A validated character sheet, an integer XP curve, and a replay-proof progression journal — deterministic RPG systems on ticks.

NEXUS RPG is a deterministic character-progression foundation for Unity. Six canonical attributes with typed modifiers, six derived stats computed in fixed order, a level curve of pure integer math, a skill tree that makes cycles impossible by construction, a clamped reputation ledger, and a four-slot party whose shared-XP tie-break is part of the contract. Every mutation is journaled under a fixed key — replays become observable refusals, never silent double-awards.

- Character sheets that validate themselves: base attributes clamp to 1..20, modifiers stack flats-first-then-percents in canonical order, duplicate keys are refused at insertion.

- An integer XP curve: 25*s^2 + 75*s per step — level 2 at 100, level 3 at 250, level 50 at 63,700. Awarding reports every level-up in order; the cap is exact.

- A cycle-proof skill tree: prerequisite tiers must be strictly lower, so cycles cannot exist; unlock spends points, refund is leaf-only, respec restores the full budget.

- Reputation with six canonical tier bands: Hostile, Wary, Neutral, Friendly, Honored, Revered — clamped at -100..100 with sorted snapshots.

- Deterministic parties: floor split with remainder units to the smallest canonical ids — server and client always agree on the split.

- Replay-proof progression journal: BeginEntry refuses a repeated key BEFORE any state changes; a rolling 32-bit checksum folds every line; print it and compare logs.

- Canonical NRG v1 snapshots: byte-stable envelopes (magic|version|length|payload|checksum, FNV-1a fold) with a strict typed decoder — Ok / BadMagic / BadVersion / Corrupt / ChecksumMismatch — that never throws for bad payloads.

- Editor tools: Create RPG Agent, the Character Designer (live sheet preview and deterministic mutations), and About — all under Tools > NEXUS RPG.

Zero shaders, zero materials, zero rendering code. Unity 2021.3 LTS or newer, all render pipelines, all renderers. 100 EditMode tests included — run them in Test Runner right after import, no Play Mode needed.

Technical details:

Deterministic by construction: canonical ordering everywhere, same inputs = same sheet, same levels, same journal

StatBlock: six canonical attributes (clamped 1..20) and six derived stats computed in fixed motion order RpgModifier: typed Flat/Percent modifiers, source-tagged, target-pinned, duplicate keys refused

RpgProgression: integer XP curve 25*s^2+75*s, ordered level-up reporting, exact cap behavior at level 50 RpgSkillTree: unique ids, existing prerequisites, strictly-lower prerequisite tiers - cycles impossible by construction

Unlock/refund/respec: points ledger with leaf-only refund and full-budget respec

RpgReputation: -100..100 clamp, six canonical tier bands, sorted canonical snapshots

RpgParty: four-slot roster, floor split with remainder units to the smallest canonical ids

RpgJournal: fixed-key entries, replay refusal before any state change, rolling 32-bit checksum

Canonical NRG v1 snapshots: byte-stable encode, strict decode with typed Ok/BadMagic/BadVersion/Corrupt/Mismatch taxonomy

Engine-free domain assembly (noEngineReferences: true) - dedicated-server projects link it directly

Unity 2021.3 LTS or newer; Built-in, URP, HDRP and custom render pipelines; zero shaders, zero materials; 100 EditMode tests included