RS-12 opening session — the bulk floor is a silent L072 URC drop, not RF

LifeTrac-v25/DESIGN-CONTROLLER/TODO.md

@@ -2254,6 +2254,27 @@ Two consequences for what is worth doing next:
   ARTIFACT (a fold scan peaks at ~the mean inter-arrival with no clock
   present) and is retracted — the shuffled-interval null that catches it
   is now part of the tool.
+- [ ] **RS-12 — the clustered bulk loss floor (campaign opened 2026-08-16,
+  issue #107). ⚠️ WORDING SUPERSEDED (review catch, PR #108): the
+  "NEVER-DEMODULATED" phrasing below reflects the opening desk finding
+  and was overturned by the final mechanism — the radio DOES demodulate
+  the penultimate (full ToA at TX, rx_ok counts it); its URC is then
+  silently overwritten when the short final fragment rides fire-on-
+  TX_DONE 42 ms behind it. Mechanism + validated fix (NoParkLast):
+  bench-evidence/RS_12_bulk_floor_2026-08-16 §7 and
+  RS_12_noparklast_ab_2026-08-17. Loss floor now 1.5%.** With the interferers escaped (902.5 MHz), the remaining
+  ~3.3 % is the RS-11.4 clustered process. **Opening desk finding: the
+  penultimate losses are NEVER-DEMODULATED, not corrupted** — at 902.5,
+  corrupt captures with readable frag headers are ~uniform across indices
+  (idx-11 = 9 % ≈ 1/13) while attributed losses concentrate at idx-11
+  (35 %). Combined with the RS-11.5 exonerations (TX FIFO readback clean,
+  receiver-side by role swap, power-independent) the target is: a
+  base-board receiver-deafness mechanism, phase-locked to the
+  second-to-last fragment, invisible to the crc_dump instrument. Plan in
+  #107: n=2 @ 902.5 → train-length sweep @ 902.5 → stats-probe deltas
+  (incl. the never-read tx_done_early counter) → software-only
+  activity-modulation legs (ethernet flood on the gigabit-marginal base
+  cable, USB, CPU) → hands only after the coupling path is named.
 - [ ] **RS-11.7 Operator spectrum survey in web_ui (proposed 2026-08-16).**
   Turn the channel-survey diagnostic into a field feature: a
   maintenance-mode button that pauses the RX daemon, sweeps 902–928 MHz

LifeTrac-v25/DESIGN-CONTROLLER/base_station/image_rx_daemon.py

@@ -220,6 +220,16 @@ def _env_float(name: str, default: float, lo: "float | None" = None,
 # convergence soak actually measured, kept as a bench A/B control.
 ALIGNED_PUMP_ENABLE = os.environ.get("LIFETRAC_ALIGNED_PUMP", "1") != "0"
 
+# RS-12 (2026-08-17): per-fragment arrival logging. One INFO line per data
+# fragment carrying the FIRMWARE microsecond RX timestamp, so the silent
+# L072 URC drop's timing shape can be read without a firmware flash: in a
+# train missing idx N-2, the fw_us gap between idx N-3 and idx N-1 says
+# whether the lost fragment's slot passed on schedule (pure emission loss),
+# was compressed (TX timing anomaly), or was followed by a stall (main-loop
+# blockage). ~2300 lines per 300 s leg at the bench rate — diagnostic only.
+LOG_FRAG_ARRIVALS = os.environ.get(
+    "LIFETRAC_LOG_FRAG_ARRIVALS", "0") == "1"
+
 
 class KeyframeRequester:
     """Rate-limited req_keyframe on reassembly failure. Publishes to the
@@ -1223,6 +1233,11 @@ def _rx_worker(self) -> None:
                             self._gap_samples.append(
                                 (d, len(data), self._last_gap_class))
 
+                if LOG_FRAG_ARRIVALS and frag_idx is not None:
+                    LOG.info("frag_arrival: seq=%d idx=%d total=%d fw_us=%s "
+                             "len=%d", frag_seq, frag_idx, frag_total,
+                             parsed.get("timestamp_us"), len(data))
+
                 saw_rx = True
                 with self._lock:
                     self.stats.rx_frames_seen += 1

LifeTrac-v25/DESIGN-CONTROLLER/bench-evidence/RS_11_6_channel_survey_2026-08-17/RESULTS.md

