session: inject operational model into restore path

Restored sessions were calling BuildRuntime without baseLayers,
so the 9P/D-Bus operational model never appeared in the system prompt.
Now computes sysPrompt, opModel, envBlock and passes them as BaseLayers.

session/session.go

@@ -846,7 +846,35 @@ func (s *Manager) restoreSession(ps *agent.PersistedSession) error {
 
 	env := []string{"OLLIE_SESSION_ID=" + sessID, "OLLIE_UNAME=" + uname, "OLLIE=" + MountPathFor(uname)}
 	env = append(env, promptEnv...)
-	rt := agent.BuildRuntime(cfg, newDisp(), cwd, env)
+
+	// Compute base layers (same as new-session path).
+	var spOverride string
+	if cfg != nil {
+		spOverride = cfg.SystemPrompt
+	}
+	sysPrompt := prompts.ResolveSystemPrompt(spOverride)
+	envMap := make(map[string]string)
+	for _, e := range env {
+		if k, v, ok := strings.Cut(e, "="); ok {
+			envMap[k] = v
+		}
+	}
+	opModel := prompts.OperationalModel(s.cfg.Enable9P, s.cfg.EnableDBus, envMap)
+	platform := "linux"
+	isGitRepo := false
+	for _, e := range promptEnv {
+		if k, v, ok := strings.Cut(e, "="); ok {
+			switch k {
+			case "PRIME_PLATFORM":
+				platform = v
+			case "PRIME_IS_GIT_REPO":
+				isGitRepo = v == "true"
+			}
+		}
+	}
+	envBlock := prompts.Environment(cwd, platform, isGitRepo, "")
+
+	rt := agent.BuildRuntime(cfg, newDisp(), cwd, env, sysPrompt, opModel, envBlock)
 
 	restoredSession := agent.RestoreSession(ps.Messages)
 	if ps.TaskState != nil {
@@ -867,6 +895,7 @@ func (s *Manager) restoreSession(ps *agent.PersistedSession) error {
 		Runtime:        rt,
 		NewDispatcher:  newDisp,
 		PromptEnvExtra: promptEnv,
+		BaseLayers:     []string{sysPrompt, opModel, envBlock},
 		Log:            s.cfg.Sink.NewLogger("core"),
 		ReadPlanStep: func() string {
 			if sessPtr == nil {
@@ -1168,6 +1197,7 @@ func (s *Manager) CreateSession(args []string) (string, error) {
 			Runtime:        rt,
 			NewDispatcher:  newDisp,
 			PromptEnvExtra: promptEnv,
+			BaseLayers:     []string{sysPrompt, opModel, envBlock},
 			Log:            s.cfg.Sink.NewLogger("core"),
 			ReadPlanStep: func() string {
 				if sessPtr == nil {