semi implemented and features implemented save checkpoint

docs/features/unchecked/binaryindex/binary-symbol-table-diff-engine.md

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+# Binary Symbol Table Diff Engine
+
+## Module
+BinaryIndex
+
+## Status
+IMPLEMENTED
+
+## Description
+Symbol table comparison between binary versions tracking exported/imported symbol changes, version map diffs, GOT/PLT table modifications, and ABI compatibility assessment. Produces content-addressed diff IDs for deterministic reporting.
+
+## Implementation Details
+- **Modules**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/`
+- **Key Classes**:
+  - `SymbolTableDiffAnalyzer` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/SymbolTableDiffAnalyzer.cs`) - computes diffs between symbol tables with `ComputeDiffAsync` and `AssessAbiCompatibility`
+  - `SymbolTableDiff` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/SymbolTableDiff.cs`) - diff result model with added/removed/changed symbols
+  - `VersionMapDiff` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/VersionMapDiff.cs`) - tracks changes in ELF version maps
+  - `AbiCompatibility` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/AbiCompatibility.cs`) - ABI compatibility assessment (FullyCompatible, Warnings, Incompatible)
+  - `DynamicLinkingDiff` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/DynamicLinkingDiff.cs`) - GOT/PLT table modification tracking
+  - `NameDemangler` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/NameDemangler.cs`) - C++ symbol name demangling
+- **Interfaces**: `ISymbolTableDiffAnalyzer` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/SymbolDiff/ISymbolTableDiffAnalyzer.cs`)
+- **Registration**: `SymbolDiffServiceExtensions` for DI setup
+
+## E2E Test Plan
+- [ ] Compute diff between two ELF binaries with known symbol changes and verify added/removed symbols are correctly identified
+- [ ] Verify `AssessAbiCompatibility` returns `FullyCompatible` when only symbols are added
+- [ ] Verify `AssessAbiCompatibility` returns `Incompatible` when exported symbols are removed
+- [ ] Verify version map diff detection for ELF version script changes
+- [ ] Verify C++ symbol demangling produces human-readable names via `NameDemangler`
+- [ ] Verify content-addressed diff IDs are deterministic for identical inputs