Help with Return Type for Pure Service Method in Effect Typescript Library

readonly validateChain: (
      state: BlockchainState
      // `Effect.Either` instead ? since `R = never`
    ) => Effect.Effect<true, ValidationError>;

...

validateChain: (state) =>
        Effect.gen(function* () {
          const blocks = Chunk.toReadonlyArray(state.chain);

          for (const [previous, current] of Array.window(blocks, 2)) {
            const { hash, ...blockWithoutHash } = current;
            const recalculatedHash = blockService.computeHash(blockWithoutHash);

            if (hash !== recalculatedHash) {
              return yield* Effect.fail(
                new ValidationError({
                  blockNumber: current.blockNumber,
                  reason: "Hash mismatch",
                })
              );
            }

            if (current.previousHash !== previous.hash) {
              return yield* Effect.fail(
                new ValidationError({
                  blockNumber: current.blockNumber,
                  reason: "Chain link broken",
                })
              );
            }

            if (current.timestamp < previous.timestamp) {
              return yield* Effect.fail(
                new ValidationError({
                  blockNumber: current.blockNumber,
                  reason: "Invalid timestamp ordering",
                })
              );
            }
          }

          return yield* Effect.succeed<true>(true);
        }),