domain.yml

Each branch (a repo or project; library::branch_for names it) can register its facet vocabulary in REMATCH_ROOT/branches/<branch>/domain.yml. Outcome records use these keys in their facets (SPEC §Session outcome records). Cross-domain transfer reads them (rematch transfer suggest, scope::transfer).

domain: <dotted subject path>   # prefix-seekable: quant.options, repo.payments, 3d.animation
facets: [<key>, <key>, ...]     # structural facet keys of this branch

domain (optional): the dotted subject.domain prefix this branch’s outcomes use. It is also the branch’s work domain (DESIGN §6 “Domain”): a session in the branch takes it unless policy.json declares one for its remote (which wins), and a transfer apply copy into the branch takes it as its trigger’s domain. Lowercase dotted segments of [a-z0-9_-]; run rematch lake migrate after changing it to re-decide recorded sessions.
facets: the structural keys. Order does not matter; keys are compared exactly after trimming.

Transfer rule. transfer suggest lists a kept lesson tagged invariant from branch A for branch B when A’s and B’s facet keys share at least two keys (MIN_OVERLAP = 2) and B has no entry with the same name, a transfers_from link to the lesson, or near-duplicate text. If a branch has no domain.yml, or the file lists no facets, its keys are the distinct facet keys of its outcome records in the ledger (outcome_facets joined to outcomes.branch). transfer apply <lesson> --branch <b> stages a provisional copy in B with lint transfer: true, which blocks domain lessons and kind: fact entries. Workspace facts/ are dropped from the copy.

Examples

Quant research (branches/quant/domain.yml):

domain: quant.options
facets: [mechanism, universe, horizon, data_snapshot]

Application repo (branches/payments/domain.yml):

domain: repo.payments
facets: [module, change_type, test_scope]

3D production (branches/exercise-rigs/domain.yml):

domain: 3d.animation
facets: [rig, exercise, bake]

These three share no keys, so none of them receives the others’ lessons. A second quant branch with facets: [mechanism, horizon, strike] overlaps quant on mechanism and horizon (two keys), so kept invariant lessons from quant are suggested for it.