Hooks and events issues

A callback never runs

Confirm that the callback is registered on the same live viewer object shown in the notebook. Reproduce one event, then inspect requests to /_cellucid/events; preserve the first non-success response and its body.

A command targets the wrong viewer

Use the viewer ID returned by the object that owns the displayed frame. This is especially important when a notebook contains multiple viewers or a cell was re-run.

Session-bundle request rejected

Session-bundle uploads require the exact registered viewer/request pair and are single-use. Start a new request instead of replaying an expired or consumed one.

Event payload rejected

Treat event and command schemas as exact contracts. Compare the emitted event name and payload fields with Reference (hooks, commands, schemas, endpoints).

For a complete symptom catalog, see Troubleshooting (hooks).