mastra-ai/mastra · error · Error

Harness session "${sessionId}" was not found

Error message

Harness session "${sessionId}" was not found

What it means

`HarnessStorage.updateSession` loads the session record by id and throws this error when `loadSession` returns nothing. It guarantees updates only apply to sessions that actually exist in the harness storage backend. All pending-item helpers (`appendPendingItem`, `updatePendingItem`, `removePendingItem`) funnel through it, so a missing session surfaces here.

Source

Thrown at packages/core/src/storage/domains/harness/base.ts:21

export abstract class HarnessStorage extends StorageDomain {
  constructor() {
    super({
      component: 'STORAGE',
      name: 'HARNESS',
    });
  }

  abstract loadSession(sessionId: string): Promise<SessionRecord | null>;

  abstract saveSession(record: SessionRecord): Promise<void>;

  abstract listSessions(): Promise<SessionRecord[]>;

  async updateSession(sessionId: string, updates: SessionRecordUpdate): Promise<SessionRecord> {
    const record = await this.loadSession(sessionId);
    if (!record) {
      throw new Error(`Harness session "${sessionId}" was not found`);
    }

    const next: SessionRecord = {
      ...record,
      ...updates,
      id: record.id,
      createdAt: record.createdAt,
      lastActivityAt: updates.lastActivityAt ?? new Date(),
    };
    await this.saveSession(next);
    return next;
  }

  async appendPendingItem(sessionId: string, item: HarnessPendingItemRecord): Promise<SessionRecord> {
    const record = await this.loadSession(sessionId);
    if (!record) {
      throw new Error(`Harness session "${sessionId}" was not found`);
    }

View on GitHub (pinned to 75dd419e61)

Solutions

  1. Create the session first (e.g. `createSession`) and use the returned record's id for subsequent updates.
  2. Check session existence with `loadSession(sessionId)` or `listSessions()` before updating.
  3. Confirm you are pointing at the same storage instance/backend where the session was created.
  4. Log/inspect the sessionId being used; verify it is not stale from an earlier run.

Example fix

// before
await harnessStorage.updateSession('sess-abc', { status: 'completed' }); // throws if absent
// after
const existing = await harnessStorage.loadSession('sess-abc');
if (existing) {
  await harnessStorage.updateSession('sess-abc', { status: 'completed' });
}
Defensive patterns

Strategy: try-catch

Validate before calling

const record = await storage.loadSession(sessionId);
if (!record) throw new Error(`Refusing to update missing session ${sessionId}`);

Type guard

function hasSession(r: SessionRecord | null | undefined): r is SessionRecord {
  return r != null && typeof r.id === 'string';
}

Try / catch

try {
  await storage.updateSession(sessionId, updates);
} catch (e) {
  if (e instanceof Error && e.message.includes('was not found')) {
    await storage.createSession({ id: sessionId, ...baseFields });
    await storage.updateSession(sessionId, updates);
    return;
  }
  throw e;
}

Prevention

When it happens

Trigger: Calling `updateSession(sessionId, updates)` with a sessionId that was never created, was already deleted, or exists only in a different storage backend/instance.

Common situations: Reusing a sessionId from a previous process run against a fresh in-memory store; using an id from one harness backend while updating another (e.g. Postgres vs in-memory); truncated or transformed ids; cleanup job deleted the session before the update arrived.

Understand the failure class

Background: "Not found" and "does not exist" errors: why "Task not found", "No such folder", and "Can't find" fire when a lookup comes back empty — this error's family across 14 libraries.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/5c58002e1cdadeaa. Report an issue: GitHub.