Sylpheed/docs/re/structures/mission-objective-counter.md

REMAINING OB — the mission's own objective counter, in RAM

Status: ✅ CONFIRMED for one Stage 02 run: a big-endian u32 whose value is exactly the HUD's REMAINING OB, verified across two transitions it was not selected by. 🟡 the address itself is from one run — cross-run stability is untested. ❔ what it counts, and whether objective-marked entities carry a flag.

Why it matters

autopilot-memory-driven.md ranks this its problem #2: a pilot that flies well but ignores the objective cannot finish a mission. Its 300 s run took no damage, killed one fighter, and watched REMAINING OB rise from 004 to 011 as waves spawned. Reading the counter is what turns "shoot whatever is nearest" into "shoot what closes the mission".

The find

Guest VA 0xbdb59668, big-endian u32, in a Stage 02 run on the upstream baseline.

time	RAM 0xbdb59668	HUD
selected on	18 → 24	018 → 024
t+40 s	24	024
t+75 s	23	023
t+110 s	22	022
t+145 s	22	022
t+180 s	22	022

The two middle rows are the ones that matter: the candidate was filtered on the 18→24 transition, and it then tracked 24→23→22 on its own.

Method, and the two traps in it

tools/re-capture/ob_scan.py. Scan one snapshot for the current value, then filter that candidate set against live /dev/shm/xenia_memory_* at the next distinct value. Only the first pass needs the 4.8 GB copy.

🔴 Filter on a change, not a repeat. The first attempt scanned at 19, filtered at 19 again, then at 18 — and left zero survivors. The value moves between the memory copy and the screenshot that reads it, so "still 19" is not reliable. Scanning 18 and filtering on 24 gave exactly one candidate on the first try.

🔴 Verify across a transition you did not select on. An earlier differential over 19→18 also gave exactly one candidate, 0xbc22e83c — and it was wrong: read live it held 26 while the HUD showed 017. It was an unrelated counter that happened to step 19→18 in the same window. One matching transition is not evidence; the same offset tracking a later, unselected change is.

What is not settled

• 🟡 Cross-run stability. 0xbdb59668 is from a single run. The corpus's other runtime finds are re-scanned per run, so the durable result here is the method, not the number. Testing whether the address repeats costs one boot.
• ❔ What it counts. It rose 18 → 24 while waves spawned and fell as things died, so it is objective targets remaining, not kills. Whether every OB-badged entity is one of them, and whether that badge is a flag in the entity object, is the natural follow-on — and it is what the pilot actually needs to choose targets rather than merely know how many are left.
• ❔ Whether the same address holds for other stages.

🔴 2026-08-23 — cross-run stability: REFUTED

0xbdb59668 does not repeat. A second Stage 02 run on the same baseline (rebuilt per ../dynamic-re-state-restore.md) reads 0 at that address for the whole mission while the HUD counts up:

HUD	RAM 0xbdb59668
004 (t+18 s, flight entry)	0
008	0
012 (held for ~5 min)	0

A second, independent run of the same mission repeats it: at TIME 01:08.96 with the HUD on REMAINING OB 004, the word is again 0 (../captures/stage02-inflight-run2-ob-address-zero.png).

Read three times back-to-back at 004 — all zero — and ±64 bytes around it are zero too. The page is not a sparse hole (SEEK_DATA at the offset returns the offset itself; the next hole is 5 MB later), so this is an allocated, zero-filled word, not an unmapped read. The number was a per-run artefact, as this file already suspected; the method is the durable part, and every future session must re-scan.

And re-finding it in the new run failed too — recorded because both failures are instructive. Two candidates were produced and both were killed by the "verify across a transition you did not select on" rule:

• 0xbc2377dc — held 12 at selection, then went 12 → 18 while the HUD stayed 012, and was reading 3 two minutes later at HUD 012.
• 0xbd295b04 — read 12 once, then 0, 21, 54, 46, 4 in the next 50 s. Noise.

🔴 A correction to this file's own method note. The trap is not that the scan is slow: ob_scan.py scan over the live /dev/shm image takes 0.9 s (9 555 hits at value 12; the SEEK_DATA extent walk skips the sparse 4.6 GB). The real trap is that REMAINING OB climbs fast early in Stage 02 — 004 → 008 → 012 inside about four minutes as waves spawn — so a scan is only valid if the HUD is confirmed to hold the same value immediately before and after it. The earlier 4 ∩ 8 intersection here came back with no survivor for exactly that reason: the value-8 scan was actually taken at 12.

What blocked finishing it: with the pilot in RETIRE (hull 340/1500) nothing was killing objectives, and the counter sat at 012 for five minutes — no transition to filter on. A run that intends to find this address needs a pilot that is still engaging, which is the same constraint ../autopilot-memory-driven.md records.

Unchanged and still open: what the counter counts, and whether an OB-badged entity carries a flag in its entity object. Nothing in this pass touched that.

🟡 2026-08-23 (later) — a third run, a HUD-clean scan, and one candidate that is very hard to explain away

With the launcher repaired the scan could finally be run the way the method asks. HUD confirmed 004 immediately before and after the scan (0.9 s), so the 39 596-entry candidate set is valid at that value; then filtered when the HUD was confirmed at 012.

step	HUD	candidates
scan	004 (confirmed both sides)	39 596
filter	012 (confirmed)	17
later sample	— (see caveat)	7 still 12

The survivor of interest is 0xbdb49668 — the run-1 address 0xbdb59668 minus exactly 0x10000, at the identical page offset 0x9668.

That is not a cheap coincidence, and it was checked rather than admired. Of all 39 596 words holding 4 at scan time, exactly 2 sit at page offset 0x9668; one of those two is in the 17, and it is this one. A survivor landing there by chance is a ~5 × 10⁻⁵ event. The reading it suggests — the counter lives at a fixed offset inside an allocation whose base moves by whole 64 KB pages between runs — is a testable claim, not a story: a third scan should again land on …9668.

Why this is 🟡 and not ✅, stated plainly. The corpus's own rule is that a candidate is believable once it tracks a transition it was not selected on, against the HUD. This one has not done that yet:

• The "later sample" that killed 10 of the 17 was taken during the GAME OVER flash — the escorted ACROPOLIS was lost at ~13 min — so the HUD counter was not on screen. The ten that moved are genuinely refuted; the seven that did not move are merely unrefuted, which is a much weaker thing, and the counter may simply be frozen once the mission ends.
• Between the filter and the mission end, REMAINING OB sat at 012 for about ten minutes: pilot.py spent the window in EVADE/RETIRE at hull 822/1500 and killed no objectives, so there was no transition to use.

The one experiment that settles it: a run where the pilot is still engaging, scanning and filtering as above, then watching 0xbdb4·9668-equivalent across a HUD-verified change. The blocker is the pilot's survival, not the method — and the same run would answer whether the page offset repeats, which is the stronger result of the two.