paper f2a: reuse-topology decomposition + mixture-sensitivity sweep

Full-trace analysis backing figure 2a on the real 2h cluster trace:

- f2a_reuse_topology_analyze.py: infinite-KV-cache (LRU) decomposition of
  prefix-cache reuse hits into intra-session vs cross-session, by most-recent
  prior holder of each content-addressed block.
- f2a_mixture_sweep.py: sensitivity of the intra/cross split to the
  single-turn session fraction (tests whether the 93%-intra sample vs 54.6%
  full-trace gap is session-mixture selection bias) -- keep all multi-turn
  sessions, downsample single-turn to each target fraction, reclassify.

Includes the result JSONs for both.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

paper/data/f2a_reuse_topology_result.json

@@ -0,0 +1,77 @@
+{
+  "trace": "051315-051317.jsonl",
+  "semantics": "LRU last-touched; reuse-hits only (new excluded from split)",
+  "n_requests": 2114220,
+  "n_sessions": 1307276,
+  "turn1_frac": 0.6183254344391785,
+  "block_size_tokens_eff": 508.1517503092776,
+  "total_input_tokens": 71116829368,
+  "total_block_occ": 139951952,
+  "distinct_blocks": 20650883,
+  "new_occ": 20650883,
+  "apc_ceiling": 0.8524430513123532,
+  "reuse_total": 119301069,
+  "reuse": {
+    "intra": 65166144,
+    "cross": 54134925
+  },
+  "reuse_frac": {
+    "intra": 0.5462326913432771,
+    "cross": 0.45376730865672293
+  },
+  "pop_labels": [
+    "1 (private)",
+    "2-9",
+    "10-99",
+    "100-999",
+    ">=1000"
+  ],
+  "pop_blocks": [
+    14581108,
+    5535433,
+    517069,
+    16153,
+    1120
+  ],
+  "pop_intra": [
+    44515497,
+    14288480,
+    5421050,
+    924419,
+    16698
+  ],
+  "pop_cross": [
+    0,
+    20230912,
+    13750153,
+    7689338,
+    12464522
+  ],
+  "gap_labels": [
+    "<1s",
+    "1-10s",
+    "10-60s",
+    "1-5min",
+    "5-30min",
+    "30-60min",
+    ">60min"
+  ],
+  "rec_intra": [
+    390952,
+    26060293,
+    31317556,
+    5877221,
+    1384772,
+    109673,
+    25677
+  ],
+  "rec_cross": [
+    13222875,
+    22254795,
+    11653445,
+    4965765,
+    1747487,
+    220816,
+    69742
+  ]
+}