D&D: class-balance pass plan doc (gogobee_class_balance.md)

Phased plan for the class-balance pass. Unlike the race pass, classes
are *measured* not modeled: combat is one-shot auto-resolved through a
seedable simulateCombatWithRNG, so the harness runs Monte Carlo over the
real engine and reads win rates directly.

Scopes the full matrix (10 classes × 30 subclasses × level checkpoints ×
monster tiers), the two hard policies to de-risk in Phase 0 (equipment
loadout, spell selection), the per-tier win-rate parity rule, and the
tuning levers. Phase 0 spike in progress.

gogobee_class_balance.md

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+# GogoBee — D&D Class Balance Pass
+
+> **Companion to:** `gogobee_dnd_design_doc_v1.1.md`, `gogobee_spell_system.md`, `gogobee_subclass_system.md`
+> **Version:** 0.1 (planning draft)
+> **Status:** Pre-implementation — Phase 0 spike in progress
+> **Sibling work:** the race-balance pass (`internal/plugin/dnd_race_balance.go`, `TestRaceBalance`) — same spirit, different method (see §1).
+
+---
+
+## 0. Why this doc exists
+
+The race-balance pass tuned the seven races to equal *effective power* via a
+hand-weighted scoring model. That model is a **proxy** — races don't fight, so
+there is nothing to measure directly.
+
+Classes are different: combat is **one-shot auto-resolved** through a single
+`simulateCombatWithRNG` call (`combat_engine.go:338`), and the RNG is
+**seedable**. So class balance does not need a proxy model — we can run
+thousands of real, reproducible fights and read the win rates directly.
+
+This doc plans that work. Endgame: a `TestClassBalance` regression fixture that
+holds per-tier win-rate parity across all 10 classes × 30 subclasses, plus the
+tuning pass that gets us there.
+
+**Non-goals.** Not a combat-engine redesign. Not adding classes/subclasses.
+"Balanced" means balanced *in gogobee's one-shot engine* — the model collapses
+tabletop action economy, and that is accepted.
+
+---
+
+## 1. Method — measure, don't model
+
+| | Race pass | Class pass |
+|---|---|---|
+| Power source | ability mods only | full combat: HP/AC, weapons, spells, passives, subclass tiers |
+| Approach | hand-weighted scoring proxy | Monte Carlo over the real engine |
+| Trust | heuristic weights (estimated) | empirical win rates (measured) |
+| Artifact | `dnd_race_balance.go` + `TestRaceBalance` | `dnd_class_balance.go` + `TestClassBalance` |
+
+---
+
+## 2. The matrix (full)
+
+For each of the 10 classes:
+- `subclass = none` at L1–L4
+- each of its 5 subclasses at the L5 / L7 / L10 / L15 / L20 tier-unlock checkpoints
+
+→ ~60 build profiles × level checkpoints × ~6 monster tiers. Each cell = N
+seeded fights through `simulateCombatWithRNG`. One-shot sims are cheap; compute
+is not the constraint.
+
+**Opponents:** the existing per-tier monster scaling curves
+(`dnd_combat.go:35–51`) — dungeon Tier and arena ThreatLevel — used as a fixed
+gauntlet.
+
+**Builds:** standard array assigned by each class's stat priority
+(`dnd_combat.go:185–218`), Human race (neutral baseline, +1 all), plus a
+standardized equipment loadout (see §3).
+
+---
+
+## 3. The two hard parts (Phase 0 de-risks these)
+
+1. **Equipment loadout policy.** Combat uses equipment-driven AC and real weapon
+   dice. The per-class, per-level kit must be standardized *fairly* or every
+   downstream number is garbage. Derive from existing starting-gear / level
+   tables if they exist; otherwise define a canonical tiered kit.
+2. **Spell-selection policy.** Caster damage flows through `applyPendingCast`.
+   Without a "what would a player cast here" heuristic per class/level, all 8
+   casters fight as naked weapon-users and read as broken — a measurement
+   artifact, not real imbalance.
+
+---
+
+## 4. Balance rule
+
+Per-tier **win-rate parity**: at each difficulty tier, every class within a
+tolerance band of the cross-class mean win rate. Band set empirically after the
+first full run (the race pass's ±0.5 was set the same way). Damage-dealt,
+HP-remaining, and near-death-rate are logged as diagnostics, not asserted.
+
+---
+
+## 5. Phases (one phase ≈ one session; each ends green + committed)
+
+- **Phase 0 — spike.** Harness skeleton; equipment + spell-selection policies;
+  run *Fighter vs. Mage only* across tiers and sanity-check plausibility
+  (both win something; casters not at 0%). If the numbers are implausible, fix
+  the policies before trusting anything. **← current**
+- **Phase 1 — harness + matrix.** Generalize to all 10 classes × 30 subclasses;
+  `TestClassBalance` logs the full report. No tuning yet — just measurement.
+- **Phase 2 — tuning pass.** Adjust the levers (class passives → subclass tiers
+  → spell dice → AC floor → attack bonus, in that order) until the parity band
+  holds. Lock the band into the test assertion.
+- **Phase 3 (if needed) — second-order.** Subclass-vs-subclass spread within a
+  class; the Paladin/Rogue MAD question if the data shows it bites.
+
+## 6. Tuning levers (priority order)
+
+1. Class passives — `dnd_passives.go`
+2. Subclass L5/7/10/15 tiers — `dnd_subclass_combat.go`
+3. Spell damage dice & upcast — `dnd_spells_data.go`, `dnd_spells_srd_data.go`
+4. Spell slot progression — `dnd_spells.go`
+5. AC floor / armor proficiency — `dnd.go:164–178`
+6. Attack bonus class matrix — `dnd_combat.go:22–33`
+7. Monster scaling curves — `dnd_combat.go:35–51` (last resort; affects PvE feel)