refactor(index): extract config loading and handlers to reduce file size

Reduce index.ts from 724 to 458 lines (37% reduction):
- Extract config loading to plugin-config.ts
- Extract ModelCacheState to plugin-state.ts
- Extract config handler to plugin-handlers/config-handler.ts

All 408 tests pass, TypeScript typecheck clean.

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/plugin-config.ts

@@ -0,0 +1,134 @@
+import * as fs from "fs";
+import * as path from "path";
+import { OhMyOpenCodeConfigSchema, type OhMyOpenCodeConfig } from "./config";
+import {
+  log,
+  deepMerge,
+  getUserConfigDir,
+  addConfigLoadError,
+  parseJsonc,
+  detectConfigFile,
+  migrateConfigFile,
+} from "./shared";
+
+export function loadConfigFromPath(
+  configPath: string,
+  ctx: unknown
+): OhMyOpenCodeConfig | null {
+  try {
+    if (fs.existsSync(configPath)) {
+      const content = fs.readFileSync(configPath, "utf-8");
+      const rawConfig = parseJsonc<Record<string, unknown>>(content);
+
+      migrateConfigFile(configPath, rawConfig);
+
+      const result = OhMyOpenCodeConfigSchema.safeParse(rawConfig);
+
+      if (!result.success) {
+        const errorMsg = result.error.issues
+          .map((i) => `${i.path.join(".")}: ${i.message}`)
+          .join(", ");
+        log(`Config validation error in ${configPath}:`, result.error.issues);
+        addConfigLoadError({
+          path: configPath,
+          error: `Validation error: ${errorMsg}`,
+        });
+        return null;
+      }
+
+      log(`Config loaded from ${configPath}`, { agents: result.data.agents });
+      return result.data;
+    }
+  } catch (err) {
+    const errorMsg = err instanceof Error ? err.message : String(err);
+    log(`Error loading config from ${configPath}:`, err);
+    addConfigLoadError({ path: configPath, error: errorMsg });
+  }
+  return null;
+}
+
+export function mergeConfigs(
+  base: OhMyOpenCodeConfig,
+  override: OhMyOpenCodeConfig
+): OhMyOpenCodeConfig {
+  return {
+    ...base,
+    ...override,
+    agents: deepMerge(base.agents, override.agents),
+    disabled_agents: [
+      ...new Set([
+        ...(base.disabled_agents ?? []),
+        ...(override.disabled_agents ?? []),
+      ]),
+    ],
+    disabled_mcps: [
+      ...new Set([
+        ...(base.disabled_mcps ?? []),
+        ...(override.disabled_mcps ?? []),
+      ]),
+    ],
+    disabled_hooks: [
+      ...new Set([
+        ...(base.disabled_hooks ?? []),
+        ...(override.disabled_hooks ?? []),
+      ]),
+    ],
+    disabled_commands: [
+      ...new Set([
+        ...(base.disabled_commands ?? []),
+        ...(override.disabled_commands ?? []),
+      ]),
+    ],
+    disabled_skills: [
+      ...new Set([
+        ...(base.disabled_skills ?? []),
+        ...(override.disabled_skills ?? []),
+      ]),
+    ],
+    claude_code: deepMerge(base.claude_code, override.claude_code),
+  };
+}
+
+export function loadPluginConfig(
+  directory: string,
+  ctx: unknown
+): OhMyOpenCodeConfig {
+  // User-level config path (OS-specific) - prefer .jsonc over .json
+  const userBasePath = path.join(
+    getUserConfigDir(),
+    "opencode",
+    "oh-my-opencode"
+  );
+  const userDetected = detectConfigFile(userBasePath);
+  const userConfigPath =
+    userDetected.format !== "none"
+      ? userDetected.path
+      : userBasePath + ".json";
+
+  // Project-level config path - prefer .jsonc over .json
+  const projectBasePath = path.join(directory, ".opencode", "oh-my-opencode");
+  const projectDetected = detectConfigFile(projectBasePath);
+  const projectConfigPath =
+    projectDetected.format !== "none"
+      ? projectDetected.path
+      : projectBasePath + ".json";
+
+  // Load user config first (base)
+  let config: OhMyOpenCodeConfig =
+    loadConfigFromPath(userConfigPath, ctx) ?? {};
+
+  // Override with project config
+  const projectConfig = loadConfigFromPath(projectConfigPath, ctx);
+  if (projectConfig) {
+    config = mergeConfigs(config, projectConfig);
+  }
+
+  log("Final merged config", {
+    agents: config.agents,
+    disabled_agents: config.disabled_agents,
+    disabled_mcps: config.disabled_mcps,
+    disabled_hooks: config.disabled_hooks,
+    claude_code: config.claude_code,
+  });
+  return config;
+}