What causes "Source-control session ID already exists" in mastra-ai/mastra?

Generate a fresh unique sessionId (e.g. randomUUID()) for each create call

mastra-ai/mastra · error · UniqueViolationError

Source-control session ID already exists

Error message

Source-control session ID already exists

What it means

The in-memory source-control storage enforces that each session ID is unique. When create() is called with a sessionId that already exists in storage (and getForBranch did not return that existing session for the same project/user/branch), it throws UniqueViolationError instead of silently duplicating the row.

Source

Thrown at mastracode/factory/src/storage/domains/source-control/inmemory.ts:362

      }
    },
    getForBranch: async ({
      projectRepositoryId,
      userId,
      branch,
    }: {
      projectRepositoryId: string;
      userId: string;
      branch: string;
    }): Promise<SourceControlSession | null> =>
      this.sessionsRows.find(
        row => row.projectRepositoryId === projectRepositoryId && row.userId === userId && row.branch === branch,
      ) ?? null,
    create: async (input: CreateSourceControlSessionInput): Promise<SourceControlSession> => {
      const existing = await this.sessions.getForBranch(input);
      if (existing) return existing;
      if (this.sessionsRows.some(row => row.sessionId === input.sessionId)) {
        throw new UniqueViolationError('Source-control session ID already exists');
      }
      const now = new Date();
      const session: SourceControlSession = {
        id: randomUUID(),
        ...input,
        title: input.title ?? null,
        visibility: input.visibility ?? 'org',
        sandboxId: null,
        sandboxWorkdir: null,
        materializedAt: null,
        firstMessageAt: null,
        firstMeaningfulExecAt: null,
        createdAt: now,
        updatedAt: now,
      };
      this.sessionsRows.push(session);
      return session;
    },

View on GitHub (pinned to 75dd419e61)

Solutions

Generate a fresh unique sessionId (e.g. randomUUID()) for each create call
Catch UniqueViolationError and look up the existing session by sessionId instead of re-creating
If resuming an existing session, fetch it first via getForBranch or a session lookup rather than calling create

Example fix

// before
await storage.sessions.create({ sessionId: 'my-session', ... });
// after
const existing = await storage.sessions.getForBranch(input);
const session = existing ?? await storage.sessions.create({ sessionId: randomUUID(), ... });

Defensive patterns

Strategy: try-catch

Validate before calling

const existing = await storage.sessions.getForBranch(input);
if (existing) return existing;

Type guard

null

Try / catch

try {
  session = await storage.sessions.create(input);
} catch (e) {
  if (e instanceof UniqueViolationError && e.message.includes('session ID already exists')) {
    session = await findSessionBySessionId(input.sessionId);
  } else throw e;
}

Prevention

Always generate sessionId values with randomUUID() or an equivalent unique generator
Check for an existing session before create when resuming workflows
Never derive sessionId from user-controlled names like repo or branch

When it happens

Trigger: Calling sourceControlStorage.sessions.create() with a sessionId string that was already used by a different project, user, or branch — the branch-scoped dedupe lookup misses it, but the global sessionId uniqueness check catches it.

Common situations: Generating session IDs client-side with a fixed or derived value (e.g. based on repo name), retrying a create after a partial failure with the same sessionId, or importing/seeding data that reuses historical session IDs.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/d8db0b144b46f543. Report an issue: GitHub.