chore(scripts): integrate filter-tsc-output from standalone branch

package.json

@@ -36,7 +36,7 @@
     "test:all": "pnpm test:parallel && pnpm test:sequential",
     "test:parallel": "pnpm --filter=!server --filter=!ckeditor5-mermaid --filter=!ckeditor5-math --parallel test",
     "test:sequential": "pnpm --filter=server --filter=ckeditor5-mermaid --filter=ckeditor5-math --sequential test",
-    "typecheck": "tsc --build",
+    "typecheck": "tsx scripts/filter-tsc-output.mts",
     "dev:format-check": "eslint -c eslint.format.config.mjs .",
     "dev:format-fix": "eslint -c eslint.format.config.mjs . --fix",
     "dev:linter-check": "cross-env NODE_OPTIONS=--max_old_space_size=4096 eslint .",

scripts/filter-tsc-output.mts

@@ -0,0 +1,56 @@
+/**
+ * Runs `tsc --build` and filters out noisy cascade errors (TS6305).
+ * Numbers each remaining error and prints a summary at the end.
+ */
+
+import { execSync } from "child_process";
+
+const SUPPRESSED_CODES = [ "TS6305" ];
+const ERROR_LINE_PATTERN = /^.+\(\d+,\d+\): error TS\d+:/;
+
+let output: string;
+try {
+    output = execSync("tsc --build", {
+        encoding: "utf-8",
+        stdio: [ "inherit", "pipe", "pipe" ]
+    });
+} catch (err: unknown) {
+    const execErr = err as { stdout?: string; stderr?: string };
+    output = (execErr.stdout ?? "") + (execErr.stderr ?? "");
+}
+
+const lines = output.split(/\r?\n/);
+const filtered = lines.filter(
+    (line) => !SUPPRESSED_CODES.some((code) => line.includes(code))
+);
+
+let errorIndex = 0;
+const numbered: string[] = [];
+const seen = new Set<string>();
+let skipContinuation = false;
+
+for (const line of filtered) {
+    if (ERROR_LINE_PATTERN.test(line)) {
+        if (seen.has(line)) {
+            skipContinuation = true;
+            continue;
+        }
+        seen.add(line);
+        skipContinuation = false;
+        errorIndex++;
+        numbered.push(`[${errorIndex}] ${line}`);
+    } else if (line.trim()) {
+        // Continuation line (indented context for multi-line errors)
+        if (!skipContinuation) {
+            numbered.push(line);
+        }
+    }
+}
+
+if (errorIndex > 0) {
+    console.log(numbered.join("\n"));
+    console.log(`\n${errorIndex} error(s) found.`);
+    process.exit(1);
+} else {
+    console.log("No errors found.");
+}