diff --git a/packages/machine/src/classes/State.spec.ts b/packages/machine/src/classes/State.spec.ts
index f32939c..3c16b0a 100644
--- a/packages/machine/src/classes/State.spec.ts
+++ b/packages/machine/src/classes/State.spec.ts
@@ -208,7 +208,7 @@ describe('State.withOverriddenHaltState', () => {
 });
 
 describe('State.toGraph — unbound Reference', () => {
-  test('skips a transition whose nextState is an unbound Reference', () => {
+  test('skips a transition whose nextState is an unbound Reference (non-wrapper context)', () => {
     // An unbound Reference throws when its `.ref` getter is read. State.toGraph
     // catches that and skips the transition rather than failing the whole walk.
     const unboundRef = new Reference();
@@ -222,6 +222,30 @@ describe('State.toGraph — unbound Reference', () => {
     // Only the haltState-bound transition survives; the unbound one is dropped.
     expect(graph.nodes[state.id].transitions).toHaveLength(1);
   });
+
+  test('skips a transition whose nextState is an unbound Reference (wrapper context)', () => {
+    // toGraph has a separate try/catch in its wrapper-context branch — when the
+    // bare being walked is inside a `withOverriddenHaltState` wrapper. Same
+    // skip-and-continue semantic.
+    const unboundRef = new Reference();
+    const bare = new State({
+      [symbol(['0'])]: {nextState: unboundRef},
+      [symbol(['1'])]: {nextState: haltState},
+    }, 'bare');
+    const override = new State({
+      [symbol(['0'])]: {nextState: haltState},
+      [symbol(['1'])]: {nextState: haltState},
+    }, 'override');
+    const wrapped = bare.withOverriddenHaltState(override);
+
+    const graph = State.toGraph(wrapped, tapeBlock);
+
+    // The collapsed wrapper node retains only the haltState-bound transition;
+    // the unbound-Ref one is dropped.
+    const collapsedNode = graph.nodes[wrapped.id];
+
+    expect(collapsedNode.transitions).toHaveLength(1);
+  });
 });
 
 describe('State.fromGraph — cyclic override-halt chain', () => {
diff --git a/packages/machine/src/utilities/graph.spec.ts b/packages/machine/src/utilities/graph.spec.ts
index e8592fd..f2efd9c 100644
--- a/packages/machine/src/utilities/graph.spec.ts
+++ b/packages/machine/src/utilities/graph.spec.ts
@@ -4,6 +4,7 @@ import {
   decodeWriteSymbol,
   parseMovementLabel,
   parsePatternString,
+  parseWriteSymbolLabel,
   splitUnescaped,
 } from './graph';
 import {fromMermaid, toMermaid} from './graphFormats';
@@ -214,6 +215,34 @@ describe('parsePatternString', () => {
   test('per-cell `B` becomes the tape blank symbol', () => {
     expect(parsePatternString("B,'a'", [[' ', '0'], [' ', 'a']])).toEqual([[' ', 'a']]);
   });
+
+  test('fallback: cell that is not marker/blank/quoted is returned as-is', () => {
+    // Defensive — the parser doesn't throw on unexpected cells; it returns
+    // them as-is, so consumer code can decide whether to reject.
+    expect(parsePatternString('Q', [[' ', '0']])).toEqual([['Q']]);
+  });
+
+  test('blank-marker fallback when alphabet for the tape is missing', () => {
+    // Defensive: if alphabets[tapeIx] is undefined, returns the marker
+    // string itself rather than throwing.
+    expect(parsePatternString('B', [])).toEqual([['B']]);
+  });
+});
+
+describe('parseWriteSymbolLabel', () => {
+  test('maps K/E to upstream symbolCommands', () => {
+    expect(parseWriteSymbolLabel('K')).toBe(symbolCommands.keep);
+    expect(parseWriteSymbolLabel('E')).toBe(symbolCommands.erase);
+  });
+
+  test('strips single quotes from a literal alphabet symbol', () => {
+    expect(parseWriteSymbolLabel("'X'")).toBe('X');
+  });
+
+  test('fallback: label that is not K/E/quoted is returned as-is', () => {
+    // Defensive — same shape as parsePatternString's fallback.
+    expect(parseWriteSymbolLabel('Z')).toBe('Z');
+  });
 });
 
 describe('parseMovementLabel', () => {