## Summary
Route-triggered logic functions were returning empty 500 responses with
zero server-side logging when the Lambda build chain failed. This PR
makes those failures observable and returns meaningful HTTP responses to
API clients.
- **Observability** — Log errors (with stack traces) at each layer of
the execution chain: `LambdaDriver` (deps-layer fetch, SDK-layer fetch,
invocation), `LogicFunctionExecutorService`, and `RouteTriggerService`.
- **Typed exceptions** — Replace raw `throw error` sites with
`LogicFunctionException` carrying an appropriate code and
`userFriendlyMessage` (new codes: `LOGIC_FUNCTION_EXECUTION_FAILED`,
`LOGIC_FUNCTION_LAYER_BUILD_FAILED`).
- **Correct HTTP semantics** — `RouteTriggerService` maps inner
exception codes to the right `RouteTriggerExceptionCode` so
`LOGIC_FUNCTION_NOT_FOUND` returns 404 and `RATE_LIMIT_EXCEEDED` returns
429 (new code + filter case) instead of a generic 500.
- **User-facing messages** — Forward the inner
`CustomException.userFriendlyMessage` when wrapping into
`RouteTriggerException`, without leaking raw internal error text into
the public exception message.
- **Infra** — Bump Lambda ephemeral storage from 2048 to 4096 MB to
prevent `ENOSPC` errors during yarn install layer builds (root cause of
the original silent failures).
