docs: record the bit-level attempts and that run attrition is the real cost now

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

docs/re/BACKLOG.md

@@ -273,7 +273,18 @@ is what the autopilot needs in order to CHOOSE a target. One run in:
   single **bit** ORed into a word that also varies (the test needs an exact
   shared value), anything outside that window, and anything on entities
   `entities2` cannot see — it types by position *changing*, so stationary
-  objectives are invisible. A bit-level differential is the follow-on.
+  objectives are invisible. A bit-level differential is the follow-on. 🔎 **Built**
+  (`ob_bitflag.py`, 2026-08-24) and run three times with **no verification
+  yet**: one window was spent on a mission that had already ended in GAME OVER,
+  one hit the same dead mission, and the third had the counter at a different
+  address and then froze after a single filter. Sample A alone gives ~187
+  set-polarity + 33 clear-polarity candidates at counter 4, so the second
+  transition is the whole test.
+* ⚠️ **Attrition is now the dominant cost of every in-mission item.** Roughly
+  half the runs that reach flight end early — a freeze, or a GAME OVER when the
+  ACROPOLIS or the craft is lost — and a scan needs the run to survive **two**
+  counter transitions. `frozen.in_flight()` at least makes a dead run say so
+  immediately instead of waiting out its window.
 * 🔴 **The counter is not "hostiles left" either.** It held at `012` for fifteen
   minutes of live flight while the ADAN population fell 132 → 93.
 * ✅ **But it decrements when the player kills**: `12 → 11` with 411 `fire=1`