refactor: batch 1 - correctness and error contract

- MID/RIGHT/LEFT integer args now coerced at call sites (RIGHT(s, n/2)
  no longer emits invalid IR); drop emitLeft's private conversion
- FOR loop direction decided at run time via select on STEP sign;
  descending FOR works, STEP evaluated once per iteration
- ArrayHandler: extract emitCheckedIndices/loadElement; index count is
  validated before emission, fixing a compiler-crash (vector OOB UB) on
  OUTPUT with too many indices
- Error contract: Lexer/Parser/CodeGen track errors; all silent failure
  paths now print Error: diagnostics with line numbers; unterminated
  char literal no longer truncates the rest of the program; module is
  verified with verifyModule; driver exits non-zero on any error

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/cps/Lexer.h b/include/cps/Lexer.h
index e8d2609..f1def3e 100644
--- a/include/cps/Lexer.h
+++ b/include/cps/Lexer.h
@@ -80,6 +80,7 @@ enum Token {
 
 class Lexer {
     int CurrentLine = 1;
+    bool HadError = false;
 public:
     std::string IdentifierStr;
     std::string StringVal;
@@ -89,6 +90,7 @@ public:
 
     int gettok();
     int getLine() const { return CurrentLine; }
+    bool hadError() const { return HadError; }
 };
 
 }