Add custom MCP server management for Studio Code

[chubes4]

Summary

• Adds studio code mcp commands to manage user-defined MCP servers for Studio Code.
• Stores config in Studio's internal config directory via getStudioCodeMcpConfigPath() using the standard mcpServers shape.
• Supports stdio, http, and sse server definitions while reserving Studio's built-in studio MCP server name.
• Wires configured custom MCP tools into the current PI runtime as mcp__<server>__<tool> custom tools.

Behavior

Users can configure generic MCP servers without Studio hardcoding a single provider. This covers Figma and other MCP servers through the same path:

studio code mcp add wporg --command node --arg /path/to/mcp-context-wporg/dist/index.js
studio code mcp add figma --type http --url https://mcp.figma.com/mcp
studio code mcp add git --command npx --arg -y --arg @modelcontextprotocol/server-git
studio code mcp list
studio code mcp remove wporg

At agent startup, Studio Code reads the config, connects to each custom MCP server, lists its tools, and registers them with PI alongside Studio's built-in tools. A Figma server tool such as get_design_context is exposed to the agent as mcp__figma__get_design_context.

The command validates transport-specific requirements and reports clean CLI errors for invalid definitions instead of surfacing raw stack traces.

Tests

• npx vitest run apps/cli/ai/tests/mcp-config.test.ts apps/cli/commands/ai/tests/mcp.test.ts apps/cli/ai/tests/pi-runtime.test.ts --config apps/cli/vitest.config.ts
• npx tsc -p apps/cli/tsconfig.json --noEmit
• npx eslint apps/cli/ai/mcp-config.ts apps/cli/ai/mcp-client-tools.ts apps/cli/ai/runtimes/pi/index.ts apps/cli/commands/ai/mcp.ts apps/cli/ai/tests/mcp-config.test.ts apps/cli/commands/ai/tests/mcp.test.ts apps/cli/ai/tests/pi-runtime.test.ts apps/cli/index.ts

Closes #3279.

AI assistance

• AI assistance: Yes
• Tool(s): GPT-5.5 via OpenCode
• Used for: Rebasing the PR, adapting the custom MCP path to the PI runtime, writing tests, running validation, and updating this PR description. Chris reviewed the behavior and owns the final submission.

[wpmobilebot]

📊 Performance Test Results

Comparing e3b4dc7 vs trunk

app-size

Metric	trunk	e3b4dc7	Diff	Change
App Size (Mac)	2341.17 MB	2341.18 MB	+0.01 MB	⚪ 0.0%

site-editor

Metric	trunk	e3b4dc7	Diff	Change
load	1067 ms	1074 ms	+7 ms	⚪ 0.0%

site-startup

Metric	trunk	e3b4dc7	Diff	Change
siteCreation	6488 ms	6496 ms	+8 ms	⚪ 0.0%
siteStartup	6983 ms	6478 ms	505 ms	🟢 -7.2%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[chubes4]

@youknowriad if we add support for any custom MCP server, then we can easily test it with Figma. What do you think, instead of hardcoding Figma MCP like #2781?

cc @Poliuk @mtias

[youknowriad]

I'm personally ok with custom MCP support, the only thing I would note though is that we should avoid surfacing this extra complexity (configuring MCPs) by default to users, it should some advanced flow.

[youknowriad]

But I think Figma should be first party support ideally. Figma to WordPress is a common flow.

[wojtekn]

Marking as draft until conflicts are fixed.