diff --git a/dev/test/cli.test.ts b/dev/test/cli.test.ts
index ab29e88..7d9680b 100644
--- a/dev/test/cli.test.ts
+++ b/dev/test/cli.test.ts
@@ -445,6 +445,17 @@ describe('CLI', () => {
     expect(report.items[0]?.reason).toBe('could not parse intent JSON');
   });
 
+  it('preserves an output sentinel when intent assembly fails', async () => {
+    const dir = await mkdtemp(path.join(tmpdir(), 'block-runner-cli-'));
+    const outPath = path.join(dir, 'out.html');
+    await writeFile(outPath, 'Keep existing output');
+    const result = await runCli(['assemble', '-', '--out', outPath],
+      '{"blocks":[{"block":"core/paragraph","text":"First"},{"text":"Second"}]}');
+    expect(result.code).toBe(1);
+    expect(result.stdout).toContain('blocks[1]: expected a node with a non-empty block name');
+    expect(await readFile(outPath, 'utf8')).toBe('Keep existing output');
+  });
+
   it('rejects styling flags on assemble and points callers to convert', async () => {
     for (const args of [
       ['assemble', '-', '--styling', 'strict'],
diff --git a/dev/test/intent.test.ts b/dev/test/intent.test.ts
index f3d265e..08e0c77 100644
--- a/dev/test/intent.test.ts
+++ b/dev/test/intent.test.ts
@@ -1,8 +1,10 @@
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
-import { describe, expect, it } from 'vitest';
-import { realize, validate } from '../../src/index.js';
+import { describe, expect, it, vi } from 'vitest';
+import { assemble, realize, validate } from '../../src/index.js';
 import { getWp } from '../../src/headless/wp.js';
+import * as media from '../../src/media/resolver.js';
+import type { IntentNode } from '../../src/types.js';
 
 const FIXTURES = path.join(path.dirname(fileURLToPath(import.meta.url)), 'fixtures');
 
@@ -142,7 +144,62 @@ describe('intent assembly', () => {
     const report = await realize('{"blocks":[{}]}');
 
     expect(report.ok).toBe(false);
-    expect(report.items[0]?.reason).toBe('intent parsed but contained no blocks');
+    expect(report.items[0]?.reason).toContain('blocks[0]: expected a node with a non-empty block name');
+  });
+
+  it.each([
+    [[{ block: 'core/paragraph', text: 'First' }, { text: 'Second' }], 'blocks[1]'],
+    [[{ block: 'core/group', children: [null] }], 'blocks[0].children[0]'],
+    [[{ block: 'core/group', children: {} }], 'blocks[0].children'],
+    [[{ block: 'core/group', children: null }], 'blocks[0].children'],
+    [[{ block: '' }], 'blocks[0]'],
+    [[{ block: 'core/list', items: ['First', { text: 'Second' }] }], 'blocks[0].items[1]'],
+    [[{ block: 'core/list', items: 'First' }], 'blocks[0].items'],
+    [[{ block: 'core/table', rows: [['First'], [{ text: 'Second' }]] }], 'blocks[0].rows[1][0]'],
+    [[{ block: 'core/table', rows: ['First'] }], 'blocks[0].rows[0]'],
+    [[{ block: 'core/table', rows: {} }], 'blocks[0].rows'],
+  ])('rejects malformed consumed input %j at %s', async (nodes, location) => {
+    const report = await realize(JSON.stringify({ blocks: nodes }), { sourcePath: 'intent.json' });
+    expect(report.ok).toBe(false);
+    expect(report.output).toBe('');
+    expect(report.items[0]).toMatchObject({ status: 'invalid', source: { path: 'intent.json' } });
+    expect(report.items[0].reason).toContain(`${location}: expected`);
+    await expect(assemble(nodes as IntentNode[])).rejects.toThrow(`${location}: expected`);
+  });
+
+  it('rejects malformed input before constructing the media resolver', async () => {
+    const resolver = vi.spyOn(media, 'createMediaResolver');
+    try {
+      const report = await realize(JSON.stringify({ blocks: [
+        { block: 'core/image', url: 'photo.jpg' }, { text: 'Missing name' },
+      ] }));
+      expect(report.ok).toBe(false);
+      expect(resolver).not.toHaveBeenCalled();
+    } finally {
+      resolver.mockRestore();
+    }
+  });
+
+  it.each([
+    '{"block":"core/paragraph","text":"Text"}',
+    '[{"block":"core/paragraph","text":"Text"}]',
+    '{"blocks":[{"block":"core/paragraph","text":"Text"}]}',
+    '```json\n{"blocks":[{"block":"core/paragraph","text":"Text"}]}\n```',
+  ])('keeps valid input wrappers', async (raw) => {
+    expect((await realize(raw)).ok).toBe(true);
+  });
+
+  it('keeps explicit tables and ignores unused list shorthand', async () => {
+    const report = await realize(JSON.stringify({ blocks: [
+      { block: 'core/list', items: { unused: true }, children: [{ block: 'core/list-item', text: 'Kept' }] },
+      { block: 'core/table', attrs: { body: [{ cells: [{ content: 'Body only', tag: 'td' }] }] } },
+      { block: 'core/table', rows: [['Header'], ['Cell']] },
+    ] }));
+    expect(report.ok).toBe(true);
+    expect(report.output).toContain('Kept');
+    expect(report.output).toContain('<td>Body only</td>');
+    expect(report.output).toContain('<th>Header</th>');
+    expect(report.output).toContain('<td>Cell</td>');
   });
 
   it('warns on an unregistered block name without failing the run', async () => {
diff --git a/src/intent/index.ts b/src/intent/index.ts
index c647d23..5d24741 100644
--- a/src/intent/index.ts
+++ b/src/intent/index.ts
@@ -74,21 +74,23 @@ export async function assemble(nodes: IntentNode[]): Promise<WpBlock[]> {
   return assembleWithWp(nodes, await getWp());
 }
 
