diff --git a/src/core.ts b/src/core.ts
index 9497dd6..5161aea 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -37,12 +37,24 @@ export function createHistory(options: HistoryOptions = {}): History {
     }
   };
 
+  const undoEntry = (): Entry | undefined => {
+    if (cursor === 0) return undefined;
+    // The cursor is kept in [0, length], so cursor - 1 names an undoable entry.
+    return entries[cursor - 1]!;
+  };
+
+  const redoEntry = (): Entry | undefined => {
+    if (cursor === entries.length) return undefined;
+    // The cursor is kept in [0, length], so cursor names a redoable entry.
+    return entries[cursor]!;
+  };
+
   const buildMeta = (): HistoryMeta =>
     Object.freeze({
       canUndo: cursor > 0,
       canRedo: cursor < entries.length,
-      undoLabel: cursor > 0 ? entries[cursor - 1].label : undefined,
-      redoLabel: cursor < entries.length ? entries[cursor].label : undefined,
+      undoLabel: undoEntry()?.label,
+      redoLabel: redoEntry()?.label,
       position: cursor,
       length: entries.length,
     });
@@ -88,11 +100,13 @@ export function createHistory(options: HistoryOptions = {}): History {
     while (remaining > 0) {
       if (dir < 0) {
         if (cursor === 0) break;
-        runGuarded(entries[cursor - 1].undo);
+        const entry = undoEntry()!;
+        runGuarded(entry.undo);
         cursor -= 1;
       } else {
         if (cursor === entries.length) break;
-        runGuarded(entries[cursor].do);
+        const entry = redoEntry()!;
+        runGuarded(entry.do);
         cursor += 1;
       }
       remaining -= 1;
@@ -154,7 +168,7 @@ export function createHistory(options: HistoryOptions = {}): History {
 
   const checkpoint = (name: string): void => {
     assertIdle();
-    checkpoints.set(name, cursor === 0 ? START : entries[cursor - 1]);
+    checkpoints.set(name, cursor === 0 ? START : undoEntry()!);
   };
 
   const hasCheckpoint = (name: string): boolean => checkpoints.has(name);
@@ -218,10 +232,10 @@ export function createHistory(options: HistoryOptions = {}): History {
       return cursor < entries.length;
     },
     get undoLabel() {
-      return cursor > 0 ? entries[cursor - 1].label : undefined;
+      return undoEntry()?.label;
     },
     get redoLabel() {
-      return cursor < entries.length ? entries[cursor].label : undefined;
+      return redoEntry()?.label;
     },
     get position() {
       return cursor;
diff --git a/src/transaction.ts b/src/transaction.ts
index 9a4c0f1..383fa76 100644
--- a/src/transaction.ts
+++ b/src/transaction.ts
@@ -86,7 +86,9 @@ export function runTransaction(
     closed = true;
     try {
       for (let i = ops.length - 1; i >= 0; i -= 1) {
-        engine.runGuarded(ops[i].undo);
+        // The reverse walk starts at the last recorded op and stops before -1.
+        const op = ops[i]!;
+        engine.runGuarded(op.undo);
       }
     } finally {
       engine.endMutation();
@@ -106,7 +108,9 @@ export function runTransaction(
     },
     undo() {
       for (let i = ops.length - 1; i >= 0; i -= 1) {
-        engine.runGuarded(ops[i].undo);
+        // The reverse walk starts at the last recorded op and stops before -1.
+        const op = ops[i]!;
+        engine.runGuarded(op.undo);
       }
     },
   });
diff --git a/tsconfig.json b/tsconfig.json
index ff4adab..2745bc3 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,20 +1,23 @@
 {
   "compilerOptions": {
-    "target": "esnext",
-    "lib": ["es2023"],
+    "target": "es2024",
+    "lib": ["es2024"],
     "moduleDetection": "force",
     "module": "nodenext",
     "moduleResolution": "nodenext",
-    "resolveJsonModule": true,
-    "types": ["node"],
+    "types": [],
     "strict": true,
+    "noUncheckedIndexedAccess": true,
     "noUnusedLocals": true,
-    "declaration": true,
+    "noUnusedParameters": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true,
+    "noImplicitOverride": true,
     "noEmit": true,
     "allowImportingTsExtensions": true,
-    "esModuleInterop": true,
     "isolatedModules": true,
     "verbatimModuleSyntax": true,
     "skipLibCheck": true
-  }
+  },
+  "include": ["src"]
 }
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..25cae3c
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,9 @@
+{
+  // Keeps editor/raw tsc coverage for Node-run files while tsconfig.json
+  // remains the shipped-source contract with no Node ambient globals.
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "types": ["node"]
+  },
+  "include": ["tests", "vite.config.ts"]
+}