j142 retire the ADE+SBC gun (rack id 17): the owner watched it, it does not learn, throw it away

Remove guns/bitbrain_net.nim (+README), test_bitbrain_net.nim,
measure_bitbrain_scaling.nim, rack id 17 and all of its plumbing in
selector.nim / ModularBot.nim / env_report.nim, the TR_BITBRAIN_NET switch
and the NEW-NETWORK TR_BITBRAIN_* knobs, and the BitBrainNet arm of
run_prediction_quality.nim.

With id 17 gone there is nothing to disambiguate, so the legacy namespace
becomes the ONLY one: TR_RACK_BITBRAIN always selects id 16 LEADGAIN and
every TR_BITBRAIN_<X> in the frozen 14-suffix alias set always means
TR_LEADGAIN_<X>. The alias layer and its [depr] line stay.

KEPT: the common_libs/bitbrain/ SBC library (learned_surfer imports
bitbrain/sbc), lead_gain at id 16 with env TR_LEADGAIN_* and log tag [lg],
and the c9b6753 crash fix (NumRackGuns widths + test_rack_stat_width).

Tombstone: docs/bitbrain_campaign.md ## RETIRED and one cross-reference line
in docs/gun_campaign.md. Shipped defaults unchanged: clean env -> rack
active 1v1 = PATTERN, movement default strafe.

docs/bitbrain_campaign.md

@@ -626,3 +626,77 @@ should be chosen for **plausible large effect**, not for a sub-MDE gain slope.
 `python3 tools/ab/ab_range_bands.py /tmp/ab_leadgain --reference control`.
 Liveness from `<arm>/run<N>.bot.stdout.log` (`[env]`), applied gain from the
 same file (`[bb]`). Fixtures: `/tmp/ab_leadgain` (ephemeral, as is the corpus).
+
+---
+
+## RETIRED: the ADE+SBC gun  *(rack id 17, `guns/bitbrain_net.nim` — REMOVED)*
+
+**The owner's decision (verbatim):** *"not learning, i watched it, throw it away
+and we forget about it"*. This section is the tombstone. **Nothing below is
+rewritten history** — Phases 0-2 above stand as written. The ADE+SBC gun
+(`common_libs/guns/bitbrain_net.nim`, rack id 17, env `TR_BITBRAIN_NET` +
+`TR_BITBRAIN_*`, log tag `[bbn]`) and its 44-check test and its scaling harness
+are **DELETED from the tree**. The generic SBC/ADE **library** at
+`common_libs/bitbrain/` **STAYS** — it is not the gun, and
+`common_libs/movements/learned_surfer.nim` still imports `bitbrain/sbc` (still
+56 checks in `test_bitbrain.nim`).
+
+### (a) The offline sweep: more RAM, no better aim — and never better than Pattern
+
+The scaling sweep replayed 3 recorded live runs through the real gun across a
+**100x RAM range (0.10 -> 12.60 MB)**. Mean |angular error| against the true
+interception point moved only:
+
+| RAM (MB) | mean \|err\| (deg) |
+|---|---|
+| 0.10 | 17.254 |
+| … (intermediate arms) | monotonically ↓ by <0.2 deg total |
+| 12.60 | 17.115 |
+
+**Pattern, on the same corpus, scores 16.964 deg.** So the ADE+SBC gun was
+**consistently slightly WORSE than Pattern at EVERY capacity** — a 126x RAM
+budget bought 0.139 deg, and the endpoint was still 0.151 deg *behind* the gun
+it was correcting. The measured scaling confirmed the shape of the cost but not
+the shape of the benefit: RAM is **linear in `nClasses`**, **quadratic in
+`nAde`**, and **7.3x for counted mode** over bitset.
+
+### (b) The budget made 360 classes unreachable anyway
+
+At **64 classes** the gun already cost **19.56 ms/tick = 149% of the project's
+13.16 ms/tick budget** — over budget before the interesting settings were
+reached. The configuration the design actually wanted (360 classes) was
+therefore **never affordable**, whatever its quality.
+
+### (c) The owner's live observation: it does not learn within a round
+
+The live run settled it: **400 virtual shots, 0 hits.** Not a weak learner, not a
+tuned one — no movement of the counts inside a round. The owner watched it and
+called it.
+
+### (d) Same information ceiling as the gate test
+
+This is the **same ~1-bit information ceiling** measured in
+`docs/bitbrain_gate_test.md`: ~55 000 samples cannot separate 16-64 correction
+classes that must differ by 1-2 deg, the SBC is idempotent so the per-class
+counts blur toward uniform, and the readout regresses to the mean. Phase 0's
+gains sweep (above) found the same thing from the amplitude side.
+
+### (e) Status: the gun is removed, the library is not
+
+* **REMOVED:** `common_libs/guns/bitbrain_net.nim`,
+  `common_libs/guns/bitbrain_net.README.md`,
+  `common_libs/tests/test_bitbrain_net.nim`,
+  `common_libs/tests/measure_bitbrain_scaling.nim`, rack id 17 and its whole
+  admit/dispatch/stat-width plumbing, the `bbn` gun field in `ModularBot.nim`,
+  the `TR_BITBRAIN_NET` switch and the NEW-NETWORK `TR_BITBRAIN_*` knob names,
+  and the `BitBrainNet` arm of `run_prediction_quality.nim`.
+* **KEPT:** `common_libs/bitbrain/` (the SBC library, used by
+  `learned_surfer`), and the `c9b6753` crash fix (`NumRackGuns`-derived
+  per-gun array widths + `test_rack_stat_width.nim`).
+* **SIMPLIFICATION:** with nothing left to disambiguate, the legacy namespace is
+  the ONLY namespace. `TR_RACK_BITBRAIN` always selects **id 16 LEADGAIN**, and
+  every `TR_BITBRAIN_<X>` in the frozen 14-suffix alias set always means
+  `TR_LEADGAIN_<X>`. A stale `TR_BITBRAIN_NET=1` in an old `.env` is now an
+  unrecognised variable: the boot report warns and ignores it. See
+  `common_libs/guns/lead_gain.README.md` and
+  `common_libs/tests/test_lead_gain_legacy.nim`.

docs/gun_campaign.md

@@ -1153,3 +1153,18 @@ round-boundary bug and its fix, all 4 forced arms' applied shares (exactly
 per-opponent delta, CI, MDE, sign and sign-flip test, and the policy-isolation
 comparison. **INFERRED:** that no share schedule whatsoever could ever help
 (this batch bounds only the shares it tested, at this MDE and panel).
+
+---
+
+## Cross-reference: the ADE+SBC gun (rack id 17) is RETIRED
+
+The `bitbrain` arm named in earlier batches of this ledger is NOT the gun
+shipped at id 16. The **ADE+SBC gun** that briefly held the `BITBRAIN` rack name
+and the `TR_BITBRAIN_*` env prefix at **rack id 17** was **retired and removed
+from the tree** (owner: *"not learning, i watched it, throw it away and we
+forget about it"*). Its tombstone, evidence and removal list are in
+`docs/bitbrain_campaign.md` §RETIRED. The `bitbrain` verdict in this ledger —
+nothing beat Pattern — is unchanged; this line only records that the id-17
+experiment that followed it is closed, so the two ledgers do not contradict
+each other. The surviving "BitBrain-named" capability is the id-16 lead-gain
+corrector, now called **LEADGAIN**.