feat: add styling_preflight single-call validation tool

.changeset/styling-preflight.md

@@ -0,0 +1,5 @@
+---
+'@anthropic/helixir-core': minor
+---
+
+Add `styling_preflight` MCP tool — single-call styling validation that combines component API discovery, CSS reference resolution, Shadow DOM anti-pattern detection, theme compatibility checking, and a pass/fail verdict. Eliminates the "forgot to check the API first" failure mode.

packages/core/src/handlers/styling-preflight.ts

@@ -0,0 +1,146 @@
+/**
+ * Styling Preflight — single-call tool that combines component API discovery,
+ * CSS reference resolution, and validation into one response.
+ *
+ * Agents call this ONCE with their CSS (and optional HTML) to get:
+ * 1. The component's full style API surface (parts, tokens, slots)
+ * 2. Resolution of every ::part() and token reference (valid vs hallucinated)
+ * 3. Validation issues (shadow DOM, theme, specificity)
+ * 4. A correct CSS snippet to use as reference
+ * 5. A pass/fail verdict
+ *
+ * This eliminates the "forgot to check the API first" failure mode.
+ */
+
+import type { ComponentMetadata } from './cem.js';
+import { resolveCssApi, type CssApiResolution } from './css-api-resolver.js';
+import { checkShadowDomUsage } from './shadow-dom-checker.js';
+import { checkThemeCompatibility } from './theme-checker.js';
+import { buildCssSnippet } from './styling-diagnostics.js';
+
+// ─── Types ───────────────────────────────────────────────────────────────────
+
+export interface PreflightInput {
+  css: string;
+  html?: string;
+  meta: ComponentMetadata;
+}
+
+export interface PreflightIssue {
+  severity: 'error' | 'warning' | 'info';
+  category: string;
+  message: string;
+  line?: number;
+  suggestion?: string;
+}
+
+export interface PreflightComponentApi {
+  tagName: string;
+  description: string;
+  parts: string[];
+  tokens: string[];
+  slots: string[];
+  hasStyleApi: boolean;
+}
+
+export interface PreflightResult {
+  componentApi: PreflightComponentApi;
+  resolution: CssApiResolution;
+  issues: PreflightIssue[];
+  correctSnippet: string;
+  verdict: string;
+}
+
+// ─── Main Entry Point ───────────────────────────────────────────────────────
+
+export function runStylingPreflight(input: PreflightInput): PreflightResult {
+  const { css, html, meta } = input;
+  const issues: PreflightIssue[] = [];
+
+  // 1. Resolve CSS references against CEM
+  const resolution = resolveCssApi(css, meta, html);
+
+  // 2. Run shadow DOM validation (if CSS is non-empty)
+  if (css.trim()) {
+    try {
+      const shadowResult = checkShadowDomUsage(css, meta.tagName, meta);
+      for (const issue of shadowResult.issues) {
+        issues.push({
+          severity: issue.severity === 'error' ? 'error' : 'warning',
+          category: 'shadowDom',
+          message: issue.message,
+          line: issue.line,
+          suggestion: issue.suggestion,
+        });
+      }
+    } catch {
+      // Shadow DOM check failed — skip
+    }
+
+    // 3. Run theme compatibility check
+    try {
+      const themeResult = checkThemeCompatibility(css);
+      for (const issue of themeResult.issues) {
+        issues.push({
+          severity: 'warning',
+          category: 'themeCompat',
+          message: issue.message,
+          line: issue.line,
+        });
+      }
+    } catch {
+      // Theme check failed — skip
+    }
+  }
+
+  // 4. Build the component API summary
+  const componentApi: PreflightComponentApi = {
+    tagName: meta.tagName,
+    description: meta.description,
+    parts: meta.cssParts.map((p) => p.name),
+    tokens: meta.cssProperties.map((p) => p.name),
+    slots: meta.slots.map((s) => (s.name === '' ? '(default)' : s.name)),
+    hasStyleApi: meta.cssParts.length > 0 || meta.cssProperties.length > 0 || meta.slots.length > 0,
+  };
+
+  // 5. Generate correct CSS snippet
+  const correctSnippet = buildCssSnippet(meta);
+
+  // 6. Build verdict
+  const verdict = buildVerdict(resolution, issues);
+
+  return {
+    componentApi,
+    resolution,
+    issues,
+    correctSnippet,
+    verdict,
+  };
+}
+
+// ─── Verdict Builder ────────────────────────────────────────────────────────
+
+function buildVerdict(resolution: CssApiResolution, issues: PreflightIssue[]): string {
+  const errors = issues.filter((i) => i.severity === 'error').length;
+  const warnings = issues.filter((i) => i.severity === 'warning').length;
+  const invalidRefs = resolution.invalidCount;
+
+  if (errors === 0 && warnings === 0 && invalidRefs === 0) {
+    return 'pass — CSS references are valid and no anti-patterns detected.';
+  }
+
+  const parts: string[] = [];
+  if (invalidRefs > 0) {
+    parts.push(
+      `${invalidRefs} invalid CSS reference${invalidRefs > 1 ? 's' : ''} (hallucinated part/token/slot names)`,
+    );
+  }
+  if (errors > 0) {
+    parts.push(`${errors} error${errors > 1 ? 's' : ''} (will break at runtime)`);
+  }
+  if (warnings > 0) {
+    parts.push(`${warnings} warning${warnings > 1 ? 's' : ''} (theme/dark mode risk)`);
+  }
+
+  return 'fail — ' + parts.join(', ') + '.';
+}

