Add guest sessions and agent VM defaults

Add daemon-backed workspace and guest-session primitives so host
orchestrators can prepare /root/repo, launch long-lived guest commands,
and attach to pipe-mode sessions over the local stdio mux bridge.

Persist richer session metadata and launch diagnostics, preflight guest
cwd/command requirements, make pipe-mode attach rehydratable from guest
state after daemon restart, and allow submodules when workspace prepare
runs in full_copy mode.

At the same time, stop vm run from auto-attaching opencode, make it
print next-step commands instead, and make glibc guest images more
agent-ready by installing node, opencode, claude, and pi while syncing
opencode/claude/pi auth files into work disks on VM start.

Validation:
- GOCACHE=/tmp/banger-gocache go test ./...
- make build
- banger vm workspace prepare --help
- banger vm session --help
- banger vm session start --help
- banger vm session attach --help

internal/api/types.go

@@ -150,6 +150,73 @@ type VMPortsResult struct {
 	Ports   []VMPort `json:"ports"`
 }
 
+type GuestSessionStartParams struct {
+	VMIDOrName       string            `json:"vm_id_or_name"`
+	Name             string            `json:"name,omitempty"`
+	Command          string            `json:"command"`
+	Args             []string          `json:"args,omitempty"`
+	CWD              string            `json:"cwd,omitempty"`
+	Env              map[string]string `json:"env,omitempty"`
+	StdinMode        string            `json:"stdin_mode,omitempty"`
+	Tags             map[string]string `json:"tags,omitempty"`
+	RequiredCommands []string          `json:"required_commands,omitempty"`
+}
+
+type GuestSessionRefParams struct {
+	VMIDOrName      string `json:"vm_id_or_name"`
+	SessionIDOrName string `json:"session_id_or_name"`
+}
+
+type GuestSessionLogsParams struct {
+	VMIDOrName      string `json:"vm_id_or_name"`
+	SessionIDOrName string `json:"session_id_or_name"`
+	Stream          string `json:"stream,omitempty"`
+	TailLines       int    `json:"tail_lines,omitempty"`
+}
+
+type GuestSessionAttachBeginParams struct {
+	VMIDOrName      string `json:"vm_id_or_name"`
+	SessionIDOrName string `json:"session_id_or_name"`
+}
+
+type GuestSessionListResult struct {
+	Sessions []model.GuestSession `json:"sessions"`
+}
+
+type GuestSessionShowResult struct {
+	Session model.GuestSession `json:"session"`
+}
+
+type GuestSessionLogsResult struct {
+	Session model.GuestSession `json:"session"`
+	Stream  string             `json:"stream"`
+	Path    string             `json:"path,omitempty"`
+	Content string             `json:"content,omitempty"`
+}
+
+type GuestSessionAttachBeginResult struct {
+	Session         model.GuestSession `json:"session"`
+	AttachID        string             `json:"attach_id"`
+	TransportKind   string             `json:"transport_kind"`
+	TransportTarget string             `json:"transport_target"`
+	SocketPath      string             `json:"socket_path,omitempty"`
+	StreamFormat    string             `json:"stream_format"`
+}
+
+type VMWorkspacePrepareParams struct {
+	IDOrName   string `json:"id_or_name"`
+	SourcePath string `json:"source_path"`
+	GuestPath  string `json:"guest_path,omitempty"`
+	Branch     string `json:"branch,omitempty"`
+	From       string `json:"from,omitempty"`
+	Mode       string `json:"mode,omitempty"`
+	ReadOnly   bool   `json:"readonly,omitempty"`
+}
+
+type VMWorkspacePrepareResult struct {
+	Workspace model.WorkspacePrepareResult `json:"workspace"`
+}
+
 type ImageBuildParams struct {
 	Name       string `json:"name,omitempty"`
 	FromImage  string `json:"from_image,omitempty"`