Node-placed agent terminal: container PTY on the agent's node + WebRTC, shared node-local drives

Completes "agent on a node" (single-node): when an agent's placement points at a
fleet node, its terminal container runs there and the browser reaches it over a
direct WebRTC DataChannel (LAN speed), sharing a node-local volume with the
sandbox. gw-04-local agents are byte-identical to before.

- cm-sandbox/docker.rs: empty drive subpath → mount the whole volume at the target
  (volume_options None), so a per-agent node-local volume auto-creates at ~/drives.
- cm-api/fleet.rs: NodeHub.open_pty/webrtc_offer carry optional container+session
  (injected only when Some); node-terminal caller passes None (host shell unchanged).
- cm-runtime/terminals.rs: TerminalManager gains node_provider + placement
  (mirrors SandboxManager, draining-aware); node_local_drive_mount(agent) =
  clawmates_agent_<id> at ~/drives; placement_for() ensures + locates the container;
  attach uses driver_for(node) (local byte-identical).
- cm-runtime/sandboxes.rs: a node-placed agent sandbox mounts the same per-agent
  volume → shares files with the terminal on that node.
- cm-api/routes/terminal.rs: ticket response gains `node`; ws() bridges node-placed
  agents through the NodeHub relay (WebRTC + fallback) execing into the container;
  local path unchanged. server main wires with_node_provider.
- frontend: agentTerminalConnector mints the ticket then picks WebRTC (node-placed,
  ⚡ direct / relayed badge) vs WS (local); webrtcConnector generalized to be
  endpoint-agnostic (node terminal reuses it).

Known follow-up: terminal (uid 65532) and sandbox (uid 10001) share the volume but
differ in uid — cross-container writes need an aligned uid/gid (group-writable).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

crates/cm-sandbox/src/docker.rs

@@ -97,10 +97,18 @@ impl SandboxDriver for DockerDriver {
                         source: Some(m.volume.clone()),
                         typ: Some(MountTypeEnum::VOLUME),
                         read_only: Some(m.read_only),
-                        volume_options: Some(MountVolumeOptions {
-                            subpath: Some(m.subpath.clone()),
-                            ..Default::default()
-                        }),
+                        // An empty subpath ⇒ mount the whole volume at the target
+                        // (the per-agent node-local drive volume, auto-created by
+                        // Docker). A non-empty subpath is per-agent isolation within
+                        // the shared gateway volume.
+                        volume_options: if m.subpath.is_empty() {
+                            None
+                        } else {
+                            Some(MountVolumeOptions {
+                                subpath: Some(m.subpath.clone()),
+                                ..Default::default()
+                            })
+                        },
                         ..Default::default()
                     })
                     .collect(),