fix: harden DGR-001 performance contract evidence

.scratch/distributed-gguf-runtime/evidence/DGR-001/known-unrelated-failure.md

@@ -0,0 +1,32 @@
+# Observed pre-existing intermittent tracker race
+
+This file records an earlier unrelated timing observation; it is **not** the
+final DGR-001 verification result.
+
+Test:
+
+```text
+tests/test_tracker_routing.py::test_tracker_dashboard_can_cancel_inflight_proxy
+```
+
+One earlier full-suite run produced:
+
+```text
+1 failed, 745 passed, 13 skipped
+```
+
+A five-run isolated retry matrix reproduced the same rate on both branches:
+
+```text
+DGR-001 branch: 4/5 passed, 1/5 failed
+clean d904c40:  4/5 passed, 1/5 failed
+```
+
+The final full-suite run on the exact hardened DGR-001 state completed green:
+
+```text
+749 passed, 13 skipped in 251.42s
+```
+
+The earlier race was therefore timing-sensitive, pre-existing, and unrelated
+to the DGR-001 benchmark/contract files.