feat(loops): wire break / continue end-to-end (closes #459)

[hyperpolymath]

Summary

Closes #459 — break and continue now parse, type-check (rejected outside loop bodies with a clear error), and lower to JS break;/continue; in the Deno-ESM and Node JS backends. Pre-fix: BREAK/CONTINUE were lexer-reserved tokens with no parser production consuming them; any use was a syntax error.

Pipeline changes

File	Change
lib/ast.ml	ExprBreak of Span.t, ExprContinue of Span.t
lib/parser.mly	BREAK/CONTINUE productions in expr_assign (diverging prefix, next to RETURN/RESUME)
lib/resolve.ml	pass-through (resolve_expr + lower_expr)
lib/typecheck.ml	new ctx.in_loop : mutable bool flipped on StmtWhile/StmtFor body entry; synth returns ty_never; new NotInLoop of string error
lib/borrow.ml	pass-through (span lookup, visit-recurse, free-var collection, main checker)
lib/quantity.ml, lib/effect_sites.ml	pass-through (no resources, no call sites)
lib/codegen_deno.ml, lib/js_codegen.ml	statement-position lowering to bare JS keywords

Test fixture

tests/codegen-deno/loop_break_continue.affine + harness — 14 assertions across:

• while + break (threshold-driven early exit)
• while + continue (skip-evens accumulator)
• for + break (find-first-match)
• for + continue (count-positive filter)
• Edge cases: break on first iteration, no-break path, empty array

Out of scope

• Non-JS backends (wasm/GC/lua/c/rust/etc.): fall through existing wildcards. Full backend support files separately if needed.
• JS-codegen expression-position IIFE wrapper (legacy MVP path) emits (() => { break; })() which would throw SyntaxError: Illegal break statement at runtime — legal AffineScript places break/continue inside loop bodies so the statement path fires. Deno backend uses the correct statement-position emit.

Test plan

• ./tools/run_codegen_deno_tests.sh: 15/15 harnesses green
• dune test: 352/352 unit tests green
• Misuse check: pub fn bad() -> () { break; } emits the new NotInLoop error with the expected message

Refs

• Closes parser: BREAK/CONTINUE tokens reserved in lexer but no production rule uses them #459
• Refs feat(scripts): AffineScript port of check-ts-allowlist (TS->AS campaign STEP 2 seed) standards#284 (workarounds documented in the "Seam findings" section that surfaced this gap)

🤖 Generated with Claude Code

[github-actions]

🔍 Hypatia Security Scan

Findings: 83 issues detected

Severity	Count
🔴 Critical	4
🟠 High	11
🟡 Medium	68

⚠️ Action Required: Critical security issues found!

View findings

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