@@ -0,0 +1,100 @@
+# Day-2 survey (post-outage) — the interferer HOPS; a pinned channel is perishable
+
+SHA `6d248b63`. Trigger: a thunderstorm/mains outage overnight
+2026-08-16→17. Neither carrier rebooted (uptime 21:45 / 22:34, counters
+continuous), so this is a pure RF-environment change.
+
+Transcript: [`survey_base_day2.jsonl`](survey_base_day2.jsonl).
+Tools: `channel_survey_sniff.py`, `tools/survey_compare.py` (new).
+
+## 1. What the outage did to the band
+
+Identical sweep to 2026-08-16 (902–928 MHz, 500 kHz steps, 30 s dwell):
+
+| | 2026-08-16 | 2026-08-17 |
+|---|---:|---:|
+| hot channels | 46 / 53 | 43 / 53 |
+| zero-hot legal centers | 5 | 8 |
+
+**11 of 53 channels (21 %) flipped state overnight**, and the flip was
+catastrophic for the pin we had chosen:
+
+| channel | 2026-08-16 | 2026-08-17 |
+|---|---|---|
+| **902.5 — the pinned escape** | clean, −94 | **HOT, −44** |
+| 905.5 | clean, −86 | **HOT, −43** |
+| 907.0 | clean, −77 | **HOT, −43** |
+| 925.5 | clean, −94 | **HOT, −44** |
+| 927.5 | clean, −75 | clean, −94 |
+| 909.0 | HOT, −43 | clean, −94 |
+| 918.0 / 918.5 / 921.0 / 924.0 | HOT, −42…−53 | clean, −91…−94 |
+
+**Four of the five channels that were clean yesterday are hot today.**
+
+### Correction to the RS-11.6 record
+
+Two earlier readings are superseded:
+
+1. **"Standing recommendation: bench legs run `-ForceFrfHz 902500000`"**
+   (leg-3 RESULTS §3.2) — withdrawn. That channel is now among the worst.
+   `-ForceFrfHz` is a **per-session parameter chosen from a same-day
+   survey**, never a config constant.
+2. **"Device A is wideband or front-end leakage; carrier unlocalised"**
+   (leg-3 RESULTS §1) — wrong branch. The device is a **frequency
+   hopper**: yesterday's "−43 dBm on essentially every channel" was one
+   emitter observed across a 24-minute sweep, and the outage restarted it
+   into a different channel sequence. This restores the original
+   utility-meter/AMI hypothesis that leg 2 had talked itself out of.
+
+Also worth recording: an intermediate claim made during this session —
+"the emitter is gone" — was made off a single 120 s sniff at 915 MHz and
+was **wrong**; targeted sweeps immediately found it alive at −42…−46 dBm
+on 922–925 with clean ~7.0 s intervals. One channel is never evidence
+about a hopper.
+
+## 2. Today's pick, and a stability alternative
+
+`survey_compare.py` ranks zero-hot legal centers by quietest peak:
+
+```
+RECOMMENDED: -ForceFrfHz 909000000   (909.0 MHz, hot=0, max=-94 dBm)
+runners-up:  918.0, 924.0, 927.5 (all hot=0, max -94)
+```
+
+**927.5 MHz was the only channel clean on BOTH days** (−75 → −94). If
+run-to-run comparability matters more than today's absolute quietest, it
+is the better long-run pin — two days is a thin basis, but it is the only
+stability signal available and worth accumulating.
+
+## 3. Re-baseline at 909.0 (leg G) — and RS-12 is untouched by any of this
+
+Standard 300 s leg, counter-bracketed
+(`../RS_12_bulk_floor_2026-08-16/stats_pre_G.txt` / `stats_post_G.txt`):
+
+| metric | leg G @ 909.0 (day 2) | leg D @ 902.5 (day 1) |
+|---|---:|---:|
+| raw loss | 6.8 % | 8.2 % |
+| firmware drop (Δrx_ok − URCs) | **78** | 88 |
+| penultimate lock | **35 %** | 28 % |
+| crc closure | 94 vs 91 | 126 vs 126 |
+| identity residue | 8 | 9 |
+
+The RS-12 mechanism reproduces on a completely different, freshly-clean
+channel: the penultimate lock is intact at 35 % and ~78 demodulated
+frames per leg still vanish inside the L072. **The firmware race is
+channel-independent**, as the counter separation always implied — the
+day-1 conclusions stand without re-work.
+
+## 4. Operational consequences
+
+1. **Survey before any measurement campaign.** Not hygiene — correctness.
+   Had we trusted yesterday's pin, leg G would have run on a −44 dBm
+   channel and shown a large "regression" that would have been hunted in
+   firmware. 28 minutes unattended prevents that.
+2. **RS-11.7 (operator survey in web_ui) is promoted** from
+   nice-to-have to the practical prerequisite for field measurement. Its
+   v0 (survey + recommend, manual apply) is exactly the workflow used
+   here, and `survey_compare.py` already implements the recommendation
+   logic the button needs.
+3. Record `force_frf_hz` with every citation of a run — it is now a
+   varying parameter (already in `params.txt`).

