#Slot Game Design Document — Hold & Win Reference

This GDD specifies a reference mechanic pack. Sections of the standard template that describe a themed product release (art, animation, audio, market/compliance matrix, telemetry dashboards) are explicitly out of scope and are marked as such rather than filled with invented content.

#1. Document control

#Change log

#2. Approval status

No internal test, simulation or handoff approval is external certification.

#3. High concept

#One-sentence pitch

Land six or more coin symbols and they lock in place, then keep respinning the empty cells for as long as new coins keep landing — fill the whole grid and take the Grand.

#Player experience goals

• The feature reads as a second, self-contained game with its own tension curve.
• Every landed coin visibly resets the respin counter, so progress feels earned.
• A full grid is a distinct, unambiguous top event rather than an incremental payout.

#Design pillars

• The locked grid is the entire game state — nothing hidden.
• Respins are the only resource; landing is the only way to buy more.
• One award, once, at the end.

#Non-goals

• No collector symbol, no multiplier, no feature buy, no additional wager in v0.1.
• No theme, art or audio identity; this pack is a mechanic reference.

#4. Game summary

#5. Core gameplay loop

1. Player commits total bet. Base grid is spun and evaluated normally.
2. Count visible BONUS symbols.
   < 6  → round ends with the base result. No feature. No feature RNG consumed.
   >= 6 → feature triggers.
3. Trigger: every BONUS position locks. Each locked cell is assigned a prize,
   in normative cell order. Remaining respins = 3.
4. Respin step: every EMPTY cell, in normative order, gets one land/miss draw.
   - Landed cells lock and receive a prize.
   - At least one land  → remaining respins reset to 3.
   - No lands           → remaining respins decrease by 1.
   - Locked cells are never redrawn.
5. Repeat step 4 until remaining respins = 0 or all 15 cells are locked.
6. Settle once:
   - All 15 cells locked → award exactly Grand 500× total bet.
   - Otherwise           → award the sum of locked prizes, capped at 500× total bet.

#6. Terminology

#7. Symbols

BONUS has no line payout — it is not a scatter pay. Its only value is the prize attached to it inside the feature.

#8. Base-game rules

Standard line evaluation on the pack's reel set. The base result is independent of the feature and is reported separately from the feature award.

#Evaluation order

#Base-game pseudocode

grid       = spinReels(reelSet)
baseWin    = evaluateLines(grid)
bonusCount = countVisible(grid, "BONUS")
featureWin = bonusCount >= 6 ? runHoldAndWin(grid) : 0
roundWin   = min(baseWin + featureWin, 500)

#9. Feature specification

#Feature: Hold & Win

Grand is not a landed prize type. It exists only as the full-grid award.

#State machine

Idle ──(>=6 BONUS)──> Triggered ──(lock imports, respins=3)──> Respinning
Respinning ──(step lands >=1)──> Respinning   (respins reset to 3)
Respinning ──(step lands 0)────> Respinning   (respins -= 1)
Respinning ──(respins == 0)────> Settled
Respinning ──(15 cells locked)─> Settled

#Feature rules

1. A step visits only empty cells, in normative order.
2. Each visited empty cell consumes exactly one land/miss draw.
3. A landed cell consumes one prize-type draw, and one regular-value draw only when the type is Regular.
4. Locked cells consume no draws.
5. Settlement consumes no draws.
6. The cap and the full-grid Grand each apply exactly once, at settlement.

#Feature edge cases

#10. Player controls and UX states

Out of scope for a reference pack beyond the contract the API must expose: while the feature is active the round reports a typed next-state of kind hold_and_win carrying respins remaining, locked cells with their prizes, step index and accumulated award.

#11-15. Win presentation, anticipation, art, animation, audio

Out of scope for a reference mechanic pack. No theme, asset inventory, animation or audio direction is specified here; a consuming game supplies its own.

#16. Help, paytable and disclosures

A consuming game must disclose: the 6-symbol trigger, 3 respins, the reset-on-land rule, the prize tiers (Regular values, Mini 10×, Minor 25×, Major 100×), that Grand 500× is awarded only for a full grid and replaces the prize sum, and that the round is capped at 500× total bet.

#17. Market and compliance matrix

Out of scope for a reference pack. DRAFT / NOT FOR CERTIFICATION.

#18. Error and recovery behavior

#19. Telemetry

Minimum mechanic metrics a consuming game should record: trigger count, steps per feature, reset count, full-grid count, per-tier prize counts, feature award distribution.

#20. Acceptance criteria

• Trigger boundary verified at five and six BONUS.
• Initial lock import and prize assignment follow normative order.
• Only empty cells are redrawn; locked cells consume no RNG.
• A land resets respins to 3; a miss-only step decrements by exactly 1.
• Zero-respin and full-grid termination both verified.
• Mini, Minor, Major and full-grid Grand semantics verified.
• Ordinary sum and a single 500× cap verified.
• Same seed, state and step identity reproduce the same result.
• Duplicate step replay consumes no RNG and charges no wager.
• Step-by-step execution equals RunToCompletion.
• Invalid configs are rejected.
• Existing games and the partial hold_and_spin feature are unchanged.
• Serialized responses carry a complete 15-cell snapshot plus the exact newly_landed delta and match the OpenAPI schema and the documented deterministic fixtures.

#21. Open decisions

#22. References

• Design spec: 2026-08-09-hold-and-win-reference-design.md
• Implementation plan: 2026-08-09-hold-and-win-reference.md
• Backend response contract: hold-and-win-backend-response.md
• Math Spec: hold-and-win-reference-math-spec.md
• Mechanic Draft math: hold-and-win-math-draft-v0.1.md