libra layer

libra layer implements Lore's local-overlay primitive (lore.md 2.4): a named, purely-local overlay of files materialized onto the working tree on explicit command that never enters a commit. It is the Phase-2 landable half of the §3.5 composition pair (its versioned sibling link is deferred to the §3.4 RFC); the §3.5 red line forbids a default auto-compose model, not this opt-in, explicit-command overlay.

Compatibility

• Level: intentionally-different — a Libra-only extension with no Git equivalent (Appendix A 无直接等价).

Design

A layer is (name, source local dir, priority, enabled). State lives in two SQLite side-tables (layer, layer_path) owned solely by internal::layer::LayerStore — never serialized into any object. Two invariants:

1. Never-enters-commit — enforced at two chokepoints: materialized paths are un-negatably excluded from the ignore engine (status/add . skip them), AND the add staging path hard-refuses any layer-owned path even under --force (which bypasses ignore). Staging one is LBR-LAYER-001.
2. Never-clobbers — a destination that collides with a tracked (index or HEAD) path is refused at apply time (LBR-LAYER-001, fail-closed); unapply/remove skip user-edited overlay files (content-hash mismatch).

Precedence on a same-destination collision between two enabled layers: higher priority wins, ties broken by name (last-writer-wins in stack order).

Examples

libra layer add scratch --source ./overlays/scratch   # register a local overlay
libra layer add ci --source ./ci --priority 10        # higher priority wins collisions
libra layer list                                      # show registered layers
libra layer apply                                     # materialize enabled overlays
libra layer status                                    # show materialized paths
libra layer unapply --layer scratch                   # remove one layer's files (keep edits)
libra layer remove scratch                            # unregister (unapplies first)

Deferred (not in v1)

Auto-materialization on checkout/switch/merge/clone (the §4.1 bypass surface — v1 is explicit-command only); versioned composition (link/subtree, §3.4-RFC-gated); remote/object-DB sources; overriding a tracked path (refused, never silently shadowed).