BabylonJS/Babylon.js · error

Session ${parsed} does not exist. Active sessions: ${list}

Error message

Session ${parsed} does not exist. Active sessions:
${list}

What it means

ValidateSessionId throws this variant when the numeric id does not match any active session, and at least one other session exists. The message enumerates the available ids/names so the caller can pick a valid one.

Source

Thrown at packages/dev/inspector-v2/src/cli/cli.ts:250

/**
 * Parses and validates an explicit session id string against the list of active sessions.
 * @param explicitId The session id string to validate.
 * @param sessions The list of active sessions from the bridge.
 * @returns The matching session info.
 */
export function ValidateSessionId(explicitId: string, sessions: SessionInfo[]): SessionInfo {
    const parsed = parseInt(explicitId, 10);
    if (isNaN(parsed)) {
        throw new Error("Session id must be a number.");
    }
    const match = sessions.find((s) => s.id === parsed);
    if (!match) {
        if (sessions.length === 0) {
            throw new Error(`Session ${parsed} does not exist. No active sessions.`);
        }
        const list = sessions.map((s) => `  [${s.id}] ${s.name}`).join("\n");
        throw new Error(`Session ${parsed} does not exist. Active sessions:\n${list}`);
    }
    return match;
}

/**
 * Resolves and validates the session id. Requires an explicit session id
 * provided via `--session <id>`. Throws if the id is missing, non-numeric,
 * or does not match an active session.
 * @param socket The WebSocket connection to the bridge.
 * @param explicitId The session id string from --session.
 * @returns The validated numeric session id.
 */
export async function ResolveSessionId(socket: WebSocket, explicitId: string | undefined): Promise<number> {
    if (explicitId === undefined) {
        throw new Error("A session id is required. Use --session to list active sessions, then pass --session <id>.");
    }

    const response = await SendAndReceive<SessionsResponse>(socket, { type: "sessions" });

View on GitHub (pinned to 0592b347b8)

Solutions

1. Use the id list printed in the error (or run the sessions command) and pass one of the currently listed ids.
2. Re-fetch session ids each run instead of hardcoding them in scripts.
3. If multiple tabs are open, target the correct one by matching s.name against the listed session names.

Example fix

// before
cli inspect --session 7   # stale id
// after
# error lists: [1] TabA, [2] TabB
cli inspect --session 2

function sessionExists(sessions: SessionInfo[], id: number): boolean {
  return sessions.some((s) => s.id === id);
}
if (!sessionExists(sessions, parsed)) {
  console.error(`Unknown id ${parsed}. Available: ${sessions.map((s) => s.id).join(", ")}`);
}

try {
  const s = ValidateSessionId(id, sessions);
} catch (e) {
  if (e instanceof Error && e.message.includes("does not exist. Active sessions:")) {
    console.error(e.message); // shows valid ids to pick from
  } else throw e;
}

When it happens

Trigger: Passing --session <n> with an id that is stale (page reloaded, bridge restarted and ids reassigned) or simply wrong while other sessions are live.

Common situations: Reusing a session id from an earlier run in a script; multiple tabs open and targeting the wrong id; ids shifted after some sessions disconnected.

Related errors

• Session id must be a number.
• Session ${parsed} does not exist. No active sessions.
• A session id is required. Use --session to list active sessi
• Sample2DRgbaToRef: widthPx and heightPx must be positive.
• At least one mesh is needed to create the nav mesh.

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/d16fa1767ab041d8. Report an issue: GitHub.