The instructions the node hands every MCP client at connect.

Home for this text rather than the mount itself, because the mount's job is wiring and this is prose with its own obligations. Two of them are worth stating, since neither is visible from the string:

The text must stay inside a 2KB budget — Claude Code truncates server instructions at 2048 bytes, a cliff rather than a warning, and a truncated paragraph is worse than an absent one. YmerNode.McpTest gates the size.

It must name ymer as the other half of one product. A client that reaches this node learns nothing about ymer from the wire surface — two servers look like two products unless one of them says otherwise. The same duty runs the other way from ymer's own instructions. There is no shared source between the two texts and there cannot be one: the repositories are standalone, so the pair is kept in step by convention and by review, and drift is a review finding rather than a build failure.