Simplify session lifecycle and MCP cleanup

internal/app/launch.go

@@ -56,14 +56,12 @@ func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, par
 		env = append(env, k+"="+v)
 	}
 
-	// Mint a per-spawn MCP config file pointing at the mcp-stdio proxy
-	// with the new child's identity. We don't know the identity until
-	// we've created the child, but the child needs the env/argv at
-	// creation time — so we reserve the identity by pre-creating the
-	// MCP config with a placeholder, then patching it post-spawn.
-	identity, mcpConfigPath, err := l.writeMCPConfig()
-	if err != nil {
-		return nil, err
+	identity := mintIdentity()
+	var cleanupPaths []string
+	cleanup := func() {
+		for _, path := range cleanupPaths {
+			_ = os.RemoveAll(path)
+		}
 	}
 
 	if p.MCPInjection != nil {
@@ -72,24 +70,33 @@ func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, par
 			if p.MCPInjection.Flag == "" {
 				return nil, fmt.Errorf("preset %s: mcp_injection.flag required for kind=flag", p.Name)
 			}
+			mcpConfigPath, err := l.writeMCPConfig(identity)
+			if err != nil {
+				return nil, err
+			}
+			cleanupPaths = append(cleanupPaths, mcpConfigPath)
 			argv = append(argv, p.MCPInjection.Flag, mcpConfigPath)
 		case "env_var":
 			if p.MCPInjection.Var == "" {
 				return nil, fmt.Errorf("preset %s: mcp_injection.var required for kind=env_var", p.Name)
 			}
+			mcpConfigPath, err := l.writeMCPConfig(identity)
+			if err != nil {
+				return nil, err
+			}
+			cleanupPaths = append(cleanupPaths, mcpConfigPath)
 			env = append(env, p.MCPInjection.Var+"="+mcpConfigPath)
 		case "config_file":
 			// Merge patterm's MCP entry into a vendored copy of the
 			// user's existing config file, then point the child at the
 			// vendored copy via the preset's home_var. The real config
 			// file is never modified.
-			envAssign, _, mErr := mcpConfigMerge(p, p.MCPInjection, identity, l.bin, l.mcpSocket)
+			envAssign, homeDir, mErr := mcpConfigMerge(p, p.MCPInjection, identity, l.bin, l.mcpSocket)
 			if mErr != nil {
-				_ = os.Remove(mcpConfigPath)
 				return nil, mErr
 			}
+			cleanupPaths = append(cleanupPaths, homeDir)
 			env = append(env, envAssign)
-			env = append(env, "PATTERM_MCP_CONFIG="+mcpConfigPath)
 		case "cli_override":
 			// Inline -c key=value overrides for agents that accept
 			// them (codex's `-c mcp_servers.patterm.command=...`). No
@@ -97,7 +104,6 @@ func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, par
 			// are untouched.
 			extra, err := mcpCLIOverrideArgs(p, p.MCPInjection, identity, l.bin, l.mcpSocket)
 			if err != nil {
-				_ = os.Remove(mcpConfigPath)
 				return nil, err
 			}
 			argv = append(argv, extra...)
@@ -108,11 +114,11 @@ func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, par
 			// XDG_CONFIG_HOME stays as the user set it.
 			assignment, err := mcpConfigEnv(p, p.MCPInjection, identity, l.bin, l.mcpSocket)
 			if err != nil {
-				_ = os.Remove(mcpConfigPath)
 				return nil, err
 			}
 			env = append(env, assignment)
 		default:
+			cleanup()
 			return nil, fmt.Errorf("preset %s: unknown mcp_injection.kind %q", p.Name, p.MCPInjection.Kind)
 		}
 	}
@@ -120,16 +126,17 @@ func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, par
 	// Spawn with the chosen identity.
 	cols, rows := l.size()
 	c, err := l.sess.Spawn(SpawnSpec{
-		Kind:      KindAgent,
-		Argv:      argv,
-		Env:       env,
-		Name:      displayName,
-		ParentID:  parentID,
-		PresetRef: p.Name,
-		Identity:  identity,
+		Kind:         KindAgent,
+		Argv:         argv,
+		Env:          env,
+		Name:         displayName,
+		ParentID:     parentID,
+		PresetRef:    p.Name,
+		Identity:     identity,
+		CleanupPaths: cleanupPaths,
 	}, cols, rows)
 	if err != nil {
-		_ = os.Remove(mcpConfigPath)
+		cleanup()
 		return nil, err
 	}
 
@@ -219,17 +226,16 @@ func (l *Launcher) LaunchTerminal(argv []string, displayName, parentID, workDir
 	}, cols, rows)
 }
 
-func (l *Launcher) writeMCPConfig() (identity, path string, err error) {
-	identity = mintIdentity()
+func (l *Launcher) writeMCPConfig(identity string) (string, error) {
 	dir, err := preset.ConfigDir()
 	if err != nil {
-		return "", "", err
+		return "", err
 	}
 	dir = filepath.Join(dir, "mcp")
 	if err := os.MkdirAll(dir, 0o700); err != nil {
-		return "", "", err
+		return "", err
 	}
-	path = filepath.Join(dir, identity+".json")
+	path := filepath.Join(dir, identity+".json")
 	cfg := map[string]any{
 		"mcpServers": map[string]any{
 			"patterm": map[string]any{
@@ -240,13 +246,13 @@ func (l *Launcher) writeMCPConfig() (identity, path string, err error) {
 	}
 	body, err := json.MarshalIndent(cfg, "", "  ")
 	if err != nil {
-		return "", "", err
+		return "", err
 	}
 	body = append(body, '\n')
 	if err := os.WriteFile(path, body, 0o600); err != nil {
-		return "", "", err
+		return "", err
 	}
-	return identity, path, nil
+	return path, nil
 }
 
 // waitForIdle polls the child's IdleMS until it exceeds idle, or until