LifeTrac-v25/DESIGN-CONTROLLER/bench-evidence/RS_11_6_channel_survey_2026-08-17/survey_base_day2.jsonl

@@ -0,0 +1,132 @@
+SURVEY_META {"start_hz": 902000000, "stop_hz": 928000000, "step_hz": 500000, "dwell_s": 30.0, "ts_start": 1786979701.1183116}
+
+Initializing regulatory profile 2 on co-processor...
+
+  FHSS mask: single channel 0 (0100000000000000)
+
+CFG_SET_REQ(FHSS_CHANNEL_MASK) OK: 07000800
+
+CFG_SET_REQ(ANTENNA_GAIN_DBI) OK: 15000100
+
+CFG_SET_REQ(HW_CEILING_DBM) OK: 16000100
+
+  FHSS seed: (0,0) legacy shared permutation [set LIFETRAC_FHSS_FARM_ID / LIFETRAC_FHSS_LINK_ID to separate pairs]
+
+CFG_SET_REQ(FHSS_FARM_ID) OK: 17000800
+
+CFG_SET_REQ(FHSS_NODE_ID) OK: 18000800
+
+CFG_SET_REQ(REG_PROFILE=2) OK: 14000100
+
+  forcing FRF -> 915.000 MHz (raw=0xE4C000 -> Msb=0xE4 Mid=0xC0 Lsb=0x00)
+
+  FRF readback: 0xE4C000 = 915.000 MHz (OK)
+
+SURVEY_CH {"freq_hz": 902000000, "n": 457, "hot": 0, "max_dbm": -94, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 902500000, "n": 456, "hot": 4, "max_dbm": -44, "hot_ts": [1786979739.099, 1786979745.667, 1786979751.279, 1786979762.275]}
+
+SURVEY_CH {"freq_hz": 903000000, "n": 457, "hot": 1, "max_dbm": -43, "hot_ts": [1786979778.282]}
+
+SURVEY_CH {"freq_hz": 903500000, "n": 456, "hot": 2, "max_dbm": -43, "hot_ts": [1786979800.667, 1786979812.198]}
+
+SURVEY_CH {"freq_hz": 904000000, "n": 456, "hot": 1, "max_dbm": -43, "hot_ts": [1786979843.182]}
+
+SURVEY_CH {"freq_hz": 904500000, "n": 456, "hot": 1, "max_dbm": -43, "hot_ts": [1786979875.092]}
+
+SURVEY_CH {"freq_hz": 905000000, "n": 456, "hot": 3, "max_dbm": -45, "hot_ts": [1786979884.148, 1786979892.704, 1786979905.211]}
+
+SURVEY_CH {"freq_hz": 905500000, "n": 456, "hot": 1, "max_dbm": -43, "hot_ts": [1786979916.164]}
+
+SURVEY_CH {"freq_hz": 906000000, "n": 456, "hot": 2, "max_dbm": -45, "hot_ts": [1786979948.452, 1786979966.195]}
+
+SURVEY_CH {"freq_hz": 906500000, "n": 455, "hot": 1, "max_dbm": -42, "hot_ts": [1786979999.179]}
+
+SURVEY_CH {"freq_hz": 907000000, "n": 456, "hot": 1, "max_dbm": -43, "hot_ts": [1786980015.629]}
+
+SURVEY_CH {"freq_hz": 907500000, "n": 455, "hot": 2, "max_dbm": -33, "hot_ts": [1786980040.172, 1786980055.148]}
+
+SURVEY_CH {"freq_hz": 908000000, "n": 456, "hot": 3, "max_dbm": -42, "hot_ts": [1786980068.239, 1786980075.227, 1786980082.209]}
+
+SURVEY_CH {"freq_hz": 908500000, "n": 455, "hot": 0, "max_dbm": -82, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 909000000, "n": 456, "hot": 0, "max_dbm": -94, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 909500000, "n": 455, "hot": 3, "max_dbm": -42, "hot_ts": [1786980157.138, 1786980171.123, 1786980178.176]}
+
+SURVEY_CH {"freq_hz": 910000000, "n": 455, "hot": 3, "max_dbm": -40, "hot_ts": [1786980192.056, 1786980199.114, 1786980213.051]}
+
+SURVEY_CH {"freq_hz": 910500000, "n": 455, "hot": 3, "max_dbm": -41, "hot_ts": [1786980219.163, 1786980233.232, 1786980240.24]}
+
+SURVEY_CH {"freq_hz": 911000000, "n": 456, "hot": 4, "max_dbm": -41, "hot_ts": [1786980247.135, 1786980254.184, 1786980261.111, 1786980275.416]}
