fix(selfhost): resolve all sema errors — 0 undeclared identifiers

- Add forward declarations for mutually-recursive parser functions
  (parserParseExpr, parserParseStmt, parserParseBlock,
   parserParsePrimary, parserParsePostfixExpr, parserParseBinaryPrec)
- Fix HIR lowering: skip forward decls (refBody==null) to avoid
  duplicate function entries and array overflow
- Bump funcs/externFuncs array size 256→512 to handle large modules
- Update PLAN.md with progress

Sema: 0 errors (was 7, then 2, now 0)
Remaining: C backend struct ordering (pre-existing, Iter/StringBuilder)

src/hir_lower.bux

@@ -601,9 +601,9 @@ func HirLower_LowerModule(mod: *Module, sema: *Sema) -> *HirModule {
     let ctx: *LowerCtx = bux_alloc(sizeof(LowerCtx)) as *LowerCtx;
     ctx.module = mod;
     ctx.scope = sema.scope;
-    ctx.funcs = bux_alloc(256 as uint * sizeof(HirFunc)) as *HirFunc;
+    ctx.funcs = bux_alloc(512 as uint * sizeof(HirFunc)) as *HirFunc;
     ctx.funcCount = 0;
-    ctx.externFuncs = bux_alloc(256 as uint * sizeof(HirFunc)) as *HirFunc;
+    ctx.externFuncs = bux_alloc(512 as uint * sizeof(HirFunc)) as *HirFunc;
     ctx.externCount = 0;
     ctx.varCounter = 0;
 
@@ -624,7 +624,7 @@ func HirLower_LowerModule(mod: *Module, sema: *Sema) -> *HirModule {
     // Iterate declarations
     var decl: *Decl = mod.firstItem;
     while decl != null as *Decl {
-        if decl.kind == dkFunc {
+        if decl.kind == dkFunc && decl.refBody != null as *Block {
             let f: *HirFunc = Lcx_LowerFunc(ctx, decl);
             ctx.funcs[ctx.funcCount] = *f;
             ctx.funcCount = ctx.funcCount + 1;
@@ -633,7 +633,7 @@ func HirLower_LowerModule(mod: *Module, sema: *Sema) -> *HirModule {
             let implTypeName: String = decl.strValue;
             var implDecl: *Decl = decl.childDecl1;
             while implDecl != null as *Decl {
-                if implDecl.kind == dkFunc {
+                if implDecl.kind == dkFunc && implDecl.refBody != null as *Block {
                     let mangled: String = String_Concat(implTypeName, "_");
                     implDecl.strValue = String_Concat(mangled, implDecl.strValue);
                     let f: *HirFunc = Lcx_LowerFunc(ctx, implDecl);

src/parser.bux

@@ -4,6 +4,14 @@ module Parser {
 
 extern func bux_strlen(s: String) -> uint;
 
+// Forward declarations for mutual recursion
+func parserParseExpr(p: *Parser) -> *Expr;
+func parserParseStmt(p: *Parser) -> *Stmt;
+func parserParseBlock(p: *Parser) -> *Block;
+func parserParsePrimary(p: *Parser) -> *Expr;
+func parserParsePostfixExpr(p: *Parser) -> *Expr;
+func parserParseBinaryPrec(p: *Parser, minPrec: int) -> *Expr;
+
 // ---------------------------------------------------------------------------
 // Parser state
 // ---------------------------------------------------------------------------
@@ -326,7 +334,7 @@ func parserParsePrimary(p: *Parser) -> *Expr {
 // Postfix: call, index, field access, as, is, ?
 // ---------------------------------------------------------------------------
 
-func parserParsePostfix(p: *Parser) -> *Expr {
+func parserParsePostfixExpr(p: *Parser) -> *Expr {
     var left: *Expr = parserParsePrimary(p);
 
     while true {
@@ -566,7 +574,7 @@ func parserPrecedence(op: int) -> int {
 }
 
 func parserParseBinaryPrec(p: *Parser, minPrec: int) -> *Expr {
-    var left: *Expr = parserParsePostfix(p);
+    var left: *Expr = parserParsePostfixExpr(p);
     while true {
         let op: int = parserPeek(p, 0);
         let prec: int = parserPrecedence(op);