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/web/server/lib/opencode/shared.js

@@ -2,7 +2,7 @@ import fs from 'fs';
 import path from 'path';
 import os from 'os';
 import yaml from 'yaml';
-import { parse as parseJsonc } from 'jsonc-parser';
+import { parse as parseJsonc, printParseErrorCode } from 'jsonc-parser';
 
 // ============== PATH CONSTANTS ==============
 
@@ -168,6 +168,31 @@ function getPrimaryUserConfigPath(userPaths) {
   return CONFIG_FILE;
 }
 
+const INVALID_JSONC = 'INVALID_JSONC';
+
+function isInvalidJsoncError(error) {
+  return Boolean(error && typeof error === 'object' && error.code === INVALID_JSONC);
+}
+
+function formatJsoncParseError(filePath, errors) {
+  const first = Array.isArray(errors) && 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}`;
+}
+
+function parseConfigObject(content, filePath) {
+  const errors = [];
+  const parsed = parseJsonc(content, errors, { allowTrailingComma: true });
+  if (errors.length > 0 || !parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
+    const error = new Error(formatJsoncParseError(filePath, errors));
+    error.code = INVALID_JSONC;
+    throw error;
+  }
+  return parsed;
+}
+
 function readConfigFile(filePath) {
   if (!filePath || !fs.existsSync(filePath)) {
     return {};
@@ -178,8 +203,13 @@ function readConfigFile(filePath) {
     if (!normalized) {
       return {};
     }
-    return parseJsonc(normalized, [], { allowTrailingComma: true });
+    // 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);
   } catch (error) {
+    if (isInvalidJsoncError(error)) {
+      throw error;
+    }
     console.error(`Failed to read config file: ${filePath}`, error);
     throw new Error('Failed to read OpenCode configuration');
   }
@@ -246,6 +276,12 @@ function getConfigForPath(layers, targetPath) {
 function writeConfig(config, filePath = CONFIG_FILE) {
   try {
     if (fs.existsSync(filePath)) {
+      // Defense in depth: never overwrite a file we cannot fully parse.
+      const existing = fs.readFileSync(filePath, 'utf8').trim();
+      if (existing) {
+        parseConfigObject(existing, filePath);
+      }
+
       const backupFile = `${filePath}.openchamber.backup`;
       fs.copyFileSync(filePath, backupFile);
       console.log(`Created config backup: ${backupFile}`);
@@ -255,6 +291,9 @@ function writeConfig(config, filePath = CONFIG_FILE) {
     fs.writeFileSync(filePath, JSON.stringify(config, null, 2), 'utf8');
     console.log(`Successfully wrote config file: ${filePath}`);
   } catch (error) {
+    if (isInvalidJsoncError(error)) {
+      throw error;
+    }
     console.error(`Failed to write config file: ${filePath}`, error);
     throw new Error('Failed to write OpenCode configuration');
   }