fix(mcp): user config overrides Claude Code .mcp.json with collision warning

Previously, Claude Code's .mcp.json would silently override OpenCode user
config when MCP server names collided. This was unexpected behavior since
users expect their explicit OpenCode configuration to take precedence.

Changes:
1. Swapped merge order: Claude Code .mcp.json is now merged BEFORE user
   config, so user config wins on collision
2. Added warning log when user config overrides a Claude Code MCP server:
   'warning: MCP server X from user config overrides Claude Code .mcp.json'
3. Added comprehensive tests for collision scenarios

Fixes #2946

src/plugin-handlers/mcp-config-handler-collision.test.ts

@@ -0,0 +1,132 @@
+/// <reference types="bun-types" />
+
+import { describe, test, expect, spyOn, beforeEach, afterEach } from "bun:test"
+import type { OhMyOpenCodeConfig } from "../config"
+
+import * as mcpLoader from "../features/claude-code-mcp-loader"
+import * as mcpModule from "../mcp"
+import * as shared from "../shared"
+
+let loadMcpConfigsSpy: ReturnType<typeof spyOn>
+let createBuiltinMcpsSpy: ReturnType<typeof spyOn>
+let logSpy: ReturnType<typeof spyOn>
+
+beforeEach(() => {
+  loadMcpConfigsSpy = spyOn(mcpLoader, "loadMcpConfigs").mockResolvedValue({
+    servers: {},
+    loadedServers: [],
+  })
+  createBuiltinMcpsSpy = spyOn(mcpModule, "createBuiltinMcps").mockReturnValue({})
+  logSpy = spyOn(shared, "log").mockImplementation(() => {})
+})
+
+afterEach(() => {
+  loadMcpConfigsSpy.mockRestore()
+  createBuiltinMcpsSpy.mockRestore()
+  logSpy.mockRestore()
+})
+
+function createPluginConfig(overrides: Partial<OhMyOpenCodeConfig> = {}): OhMyOpenCodeConfig {
+  return {
+    disabled_mcps: [],
+    ...overrides,
+  } as OhMyOpenCodeConfig
+}
+
+const EMPTY_PLUGIN_COMPONENTS = {
+  commands: {},
+  skills: {},
+  agents: {},
+  mcpServers: {},
+  hooksConfigs: [],
+  plugins: [],
+  errors: [],
+}
+
+describe("applyMcpConfig collision handling", () => {
+  test("merges without collision when names are unique", async () => {
+    //#given
+    const userMcp = {
+      userServer: { type: "remote", url: "https://user.example.com", enabled: true },
+    }
+
+    loadMcpConfigsSpy.mockResolvedValue({
+      servers: {
+        claudeServer: { type: "remote", url: "https://claude.example.com", enabled: true },
+      },
+      loadedServers: [],
+    })
+
+    const config: Record<string, unknown> = { mcp: userMcp }
+    const pluginConfig = createPluginConfig()
+
+    //#when
+    const { applyMcpConfig } = await import("./mcp-config-handler")
+    await applyMcpConfig({ config, pluginConfig, pluginComponents: EMPTY_PLUGIN_COMPONENTS })
+
+    //#then
+    const mergedMcp = config.mcp as Record<string, Record<string, unknown>>
+    expect(mergedMcp).toHaveProperty("userServer")
+    expect(mergedMcp).toHaveProperty("claudeServer")
+    expect(mergedMcp.userServer.enabled).toBe(true)
+    expect(mergedMcp.claudeServer.enabled).toBe(true)
+    expect(logSpy).not.toHaveBeenCalledWith(expect.stringContaining("overrides Claude Code"))
+  })
+
+  test("user config wins on collision with Claude Code and logs warning", async () => {
+    //#given
+    const userMcp = {
+      sharedServer: { type: "remote", url: "https://user.example.com", enabled: true },
+    }
+
+    loadMcpConfigsSpy.mockResolvedValue({
+      servers: {
+        sharedServer: { type: "remote", url: "https://claude.example.com", enabled: true },
+      },
+      loadedServers: [],
+    })
+
+    const config: Record<string, unknown> = { mcp: userMcp }
+    const pluginConfig = createPluginConfig()
+
+    //#when
+    const { applyMcpConfig } = await import("./mcp-config-handler")
+    await applyMcpConfig({ config, pluginConfig, pluginComponents: EMPTY_PLUGIN_COMPONENTS })
+
+    //#then
+    const mergedMcp = config.mcp as Record<string, Record<string, unknown>>
+    expect(mergedMcp.sharedServer.url).toBe("https://user.example.com")
+    expect(logSpy).toHaveBeenCalledWith(
+      'warning: MCP server "sharedServer" from user config overrides Claude Code .mcp.json'
+    )
+  })
+
+  test("preserves enabled:false from user config after collision with Claude Code", async () => {
+    //#given
+    const userMcp = {
+      sharedServer: { type: "remote", url: "https://user.example.com", enabled: false },
+    }
+
+    loadMcpConfigsSpy.mockResolvedValue({
+      servers: {
+        sharedServer: { type: "remote", url: "https://claude.example.com", enabled: true },
+      },
+      loadedServers: [],
+    })
+
+    const config: Record<string, unknown> = { mcp: userMcp }
+    const pluginConfig = createPluginConfig()
+
+    //#when
+    const { applyMcpConfig } = await import("./mcp-config-handler")
+    await applyMcpConfig({ config, pluginConfig, pluginComponents: EMPTY_PLUGIN_COMPONENTS })
+
+    //#then
+    const mergedMcp = config.mcp as Record<string, Record<string, unknown>>
+    expect(mergedMcp.sharedServer.enabled).toBe(false)
+    expect(mergedMcp.sharedServer.url).toBe("https://user.example.com")
+    expect(logSpy).toHaveBeenCalledWith(
+      'warning: MCP server "sharedServer" from user config overrides Claude Code .mcp.json'
+    )
+  })
+})

src/plugin-handlers/mcp-config-handler.test.ts

@@ -164,4 +164,5 @@ describe("applyMcpConfig", () => {
     const mergedMcp = config.mcp as Record<string, Record<string, unknown>>
     expect(mergedMcp).not.toHaveProperty("plugin:custom")
   })
+
 })

src/plugin-handlers/mcp-config-handler.ts

@@ -2,6 +2,7 @@ import type { OhMyOpenCodeConfig } from "../config";
 import { loadMcpConfigs } from "../features/claude-code-mcp-loader";
 import { createBuiltinMcps } from "../mcp";
 import type { PluginComponents } from "./plugin-components-loader";
+import { log } from "../shared";
 
 type McpEntry = Record<string, unknown>;
 
@@ -38,10 +39,18 @@ export async function applyMcpConfig(params: {
     ? await loadMcpConfigs(disabledMcps)
     : { servers: {} };
 
+  if (userMcp) {
+    for (const name of Object.keys(userMcp)) {
+      if (name in mcpResult.servers) {
+        log(`warning: MCP server "${name}" from user config overrides Claude Code .mcp.json`);
+      }
+    }
+  }
+
   const merged = {
     ...createBuiltinMcps(disabledMcps, params.pluginConfig),
-    ...(userMcp ?? {}),
     ...mcpResult.servers,
+    ...(userMcp ?? {}),
     ...params.pluginComponents.mcpServers,
   } as Record<string, McpEntry>;