+
+SURVEY_CH {"freq_hz": 911500000, "n": 455, "hot": 2, "max_dbm": -41, "hot_ts": [1786980280.118, 1786980287.128]}
+
+SURVEY_CH {"freq_hz": 912000000, "n": 456, "hot": 2, "max_dbm": -42, "hot_ts": [1786980312.179, 1786980333.268]}
+
+SURVEY_CH {"freq_hz": 912500000, "n": 455, "hot": 1, "max_dbm": -43, "hot_ts": [1786980351.045]}
+
+SURVEY_CH {"freq_hz": 913000000, "n": 455, "hot": 4, "max_dbm": -40, "hot_ts": [1786980372.25, 1786980380.108, 1786980386.438, 1786980394.095]}
+
+SURVEY_CH {"freq_hz": 913500000, "n": 455, "hot": 1, "max_dbm": -43, "hot_ts": [1786980401.19]}
+
+SURVEY_CH {"freq_hz": 914000000, "n": 455, "hot": 2, "max_dbm": -40, "hot_ts": [1786980440.399, 1786980455.052]}
+
+SURVEY_CH {"freq_hz": 914500000, "n": 455, "hot": 2, "max_dbm": -40, "hot_ts": [1786980471.082, 1786980485.268]}
+
+SURVEY_CH {"freq_hz": 915000000, "n": 455, "hot": 2, "max_dbm": -40, "hot_ts": [1786980499.1, 1786980513.108]}
+
+SURVEY_CH {"freq_hz": 915500000, "n": 454, "hot": 2, "max_dbm": -40, "hot_ts": [1786980522.187, 1786980536.218]}
+
+SURVEY_CH {"freq_hz": 916000000, "n": 455, "hot": 1, "max_dbm": -41, "hot_ts": [1786980551.402]}
+
+SURVEY_CH {"freq_hz": 916500000, "n": 454, "hot": 1, "max_dbm": -40, "hot_ts": [1786980605.236]}
+
+SURVEY_CH {"freq_hz": 917000000, "n": 454, "hot": 1, "max_dbm": -40, "hot_ts": [1786980632.41]}
+
+SURVEY_CH {"freq_hz": 917500000, "n": 454, "hot": 2, "max_dbm": -40, "hot_ts": [1786980647.159, 1786980654.158]}
+
+SURVEY_CH {"freq_hz": 918000000, "n": 455, "hot": 0, "max_dbm": -94, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 918500000, "n": 454, "hot": 0, "max_dbm": -93, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 919000000, "n": 454, "hot": 3, "max_dbm": -40, "hot_ts": [1786980731.23, 1786980738.242, 1786980760.123]}
+
+SURVEY_CH {"freq_hz": 919500000, "n": 454, "hot": 1, "max_dbm": -40, "hot_ts": [1786980780.166]}
+
+SURVEY_CH {"freq_hz": 920000000, "n": 454, "hot": 2, "max_dbm": -41, "hot_ts": [1786980812.214, 1786980818.428]}
+
+SURVEY_CH {"freq_hz": 920500000, "n": 454, "hot": 3, "max_dbm": -41, "hot_ts": [1786980833.423, 1786980840.169, 1786980847.173]}
+
+SURVEY_CH {"freq_hz": 921000000, "n": 454, "hot": 0, "max_dbm": -91, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 921500000, "n": 454, "hot": 2, "max_dbm": -42, "hot_ts": [1786980889.258, 1786980910.677]}
+
+SURVEY_CH {"freq_hz": 922000000, "n": 454, "hot": 0, "max_dbm": -79, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 922500000, "n": 453, "hot": 4, "max_dbm": -35, "hot_ts": [1786980950.038, 1786980956.393, 1786980964.049, 1786980971.06]}
+
+SURVEY_CH {"freq_hz": 923000000, "n": 454, "hot": 3, "max_dbm": -42, "hot_ts": [1786980988.092, 1786980995.174, 1786981002.125]}
+
+SURVEY_CH {"freq_hz": 923500000, "n": 454, "hot": 3, "max_dbm": -43, "hot_ts": [1786981008.13, 1786981022.172, 1786981029.063]}
+
+SURVEY_CH {"freq_hz": 924000000, "n": 454, "hot": 0, "max_dbm": -94, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 924500000, "n": 455, "hot": 3, "max_dbm": -43, "hot_ts": [1786981065.064, 1786981072.048, 1786981086.05]}
