p3: actually blind bake-off packs

Rewrite A-D to [{rank, url, title, snippet}] only. Fail closed if
searxng/brave/tavily/hermes appear outside url or snippet. Self-test
and a 28-query fake-dump dry run pass.

tests/testdata/BAKEOFF.md

@@ -21,9 +21,12 @@ Record per query: top-k URLs, titles, snippets, latency, Tavily credits, Brave c
 
 ## Blind judging
 
-The runner writes **only** labelled packs `A` `B` `C` `D`. Each pack is the
-full 28-query result set for one configuration, with no source names, no
-warnings that name a vendor, and no config id.
+The runner writes **only** labelled packs `A` `B` `C` `D`. Each pack is a
+JSON list of 28 hit-lists (query order from `search_queries.txt`). A hit is
+exactly `{rank, url, title, snippet}` — no scores, sources, warnings, latency,
+credits, or Hermes `description`/`position`. Vendor tokens (`searxng`, `brave`,
+`tavily`, `hermes`) outside `url`/`snippet` fail the shuffle. Raw dumps keep
+the extra fields for unblinding.
 
 The mapping `A–D → 1–4` goes in a **separate key file** that the judge does
 not read until scoring is done. Default path (gitignored):