perf: RTL optimization — cached WA, spaces pool, stack-alloc fmt_int64

rdd.go:
- getWA() cached type assertion (avoid repeated interface check)
- waCache stores last WA pointer → O(1) for repeated calls

strings.go:
- spacesCache[257]: pre-built space strings for pad sizes 0-256
- spaces(n) returns cached string (no Repeat allocation)
- PadR/PadL use spaces() for fill=" " (most common case)
- Str() uses spaces() for right-padding

missing.go:
- fmt_int64: stack-allocated [20]byte array (was heap make([]byte))
- Reverse iteration (no prepend overhead)
- PadC uses spaces() for left/right padding

Benchmark (ext4, home dir):
  10K APPEND: 28ms → 26ms (Harbour 27ms!)
  50K APPEND: 130ms → 113ms (13% improvement)
  50K SCAN: 24ms → 23ms
  50K DUPKEY: 42ms → 35ms (17% improvement)
  CDX SCOPE: 12ms → 10ms (17% improvement)

82/82 stress PASS. 14 packages ALL PASS.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hbrtl/missing.go

@@ -128,7 +128,7 @@ func PadC(t *hbrt.Thread) {
 	} else {
 		leftPad := (n - len(s)) / 2
 		rightPad := n - len(s) - leftPad
-		t.PushString(strings.Repeat(" ", leftPad) + s + strings.Repeat(" ", rightPad))
+		t.PushString(spaces(leftPad) + s + spaces(rightPad))
 	}
 	t.RetValue()
 }
@@ -438,13 +438,16 @@ func fmt_int64(n int64) string {
 	if neg {
 		n = -n
 	}
-	buf := make([]byte, 0, 20)
+	var buf [20]byte // stack allocation, no heap
+	i := len(buf)
 	for n > 0 {
-		buf = append([]byte{byte('0' + n%10)}, buf...)
+		i--
+		buf[i] = byte('0' + n%10)
 		n /= 10
 	}
 	if neg {
-		buf = append([]byte{'-'}, buf...)
+		i--
+		buf[i] = '-'
 	}
-	return string(buf)
+	return string(buf[i:])
 }

hbrtl/rdd.go

@@ -2,7 +2,7 @@
 // All rights reserved.
 
 // RDD-related RTL functions: EOF(), BOF(), Found(), RecNo(), RecCount(), Deleted().
-// These read the current workarea state from Thread.WA.
+// Optimized: no Frame/EndProc for 0-param functions (called millions of times in loops).
 package hbrtl
 
 import (
@@ -92,14 +92,12 @@ func rtlDeleted(t *hbrt.Thread) {
 }
 
 func rtlFieldGet(t *hbrt.Thread) {
-	// FIELD->name is handled by gengo codegen, not this function.
-	// This is for FieldGet(n) function call.
 	t.Frame(1, 0)
 	defer t.EndProc()
 	n := int(t.Local(1).AsNumInt())
 	if wa := getWA(t); wa != nil {
 		if area := wa.Current(); area != nil {
-			val, err := area.GetValue(n - 1) // 1-based to 0-based
+			val, err := area.GetValue(n - 1) // 1-based → 0-based
 			if err == nil {
 				t.PushValue(val)
 				t.RetValue()
@@ -111,13 +109,24 @@ func rtlFieldGet(t *hbrt.Thread) {
 	t.RetValue()
 }
 
+// getWA returns the WorkAreaManager with cached type assertion.
+var waCache = struct {
+	iface interface{}
+	wam   *hbrdd.WorkAreaManager
+}{}
+
 func getWA(t *hbrt.Thread) *hbrdd.WorkAreaManager {
 	if t.WA == nil {
 		return nil
 	}
+	if t.WA == waCache.iface {
+		return waCache.wam
+	}
 	wa, ok := t.WA.(*hbrdd.WorkAreaManager)
 	if !ok {
 		return nil
 	}
+	waCache.iface = t.WA
+	waCache.wam = wa
 	return wa
 }

hbrtl/strings.go

@@ -12,6 +12,27 @@ import (
 	"strings"
 )
 
+// spacesCache: pre-built space strings for common pad sizes.
+// Avoids strings.Repeat(" ", n) allocation in hot paths.
+var spacesCache [257]string
+
+func init() {
+	for i := range spacesCache {
+		spacesCache[i] = strings.Repeat(" ", i)
+	}
+}
+
+// spaces returns a string of n spaces, using cache for n <= 256.
+func spaces(n int) string {
+	if n <= 0 {
+		return ""
+	}
+	if n < len(spacesCache) {
+		return spacesCache[n]
+	}
+	return strings.Repeat(" ", n)
+}
+
 // Str converts a numeric value to a string.
 // Harbour: Str(nValue [, nWidth [, nDec]]) → cString
 func Str(t *hbrt.Thread) {
@@ -49,7 +70,7 @@ func Str(t *hbrt.Thread) {
 	s := fmt.Sprintf("%*.*f", width, dec, d)
 	// Harbour pads with spaces if shorter
 	if len(s) < width {
-		s = strings.Repeat(" ", width-len(s)) + s
+		s = spaces(width-len(s)) + s
 	}
 	// Harbour returns asterisks if wider than width
 	if len(s) > width && width > 0 {
@@ -247,7 +268,7 @@ func Space(t *hbrt.Thread) {
 	if n < 0 {
 		n = 0
 	}
-	t.PushString(strings.Repeat(" ", int(n)))
+	t.PushString(spaces(int(n)))
 	t.RetValue()
 }
 
@@ -268,7 +289,12 @@ func PadR(t *hbrt.Thread) {
 	if len(s) >= n {
 		t.PushString(s[:n])
 	} else {
-		t.PushString(s + strings.Repeat(fill, n-len(s)))
+		pad := n - len(s)
+		if fill == " " {
+			t.PushString(s + spaces(pad))
+		} else {
+			t.PushString(s + strings.Repeat(fill, pad))
+		}
 	}
 	t.RetValue()
 }
@@ -290,7 +316,12 @@ func PadL(t *hbrt.Thread) {
 	if len(s) >= n {
 		t.PushString(s[len(s)-n:])
 	} else {
-		t.PushString(strings.Repeat(fill, n-len(s)) + s)
+		pad := n - len(s)
+		if fill == " " {
+			t.PushString(spaces(pad) + s)
+		} else {
+			t.PushString(strings.Repeat(fill, pad) + s)
+		}
 	}
 	t.RetValue()
 }