save checkpoint: save features

docs/features/checked/binaryindex/patchdiffengine.md

@@ -0,0 +1,31 @@
+# PatchDiffEngine (Binary Pre/Post Patch Comparison for Fix Verification)
+
+## Module
+BinaryIndex
+
+## Status
+IMPLEMENTED
+
+## Description
+Compares pre-patch and post-patch binaries at multiple levels (BasicBlock, CFG, StringRefs, Semantic/KSG fingerprints) to determine if a vulnerability has been remediated. Produces structured verification results with confidence scores based on match depth. Core verification logic for the Golden Set Diff Layer.
+
+## Implementation Details
+- **Modules**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/`, `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/`
+- **Key Classes**:
+  - `PatchDiffEngine` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/PatchDiffEngine.cs`) - core engine comparing pre/post binaries using `ISignatureMatcher`, `IFunctionFingerprintExtractor`, and `IFunctionDiffer`; produces `PatchDiffResult` with confidence scores
+  - `PatchDiffEngine` (builders) (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Builders/PatchDiffEngine.cs`) - builder-level diff engine
+  - `FunctionDiffer` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/FunctionDiffer.cs`) - function-level comparison with semantic analysis, call-graph edge diffing, and string reference comparison
+  - `FunctionRenameDetector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/FunctionRenameDetector.cs`) - detects renamed functions between versions
+  - `VerdictCalculator` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/VerdictCalculator.cs`) - computes fix verification verdict from diff results
+- **Models**: `PatchDiffResult`, `PatchDiffModels`, `DiffEvidenceModels`, `DiffOptions` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/Models/`)
+- **Storage**: `IDiffResultStore`, `InMemoryDiffResultStore` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Diff/Storage/`)
+- **Source**: SPRINT_20260110_012_004_BINDEX_golden_set_diff_verify.md
+
+## E2E Test Plan
+- [ ] Submit pre-patch and post-patch binaries for a known CVE fix and verify the diff result shows patch applied
+- [ ] Verify multi-level comparison: BasicBlock, CFG, StringRefs, and semantic fingerprints all contribute to confidence
+- [ ] Verify `FunctionDiffer` with `IncludeSemanticAnalysis=true` computes semantic similarity
+- [ ] Verify `FunctionRenameDetector` handles renamed functions between versions
+- [ ] Verify `VerdictCalculator` produces correct verdict (Fixed, Vulnerable, Unknown) based on diff evidence
+- [ ] Verify `NoPatchDetected` result is returned when binaries are identical
+- [ ] Verify diff results are persistable via `IDiffResultStore` with content-addressed IDs