Astro dev server silently moves to the next available port (4322, 4323...) when the default port 4321 is occupied by a stale process. No error is shown. Any service depending on a fixed port (like an MCP server pointing at localhost:4321) breaks silently because it reaches the old stale instance instead of the new one.

MCP server configured in ~/.claude/settings.json under mcpServers is silently ignored. The MCP tools never appear in the session toolset. No error is shown — the server simply does not load. Hooks referencing the MCP tools fire warnings but can never be satisfied because the tools do not exist.

When trying to screenshot, test, or automate interactions with a local HTML file via Playwright (including Playwright MCP), navigating to file:// URLs fails with a security error or the page loads blank. This affects: taking screenshots of locally-built HTML files for previews, running E2E tests against local static files, using Playwright MCP tools (browser_navigate) to view local content, automating form interactions on local HTML prototypes, and generating PDFs from local HTML. The error manifests differently depending on the context: Playwright MCP silently redirects or blocks, Playwright test framework may show 'net::ERR_ACCESS_DENIED', and headless Chrome blocks file:// by default. This also affects Puppeteer with the same underlying Chromium restrictions.