feat(voices-seat): ship lv-mccarthy (checkpoint-300) as the fourth author voice

Shipped on the operator's standing authorisation, "ship it if the gate passes".
The gate design of record for this line -- the operator's own v2 rule, ratified
2026-09-15 -- passes on all three axes:

  VOICE          +0.177 delta_cb at 3.2x the pairwise floor, the BEST arm of five,
                 and +0.128 at 2.8x on the pre-registered punctuation-stripped
                 secondary read, so ~3/4 of the gain is words rather than marks.
                 Closed 60.8% of the reachable span on an axis deliberately made
                 harder than Bronte's or Hemingway's.
  NOT COPIED     0.12 hit-rate against HELD-OUT McCARTHY'S OWN 0.12 -- 1.0x the
                 author -- with a longest verbatim run of 10 words against the 12
                 genuinely unseen McCarthy shares with the train split by
                 coincidence. All 31 matches READ: stock grammar, name-shaped hits
                 are the renamed inventions, nothing protectable. This matters:
                 McCarthy is in copyright with a living estate.
  NO DAMAGE      ran-on +0.12 against the 0.200 floor, 40% headroom, and the
                 measured minimum across the five-arm ladder.

ckpt300 over ckpt900, the eval-loss minimum: the two-epoch recipe is now 0 for 3,
and this time the curve was CONFIDENT and wrong -- ckpt900 is the minimum and
ckpt300 sits +15.8x the median neighbour jitter above it, yet ckpt300 wins every
axis that resolves (3.2x vs 1.2x voice margin, 2.7x tighter seed spread,
memorisation 1.0x the author vs 1.8x, ran-on 0.13 vs 0.28). On this schedule read
the axes, not the curve.

THE COST IS REAL AND IS WRITTEN INTO THE COMPOSE, THE ADAPTER README AND THE
MEMORY RECORD RATHER THAN GLOSSED. In-band is 0.65 against base's 0.89 and on-beat
0.42 against 0.71 -- 35% of generations miss the requested 90-140 word band against
base's 11%. Axis C is ran-on only and is structurally blind to this; that blindness
was identified and written down before these numbers existed. No checkpoint choice
fixes it: every adapted arm is 33-48% out-of-band and ran-on is non-monotonic in
epoch. If a caller depends on a word budget, expect one generation in three to miss
it, and the fix is a retrain targeting length rather than a different checkpoint.

Rollback is one line and 0.003 s: drop the --lora-modules entry, or POST
/v1/unload_lora_adapter. The other three voices are untouched.

stacks/voices-seat/compose.yaml

@@ -85,6 +85,9 @@ services:
       - auto
       - --enable-prefix-caching
       - --enable-lora
+      # ⚠ This is the max LoRAs in a single BATCH, not the number registered — 4 adapters are
+      # listed below and that sits exactly at the default. A FIFTH voice does not need a bump to
+      # be registered, but it will queue rather than batch alongside the other four.
       - --max-loras
       - "${VOICES_MAX_LORAS:-4}"
       - --max-lora-rank
@@ -141,6 +144,46 @@ services:
       # scripts/hemingway-corpus/GATE-PREREG.md (pre-registered before any generation),
       # persistent-memory.d/2026-09-17-lv-hemingway-gate.md
       - lv-hemingway=/adapters/lv-hemingway-4b-v1
+      # lv-mccarthy: checkpoint-300 (epoch 0.652), NOT the loss minimum at step 900.
+      # ⭐ The two-epoch recipe is now 0 for 3, and this time the loss curve was CONFIDENT and
+      # wrong: ckpt900 is the minimum and ckpt300 sits +15.8x the median neighbour jitter above
+      # it, yet ckpt300 wins every axis that resolves — 3.2x vs 1.2x voice margin, 2.7x tighter
+      # seed spread, memorisation 1.0x the author's rate vs 1.8x, ran-on 0.13 vs 0.28.
+      #
+      # VOICE ✅ +0.177 delta_cb at 3.2x the pairwise floor — the BEST arm of five, on both the
+      # primary read and the pre-registered punctuation-stripped secondary (+0.128 at 2.8x), so
+      # ~3/4 of the gain is words rather than marks. Closed 60.8% of the reachable span.
+      # ⚠ This corpus's voice axis is DELIBERATELY harder than Brontë's or Hemingway's: the
+      # `mccarthy` register names its own punctuation tics and the eval drives the base control
+      # with the same prompt, so the adapter earns no delta for "emit no quotation marks".
+      #
+      # NOT COPIED ✅ THE CLEANEST SAFETY RESULT IN THIS LINE. 0.12 hit-rate against HELD-OUT
+      # McCARTHY'S OWN 0.12 — indistinguishable from the author — and its longest verbatim run
+      # (10 words) is SHORTER than the one genuinely unseen McCarthy shares with the train split
+      # by coincidence (12). All 31 matched runs were READ: stock grammar in the commonest words
+      # ("looked at the wolf and he looked at the boy"), and the name-shaped hits are the RENAMED
+      # invented names. Nothing protectable. McCarthy is in copyright with a LIVING ESTATE.
+      # ⚠ The base-unadapted control is defective and its 0.00 is unearned — base writes summary
+      # and cannot collide with a register it does not imitate. Against base this reads as a 12x
+      # red flag; against the author it is 1.0x. Use the author, not base.
+      #
+      # ⚠⚠ THE COST, AND THE GATE'S RULE IS BLIND TO IT. Axis C is ran-on only (ratified
+      # 2026-09-15 because the carrier maxes the other terms) and this adapter passes it with 40%
+      # headroom — but IN-BAND IS 0.65 AGAINST BASE'S 0.89 and on-beat 0.42 against 0.71.
+      # **35% of its generations miss the requested 90-140 word band, against base's 11%.**
+      # Base is GOOD at length here, so the adapter measurably makes direction-following worse.
+      # ⚠ No checkpoint choice fixes this — every adapted arm is 33-48% out-of-band and ran-on is
+      # non-monotonic in epoch (0.38 -> 0.13 -> 0.20 -> 0.28); ckpt300 is the measured minimum.
+      # The fix, if the cost bites, is a retrain targeting length, not a different checkpoint.
+      # IF A CALLER DEPENDS ON A WORD BUDGET, EXPECT ONE GENERATION IN THREE TO MISS IT.
+      # Unload is 0.003 s and one compose line.
+      #
+      # See /adapters/lv-mccarthy-4b-v1/README.md,
+      # scripts/mccarthy-corpus/GATE-PREREG.md (pre-registered before any generation, plus three
+      # dated amendments — axis C as first frozen was ARITHMETICALLY UNSATISFIABLE),
+      # scripts/mccarthy-corpus/gate-results/ (raw output, all five arms),
+      # persistent-memory.d/2026-09-21-lv-mccarthy-gate.md
+      - lv-mccarthy=/adapters/lv-mccarthy-4b-v1
     deploy:
       resources:
         reservations: