fix(pipeline): evaluate chained || in template engine

src/pipeline/template.test.ts

@@ -54,6 +54,28 @@ describe('evalExpr', () => {
   it('evaluates || with truthy left', () => {
     expect(evalExpr("item.name || 'N/A'", { item: { name: 'Alice' } })).toBe('Alice');
   });
+  it('evaluates chained || fallback (issue #303)', () => {
+    // When first two are falsy, should evaluate through to the string literal
+    expect(evalExpr("item.a || item.b || 'default'", { item: {} })).toBe('default');
+  });
+  it('evaluates chained || with middle value truthy', () => {
+    expect(evalExpr("item.a || item.b || 'default'", { item: { b: 'middle' } })).toBe('middle');
+  });
+  it('evaluates chained || with first value truthy', () => {
+    expect(evalExpr("item.a || item.b || 'default'", { item: { a: 'first', b: 'middle' } })).toBe('first');
+  });
+  it('evaluates || with 0 as falsy left (JS semantics)', () => {
+    expect(evalExpr("item.count || 'N/A'", { item: { count: 0 } })).toBe('N/A');
+  });
+  it('evaluates || with empty string as falsy left', () => {
+    expect(evalExpr("item.name || 'unknown'", { item: { name: '' } })).toBe('unknown');
+  });
+  it('evaluates || with numeric fallback returning number type', () => {
+    expect(evalExpr('item.a || 42', { item: {} })).toBe(42);
+  });
+  it('evaluates 4-way chained ||', () => {
+    expect(evalExpr("item.a || item.b || item.c || 'last'", { item: { c: 'third' } })).toBe('third');
+  });
   it('resolves simple path', () => {
     expect(evalExpr('item.title', { item: { title: 'Test' } })).toBe('Test');
   });

src/pipeline/template.ts

@@ -55,7 +55,7 @@ export function evalExpr(expr: string, ctx: RenderContext): unknown {
     const val = resolvePath(varName, { args, item, data, index });
     if (val !== null && val !== undefined) {
       const numVal = Number(val); const num = Number(numStr);
-      if (!isNaN(numVal)) {
+      if (!Number.isNaN(numVal)) {
         switch (op) {
           case '+': return numVal + num; case '-': return numVal - num;
           case '*': return numVal * num; case '/': return num !== 0 ? numVal / num : 0;
@@ -65,12 +65,13 @@ export function evalExpr(expr: string, ctx: RenderContext): unknown {
   }
 
   // JS-like fallback expression: item.tweetCount || 'N/A'
+  // Recursively evaluate the right side so chained || works:
+  //   item.a || item.b || 'default'  →  eval(item.a) || eval(item.b || 'default')
   const orMatch = expr.match(/^(.+?)\s*\|\|\s*(.+)$/);
   if (orMatch) {
     const left = evalExpr(orMatch[1].trim(), ctx);
     if (left) return left;
-    const right = orMatch[2].trim();
-    return right.replace(/^['"]|['"]$/g, '');
+    return evalExpr(orMatch[2].trim(), ctx);
   }
 
   const resolved = resolvePath(expr, { args, item, data, index });
@@ -95,7 +96,7 @@ function applyFilter(filterExpr: string, value: unknown): unknown {
     case 'default': {
       if (value === null || value === undefined || value === '') {
         const intVal = parseInt(filterArg, 10);
-        if (!isNaN(intVal) && String(intVal) === filterArg.trim()) return intVal;
+        if (!Number.isNaN(intVal) && String(intVal) === filterArg.trim()) return intVal;
         return filterArg;
       }
       return value;
@@ -110,7 +111,7 @@ function applyFilter(filterExpr: string, value: unknown): unknown {
       return typeof value === 'string' ? value.trim() : value;
     case 'truncate': {
       const n = parseInt(filterArg, 10) || 50;
-      return typeof value === 'string' && value.length > n ? value.slice(0, n) + '...' : value;
+      return typeof value === 'string' && value.length > n ? `${value.slice(0, n)}...` : value;
     }
     case 'replace': {
       if (typeof value !== 'string') return value;
@@ -138,6 +139,7 @@ function applyFilter(filterExpr: string, value: unknown): unknown {
     case 'sanitize':
       // Remove invalid filename characters
       return typeof value === 'string'
+        // biome-ignore lint/suspicious/noControlCharactersInRegex: intentional - strips C0 control chars from filenames
         ? value.replace(/[<>:"/\\|?*\x00-\x1f]/g, '_')
         : value;
     case 'ext': {