Gotchas

A checklist of idioms that trip people up — each with the working shape. Grown as findings land (the backlog’s “idiom traps”, promoted here).

Arriving with an error message in hand? The error index is organized by message instead of by topic.

Language

Chained element access on a call result loses the element type. shared.read()[i] → bind, then index: let list = shared.read(); list[i].
match can’t be an operator operand. (match x { … }) + 1 → bind the match to a local first.
A bare integer literal adapts to its peer; two typed variables don’t. stamp + 1000 and stamp < 1000 are fine on an i53 (the literal takes the peer’s type), but mixing two differently-typed variables in a comparison is an error — there are no implicit conversions; convert with as_* or unify the declarations.

shared.read() is a copy — shared.read().push(x) is lost; write through the cell: shared.write().push(x).
Mutate signal lists with set_with, never by mutating a get() result (also a copy).
bind_value fights remote updates — for server-backed fields use bind_draft.
show keeps bindings live while hidden; use when to drop state and subscriptions.
Disposal doesn’t cancel the in-flight wave: a subscriber already queued in the draining turn may fire once more; only later deliveries are guaranteed gone.

Contract-mismatch errors on connect usually mean a leaked old server still holding the port — ss -tlnp | grep <port>, kill by PID.
desc is an SQL keyword — name the column description (any SQL keyword as a column name fails in CREATE TABLE).
Value semantics cross the wire: a mirrored list is a fresh copy per update; mutate via rpcs, never by writing the client’s mirror signal.

A completed node main exits the process — long-lived clients/servers must hold main open.
pkill -f <pattern> can match your own shell’s command string — kill by tracked PID.
Rebuild the debug binary before regenerating corpus goldens — a stale binary silently writes wrong goldens.