Add detached source lookup to results and errors

docs/config.md

@@ -172,6 +172,18 @@ the returned configuration or inspection records cannot alter ConfigKit's privat
 snapshot. ConfigKit performs no logging. `Result.WriteEffective` exposes only the
 frozen redacted projection.
 
+`Result.Source(id)` returns the detached record for an acquired source already
+listed by `Result.Sources()`. Source IDs are local to one load; empty and unknown
+IDs return false. This passive lookup uses retained evidence and does not reacquire
+the source, access the filesystem, or look up credentials. A source ID can be
+obtained from the source records or exact origin locations.
+
+`LoadError.Source(id)` performs the same lookup over the partial, already-sanitized
+inventory returned by `LoadError.Sources()`. It preserves the source evidence and
+placement available when loading failed, which may be incomplete; it does not
+promise a record for every attempted source. Nil or zero-valued errors and empty
+or unknown IDs return false.
+
 ### Completion and resource lifetime
 
 `Load` is synchronous and complete on return. Success means input assembly,