D1072 — source_register provides the source template

Decision. The first source_register into a ledger journal writes templates/source.md when it is absent (built by kb.SourceTemplate from the server's own shape of a Source) and, only when the journal holds Source concepts only and every one of them already follows the template, sets templates: [source] and default_template: source on the map. Nothing that exists is overwritten or overridden; the response carries notes, and a setup failure is a warnings entry, never a refusal.

Why. The server knows the shape of a Source, yet the ledger started without a template and kb_review proposed one only after a few pages, from a vocabulary limited to what it had seen. The template is a visible KB artifact (D109) the operator can read and widen, not a bundled fallback resolved behind the KB's back. source_register is exempt from the write gate, so it must not introduce a finding by itself: declaring templates makes a map strict (D371, D907), hence the Source-only and already-conforming preconditions. It costs a write into the KB beyond the concept, in one commit.

Alternatives rejected. A bundled fallback template: invisible and not editable. Declaring the map unconditionally: a mixed journal or an older page would start failing template_missing / template_field_missing. Declaring default_template alone: UpdateMapContract refuses it unless the slug is also in templates, so both keys are set (the plan assumed templates stayed unset).

Consequences. A Source journal becomes strict once declared; the pages the tool writes conform by construction (timestamp is optional because it is omitted when the caller gives none, sections are open). The vocabulary lives in one place, kb.SourceIngestStatuses, pinned by a test.