Compiler: do-blocks containing IO commands (hs-fetch, hs-wait, perform)
are compiled as (let ((it cmd1)) (let ((it cmd2)) ...)) to chain the
it variable through IO suspensions. Non-IO do-blocks stay as plain
(do cmd1 cmd2). This enables fetch X then put it into me pattern.
Parser: then-separator handled via __then__ markers (stripped in output).
fetch URL /path parsing. Default format "text".
Runtime: hs-fetch simplified to single perform (io-fetch url format).
Test runner: mock fetch routes with format-specific responses.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>