semi implemented and features implemented save checkpoint

docs/features/unchecked/attestor/canonicalization-and-content-addressing.md

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+# Canonicalization and Content Addressing
+
+## Module
+Attestor
+
+## Status
+IMPLEMENTED
+
+## Description
+RFC 8785 JSON canonicalization, deterministic Merkle tree building, and content-addressed ID generation for all proof chain artifacts ensuring stable hashing.
+
+## Implementation Details
+- **RFC 8785 Canonicalizer**: `src/Attestor/__Libraries/StellaOps.Attestor.ProofChain/Json/Rfc8785JsonCanonicalizer.cs` -- implements `IJsonCanonicalizer`. Partials:
+  - `.DecimalPoint` -- decimal point handling per RFC 8785
+  - `.NumberSerialization` -- IEEE 754 number serialization
+  - `.StringNormalization` -- Unicode escape and string normalization
+  - `.WriteMethods` -- low-level write operations
+- **SBOM Canonicalizer**: `src/Attestor/__Libraries/StellaOps.Attestor.StandardPredicates/Canonicalization/SbomCanonicalizer.cs` (with `.Elements`) -- implements `ISbomCanonicalizer` for deterministic SBOM element ordering.
+- **Content-Addressed ID Generator**: `__Libraries/StellaOps.Attestor.ProofChain/Identifiers/ContentAddressedIdGenerator.cs` (with `.Graph`) -- `IContentAddressedIdGenerator` implementation. Generates SHA-256 content-addressed IDs.
+- **ID Types**: `ContentAddressedId.cs` (base), `GenericContentAddressedId.cs`, `ArtifactId.cs`, `EvidenceId.cs`, `ProofBundleId.cs`, `VexVerdictId.cs`, `ReasoningId.cs`, `SbomEntryId.cs`, `TrustAnchorId.cs`, `GraphRevisionId.cs`.
+- **SHA-256 Parser**: `Sha256IdParser.cs` -- parses `sha256:<hex>` formatted IDs.
+- **Proof Hashing**: `ProofHashing.cs` -- utility methods for proof chain hashing.
+- **Merkle Tree**: `Merkle/DeterministicMerkleTreeBuilder.cs` (with `.Helpers`, `.Proof`) -- deterministic tree construction.
+- **Tests**: `__Tests/StellaOps.Attestor.ProofChain.Tests/JsonCanonicalizerTests.cs`, `ContentAddressedIdTests.cs`, `ContentAddressedIdGeneratorTests.cs`, `MerkleTreeBuilderTests.cs`
+
+## E2E Test Plan
+- [ ] Canonicalize JSON with out-of-order keys and verify output has keys in lexicographic order per RFC 8785
+- [ ] Canonicalize JSON with Unicode escapes (e.g., `\u00e9`) and verify normalization to UTF-8
+- [ ] Canonicalize JSON with floating-point numbers and verify IEEE 754 serialization
+- [ ] Generate a content-addressed ID for a proof blob and verify it matches `sha256:<64-hex-chars>` format
+- [ ] Verify `Sha256IdParser` correctly parses valid IDs and rejects malformed ones
+- [ ] Canonicalize an SBOM document via `SbomCanonicalizer` and verify element ordering is deterministic
+- [ ] Build a Merkle tree from canonicalized artifacts and verify the root hash is stable across invocations
+- [ ] Generate `SbomEntryId` for identical SBOM component content and verify ID equality