-async function assembleWithWp(nodes: IntentNode[], wp: WpModules): Promise<WpBlock[]> {
+async function assembleWithWp(nodes: IntentNode[], wp: WpModules, intentPath = 'blocks'): Promise<WpBlock[]> {
+  if (!Array.isArray(nodes)) throw new Error(`${intentPath}: expected an array of block nodes`);
   const out: WpBlock[] = [];
-  for (const node of nodes) {
-    const block = await assembleNode(node, wp);
-    if (block) out.push(block);
+  for (const [index, node] of nodes.entries()) {
+    out.push(await assembleNode(node, wp, `${intentPath}[${index}]`));
   }
   return out;
 }
 
-async function assembleNode(node: IntentNode, wp: WpModules): Promise<WpBlock | null> {
-  if (!node || typeof node.block !== 'string') return null;
+async function assembleNode(node: IntentNode, wp: WpModules, intentPath: string): Promise<WpBlock> {
+  if (!node || typeof node.block !== 'string' || !node.block.trim()) {
+    throw new Error(`${intentPath}: expected a node with a non-empty block name`);
+  }
   const name = node.block;
   const text = node.text;
   const attrs: Record<string, unknown> = { ...(node.attrs ?? {}) };
-  const children = await assembleWithWp(node.children ?? [], wp);
+  const children = await assembleWithWp(node.children === undefined ? [] : node.children, wp, `${intentPath}.children`);
 
   switch (name) {
     case 'core/heading':
@@ -116,8 +118,12 @@ async function assembleNode(node: IntentNode, wp: WpModules): Promise<WpBlock |
 
     case 'core/list': {
       let items = children;
-      if (items.length === 0 && Array.isArray(node.items)) {
-        items = node.items.map((item) => wp.createBlock('core/list-item', { content: item }, []));
+      if (items.length === 0 && node.items !== undefined) {
+        if (!Array.isArray(node.items)) throw new Error(`${intentPath}.items: expected an array of strings`);
+        items = node.items.map((item, index) => {
+          if (typeof item !== 'string') throw new Error(`${intentPath}.items[${index}]: expected a string`);
+          return wp.createBlock('core/list-item', { content: item }, []);
+        });
       }
       return wp.createBlock(name, attrs, items);
     }
@@ -141,12 +147,19 @@ async function assembleNode(node: IntentNode, wp: WpModules): Promise<WpBlock |
       return wp.createBlock(name, attrs, []);
 
     case 'core/table': {
-      if (Array.isArray(node.rows) && node.rows.length > 0) {
-        const toCells = (row: string[], tag: 'th' | 'td'): { cells: { content: string; tag: string }[] } => ({
-          cells: row.map((content) => ({ content, tag })),
-        });
-        attrs.head = [toCells(node.rows[0], 'th')];
-        attrs.body = node.rows.slice(1).map((row) => toCells(row, 'td'));
+      if (node.rows !== undefined && !Array.isArray(node.rows)) {
+        throw new Error(`${intentPath}.rows: expected an array of string arrays`);
+      }
+      if (node.rows && node.rows.length > 0) {
+        const toCells = (row: string[], index: number, tag: 'th' | 'td'): { cells: { content: string; tag: string }[] } => {
+          if (!Array.isArray(row)) throw new Error(`${intentPath}.rows[${index}]: expected an array of strings`);
+          return { cells: row.map((content, cell) => {
+            if (typeof content !== 'string') throw new Error(`${intentPath}.rows[${index}][${cell}]: expected a string`);
+            return { content, tag };
+          }) };
+        };
+        attrs.head = [toCells(node.rows[0], 0, 'th')];
+        attrs.body = node.rows.slice(1).map((row, index) => toCells(row, index + 1, 'td'));
       }
       return wp.createBlock(name, attrs, []);
     }
@@ -191,6 +204,7 @@ export async function realize(rawIntent: string, options: AssembleOptions = {}):
   try {
     const config = await loadConfig(options);
     const wp = await getWp();
+    const blocks = await assembleWithWp(extracted.tree.blocks, wp);
     const warnings = unknownBlockWarnings(extracted.tree.blocks, wp, options.sourcePath);
     if (config.styling !== DEFAULT_CONFIG.styling) {
       warnings.push({
@@ -200,7 +214,6 @@ export async function realize(rawIntent: string, options: AssembleOptions = {}):
         source: options.sourcePath ? { path: options.sourcePath } : undefined,
       });
     }
-    const blocks = await assembleWithWp(extracted.tree.blocks, wp);
     if (blocks.length === 0) {
       return invalidInputReport('intent parsed but contained no blocks', options);
     }