Tests: isolate HOME so user-global MCP config cannot leak into test runs #1682

MCP discovery reads ~/.claude.json and other home-level config from the real home directory, so tests fail on developer machines that have MCP servers configured.

Items

• test: httpapi-mcp status test is not hermetic against user-global MCP config #1024: httpapi-mcp status test expects only the fixture server; keep it as a regression case.
• test: MCP tests fail when the developer's ~/.claude.json has MCP servers (HOME is not sandboxed) #1386: MCP tests fail when the developer's ~/.claude.json lists MCP servers; all home-config discovery should honor the test home.

The linked issues hold the original reports and reproductions. Most are closed in favor of this tracker; any child with an open fix PR stays open until that PR lands.