feat(diagnostics): cap diagnostic output with truncation notice

Add a limit parameter to formatDiagnostics (default 20 for explicit
lsp_diagnostics calls, 10 for auto-check after edit/write). When
truncated, a summary line indicates how many more diagnostics exist.

index.ts

@@ -194,7 +194,7 @@ function formatDocumentSymbols(result: unknown): string {
 }
 
 // Format Diagnostics - Turn diagnostic messages into readable text.
-function formatDiagnostics(result: unknown): string {
+function formatDiagnostics(result: unknown, limit = 20): string {
   if (
     !result ||
     typeof result !== "object" ||
@@ -212,7 +212,8 @@ function formatDiagnostics(result: unknown): string {
     4: "Hint",
   };
 
-  return diags
+  const shown = diags.slice(0, limit);
+  const formatted = shown
     .map((d: any, i: number) => {
       const sev = severityNames[d.severity] ?? `sev:${d.severity}`;
       const range = d.range;
@@ -222,6 +223,11 @@ function formatDiagnostics(result: unknown): string {
       return `${i + 1}. [${sev}] ${d.message} (line ${line}, col ${col})`;
     })
     .join("\n");
+
+  if (diags.length > limit) {
+    return `${formatted}\n\n... and ${diags.length - limit} more diagnostics (showing first ${limit})`;
+  }
+  return formatted;
 }
 
 // Is Expected Error - Returns true if the error is an expected condition
@@ -505,7 +511,7 @@ export default function (pi: ExtensionAPI) {
     try {
       // Run LSP diagnostics
       const result = await runDiagnostics(absolutePath);
-      const formatted = formatDiagnostics(result);
+      const formatted = formatDiagnostics(result, 10);
 
       // Only send a message if there are actual diagnostics
       if (formatted !== "(no diagnostics)") {