fix(codegen): restore runtime diagnostics before throwing

Reuse historical runtime messages and source-line reporting for arithmetic,
array, enum, pointer and file checks while preserving anonymous exceptions.
Update the manuals and subsystem guidance to describe diagnostic output.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

2 files changed, 24 insertions, 4 deletions

diff --git a/include/cps/FileHandler.h b/include/cps/FileHandler.h
index 8b8ddf4..50593de 100644
--- a/include/cps/FileHandler.h
+++ b/include/cps/FileHandler.h
@@ -38,6 +38,10 @@ class FileHandler {
 
     llvm::Value *ModeReadStr = nullptr, *ModeWriteStr = nullptr, *ModeAppendStr = nullptr;
 
+    llvm::Value *ErrOpenFail = nullptr, *ErrAlreadyOpen = nullptr, *ErrTableFull = nullptr,
+                *ErrNotOpen = nullptr, *ErrNotRead = nullptr, *ErrNotWrite = nullptr,
+                *ErrPastEof = nullptr;
+
     // synthesized helpers (internal linkage; pseudocode identifiers cannot
     // start with '_', so these names are un-collidable)
     llvm::Function *FindFn = nullptr, *OpenFn = nullptr, *ReadFn = nullptr,
diff --git a/include/cps/RuntimeCheck.h b/include/cps/RuntimeCheck.h
index d9a69b6..f5a8aa7 100644
--- a/include/cps/RuntimeCheck.h
+++ b/include/cps/RuntimeCheck.h
@@ -10,15 +10,24 @@ namespace cps {
 class ExceptionHandler;
 
 class RuntimeCheck {
+    llvm::Module &TheModule;
     llvm::LLVMContext &TheContext;
     llvm::IRBuilder<> &Builder;
+
+    llvm::FunctionCallee PrintfFunc;
     ExceptionHandler &Exceptions;
+    llvm::Value *DivZeroMsg;
+    llvm::Value *OutOfBoundsMsg;
+    llvm::Value *EnumRangeMsg;
+    llvm::Value *NullDerefMsg;
+    llvm::Value *ArrayArgBoundsMsg;
 
-public:
-    RuntimeCheck(llvm::LLVMContext &C, llvm::IRBuilder<> &B, ExceptionHandler &EH);
+    void setupExternalFunctions();
+    void emitCheck(llvm::Value *Condition, llvm::Value *Msg, int Line);
 
-    // Split the block, throwing an anonymous exception when Condition is true.
-    void emitCheck(llvm::Value *Condition);
+public:
+    RuntimeCheck(llvm::Module &M, llvm::LLVMContext &C, llvm::IRBuilder<> &B,
+                 ExceptionHandler &EH);
 
     void emitDivZeroCheck(llvm::Value *Divisor, int Line);
     void emitIndexCheck(llvm::Value *Index, llvm::Value *Lower, llvm::Value *Upper, int Line);
@@ -35,6 +44,13 @@ public:
     void emitArrayArgBoundsCheck(llvm::Value *ActualLower, llvm::Value *ActualUpper,
                                  int64_t DeclaredLower, int64_t DeclaredUpper, int Line);
 
+    // Print the diagnostic, then throw an anonymous exception on failure.
+    // Runtime-computed variant: FmtArgs are the printf varargs after Msg
+    // (e.g. {i32 line, ptr filename}). Needed when the failure site is inside
+    // a synthesized helper function, where the line number is an argument
+    // rather than a compile-time constant.
+    void emitCheck(llvm::Value *Condition, llvm::Value *Msg,
+                   llvm::ArrayRef<llvm::Value *> FmtArgs);
 };
 
 }