D853 — Types the server keys on are known to unknown_type

Decision. internal/kb/keyedtype.go is the one list of the concept types the server keys on: Source and Contradiction (matched exactly), Service and digest (matched in any case, D158, D322). unknown_type skips such a type when no declared type matches it case-insensitively and the page's map is not strict. In a strict map that does not list it the warning stays, with the fix "add it to the map's concept_types (map_update), or move the page".

Why. source_register writes a Source page, and the tools find the ledger by that type (D278). In a KB with a type palette the page got unknown_type, and neither suggested fix worked: changing the type takes the page out of the ledger, and template_proposal never fires below three pages. The palette stays what the KB declares, so lint.Inactive (D357) and the message are unchanged. The cost is a second source of truth for "known", the exemption, kept next to the predicates the match sites already use.

Alternatives rejected. - Keyed types in the palette: it would activate unknown_type on KBs with no vocabulary (D357), list undeclared types in the message, turn the case fix of source into a ledger entry and of contradiction into a gate blocker, and leave lint silent in strict maps where validate errors. - A built-in Source template: changes the template catalogue and concept_new, and covers one type of four. - source_register or map_create writing a template or concept_types: per-KB state as a side effect, against D278's explicit map creation. - Documenting lint_accept: a finding whose only resolution is dismissal is noise.

Consequences. A new type the server keys on is added to keyedtype.go and matched through its predicate, never with a literal. A misspelled keyed type (source) stays an info finding with no fix and sits silently outside its ledger; a dedicated finding is a follow-up, as is template_proposal skipping keyed types (#832).