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.

common_libs/tests/test_lead_gain_legacy.nim

@@ -2,18 +2,17 @@
 ##
 ## The owner's live `.env` predates the rename and carries `TR_RACK_BITBRAIN`,
 ## `TR_BITBRAIN_GAINS`, `TR_BITBRAIN_MEM`, `TR_BITBRAIN_LOG`. Those names used to
-## address the corrector that is now called LEADGAIN, and they MUST keep working,
-## because the `TR_BITBRAIN_*` prefix now belongs to the new ADE+SBC gun
-## (`guns/bitbrain_net.nim`, rack id 17). This test pins the disambiguation:
+## address the corrector that is now called LEADGAIN, and they MUST keep working.
 ##
-##   * `TR_BITBRAIN_NET` unset/0 -> LEGACY MODE: every `TR_BITBRAIN_<X>` in the
-##     frozen `LegacyKnobEnvNames` set is an alias for `TR_LEADGAIN_<X>`, and
-##     `TR_RACK_BITBRAIN` still selects rack id 16.
-##   * `TR_BITBRAIN_NET=1`      -> NEW-NETWORK MODE: the `TR_BITBRAIN_*` names
-##     belong to the new gun; this gun reads only `TR_LEADGAIN_<X>`.
+## The ADE+SBC gun that briefly owned the `TR_BITBRAIN_*` prefix (rack id 17,
+## `guns/bitbrain_net.nim`) was RETIRED and removed, so there is nothing left to
+## disambiguate: this gun is the SOLE owner of that namespace and
 ##
-## The two name sets are DISJOINT, so the mapping is total and deterministic.
-## No Java, no battle, no network build.
+##   * every `TR_BITBRAIN_<X>` in the frozen `LegacyKnobEnvNames` set is an
+##     alias for `TR_LEADGAIN_<X>`, unconditionally;
+##   * `TR_RACK_BITBRAIN` selects rack id 16, unconditionally;
+##   * a stale `TR_BITBRAIN_NET=1` left in a `.env` is an unrecognised
+##     variable — the boot report warns about it and nothing reads it.
 ##
 ## Run: nim c -r common_libs/tests/test_lead_gain_legacy.nim
 
@@ -35,7 +34,7 @@ proc clearEnv() =
     delEnv(NewPrefix & suffix)
   delEnv(LegacyRackEnvName)
   delEnv("TR_RACK_" & RackGunNames[LeadGainId])
-  delEnv(LG_NET_SWITCH_ENV)
+  delEnv("TR_BITBRAIN_NET")
 
 # ── the alias table itself ───────────────────────────────────────────────────
 
@@ -61,19 +60,29 @@ proc testAliasTableIsDisjoint() =
 
 # ── the switch ───────────────────────────────────────────────────────────────
 
-proc testSwitch() =
+proc testNamespaceIsUnconditional() =
+  ## There is no namespace switch any more. The ADE+SBC gun is gone, so a stale
+  ## `TR_BITBRAIN_NET` left in an old `.env` is inert: it must neither disown
+  ## the legacy knob aliases, nor the legacy rack knob, nor the deprecation line.
   clearEnv()
-  check "switch: unset => legacy mode (new ADE+SBC namespace disowned)",
-        not netSwitchOn()
-  putEnv(LG_NET_SWITCH_ENV, "0")
-  check "switch: 0 => legacy mode", not netSwitchOn()
-  putEnv(LG_NET_SWITCH_ENV, "1")
-  check "switch: 1 => new-network mode", netSwitchOn()
-  putEnv(LG_NET_SWITCH_ENV, "yes")
-  check "switch: yes => new-network mode", netSwitchOn()
-  putEnv(LG_NET_SWITCH_ENV, "banana")
-  check "switch: an unknown value is NOT new-network mode (fails safe)",
-        not netSwitchOn()
+  putEnv("TR_BITBRAIN_MEM", "decay")
+  putEnv("TR_BITBRAIN_LOG", "1")
+  putEnv(LegacyRackEnvName, "both")
+  var g = initLeadGainGun()
+  check "ns: the legacy prefix is unconditional (no switch set at all)",
+        g.memMode == lgDecay and g.logEnabled
+  putEnv("TR_BITBRAIN_NET", "1")
+  var g1 = initLeadGainGun()
+  check "ns: a stale TR_BITBRAIN_NET=1 does not disown the legacy knob names",
+        g1.memMode == lgDecay and g1.logEnabled
+  putEnv("TR_BITBRAIN_NET", "0")
+  var g2 = initLeadGainGun()
+  check "ns: a stale TR_BITBRAIN_NET=0 is equally inert", g2.memMode == lgDecay
+  putEnv("TR_BITBRAIN_NET", "1")
+  check "ns: a stale TR_BITBRAIN_NET=1 does not disown the legacy rack knob",
+        loadRackMembership()[LeadGainId] == rmBoth
+  check "ns: a stale TR_BITBRAIN_NET=1 does not suppress the deprecation line",
+        lgDeprecationLine().len > 0
   clearEnv()
 
