fusion/packages/engine/src/active-session-registry.ts

export type ActiveSessionKind = "executor" | "step-session" | "workflow-step" | "step-session-parallel";

export interface ActiveSessionRegistration {
  taskId: string;
  kind: ActiveSessionKind;
  ownerKey: string;
}

export interface ActiveSessionRecord extends ActiveSessionRegistration {
  registeredAt: number;
}

export interface ReconcileStaleSelfOwnedResult {
  reconciled: boolean;
  reason: "no-entry" | "foreign-task" | "reconciled";
}

export type LiveBindingProbe = (worktreePath: string, taskId: string) => boolean;
export type ProcessActiveProbe = (taskId: string) => boolean;

export type SelfOwnedReconcileOutcome =
  | { action: "no-entry" }
  | { action: "foreign-task"; ownerTaskId: string }
  | { action: "live-binding-refuses"; ownerTaskId: string }
  | { action: "process-active-refuses"; ownerTaskId: string }
  | { action: "too-recent-refuses"; ownerTaskId: string; ageMs: number; minIdleMs: number }
  | { action: "reconciled" };

/**
 * FN-5256: default minimum age before a self-owned registry entry can be classified
 * as stale. Recently-registered entries belong to an executor cycle that is still
 * warming up (e.g., a pause/resume that hasn't repopulated activeWorktrees yet), so
 * dropping them races with the live shell that just attached to the worktree.
 */
export const DEFAULT_SELF_OWNED_MIN_IDLE_MS = 5000;

export class ActiveSessionRegistry {
  private readonly records = new Map<string, ActiveSessionRecord>();

  registerPath(worktreePath: string, registration: ActiveSessionRegistration): void {
    if (this.records.has(worktreePath)) {
      console.warn(`[active-session-registry] overwriting existing registration for ${worktreePath}`);
    }
    this.records.set(worktreePath, {
      ...registration,
      registeredAt: Date.now(),
    });
  }

  unregisterPath(worktreePath: string): void {
    this.records.delete(worktreePath);
  }

  lookupByPath(worktreePath: string): ActiveSessionRecord | null {
    return this.records.get(worktreePath) ?? null;
  }

  isPathActive(worktreePath: string): boolean {
    return this.records.has(worktreePath);
  }

  pathsForTask(taskId: string): string[] {
    const paths: string[] = [];
    for (const [path, record] of this.records.entries()) {
      if (record.taskId === taskId) {
        paths.push(path);
      }
    }
    return paths;
  }

  reconcileStaleSelfOwned(worktreePath: string, expectedTaskId: string): ReconcileStaleSelfOwnedResult {
    const record = this.lookupByPath(worktreePath);
    if (!record) {
      return { reconciled: false, reason: "no-entry" };
    }
    if (record.taskId !== expectedTaskId) {
      return { reconciled: false, reason: "foreign-task" };
    }

    this.unregisterPath(worktreePath);
    return { reconciled: true, reason: "reconciled" };
  }

  clear(): void {
    this.records.clear();
  }
}

export interface SelfOwnedReconcileOptions {
  /**
   * Process-wide "executor still owns this task" probe. When this returns true the
   * caller's task is still in the middle of an `execute()` invocation, so dropping
   * the registry entry would yank the worktree from a live shell (FN-5256).
   */
  processActiveProbe?: ProcessActiveProbe;
  /**
   * Minimum age (ms since `registeredAt`) before a same-task entry is eligible for
   * stale reconciliation. Recently-registered entries belong to a warming executor
   * cycle and must be left alone. Defaults to `DEFAULT_SELF_OWNED_MIN_IDLE_MS`.
   */
  minIdleMs?: number;
  /** Test seam — defaults to `Date.now()`. */
  now?: () => number;
}

export function reconcileSelfOwnedActiveSessionForRemoval(
  registry: ActiveSessionRegistry,
  worktreePath: string,
  requestingTaskId: string,
  liveBindingProbe: LiveBindingProbe,
  options: SelfOwnedReconcileOptions = {},
): SelfOwnedReconcileOutcome {
  const record = registry.lookupByPath(worktreePath);
  if (!record) {
    return { action: "no-entry" };
  }

  if (record.taskId !== requestingTaskId) {
    return { action: "foreign-task", ownerTaskId: record.taskId };
  }

  if (liveBindingProbe(worktreePath, requestingTaskId)) {
    return { action: "live-binding-refuses", ownerTaskId: requestingTaskId };
  }

  if (options.processActiveProbe?.(requestingTaskId)) {
    return { action: "process-active-refuses", ownerTaskId: requestingTaskId };
  }

  const minIdleMs = options.minIdleMs ?? DEFAULT_SELF_OWNED_MIN_IDLE_MS;
  if (minIdleMs > 0) {
    const now = options.now?.() ?? Date.now();
    const ageMs = now - record.registeredAt;
    if (ageMs < minIdleMs) {
      return { action: "too-recent-refuses", ownerTaskId: requestingTaskId, ageMs, minIdleMs };
    }
  }

  registry.unregisterPath(worktreePath);
  return { action: "reconciled" };
}

export const activeSessionRegistry = new ActiveSessionRegistry();

/**
 * FN-4811 follow-up: process-wide "executing" lock for `TaskExecutor.execute()`.
 *
 * Per-instance `executing: Set<string>` is insufficient when there can be more than
 * one TaskExecutor instance in the same Node process (e.g., multi-project setups,
 * engine restarts that race with old instance teardown, hybrid-executor path).
 * Production failure shape: two execute() invocations for the same task ID both
 * generated runIds (y2nb + 9gde for FN-4809), both reached "Executor detected stale
 * merge state" (executor.ts:2661), both attempted worktree creation — producing
 * duplicate "Worktree created at /..." log entries within the same second
 * (FN-4809, FN-4814, FN-4781, FN-4804, FN-4811).
 *
 * This module-level Set is shared across all TaskExecutor instances in the process,
 * providing a process-wide claim. Values are taskId strings; presence means
 * "someone is actively executing this task". Callers MUST claim synchronously
 * via `tryClaim()` and MUST release on every exit path.
 */
const executingTasks = new Set<string>();

export const executingTaskLock = {
  has(taskId: string): boolean {
    return executingTasks.has(taskId);
  },
  /** Synchronously claim the lock. Returns true if claimed, false if already held. */
  tryClaim(taskId: string): boolean {
    if (executingTasks.has(taskId)) return false;
    executingTasks.add(taskId);
    return true;
  },
  release(taskId: string): void {
    executingTasks.delete(taskId);
  },
  /** Test-only: clear all entries. */
  _clearForTest(): void {
    executingTasks.clear();
  },
};