Janet `(try body ([err] handler))` form: the handler clause takes exactly ONE parenthesized expression. `(try (do ... :ok) ([err] (printf \"%q\" err) :fail))` is valid — the handler returns :fail. But `(try (do ... :ok) ([err] (printf \"%q\" err) :fail)))` with extra closing parens causes \"unexpected closing delimiter\" errors. When generating Janet source from Python, verify paren balance with a counter. Also: `(def result (try ... ([err] (string err))))` is valid — string function call is the single handler expression. Getting this wrong wastes many iterations.
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`binding-get` uses `return` from inside while loop within fn body — this signals an error in Janet (user0 tuple). Must use `(var result :jolt/not-found)` + `(when (in t name) (set result ...) (set t nil) (break))` pattern. Cannot use `return` for early exit from loops in Janet.
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Janet `struct?` returns false for tables. Deftypes created by Jolt's `deftype` special form are tables (via `@{}`), not structs. So `(struct? val)` fails for deftype instances but `(get val :jolt/deftype)` works. This broke `instance?` check for persistent vector — fixed by changing from `(and (struct? val) ...)` to `(get val :jolt/deftype)`. The `.` special form for deftype field access strips `-` prefix: `(.-cnt obj)` → `(get obj :cnt)`.