docs: open the "what does REMAINING OB count" item, with the freeze noted as the blocker in front of it

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

docs/re/BACKLOG.md

@@ -259,6 +259,31 @@ The follow-on that the autopilot actually needs is unchanged and untouched:
 ❔ what the counter counts, and whether an `OB`-badged entity carries a flag in
 its entity object.
 
+## What `REMAINING OB` counts — and an in-mission freeze in the way
+
+**2026-08-23.** The address is settled (above); *what it counts* is not, and it
+is what the autopilot needs in order to CHOOSE a target. One run in:
+
+* 🔴 **Not a live class head-count.** Counter 4 against 8 attackers / 7 friendly
+  Delta Sabers / 7 turrets / 1 player — no class matches, no pair sums to it.
+* ❔ **20 candidate per-entity flag offsets** exist (offsets where exactly 4 of
+  23 entities share a value) and have **never been put to the second test**,
+  because the guest froze before the counter could move.
+* 🔴 **An in-mission freeze**, intermittent: this run stopped advancing ~10 s
+  into flight — 724 s of identical `pilot.py` state, two screenshots six seconds
+  apart byte-identical — while `screen_id` said `flight`, the emulator burned
+  212 % CPU and every liveness check passed. `frozen.py` detects it in one call
+  now, and `ob_hunt.py`/`ob_flag.py` abort on it instead of waiting out a
+  timeout. **What causes it is untouched.**
+
+**First step:** re-run `ob_flag.py` on a run that is advancing — it aborts early
+now if it is not. Second step, if that comes back empty: `entities2.typed` only
+sees entities whose position *changes*, so a stationary objective is invisible to
+it, and the enumeration itself would need widening before a null result means
+anything.
+
+See [`mission-freeze-and-ob-flag.md`](mission-freeze-and-ob-flag.md).
+
 ## The declaration table is not a paint order on every screen
 
 **Found 2026-08-17**, building the Explorer's UI Screens browser on