application: add graceful shutdown config for Bandit

Configures Bandit with 615s drain timeout and 620s OTP shutdown window
so in-flight Claude CLI calls (up to 600s) complete before systemd kills
the process on restart.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/symbiont/application.ex

@@ -12,9 +12,26 @@ defmodule Symbiont.Application do
     └── Bandit (Symbiont.API)  — HTTP API
 
   In test mode, the supervisor starts empty — tests manage their own processes.
+
+  ## Graceful shutdown
+
+  Bandit is configured with a long ThousandIsland `shutdown_timeout` so that
+  in-flight `/task` requests (which can take up to 600s while Claude runs)
+  are not killed when systemd restarts the service. The Bandit child spec
+  also carries a matching `:shutdown` value so the OTP supervisor itself
+  waits long enough before forcing a kill.
+
+  The matching systemd unit must set `TimeoutStopSec=620` for this to take
+  effect end to end.
   """
   use Application
 
+  # 615s for Bandit to drain its sockets, 620s for the OTP child shutdown
+  # window. Keep these slightly larger than the Claude CLI timeout (600s)
+  # used by Muse's SMTP dispatcher.
+  @bandit_drain_ms 615_000
+  @bandit_child_shutdown_ms 620_000
+
   @impl true
   def start(_type, _args) do
     if Application.get_env(:symbiont, :port) == 0 do
@@ -32,13 +49,23 @@ defmodule Symbiont.Application do
     port = Application.get_env(:symbiont, :port, 8111)
     engram_db = Application.get_env(:symbiont, :engram_db, "/data/symbiont/engram.db")
 
+    bandit_spec =
+      Supervisor.child_spec(
+        {Bandit,
+         plug: Symbiont.API,
+         port: port,
+         scheme: :http,
+         thousand_island_options: [shutdown_timeout: @bandit_drain_ms]},
+        shutdown: @bandit_child_shutdown_ms
+      )
+
     children = [
       {Task.Supervisor, name: Symbiont.TaskSupervisor},
       {Symbiont.Ledger, data_dir: data_dir},
       {Symbiont.Queue, data_dir: data_dir},
       {Symbiont.Engram, db_path: engram_db},
       {Symbiont.Heartbeat, []},
-      {Bandit, plug: Symbiont.API, port: port, scheme: :http}
+      bandit_spec
     ]
 
     opts = [strategy: :rest_for_one, name: Symbiont.Supervisor]