fix(config): refuse partial JSONC parses that wipe opencode.jsonc

jsonc-parser was returning truncated trees (often only `$schema`) when
configs contained JSON5-style unquoted keys. Config mutations then backed
up and overwrote the full file with that stub. Check parse errors on read
and refuse to overwrite unparseable files on write in web and VS Code.

Fixes #2923

Co-authored-by: serkraser <serkraser@gmail.com>

packages/vscode/src/opencodeConfig.ts

@@ -2,7 +2,7 @@ import fs from 'node:fs';
 import path from 'node:path';
 import os from 'node:os';
 import yaml from 'yaml';
-import { parse as parseJsonc } from 'jsonc-parser';
+import { parse as parseJsonc, printParseErrorCode, type ParseError } from 'jsonc-parser';
 
 const OPENCODE_CONFIG_DIR = path.join(os.homedir(), '.config', 'opencode');
 const AGENT_DIR = path.join(OPENCODE_CONFIG_DIR, 'agents');
@@ -554,12 +554,33 @@ const getPrimaryUserConfigPath = (userPaths: string[]): string => {
   return CONFIG_FILE;
 };
 
+const INVALID_JSONC = 'INVALID_JSONC';
+
+const formatJsoncParseError = (filePath: string, errors: ParseError[]): string => {
+  const first = errors.length > 0 ? errors[0] : null;
+  const location = first && Number.isFinite(first.offset)
+    ? ` (${printParseErrorCode(first.error)} at offset ${first.offset})`
+    : '';
+  return `OpenCode configuration at ${filePath} contains invalid JSONC and cannot be loaded safely${location}`;
+};
+
+const parseConfigObject = (content: string, filePath: string): Record<string, unknown> => {
+  const errors: ParseError[] = [];
+  const parsed = parseJsonc(content, errors, { allowTrailingComma: true });
+  if (errors.length > 0 || !parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
+    throw codedError(formatJsoncParseError(filePath, errors), INVALID_JSONC);
+  }
+  return parsed as Record<string, unknown>;
+};
+
 const readConfigFile = (filePath?: string | null): Record<string, unknown> => {
   if (!filePath || !fs.existsSync(filePath)) return {};
   const content = fs.readFileSync(filePath, 'utf8');
   const normalized = content.trim();
   if (!normalized) return {};
-  return parseJsonc(normalized, [], { allowTrailingComma: true }) as Record<string, unknown>;
+  // Refuse partial jsonc-parser trees. Ignoring errors previously let mutations
+  // rewrite a truncated object (often only `$schema`) over the full config.
+  return parseConfigObject(normalized, filePath);
 };
 
 const isPlainObject = (value: unknown): value is Record<string, unknown> =>
@@ -695,6 +716,11 @@ const getConfigForPath = (layers: ReturnType<typeof readConfigLayers>, targetPat
 
 const writeConfig = (config: Record<string, unknown>, filePath: string = CONFIG_FILE) => {
   if (fs.existsSync(filePath)) {
+    // Defense in depth: never overwrite a file we cannot fully parse.
+    const existing = fs.readFileSync(filePath, 'utf8').trim();
+    if (existing) {
+      parseConfigObject(existing, filePath);
+    }
     const backupFile = `${filePath}.openchamber.backup`;
     try {
       fs.copyFileSync(filePath, backupFile);