What it means. The inference engine was asked to type an expression node it does not know how to handle. Well-formed GALA source should always reach a recognized branch.
This is a transpiler bug, not an error in your program.
The header reads error[GALA-E0024]: unknown expression type: *infer.…, with a hint asking you to file an issue.
No triggering program is quoted here: the code exists to catch a missing case inside the inference engine, so there is no stable repro to show. The node type named in the message is the missing case — include it verbatim in your report.
Simplify the surrounding expression and re-run. If a simpler form transpiles cleanly, the shape of the original is the trigger — that reduced snippet is exactly what to attach to an issue.
This mirrors GALA-E0017 (internal transformer panic) for the inference layer. A coded failure gives maintainers a stable search target and users one clear instruction about how to file the bug.