cl: block + return-from — 13 new tests (140 eval, 312 total green)

Sentinel propagation in cl-eval-body; cl-eval-block catches matching
sentinels; BLOCK/RETURN-FROM/RETURN dispatch added to cl-eval-list.
Parser: CL strings now {:cl-type "string"} dicts for proper CL semantics.

plans/common-lisp-on-sx.md

@@ -57,7 +57,7 @@ Core mapping:
 
 ### Phase 2 — sequential eval + special forms
 - [x] `cl-eval-ast`: `quote`, `if`, `progn`, `let`, `let*`, `flet`, `labels`, `setq`, `setf` (subset), `function`, `lambda`, `the`, `locally`, `eval-when`
-- [ ] `block` + `return-from` via captured continuation
+- [x] `block` + `return-from` via captured continuation
 - [ ] `tagbody` + `go` via per-tag continuations
 - [ ] `unwind-protect` cleanup frame
 - [ ] `multiple-value-bind`, `multiple-value-call`, `multiple-value-prog1`, `values`, `nth-value`
@@ -124,6 +124,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-05: block + return-from — sentinel propagation in cl-eval-body; cl-eval-block catches matching sentinels; BLOCK/RETURN-FROM/RETURN dispatch in cl-eval-list; 13 new tests (140 eval, 312 total green). Parser: CL strings → {:cl-type "string"} dicts.
 - 2026-04-25: Phase 2 eval — 127 tests, 299 total green. `lib/common-lisp/eval.sx`: cl-eval-ast with quote/if/progn/let/let*/flet/labels/setq/setf/function/lambda/the/locally/eval-when; defun/defvar/defparameter/defconstant; built-in arithmetic (+/-/*//, min/max/abs/evenp/oddp), comparisons, predicates, list ops (car/cdr/cons/list/append/reverse/length/nth/first/second/third/rest), string ops, funcall/apply/mapcar. Key gotchas: SX reduce is (reduce fn init list) not (reduce fn list init); CL true literal is t not true; builtins registered in cl-global-env.fns via wrapper dicts for #' syntax.
 - 2026-04-25: Phase 1 lambda-list parser — 31 new tests, 172 total green. `cl-parse-lambda-list` in `parser.sx` + `tests/lambda.sx`. Handles &optional/&rest/&body/&key/&aux/&allow-other-keys, defaults, supplied-p. Key gotchas: `(when (> (len items) 0) ...)` not `(when items ...)` (empty list is truthy); custom `cl-deep=` needed for dict/list structural equality in tests.
 - 2026-04-25: Phase 1 reader/parser — 62 new tests, 141 total green. `lib/common-lisp/parser.sx`: cl-read/cl-read-all, lists, dotted pairs, quote/backquote/unquote/splice/#', vectors, #:uninterned, NIL→nil, T→true, reader macro wrappers.