MCP warm-degradation messages carry their tool prefix

The ambient MCP instructions promise an agent that "a paged result’s first line summarises the whole set, including the total before paging", and ServerInstructionsTest.everyPagedToolLeadsWithTheUnpagedTotal pins that claim across the six tools that page through McpWire.page. The warm-degradation arms of docs.search and catalog.search break the surrounding pattern: WarmState.degradationMessage returns a bare notice carrying neither a tool prefix nor a count, so an agent that has learned to read the first line gets a sentence about index warming with no coordinate telling it which call produced it. catalog.search’s cold arm (GraphitronMcpServer` composes the same message directly) and DocsSearchTool.degraded are the two call sites, plus CatalogSearchIndex’s `SearchOutcome.Degraded.

Prefixing those messages with the tool name (and, where one exists, a count) makes the first-line convention uniform across the whole result surface rather than true only of the paged tools, and would let the summary-line pin widen from the six paged tools to every list-shaped tool. Small main-code change; the reason it is a separate item is that it is wire-visible and has its own argument about what a degraded result should say, which is why the instruction-routing work deliberately scoped its convention to the paged tools instead of widening the message format in passing.

Filed at the In Review → Done gate of the MCP instruction-routing item, whose Out of scope section committed to filing it separately.