Debugging Agent-to-Semantic-View Permission Errors in Key-Pair connection

A practical, step-by-step account of tracing a missing Cortex agent from Sigma’s connection settings down to Snowflake grants. I ran into a case recently, where a month ago I was able to use a cortex agent (called RETAIL_ASSISTANT) in Sigma which had access to the underlying semantic view but when I reopened Sigma account after a month, I was unable to find that cortex agent present under chat element on home page of Sigma. The screenshot below shows that I cannot see RETAIL_ASSISTANT(which was the name of cortex agent) as an option to select.