docs(cpg): name the upstream issue for joern-parse --overlaysonly (joernio/joern#6283)

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

src/openultrasast/cpg/backend.py

@@ -616,7 +616,7 @@ class JoernBackend:
         CVE-2022-25148 on, one hour before the switch, from a `joern-parse` build. Task 5.13.
 
         `queries/overlay.sc` is that once: `importCpg`, `save`, and the saved graph replaces the raw one
-        under the same path. (`joern-parse --overlaysonly` is the obvious tool and is broken in 4.0.623.)
+        under the same path. (`joern-parse --overlaysonly` is the obvious tool and is broken in 4.0.623: joernio/joern#6283.)
         A failure here is logged and the raw graph kept, so the scan degrades to the old cost rather than
         losing its graph.
         """

src/openultrasast/cpg/queries/overlay.sc

@@ -10,7 +10,7 @@
 //
 // Measured after: the saved graph reloads in 8 s where the raw one took 64 s, and the request that had
 // timed out at 520 s answered in 39 s including the JVM. `joern-parse --overlaysonly` would be the
-// obvious tool and is broken in 4.0.623 (NullPointerException in a post-processing step that needs the
+// obvious tool and is broken in 4.0.623 -- joernio/joern#6283 (NullPointerException in a post-processing step that needs the
 // frontend it did not run), so the once is this script.
 //
 // `save` writes to `workspace/<cpg name>/cpg.bin` under the working directory; the driver moves that over