Twinned (Splintered Pair) build

The Twinned axis (Splintered Pair) closes the verb-deviation cluster. It activates basic-strategy-wrong splits — especially the famous “never split 10s” — for cascade explosion when both halves resolve well.

Charm	Tier	Trigger	Effect
The Cracked Vow	uncommon	onWin (post-split)	10/5/4 pair vs dealer 7+ → ×1.5 mult
The Splintered Mirror	rare	onWin (post-split)	10/5/4 pair → +5 mult per winning half (both halves = +10 total)
The Twin Marks	mythic	onWin (post-split)	10s-split with hard-19+ → ×3 mult (×2 after first fire)
The Stranger’s Half	rare/drawback	onResolve	sets any_split_allowed + split_loss_penalty=1.5 flags

How “wrong-pair split” is detected

Original pair rank is inferred from cards[0] of the current split-half. Each split-half starts with one of the original pair cards, so the post-split first card IS the pair-rank witness.

The “never split” pairs per basic strategy are 10-valued (T/J/Q/K), 5s, and 4s. Splitting any of these pairs trips the Cracked Vow / Splintered Mirror gates.

The Twin Marks 10s-only mythic

Twin Marks gates more strictly: split must be 10s (or any 10-valued: T/J/Q/K) AND the half must reach hard 19+. Soft 19 doesn’t qualify — hard only.

Once-per-campaign full effect (×3), then ×2 thereafter. The dealer voice for a Twin Marks fire:

“Two marks. One place. He is impressed.”

The Stranger’s Half drawback

Allows split on any pair, including non-pair “pairs” of same value (10+J, J+Q, Q+K). Compensation: every split-lose costs 1.5× the normal capital settlement. Joins the drawback-negotiation UX.

Worked example

Holding Splintered Mirror, splitting 10♠ + 10♣ vs dealer 6:

• Half 1 wins → +5 mult on its cascade.
• Half 2 wins → +5 mult on its cascade.
• Total: +10 mult applied across the pair, when both halves win.

If only one half wins, only +5 mult fires. The “both halves win” condition is achieved by per-half independent firing — a losing half just doesn’t fire.

Composition with Long-Game

Splits typically have hitCount = 0 or 1 per half. Long-Game on a one-hit half:

archetype mult × 1.3 (long-game)
× 3.0 (Twin Marks first fire)
+ 5 multDelta (Splintered Mirror, post-additive)

Both half-winning gives a doubled cascade total since each half is its own resolution.

Dealer’s voice on a Twinned play

“He breaks the pair. Both halves come back. He says nothing.” — Splintered Mirror fires

“Two marks. One place. He is impressed.” — Twin Marks fires

“A vow cracked. The cup pays both halves.” — Cracked Vow fires

Where this lives

• lib/sim/arcana/arcana.dart — TheCrackedVow, TheSplinteredMirror, TheTwinMarks, TheStrangersHalf.
• test/sim/twinned_build_test.dart — 20 unit tests.

Engine prereq notes

active_from_split flag already exists for hollow_mirror. Stranger’s Half’s any_split_allowed + split_loss_penalty are NightRunner-side data primitives; engine wiring follows in Phase 5 recalibration.