X_MCP_IDEMPOTENCY_KEY_SHADOWED
Means
an idempotent action's input declares idempotencyKey, the MCP argument reserved for the idempotency key
Typical cause
the tool argument would be both the action's input and the retry key
Fix
rename the action's idempotencyKey input field — MCP clients pass the Idempotency-Key as the reserved idempotencyKey argument