semi implemented and features implemented save checkpoint

docs/features/unchecked/attestor/sbom-delta-system.md

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+# SBOM Delta System (Component Diffing, Predicates, Signed Evidence)
+
+## Module
+Attestor
+
+## Status
+IMPLEMENTED
+
+## Description
+Complete SBOM delta system: component-level diff tracking (added/removed/version changes), formal JSON schema for delta predicates, structured taxonomy, DSSE-signed delta evidence objects, and dedicated UI visualization. SBOM diffs are first-class signed evidence objects with attestation service producing DSSE-signed delta predicates.
+
+## Implementation Details
+- **SBOM Delta Predicate**: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/Predicates/SbomDeltaPredicate.cs` -- predicate containing the full SBOM delta (added, removed, changed components).
+- **SBOM Delta Component**: `Predicates/SbomDeltaComponent.cs` -- individual component in the delta (name, version, purl, change type).
+- **SBOM Delta Summary**: `Predicates/SbomDeltaSummary.cs` -- summary statistics (added count, removed count, version change count).
+- **SBOM Delta Version Change**: `Predicates/SbomDeltaVersionChange.cs` -- version change detail (from_version, to_version, component).
+- **SBOM Reference**: `Predicates/SbomReference.cs` -- reference to the baseline and current SBOM documents.
+- **Predicate Schema Validator**: `Json/PredicateSchemaValidator.DeltaValidators.cs` -- schema validation for SBOM delta predicates.
+- **DSSE Signing**: `Signing/ProofChainSigner.cs` -- signs SBOM delta predicates into DSSE envelopes.
+- **Content-Addressed ID**: `Identifiers/ContentAddressedIdGenerator.cs` -- generates deterministic IDs for delta predicates.
+- **Change Trace**: `ChangeTrace/ChangeTraceAttestationService.cs` -- creates change trace attestations that can include SBOM delta data.
+- **Tests**: `__Tests/StellaOps.Attestor.ProofChain.Tests/SbomDeltaTests.cs`
+
+## E2E Test Plan
+- [ ] Create an `SbomDeltaPredicate` with 3 added components, 2 removed, and 1 version change; verify all entries are captured
+- [ ] Verify `SbomDeltaComponent` correctly identifies component name, version, purl, and change type (Added/Removed/Modified)
+- [ ] Verify `SbomDeltaSummary` counts: 3 added, 2 removed, 1 version changed
+- [ ] Verify `SbomDeltaVersionChange` captures from_version="1.0" to_version="2.0" for a specific component
+- [ ] Sign the SBOM delta predicate into a DSSE envelope and verify the signature
+- [ ] Validate the delta predicate via `PredicateSchemaValidator.DeltaValidators` and verify schema compliance
+- [ ] Generate a content-addressed ID for the delta and verify determinism (same delta = same ID)
+- [ ] Create an SBOM delta between two `SbomReference` documents and verify cross-reference integrity