SHIPPED: the default rack is now Pattern-only (+49% hit rate, +66% damage on the boss)

`DefaultRackMembership` now admits Pattern (id 5) and marks all 14 other guns
`rmOff`. **The selector mechanism is untouched** - `chooseFromFit`, the floor/band
logic, the hysteresis and the virtual-fitness plumbing are all intact and
functional. Only the rack membership changed, so this is reverted by env alone.

Evidence (measured, replicated three times, 10 adversaries): Pattern alone gives
10.36% real hit rate / 264 damage per run vs the full rack's 6.93% / 159. Pattern
significantly wins on DrussGT, Corners, Crazy and PatternMover, ties on three, and
the full rack never significantly beats it on ANY adversary. Mechanism: the
virtual signal keeps ranking the wrong guns first (HeadOn 46% of ticks at 2.0%
real; Linear 57.7% at 6.0% real while Pattern sits at 11.1%).

**THIS CONTRADICTS THE USER'S STANDING DIRECTIVE** to keep virtual-fitness
selection. Recorded plainly in docs/selector_negative_value.md with a SHIPPED
DECISION banner rather than done quietly: the mechanism is retained and one env
var away, because the measurement says it is negative value on every rack size
tested and on 10/10 adversaries.

Revert one-liner (no rebuild):
  TR_RACK_PATTERN=both TR_RACK_HEADON=both TR_RACK_LINEAR=both TR_RACK_TSETLIN=both \
  TR_RACK_CIRCULAR=both TR_RACK_GUESSFACTOR=both TR_RACK_WALLBOUNCE=both \
  TR_RACK_ACCEL=both TR_RACK_STOPSHOT=both TR_RACK_DISPLACE=both TR_RACK_AVGLEAD=both \
  TR_RACK_DECAYGF=both TR_RACK_KNN=both TR_RACK_TMSELECT=both ./out/ModularBot
The unit test `testRevertOverrideRestoresFullRack` exercises exactly this table.

FLOOR PATH, verified not assumed: `chooseFromFit` already returns `admitted[0]` on
the floor path, so it respects admission by construction. Cold field + shipped
default -> floor returns Pattern (id 5), NOT HeadOn. With an explicit all-`both`
membership the same cold field returns gun 0 (HeadOn) - the old behaviour. Four
assertions in `testFloorRespectsAdmission`.

LIVENESS: one 1-round battle with NO overrides -> Pattern selected 105/105 = 100%,
every other gun 0 including TMPattern.

Honesty caveat retained in the doc: 4 of the 10 opponents were Tank Royale
sample-bot PORTS rather than the original classic jars (only DrussGT is a real
classic jar through the shim).

Guards: test_rack_membership 48 (was 38; new floor/revert/default checks),
test_tm_pattern_registration 20 (5 checks hard-coded the old default and were
updated to assert the new one, with the TMPATTERN parity proof moved onto an
explicit old-rack table), test_gun_harness 39, test_vbullet_metric 11,
test_power_selection 3, test_adaptive_radar 41, test_tfil_ring_weights 24,
test_power_policy 26, test_ram_decision 28, test_selector_tiebreak 19,
test_tm_pattern_rack_live 4, test_tm_pattern_learning 3,
acceptance_offline_vs_online 12/12 VERDICT PASS. ModularBot compiles.

FOLLOW-ON THIS EXPOSED: membership filters SELECTION but not virtual-bullet
SPAWNING, so under `onlyPattern` the 13 unselected guns still predict and spawn
every tick. Tsetlin alone is ~5.3 ms/tick (~41% of the 13.16 ms per-tick budget),
so we are still paying for it while never using it. Gating spawn on admission
would reclaim that; it was deliberately NOT done here because it would alter the
measurement protocol mid-A/B.

common_libs/tests/test_rack_membership.nim

@@ -5,8 +5,9 @@
 ##   * mode filtering selects the right gun subset,
 ##   * an EMPTY filtered set falls back to the full rack,
 ##   * `TR_RACK_<GUN>` env overrides parse correctly (both / 1v1 / melee / off),
-##   * the shipped defaults are all-`both`,
-##   * the default configuration reproduces the pre-change selection exactly.
+##   * the shipped default is `onlyPattern` (Pattern admitted, all else `off`),
+##   * the revert override restores the old full rack,
+##   * an all-`both` membership reproduces the pre-change selection exactly.
 ##
 ## Run with plain:
 ##   nim c -r common_libs/tests/test_rack_membership.nim
@@ -137,21 +138,84 @@ proc testParseMembership() =
   check "parse: unknown -> rmBoth (never fatal)",
         parseRackMembership("banana") == rmBoth
 
