diff --git a/docs/.pdca-status.json b/docs/.pdca-status.json
index 34f3544..6c3b3db 100644
--- a/docs/.pdca-status.json
+++ b/docs/.pdca-status.json
@@ -1,6 +1,6 @@
 {
   "version": "2.0",
-  "lastUpdated": "2026-04-01T11:59:53.709Z",
+  "lastUpdated": "2026-04-01T12:09:42.812Z",
   "activeFeatures": [
     "hbrt",
     "hbrtl",
@@ -33,9 +33,9 @@
       "documents": {},
       "timestamps": {
         "started": "2026-03-27T09:33:04.512Z",
-        "lastUpdated": "2026-04-01T01:50:29.560Z"
+        "lastUpdated": "2026-04-01T12:08:54.344Z"
       },
-      "lastFile": "/mnt/d/charles/five/hbrt/macroeval.go"
+      "lastFile": "/mnt/d/charles/five/hbrt/frb.go"
     },
     "hbrtl": {
       "phase": "do",
@@ -137,7 +137,7 @@
       "documents": {},
       "timestamps": {
         "started": "2026-03-27T11:50:31.420Z",
-        "lastUpdated": "2026-04-01T08:11:30.993Z"
+        "lastUpdated": "2026-04-01T12:09:42.812Z"
       },
       "lastFile": "/mnt/d/charles/five/cmd/five/main.go"
     },
@@ -280,7 +280,7 @@
   "session": {
     "startedAt": "2026-03-27T06:06:49.620Z",
     "onboardingCompleted": false,
-    "lastActivity": "2026-04-01T11:59:53.709Z"
+    "lastActivity": "2026-04-01T12:09:42.812Z"
   },
   "history": [
     {
@@ -5826,6 +5826,60 @@
       "feature": "parser",
       "phase": "do",
       "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:05:42.359Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:05:56.744Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:06:26.236Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:06:46.834Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:07:10.287Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:07:54.070Z",
+      "feature": "five",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:08:54.344Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:09:06.847Z",
+      "feature": "five",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-04-01T12:09:42.812Z",
+      "feature": "five",
+      "phase": "do",
+      "action": "updated"
     }
   ]
 }
\ No newline at end of file
diff --git a/hbrt/frb.go b/hbrt/frb.go
index 61faeaa..a218f0e 100644
--- a/hbrt/frb.go
+++ b/hbrt/frb.go
@@ -38,10 +38,16 @@ var frbMagic = []byte{0xC0, 'F', 'R', 'B'}
 
 const frbVersion = 2
 
-// FRB mode flags
+// FRB file format constants
 const (
+	FrbMagic0     byte = 0xC0 // magic byte 0
+	FrbMagic1     byte = 'F'  // magic byte 1
+	FrbMagic2     byte = 'R'  // magic byte 2
+	FrbMagic3     byte = 'B'  // magic byte 3
+	FrbVersion1   byte = 1    // format version
 	FrbModeNative byte = 0x01 // Go plugin (.so)
 	FrbModePcode  byte = 0x02 // Five pcode (interpreter)
+	FrbHeaderSize      = 12   // header bytes before payload
 )
 
 // FrbModule represents a loaded FRB module.
diff --git a/hbrt/symbol.go b/hbrt/symbol.go
index e60f3be..da2eb4b 100644
--- a/hbrt/symbol.go
+++ b/hbrt/symbol.go
@@ -30,6 +30,7 @@ type Symbol struct {
 type Module struct {
 	Name    string
 	Symbols []Symbol
+	index   map[string]int // lazy-built name → Symbols index
 }
 
 // Sym creates a Symbol (convenience constructor for generated code).
@@ -47,12 +48,16 @@ func (m *Module) At(index int) *Symbol {
 	return &m.Symbols[index]
 }
 
-// Find returns a symbol by name within this module.
+// Find returns a symbol by name within this module. O(1) via lazy index.
 func (m *Module) Find(name string) *Symbol {
-	for i := range m.Symbols {
-		if m.Symbols[i].Name == name {
-			return &m.Symbols[i]
+	if m.index == nil {
+		m.index = make(map[string]int, len(m.Symbols))
+		for i := range m.Symbols {
+			m.index[m.Symbols[i].Name] = i
 		}
 	}
+	if idx, ok := m.index[name]; ok {
+		return &m.Symbols[idx]
+	}
 	return nil
 }
diff --git a/hbrt/thread.go b/hbrt/thread.go
index a902fd5..48b0a52 100644
--- a/hbrt/thread.go
+++ b/hbrt/thread.go
@@ -10,9 +10,10 @@ import (
 
 // Default stack/frame sizes
 const (
-	DefaultStackSize = 2048 // initial eval stack capacity
-	MaxStackSize     = 65536
-	MaxCallDepth     = 256
+	DefaultStackSize    = 2048 // initial eval stack capacity
+	MaxStackSize        = 65536
+	MaxCallDepth        = 256
+	InitialCallDepth    = 32  // start small, grow if needed
 )
 
 // CallFrame saves the state of a function call.
@@ -94,7 +95,7 @@ func NewThread(vm *VM) *Thread {
 		stack:   make([]Value, DefaultStackSize),
 		sp:      0,
 		locals:  make([]Value, 256), // will grow as needed
-		calls:   make([]CallFrame, MaxCallDepth),
+		calls:   make([]CallFrame, InitialCallDepth),
 		callSP:  0,
 		statics: make(map[string][]Value),
 		vm:      vm,
@@ -182,6 +183,16 @@ func (t *Thread) Frame(params, locals int) {
 	if t.callSP >= MaxCallDepth {
 		panic(t.runtimeError("call stack overflow"))
 	}
+	// Grow call stack dynamically if needed
+	if t.callSP >= len(t.calls) {
+		newSize := len(t.calls) * 2
+		if newSize > MaxCallDepth {
+			newSize = MaxCallDepth
+		}
+		newCalls := make([]CallFrame, newSize)
+		copy(newCalls, t.calls)
+		t.calls = newCalls
+	}
 
 	// Ensure locals slice has enough space
 	localBase := 0