Add Technical_Decomp_Diff

Technical_Decomp_Diff.md

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+## enroll/diff.py
+
+### BundleRef (dataclass)
+
+Purpose: represents a prepared harvest bundle that diff can read from.
+
+#### Fields:
+
+`dir`: Path: directory containing at least `state.json` and (optionally) artifacts/
+
+`tempdir`: Optional[tempfile.TemporaryDirectory]: Set only when the bundle had to be extracted/decrypted into a temporary directory. Lets the caller clean up later
+
+#### Property:
+
+`state_path` -> Path: dir / "state.json"
+
+#### Lifecycle / where it’s used:
+
+Constructed by _bundle_from_input(path, sops_mode=...) which accepts:
+
+- bundle directory
+- direct state.json path
+- .tar.gz/.tgz
+- .sops encrypted tarball (or when --sops is enabled)
+
+`compare_harvests()` uses `ExitStack` to ensure any `tempdir.cleanup()` happens.
+
+#### Key design detail:
+
+This class is the bridge between "user supplied something" and “we have a real directory with files”.