refactor(flags): route session workspaces through runtime flags (#27335)

packages/opencode/test/preload.ts

@@ -35,6 +35,7 @@ process.env["XDG_CONFIG_HOME"] = path.join(dir, "config")
 process.env["XDG_STATE_HOME"] = path.join(dir, "state")
 process.env["OPENCODE_MODELS_PATH"] = path.join(import.meta.dir, "tool", "fixtures", "models-api.json")
 process.env["OPENCODE_EXPERIMENTAL_EVENT_SYSTEM"] = "true"
+process.env["OPENCODE_EXPERIMENTAL_WORKSPACES"] = "true"
 
 // Set test home directory to isolate tests from user's actual home directory
 // This prevents tests from picking up real user configs/skills from ~/.claude/skills