Merge forge/main into atlas/5034-s4-remove-hive-model

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
@@ -338,7 +348,7 @@ 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.
@@ -347,9 +357,10 @@ 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`).