What problems was I solving

After serializeUiLayoutForLlm was removed in a previous refactor, serializeAgentStateForLlm and its internal PropsWithImageFileSchema were left behind as dead code with no production callers. These remnants created unnecessary maintenance surface and broke compilation for any stale references.

What user-facing changes did I ship

There are no user-facing changes; this is a pure internal cleanup of unused serialization code.

How I implemented it

Deleted the unused serializeAgentStateForLlm function from the event-handler-agent mapper, removed the PropsWithImageFileSchema schema it depended on, cleaned up the corresponding re-exports in mapper/index.ts and the page-data-plane-service backwards-compatibility shim, and removed the two test cases that exercised the deleted helper.

Description for the changelog

Removes the unused serializeAgentStateForLlm helper and its internal PropsWithImageFileSchema Zod schema from the event-handler-agent mapper, along with their re-exports and associated tests. These symbols have had no production callers since a prior refactoring and their removal reduces dead code and maintenance burden.