Snapshot optimized solver and audit diagnostics before numerical experiments

DEFERRED_REMOVAL_REGISTRY.md

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+# Deferred Removal Registry
+
+This registry records migration-era code that may become removable after the
+physics-facing `StellarModel` and `StellarEquilibriumProblem` APIs have replaced
+all legacy construction paths. Nothing listed here is currently approved for
+removal, and no listed code was removed during the migration.
+
+## `mean_field::models::Model<...>`
+
+- Location: `libmeanfield/interface/models/specifications.cppm`
+- Current status: required compatibility storage
+- Current consumers: root-manifest tests and the implementation of
+  `mean_field::model::StellarModel`
+- Removal gate: migrate remaining direct consumers to the public
+  `mean_field::model::StellarModel` type, then move the canonical storage into
+  an implementation namespace
+- Evidence required before removal: no direct consumers found by repository
+  search and the complete specification/type-contract suite passes
+
+## Legacy structure-based `mean_field::models::StellarModel`
+
+- Location: `libmeanfield/interface/models/stellar_model.cppm`
+- Current status: retained legacy API, but no longer used by the authoritative
+  `StellarEquilibriumProblem` construction path
+- Current consumers: direct prepared-operator tests, experiments, and
+  heterogeneous runtime-model views. Its polytropic initial-seed method now
+  delegates to the physics-facing Lane-Emden seed generator.
+- Removal gate: numerical operators consume compiled specification
+  contributions directly, initial-seed generation has a physics-facing owner,
+  and deformation policies have migrated into the typed model
+- Evidence required before removal: legacy-adapter equivalence tests pass for
+  all supported formulations and repository search finds no direct consumers
+
+## `PolytropicStructure` as a mass-owning adapter
+
+- Location: `libmeanfield/interface/models/structure/polytropic.cppm`
+- Current status: compatibility adapter for remaining legacy API consumers; it
+  no longer owns Lane-Emden integration and is not constructed by
+  `StellarEquilibriumProblem`
+- Potentially obsolete responsibility: ownership of the fixed-total-mass
+  target, which now belongs to `FixedTotalMass`
+- Removal gate: migrate remaining callers to `seed::LaneEmden` and the typed
+  model. Lane-Emden generation is now separate from invariant ownership.
+- Evidence required before removal: initial-seed regression tests and
+  model-driven equilibrium equivalence tests pass
+
+## Legacy combined prepared operators
+
+- Locations:
+  `libmeanfield/interface/operators/prepared_fixed_angular_momentum_stellar_equilibrium.cppm`
+  and
+  `libmeanfield/interface/operators/prepared_central_density_stellar_equilibrium.cppm`
+- Current status: retained as migration-era source references, but removed from
+  the build graph and no longer re-exported by the public `mean_field` module
+- Physics-facing replacement:
+  `PreparedVariadicStellarEquilibriumOperator<Model>`, selected solely by
+  `StellarEquilibriumProblem<Model, Discretization>`
+- Reactivation gate: migrate the source snapshots to the model-driven manifest
+  constructor; they intentionally do not compile against the authoritative API
+- Removal gate: delete the source snapshots after the historical comparison
+  window closes
+- Evidence required before removal: the full variadic residual/Jacobian
+  equivalence suite and distributed tests pass without either partition being
+  imported by a user translation unit
+
+## Completed: typed equilibrium-problem adapter removal
+
+- Removed the former typed system's `NumericalModelAdapter`, its
+  `PolytropicStructure`, and the corresponding legacy model storage.
+- The typed problem now owns its compiled surface constraint and constructs the
+  prepared operator directly from specification-generated contributions.
+- Default radial deformation is compiled at the numerical equilibrium-problem
+  boundary rather than being smuggled through a legacy stellar model.
+
+## `StellarEquilibriumSystem` compatibility vocabulary
+
+- Location: `libmeanfield/interface/operators/stellar_equilibrium_system.cppm`
+- Current status: source-compatible aliases and factory forwarding to
+  `StellarEquilibriumProblem` and `equilibrium::discretize`
+- Removal gate: migrate remaining external consumers and provide a documented
+  deprecation interval
+- Evidence required before removal: repository search finds only the explicit
+  compatibility type-contract test
+
+## Root-oriented public aliases and accessors
+
+- Locations:
+  `libmeanfield/interface/operators/root_manifest.cppm`,
+  `libmeanfield/interface/operators/prepared_stellar_equilibrium.cppm`, and
+  `libmeanfield/interface/operators/prepared_central_density_stellar_equilibrium.cppm`
+- Current status: retained for source compatibility
+- Physics-facing replacements: `EquilibriumSystemManifest`,
+  `EquilibriumStateView`, `EquilibriumResidualView`, and
+  `StellarEquilibriumProblem::GetManifest()`
+- Removal gate: all solver and test consumers use equilibrium-system
+  terminology
+- Evidence required before removal: repository search finds no uses of the old
+  aliases/accessors and all manifest/type-contract tests pass
+
+## Conclusion for this phase
+
+No code examined during this migration is presently truly dead. Each candidate
+still has active consumers or carries a compatibility/lifetime responsibility.
+The entries above are therefore deferred migration candidates, not deletion
+recommendations.