+
+SURVEY_CH {"freq_hz": 925000000, "n": 454, "hot": 1, "max_dbm": -44, "hot_ts": [1786981108.177]}
+
+SURVEY_CH {"freq_hz": 925500000, "n": 455, "hot": 1, "max_dbm": -44, "hot_ts": [1786981136.042]}
+
+SURVEY_CH {"freq_hz": 926000000, "n": 456, "hot": 3, "max_dbm": -45, "hot_ts": [1786981158.06, 1786981176.039, 1786981182.11]}
+
+SURVEY_CH {"freq_hz": 926500000, "n": 453, "hot": 3, "max_dbm": -44, "hot_ts": [1786981187.198, 1786981193.417, 1786981205.2]}
+
+SURVEY_CH {"freq_hz": 927000000, "n": 454, "hot": 2, "max_dbm": -46, "hot_ts": [1786981224.041, 1786981238.603]}
+
+SURVEY_CH {"freq_hz": 927500000, "n": 453, "hot": 0, "max_dbm": -94, "hot_ts": []}
+
+SURVEY_CH {"freq_hz": 928000000, "n": 455, "hot": 0, "max_dbm": -100, "hot_ts": []}
+
+SURVEY_SUMMARY {"hot_channels": [{"freq_hz": 902500000, "hot": 4, "max_dbm": -44}, {"freq_hz": 903000000, "hot": 1, "max_dbm": -43}, {"freq_hz": 903500000, "hot": 2, "max_dbm": -43}, {"freq_hz": 904000000, "hot": 1, "max_dbm": -43}, {"freq_hz": 904500000, "hot": 1, "max_dbm": -43}, {"freq_hz": 905000000, "hot": 3, "max_dbm": -45}, {"freq_hz": 905500000, "hot": 1, "max_dbm": -43}, {"freq_hz": 906000000, "hot": 2, "max_dbm": -45}, {"freq_hz": 906500000, "hot": 1, "max_dbm": -42}, {"freq_hz": 907000000, "hot": 1, "max_dbm": -43}, {"freq_hz": 907500000, "hot": 2, "max_dbm": -33}, {"freq_hz": 908000000, "hot": 3, "max_dbm": -42}, {"freq_hz": 909500000, "hot": 3, "max_dbm": -42}, {"freq_hz": 910000000, "hot": 3, "max_dbm": -40}, {"freq_hz": 910500000, "hot": 3, "max_dbm": -41}, {"freq_hz": 911000000, "hot": 4, "max_dbm": -41}, {"freq_hz": 911500000, "hot": 2, "max_dbm": -41}, {"freq_hz": 912000000, "hot": 2, "max_dbm": -42}, {"freq_hz": 912500000, "hot": 1, "max_dbm": -43}, {"freq_hz": 913000000, "hot": 4, "max_dbm": -40}, {"freq_hz": 913500000, "hot": 1, "max_dbm": -43}, {"freq_hz": 914000000, "hot": 2, "max_dbm": -40}, {"freq_hz": 914500000, "hot": 2, "max_dbm": -40}, {"freq_hz": 915000000, "hot": 2, "max_dbm": -40}, {"freq_hz": 915500000, "hot": 2, "max_dbm": -40}, {"freq_hz": 916000000, "hot": 1, "max_dbm": -41}, {"freq_hz": 916500000, "hot": 1, "max_dbm": -40}, {"freq_hz": 917000000, "hot": 1, "max_dbm": -40}, {"freq_hz": 917500000, "hot": 2, "max_dbm": -40}, {"freq_hz": 919000000, "hot": 3, "max_dbm": -40}, {"freq_hz": 919500000, "hot": 1, "max_dbm": -40}, {"freq_hz": 920000000, "hot": 2, "max_dbm": -41}, {"freq_hz": 920500000, "hot": 3, "max_dbm": -41}, {"freq_hz": 921500000, "hot": 2, "max_dbm": -42}, {"freq_hz": 922500000, "hot": 4, "max_dbm": -35}, {"freq_hz": 923000000, "hot": 3, "max_dbm": -42}, {"freq_hz": 923500000, "hot": 3, "max_dbm": -43}, {"freq_hz": 924500000, "hot": 3, "max_dbm": -43}, {"freq_hz": 925000000, "hot": 1, "max_dbm": -44}, {"freq_hz": 925500000, "hot": 1, "max_dbm": -44}, {"freq_hz": 926000000, "hot": 3, "max_dbm": -45}, {"freq_hz": 926500000, "hot": 3, "max_dbm": -44}, {"freq_hz": 927000000, "hot": 2, "max_dbm": -46}]}
+

