feat: add semantic CSS stylesheets (#3274)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

packages/api/src/features/resume/stylesheet-observability.ts

@@ -0,0 +1,46 @@
+import type { Template } from "@reactive-resume/schema/templates";
+import { createHash } from "node:crypto";
+
+type SemanticCssEventName =
+	| "semantic_css.compile"
+	| "semantic_css.preflight"
+	| "semantic_css.convert_legacy"
+	| "semantic_css.parity_check"
+	| "semantic_css.activate";
+
+export type SemanticCssEventInput = {
+	name: SemanticCssEventName;
+	resumeId: string;
+	durationMs: number;
+	languageVersion: number;
+	sourceBytes: number;
+	template: Template;
+	diagnosticCodes: readonly string[];
+	pageCount: number | null;
+	revision: number;
+	success: boolean;
+};
+
+export const hashSemanticCssResumeId = (resumeId: string): string =>
+	createHash("sha256").update(`reactive-resume:semantic-css:resume:${resumeId}`).digest("hex");
+
+const safeDiagnosticCode = (code: string): string =>
+	/^[A-Z][A-Z0-9_]{0,63}$/.test(code) ? code : "UNKNOWN_DIAGNOSTIC";
+
+export function recordSemanticCssEvent(
+	event: SemanticCssEventInput,
+	logger: (event: Readonly<Record<string, unknown>>) => void = console.info,
+): void {
+	logger({
+		name: event.name,
+		resumeIdHash: hashSemanticCssResumeId(event.resumeId),
+		durationMs: event.durationMs,
+		languageVersion: event.languageVersion,
+		sourceBytes: event.sourceBytes,
+		template: event.template,
+		diagnosticCodes: event.diagnosticCodes.map(safeDiagnosticCode),
+		pageCount: event.pageCount,
+		revision: event.revision,
+		success: event.success,
+	});
+}