The handle regex matches hex case-insensitively, but store keys are
lowercase uuid4 strings. Normalize the captured uuid to lowercase before
lookup so a handle echoed by the model with uppercase hex still resolves
to its bytes instead of leaking the raw token to the downstream tool.
Binary file data (PPTX, PDF, images) returned by one tool and echoed by
the model as a base64 argument to another tool drifts by a few characters,
invalidating the base64 and corrupting the resulting file.
Tools can now return a FileArtifact instead of a base64 string. The agent
executor stores the bytes out-of-band (execution-scoped, TTL-backed) and
shows the model a short, namespaced `crewai+file://` handle, expanding it
back to exact base64 just before the consuming tool runs. Wired into the
native (default AgentExecutor + legacy) and ReAct execution paths with
per-run cleanup.