LifeTrac-v25/DESIGN-CONTROLLER/bench-evidence/RS_11_6_channel_survey_2026-08-17b/RESULTS.md

@@ -0,0 +1,52 @@
+# Third band survey — 927.5 MHz is the stability pick (3/3 clean)
+
+SHA at sweep: `8ef0aa5d`. Trigger: possible second mains blink (both
+carriers again survived on continuous uptime — this is a pure RF check).
+Transcript: [`survey_base_day2b.jsonl`](survey_base_day2b.jsonl).
+Analysis: `tools/survey_compare.py` (now with `--history` stability mode).
+
+## 1. The band reshuffled again — in ~4.5 hours this time
+
+10 of 53 channels flipped vs the morning survey (19 %), including:
+
+- **909.0 — the morning's pick and the depth-A/B channel — went −94 → −41**
+  (confirming the mid-A/B contamination the pre/post checks caught)
+- 918.0 went −94 → −40; 921.0 went −91 → −41
+- **924.0 lit up at −30 dBm — device B's signature level**, its first
+  reappearance at that strength since the day-1 survey localized it
+
+Flip rates are now ~20 % per survey interval at both ~14 h and ~4.5 h
+spacings, so the reshuffle cadence is faster than daily and may not need
+a power event at all. Either way the operational rule is unchanged and
+now triply confirmed: **a channel pick is valid for hours, not days.**
+
+## 2. The stability ranking — one channel stands alone
+
+Across all three surveys (`--history` mode):
+
+```
+927.5 MHz   clean 3/3   worst max −75 dBm   <== clean in every survey
+(every other channel: clean in at most 1 of 3)
+```
+
+927.5 is also today's absolute quietest (−96 dBm). **Standing bench
+recommendation: `-ForceFrfHz 927500000`**, held not because any pin is
+durable but because it is the only channel with a perfect record — and
+still subject to the same-day check before any measurement leg
+(`hunt_sniff.ps1`-style spot check or the sweep).
+
+Plausible physics for why the top edge stays clean: 927.5+250 kHz grazes
+the 928 MHz band edge, which hopping devices typically back away from to
+keep their occupied bandwidth legal — the same reason our own 902.0 was
+rejected as a center. The hopper may simply never park there. Two more
+clean surveys would make that a confident claim; it is a hypothesis today.
+
+## 3. Consequences
+
+1. RS-12's flash-session leg should run at **927.5** with the usual
+   same-day verification.
+2. RS-11.7 v1 should rank by **stability across accumulated surveys**,
+   not per-day quietness — `survey_compare.py --history` is that logic,
+   already written and validated.
+3. The depth-A/B absolute loss numbers (909.0, mid-drift) keep their
+   contamination caveat; the arm comparison stands.