End stream within map()

How can I force a stream to end from within a map() function?

Scenario:
- Processing a very large stream of data
- Calling a promise via `.map($(promise)).merge()`
- The promise called above is to an external API that has a hard QUERY LIMIT.
- When the query limit is detected (via value on the stream === QUERY_LIMIT_MESSAGE), I would like to terminate all processing.

No repository file or test is named. Start by reading the stream API documentation and the entry points for map() and merge(), then trace how upstream termination and pending promises are handled. Done would require a clearly documented or supported way to stop processing when QUERY_LIMIT_MESSAGE appears.

Written by the indexing model from the issue text.