jaw export --transpile: translate marker semantics to real code

[dishmint]

Background

#42 shipped jaw export in comment-only mode — every jaw line becomes a comment in the target language. That's V1; transpilation was explicitly deferred during the design discussion.

Proposal

Add a --transpile flag (initially) that instead of emitting comments translates jaw constructs into roughly-equivalent target-language code. Once stable, the behavior could become the default and --comments-only would be the opt-out.

Rough mapping (target-lang dependent):

jaw	python	rust
[!] — message	print("message")	println!("message");
[>] expr	return expr	return expr;
[1] — [X] += 1	X += 1	X += 1;
/foo [A]: an int	def foo(A):	fn foo(A: i32) {
[~] — [P] in [V]	for P in V:	for P in V {
[~] — [P] < [L]	while P < L:	while P < L {
[+] / [-]	if cond: / else:	if cond { / } else {
[V]@[P]	V[P]	V[P]
[*] / [^] comments	(still comments)	(still comments)

Open questions before implementation

• Type inference: jaw is descriptive; types are usually in the description text (e.g., [A]: an integer). Do we parse description text for type hints, or default to a // TODO: type placeholder? Latter is simpler.
• Function dispatch: /Add[ [X], [T] ] — is Add always a free function, or sometimes a method? Without context, free-function is the safe default.
• Strings vs identifiers in logs: [!] — current value: [X] — how should [X] be inlined? Python f-string (f"current value: {X}")? Concatenation? Keep simple with print("current value:", X)?
• Idiomatic vs literal: [1] — [R] << [A] (append) — translate to R.append(A) (Python idiom) or R << A (literal << operator)? Idiom is more useful but more language-knowledge baked in.
• Statement terminators: rust/c need ;; python doesn't. Per-language config.

Requires

• Real AST traversal (V1 export does line-by-line text munging; transpilation needs the parse tree to reason about expressions, control flow, args).
• Per-language code generators with shared expression-translation logic.
• Probably a LangSpec extension to carry codegen rules alongside the comment syntax already present.

Refs

• Spec / glossary: docs/glossary.md, jaw-grammar.md
• V1 implementation: jaw-cli/src/export.rs, jaw-cli/src/lang.rs
• Original feature discussion: Export as lang #42