docs: enforce benchmark disk cleanup

Author: metaphorics

AGENTS.md

@@ -1,7 +1,16 @@
 # AGENTS.md
 
 - Before debugging a recurring issue or designing in an already-touched area,
-  search `docs/solutions/` and `CONCEPTS.md` for existing decisions and terms.
+  search `docs/solutions/` and `CONCEPTS.md` for existing decisions and terms;
+  otherwise work can repeat settled failures or contradict project knowledge.
 - Before adding or changing durable project knowledge, update any overlapping
   `docs/solutions/` learning and reconcile each affected project-specific term in
   `CONCEPTS.md`; otherwise diagnoses and shared vocabulary drift independently.
+- During benchmark campaigns, retain one canonical corpus and at most one disposable
+  run fixture. Before every corpus build, clone, or run, declare its worst-case
+  additional disk footprint, reserve threshold, and free-space check cadence; refuse
+  to start unless free space covers both the footprint and reserve. During long runs,
+  recheck at that cadence and stop the run and delete its disposable fixture if free
+  space reaches the reserve. Record compact results and delete the disposable fixture
+  before starting the next run, because accumulated benchmark copies have exhausted
+  the workstation's home dataset.