 # ── knob aliasing ────────────────────────────────────────────────────────────
@@ -93,13 +102,13 @@ proc testKnobAlias() =
   putEnv("TR_LEADGAIN_GAINS", "0.5,0.75")
   var g2 = initLeadGainGun()
   check "alias: the NEW name wins when both are set", g2.cands == @[0.5, 0.75]
-  # the switch disowns the whole legacy namespace
-  putEnv(LG_NET_SWITCH_ENV, "1")
+  # the legacy namespace is unconditional, even next to a stale NET switch
+  putEnv("TR_BITBRAIN_NET", "1")
   delEnv("TR_LEADGAIN_GAINS")
   var g3 = initLeadGainGun()
-  check "alias: TR_BITBRAIN_NET=1 makes the legacy names inert for this gun",
-        g3.memMode == lgPerRound and not g3.logEnabled and
-        g3.cands == @[0.0, 0.25, 0.5, 0.75, 1.0]
+  check "alias: a stale TR_BITBRAIN_NET=1 does NOT make the legacy names inert",
+        g3.memMode == lgDecay and g3.logEnabled and
+        g3.cands == @[0.25, 0.5, 1.0]
   # ... and then the NEW names still work
   putEnv("TR_LEADGAIN_MEM", "retained")
   var g4 = initLeadGainGun()
@@ -116,10 +125,10 @@ proc testRackAlias() =
   check "rack: TR_RACK_BITBRAIN=both still selects LEADGAIN (id 16)",
         m[LeadGainId] == rmBoth and
         vBulletAdmitted(LeadGainId, rm1v1, m, true)
-  putEnv(LG_NET_SWITCH_ENV, "1")
+  putEnv("TR_BITBRAIN_NET", "1")
   let m2 = loadRackMembership()
-  check "rack: TR_BITBRAIN_NET=1 hands the name to the new ADE+SBC gun (id 17)",
-        m2[LeadGainId] == rmOff and m2.len == 18
+  check "rack: a stale TR_BITBRAIN_NET=1 no longer disowns the name — LEADGAIN (id 16) stays selected",
+        m2[LeadGainId] == rmBoth and m2.len == NumRackGuns
   clearEnv()
   putEnv("TR_RACK_LEADGAIN", "both")
   putEnv(LegacyRackEnvName, "off")
@@ -140,9 +149,9 @@ proc testDeprecationLine() =
         line.startsWith("[depr]") and
         line.contains("TR_BITBRAIN_GAINS -> TR_LEADGAIN_GAINS") and
         line.contains(NewPrefix)
-  putEnv(LG_NET_SWITCH_ENV, "1")
-  check "depr: the line is silent once the switch is flipped",
-        lgDeprecationLine().len == 0
+  putEnv("TR_BITBRAIN_NET", "1")
+  check "depr: the line still fires with a stale TR_BITBRAIN_NET=1 present",
+        lgDeprecationLine().len > 0
   clearEnv()
 
 # ── shipped-default parity ───────────────────────────────────────────────────
@@ -155,15 +164,15 @@ proc testDefaultParity() =
     let want = if i == 5: rmBoth else: rmOff
     if m[i] != want: onlyPattern = false
   check "parity: a clean env still loads the shipped onlyPattern rack", onlyPattern
-  check "parity: the rack is still 18 guns at id 16 = LEADGAIN",
-        RackGunNames.len == 18 and RackGunNames[LeadGainId] == "LEADGAIN"
+  check "parity: the rack is still 17 guns at id 16 = LEADGAIN",
+        RackGunNames.len == 17 and RackGunNames[LeadGainId] == "LEADGAIN"
   var g = initLeadGainGun()
   check "parity: a clean env resolves the shipped candidate set",
         g.cands == @[0.0, 0.25, 0.5, 0.75, 1.0] and g.memMode == lgPerRound
   clearEnv()
 
 testAliasTableIsDisjoint()
-testSwitch()
+testNamespaceIsUnconditional()
 testKnobAlias()
 testRackAlias()
 testDeprecationLine()