
     #[test]
     fn a_cancelled_run_stops_with_turns_still_on_its_clock() {
         // The loop half of the same fact, asserted directly: `Cancelled` is
@@ -3985,7 +4205,12 @@ mod tests {
 
     #[test]
     fn status_reports_the_turn_counter_in_every_state_a_goal_run_reaches() {
-        for occupancy in [Some(true), Some(false), None] {
+        for occupancy in [
+            Some(Occupancy::Running),
+            Some(Occupancy::Starting),
+            Some(Occupancy::Stopping),
+            None,
+        ] {
             let answer = describe_status(&StatusFacts {
                 occupancy,
                 session_exists: true,
@@ -4000,7 +4225,7 @@ mod tests {
             );
         }
         let goalless = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             ..StatusFacts::new("n")
         })
         .expect("status");
@@ -4016,7 +4241,7 @@ mod tests {
         // it is blocked, its turn hasn't ended yet, and plain "running" would
         // tell the parent to leave it alone.
         let answer = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             stop: Some(StopReason::NeedHelp("no credential".to_owned())),
             ..StatusFacts::new("n")
         })
@@ -4026,7 +4251,7 @@ mod tests {
             "both facts are true at once and both have to be in the answer: {answer}"
         );
         let quiet = describe_status(&StatusFacts {
-            occupancy: Some(true),
+            occupancy: Some(Occupancy::Running),
             stop: Some(StopReason::Done),
             ..StatusFacts::new("n")
         })
@@ -4539,10 +4764,8 @@ done
             turns_spawned(&dir.join("claude-turns")) == 1
         })
         .await;
-        interrupt(&state, "n", false).expect("a running claude turn is interruptible");
-        // `interrupt` drops the tracking entry itself; the run is over once
-        // `finish_turn` has cleared its liveness clock too.
-        until("the run ends", || state.last_event_age("n").is_none()).await;
+        interrupt(&state, "n").expect("a running claude turn is interruptible");
+        until("the run ends", || state.occupancy("n").is_none()).await;
 
         // This `start` had no goal, so the fake claude's clean exit after
         // SIGINT (`TurnEnd::Complete`) is exactly the case that used to
@@ -4889,7 +5112,7 @@ echo '{"type":"result","subtype":"success","is_error":false}'
         })
         .await;
 
-        interrupt(&state, "n", false).expect("a running ACP turn is interruptible");
+        interrupt(&state, "n").expect("a running ACP turn is interruptible");
         until("the run ends", || state.last_event_age("n").is_none()).await;
 
         assert_eq!(lines(&dir.join("prompts")).len(), 1, "no second goal turn");
@@ -4912,7 +5135,7 @@ echo '{"type":"result","subtype":"success","is_error":false}'
 
         // The test runtime is single-threaded, so the run's task has not
         // been polled yet: no turn is in flight.
-        let err = interrupt(&state, "n", false).expect_err("nothing to cancel yet");
+        let err = interrupt(&state, "n").expect_err("nothing to cancel yet");
         assert!(err.to_string().contains("still starting"), "{err}");
         assert_eq!(state.stop_reason("n"), None);