container: Stop gracefully on podman stop

Containers used `sleep infinity` as PID 1, which never reacts to
SIGTERM: the kernel does not apply default signal dispositions to PID 1,
and sleep has no SIGTERM handler, so every `podman stop` silently
ignored the signal, waited out the full 10-second grace period, and fell
back to SIGKILL.

PID 1 now traps TERM and INT itself and exits on request, so one-off
manual stops of a still-running agent container end immediately instead
of after the kill timeout.

The PID 1 command is baked in at create time, so containers predating
this change are detected and recreated automatically on the next run.

agent-container.py

@@ -179,6 +179,12 @@ class AgentContainer:
             )
             self.remove_container()
 
+        if self.container_exists() and not self._container_cmd_matches():
+            logger.info(
+                "Recreating container: it predates the SIGTERM-aware PID 1"
+            )
+            self.remove_container()
+
         if not self.container_exists():
             self.create_container()
 
@@ -513,7 +519,11 @@ class AgentContainer:
                 self.IMAGE,
                 "sh",
                 "-c",
-                "sleep infinity",
+                # PID 1 ignores signals with default dispositions, so a bare
+                # `sleep infinity` never reacts to SIGTERM and every
+                # `podman stop` times out into SIGKILL. Trapping TERM (and
+                # INT) makes stop requests end the container immediately.
+                'trap "exit 0" TERM INT; sleep infinity & wait',
             ]
         )
 
@@ -555,6 +565,26 @@ class AgentContainer:
         ).stdout
         return "AGENT_CONTAINER=1" in env
 
+    def _container_cmd_matches(self) -> bool:
+        """Whether the container runs the current PID 1 command.
+
+        The PID 1 entrypoint is baked in at create time and can only change
+        by recreating the container. Comparing against Config.Cmd catches
+        containers created before the SIGTERM-aware fix."""
+        cmd = subprocess.run(
+            [
+                self.RUNTIME,
+                "container",
+                "inspect",
+                "-f",
+                "{{json .Config.Cmd}}",
+                self.container_name,
+            ],
+            capture_output=True,
+            text=True,
+        ).stdout.strip()
+        return "TERM INT" in cmd
+
     def start_container(self) -> bool:
         subprocess.run(
             [self.RUNTIME, "start", self.container_name],