This branch develops target recoverability when only constrained records are available. It formalizes when a target can be reconstructed exactly from observation fibers and when observation structure is insufficient.
The key results combine fiber/factorization exactness with restricted-linear kernel/row-space criteria and threshold behavior in supported families. This is the main bridge from theorem statements to measurable recoverability diagnostics.
Canonical references are docs/theorem-candidates/constrained-observation-theorems.md, docs/theorem-candidates/pvrt-theorem-spine.md, and docs/impossibility-results/constrained-observation-no-go.md.
The branch is intentionally scoped to declared families; it does not claim universal observability classification.