packages/core/src/tools/styling.ts

@@ -28,6 +28,7 @@ import { checkColorContrast } from '../handlers/color-contrast-checker.js';
 import { checkTransitionAnimation } from '../handlers/transition-checker.js';
 import { checkShadowDomJs } from '../handlers/shadow-dom-js-checker.js';
 import { resolveCssApi } from '../handlers/css-api-resolver.js';
+import { runStylingPreflight } from '../handlers/styling-preflight.js';
 import { createErrorResponse, createSuccessResponse } from '../shared/mcp-helpers.js';
 import type { MCPToolResult } from '../shared/mcp-helpers.js';
 import { handleToolError } from '../shared/error-handling.js';
@@ -166,6 +167,12 @@ const ResolveCssApiArgsSchema = z.object({
   htmlText: z.string().optional(),
 });
 
+const StylingPreflightArgsSchema = z.object({
+  cssText: z.string(),
+  tagName: z.string(),
+  htmlText: z.string().optional(),
+});
+
 export const STYLING_TOOL_DEFINITIONS = [
   {
     name: 'diagnose_styling',
@@ -788,6 +795,35 @@ export const STYLING_TOOL_DEFINITIONS = [
       required: ['cssText', 'tagName'],
     },
   },
+  {
+    name: 'styling_preflight',
+    description:
+      "Single-call styling validation that combines component API discovery, CSS reference resolution, and anti-pattern detection. Returns: the component's full style API surface (parts, tokens, slots), valid/invalid status for every ::part() and token reference, Shadow DOM and theme validation issues, a correct CSS snippet, and a pass/fail verdict. Call this ONCE before finalizing any component CSS to prevent hallucinated part names, invalid tokens, and Shadow DOM mistakes.",
+    inputSchema: {
+      type: 'object' as const,
+      properties: {
+        libraryId: {
+          type: 'string',
+          description:
+            'Optional library ID to target a specific loaded library instead of the default.',
+        },
+        cssText: {
+          type: 'string',
+          description: 'The CSS code to validate against the component API.',
+        },
+        tagName: {
+          type: 'string',
+          description: 'The custom element tag name (e.g. "hx-button").',
+        },
+        htmlText: {
+          type: 'string',
+          description:
+            'Optional HTML code to validate slot attribute references against the component API.',
+        },
+      },
+      required: ['cssText', 'tagName'],
+    },
+  },
 ];
 
 /**
@@ -974,6 +1010,13 @@ export function handleStylingCall(
       return createSuccessResponse(JSON.stringify(result, null, 2));
     }
 
+    if (name === 'styling_preflight') {
+      const { cssText, tagName, htmlText } = StylingPreflightArgsSchema.parse(args);
+      const meta = parseCem(tagName, cem);
+      const result = runStylingPreflight({ css: cssText, html: htmlText, meta });
+      return createSuccessResponse(JSON.stringify(result, null, 2));
+    }
+
     return createErrorResponse(`Unknown styling tool: ${name}`);
   } catch (err) {
     const mcpErr = handleToolError(err);