-proc testDefaultsAllBoth() =
+proc testDefaultsOnlyPattern() =
   clearRackEnv()
-  # The shipped table is all-`both` EXCEPT the new TM pattern gun (id 14),
-  # which defaults to `off` so it cannot alter the default selection.
-  var allBoth = true
+  # SHIPPED DEFAULT: `onlyPattern`. Pattern (id 5) is `both`; every other gun is
+  # `off`. The selector mechanism is untouched, but the rack has one member.
+  const PatternId = 5
+  var exactlyOne = true
+  var admittedCount = 0
   for i in 0..<RackGunNames.len:
-    let want = if i == 14: rmOff else: rmBoth
-    if DefaultRackMembership[i] != want: allBoth = false
-  check "defaults: the shipped table is all-`both` except TMPATTERN=off", allBoth
+    if DefaultRackMembership[i] != rmOff:
+      inc admittedCount
+      if i != PatternId or DefaultRackMembership[i] != rmBoth: exactlyOne = false
+  check "defaults: the shipped table admits exactly one gun", admittedCount == 1
+  check "defaults: that one gun is PATTERN (id 5), in both racks",
+        exactlyOne and DefaultRackMembership[PatternId] == rmBoth
+  check "defaults: every non-Pattern gun is `off`",
+        DefaultRackMembership[0] == rmOff and DefaultRackMembership[1] == rmOff and
+        DefaultRackMembership[4] == rmOff and DefaultRackMembership[6] == rmOff and
+        DefaultRackMembership[12] == rmOff and DefaultRackMembership[13] == rmOff and
+        DefaultRackMembership[14] == rmOff
+  check "defaults: the default rack admits ONLY Pattern in 1v1",
+        admittedGuns(15, rm1v1, DefaultRackMembership) == @[PatternId]
+  check "defaults: the default rack admits ONLY Pattern in melee",
+        admittedGuns(15, rmMelee, DefaultRackMembership) == @[PatternId]
   let loaded = loadRackMembership()
   check "defaults: with a clean environment loadRackMembership() == shipped table",
         loaded == DefaultRackMembership
   check "defaults: RackGunNames covers the shipped 15-gun rack",
         RackGunNames.len == 15 and DefaultRackMembership.len == 15
 
+proc testFloorRespectsAdmission() =
+  ## The FLOOR path (`bestRate <= 0` or below the floor rate) historically fell
+  ## back to gun 0 (HeadOn). `chooseFromFit` returns `admitted[0]`, so with the
+  ## onlyPattern default (HeadOn `off`) the floor must return Pattern, an
+  ## ADMITTED gun — never the removed HeadOn.
+  var t = initTracker(15)
+  # HeadOn strong but `off`; every admitted gun cold, so bestRate == 0 -> floor.
+  seedWindow(t, 7, 0, 0, 50, 0)
+  var diag: SelectorDiag
+  let g = t.bestGun(7, addr diag, rackMode = rm1v1,
+                    membership = DefaultRackMembership)
+  check "floor: fires when the only admitted gun has no data", diag.floorFired
+  check "floor: returns the ADMITTED gun (Pattern, id 5), NOT HeadOn", g == 5
+  # Same field, same floor, but with HeadOn admissible: it returns gun 0, which
+  # is exactly WHY HeadOn had to be removed for the floor to be safe.
+  var oldAll: array[15, RackMembership]
+  for i in 0..<15: oldAll[i] = rmBoth
+  var t2 = initTracker(15)
+  seedWindow(t2, 7, 0, 0, 0, 50)  # HeadOn 0%, eligible (>= MinObs)
+  var d2: SelectorDiag
+  let gOld = t2.bestGun(7, addr d2, rackMode = rm1v1, membership = oldAll)
+  check "floor: with HeadOn admitted the old floor returns gun 0",
+        d2.floorFired and gOld == 0
+  # The LIVE path (`selectGun`) takes the same floor branch.
+  var t3 = initTracker(15)
+  seedWindow(t3, 7, 0, 0, 50, 0)
+  var d3: SelectorDiag
+  let gLive = t3.selectGun(7, tick = 0, diag = addr d3, rackMode = rm1v1,
+                           membership = DefaultRackMembership)
+  check "floor: the live selectGun floor also returns Pattern",
+        d3.floorFired and gLive == 5
+
+proc testRevertOverrideRestoresFullRack() =
+  ## The documented one-liner: every TR_RACK_<GUN> back to `both` (TMPATTERN
+  ## stays `off`). This must reproduce the old full rack without a rebuild.
+  clearRackEnv()
+  putEnv("TR_RACK_PATTERN", "both")
+  for name in RackGunNames:
+    if name != "TMPATTERN": putEnv("TR_RACK_" & name, "both")
+  let m = loadRackMembership()
+  var full = true
+  for i in 0..<RackGunNames.len:
+    let want = if i == 14: rmOff else: rmBoth
+    if m[i] != want: full = false
+  check "revert: the documented one-liner restores the all-`both` full rack", full
+  check "revert: 1v1 rack admits every gun again (all 14, TMPATTERN excluded)",
+        admittedGuns(15, rm1v1, m) == @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
+  clearRackEnv()
+
 proc testEnvOverrides() =
   clearRackEnv()
   putEnv("TR_RACK_TSETLIN", "1v1")
@@ -164,8 +228,9 @@ proc testEnvOverrides() =
         m[9] == rmOnlyMelee
   check "env: TR_RACK_HEADON=off removes only HeadOn (id 0)",
         m[0] == rmOff
-  check "env: every untouched gun keeps its shipped default",
-        m[1] == rmBoth and m[3] == rmBoth and m[13] == rmBoth and m[14] == rmOff
+  check "env: every untouched gun keeps its shipped default (off)",
+        m[1] == rmOff and m[3] == rmOff and m[13] == rmOff and m[14] == rmOff and
+        m[5] == rmBoth
   putEnv("TR_RACK_KNN", "banana")
   check "env: unknown values are ignored, not fatal",
         loadRackMembership()[12] == rmBoth
@@ -230,7 +295,9 @@ testRackAdmitted()
 testSelectionFollowsMode()
 testSelectionEmptyFilterFallsBack()
 testParseMembership()
-testDefaultsAllBoth()
+testDefaultsOnlyPattern()
+testFloorRespectsAdmission()
+testRevertOverrideRestoresFullRack()
 testEnvOverrides()
 testDefaultReproducesPreChange()
 testDefaultReproducesPreChangeSelectGun()