refactor: centralize task runtime contracts (#199)

runners/shared/src/task-runtime.ts

@@ -0,0 +1,18 @@
+export const TASK_CONTEXT_MODES = ['group', 'isolated'] as const;
+export type TaskContextMode = (typeof TASK_CONTEXT_MODES)[number];
+
+export const DEFAULT_TASK_CONTEXT_MODE: TaskContextMode = 'isolated';
+export const DEFAULT_SCHEDULE_TASK_CONTEXT_MODE: TaskContextMode = 'group';
+export const DEFAULT_WATCH_CI_CONTEXT_MODE: TaskContextMode = 'isolated';
+export const WATCH_CI_PROMPT_PREFIX = '[BACKGROUND CI WATCH]';
+
+export function isTaskContextMode(value: unknown): value is TaskContextMode {
+  return value === 'group' || value === 'isolated';
+}
+
+export function normalizeTaskContextMode(
+  value: unknown,
+  fallback: TaskContextMode = DEFAULT_TASK_CONTEXT_MODE,
+): TaskContextMode {
+  return isTaskContextMode(value) ? value : fallback;
+}