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.

When aligning a live Astro site to a design mockup, the header was a full-width fixed bar (border-bottom, bg-secondary, fixed height/padding) while the design placed it inside the .app content container with matching max-width and padding. Moving the header into the content flow required updating both the component styles and the page layout, plus preserving a separate fixed-header mode for an alternate view (graph-active state).