# ADR 0001: Typed source coverage and supersession

Status: Accepted, 2026-09-13.

Source snapshots declare `full`, `partition`, or `delta` coverage. Partitions use
stable disjoint coordinates. Deltas name one exact base, a consecutive sequence,
and every directly superseded object. The build rejects ambiguous frontiers,
cycles, missing bases, cross-source links, overlaps, and mixed legacy/typed active
sets. Older objects and facts remain available for audit.

Free-form scope strings were insufficient to distinguish replacement from
composition. Explicit coverage makes selection reproducible and prevents a
partial object from silently replacing unrelated source data.

## Rejected alternatives

Selecting the newest retrieval time repeats the v0.3 ambiguity and lets clock
skew choose authority. Treating every object as additive retains deleted facts.
Inferring overlap from source URLs or file names is source-specific and unsafe.

## Compatibility

V1 manifests remain isolated by exact provider and scope. A typed object may
replace legacy evidence only by naming its exact manifest ID in `supersedes`.
Readers that do not understand v2 must reject it. See the source-manifest and
coverage contracts in [FORMATS.md](../FORMATS.md).