semi implemented and features implemented save checkpoint

docs/features/unchecked/binaryindex/symbol-source-connectors.md

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+# Symbol Source Connectors (Debuginfod, Buildinfo, Ddeb, SecDb)
+
+## Module
+BinaryIndex
+
+## Status
+IMPLEMENTED
+
+## Description
+Four symbol source connector implementations (Debuginfod, Debian Buildinfo, Ubuntu Ddeb, Alpine SecDb), each with plugin registration and configuration support.
+
+## Implementation Details
+- **Modules**: `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus/`, `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Alpine/`, `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Debian/`, `src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Rpm/`
+- **Key Classes**:
+  - **Alpine SecDb**: `AlpineCorpusConnector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Alpine/AlpineCorpusConnector.cs`) - connects to Alpine security database; `ApkBuildSecfixesExtractor` - extracts secfixes from APK build files
+  - **Debian Buildinfo**: `DebianCorpusConnector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Debian/DebianCorpusConnector.cs`) - connects to Debian buildinfo sources; `DebianMirrorPackageSource` - mirrors Debian repositories
+  - **RPM**: `RpmCorpusConnector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus.Rpm/RpmCorpusConnector.cs`) - connects to RPM repositories; `SrpmChangelogExtractor` - extracts changelogs from source RPMs
+  - **Library-specific**: `CurlCorpusConnector`, `GlibcCorpusConnector`, `OpenSslCorpusConnector`, `ZlibCorpusConnector` (`src/BinaryIndex/__Libraries/StellaOps.BinaryIndex.Corpus/Connectors/`)
+- **Interfaces**: `IBinaryCorpusConnector`, `ILibraryCorpusConnector`, `IAlpinePackageSource`, `IDebianPackageSource`, `IRpmPackageSource`
+- **Package Extractors**: `AlpinePackageExtractor`, `DebianPackageExtractor`, `RpmPackageExtractor` - extract binaries from packages using `IBinaryFeatureExtractor`
+
+## E2E Test Plan
+- [ ] Connect via `AlpineCorpusConnector` and verify secfixes data is extracted from APK builds
+- [ ] Connect via `DebianCorpusConnector` and verify buildinfo data is retrieved from Debian mirrors
+- [ ] Connect via `RpmCorpusConnector` and verify RPM changelog extraction works
+- [ ] Verify library-specific connectors (OpenSSL, glibc, curl, zlib) retrieve correct binary versions
+- [ ] Verify all connectors produce `CorpusSnapshot` with consistent snapshot IDs
+- [ ] Verify package extractors use `IBinaryFeatureExtractor` to extract identity features from packages