Adv 2.0 D&D Phase 10 SUB2a-ii: Battle Master + Assassin L5/L7

Battle Master:
  - New "superiority" resource pool (4/long-rest at L5), provisioned via
    initSubclassResources at !subclass selection.
  - Three armed maneuvers fueled by superiority dice:
    * Precision Attack — +d8 (≈+4) to first attack roll
    * Tripping Attack  — enemy skips first attack (reuses Phase 9
      SpellEnemySkipFirst)
    * Rally            — +(d8 + CHA) HealItem at <50% HP
  - L7 Know Your Enemy proxied as +1 AttackBonus passive.

Assassin:
  - L5 Assassinate: AssassinateAdvantage (re-roll first miss, take better
    of two d20s) + AssassinateBonusDmg = level (5 at L5) stacked on top
    of the Rogue's existing Sneak Attack auto-crit.
  - L7 Impostor bumps the bonus damage by +3.
  - L5 Infiltration Expertise → +5 Deception; L7 Impostor → +10.

Engine:
  - CombatModifiers gains FirstAttackBonus, AssassinateAdvantage,
    AssassinateBonusDmg.
  - resolvePlayerAttack consumes each on the first attack only via new
    combatState one-shot flags.

Tests added: 14 covering passive gating (BM L7+, Assassin L5/L7),
maneuver Apply flags, superiority pool init for BM only, !arm gating
across class/subclass for precision_attack, Deception bonus tiers,
statistical lift from FirstAttackBonus and AssassinateBonusDmg in
SimulateCombat.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/dnd_subclass_combat.go

@@ -22,6 +22,27 @@ func applySubclassPassives(stats *CombatStats, mods *CombatModifiers, c *DnDChar
 		if c.Level >= 5 {
 			mods.CritThreshold = 19
 		}
+	case SubclassBattleMaster:
+		// L7 Know Your Enemy: 5e gives factual info about the target after
+		// 1 min observation. We don't model "observation time" — proxy the
+		// tactical edge as a flat +1 to attack rolls from L7 onward.
+		if c.Level >= 7 {
+			stats.AttackBonus++
+		}
+	case SubclassAssassin:
+		// L5 Assassinate: advantage on the opening strike + bonus damage
+		// stacked on top of the Rogue's existing Sneak Attack auto-crit
+		// (proxy for "crits vs. surprised targets"). Bonus scales with
+		// level; L7 Impostor — flavored as deeper study of the mark — adds
+		// a small surprise-damage bump.
+		if c.Level >= 5 {
+			mods.AssassinateAdvantage = true
+			bonus := c.Level
+			if c.Level >= 7 {
+				bonus += 3
+			}
+			mods.AssassinateBonusDmg = bonus
+		}
 	}
 }
 
@@ -56,6 +77,52 @@ func init() {
 			mods.FrenzyDmgBonus = 0.5
 		},
 	}
+
+	// Phase 10 SUB2a-ii — Battle Master superiority-die maneuvers. Each
+	// consumes one die from the new "superiority" resource pool (4/long-rest
+	// at L5; long-rest refresh in our model — 5e refreshes on short rest).
+	// We don't model 5e's interactive "before/after the roll" choice; a die
+	// commits at !arm time and fires on the next combat.
+	//
+	// Three non-reaction maneuvers covered:
+	//   - Precision Attack → +d8 (≈+4 flat) on first attack roll
+	//   - Tripping Attack  → enemy skips its first attack (reuses Phase 9
+	//     SpellEnemySkipFirst)
+	//   - Rally            → temp-HP buffer at <50% (reuses HealItem; self
+	//     buff since one-shot combat has no ally-target UI)
+	dndActiveAbilities["precision_attack"] = DnDAbility{
+		ID:          "precision_attack",
+		Name:        "Precision Attack",
+		Class:       ClassFighter,
+		Subclass:    SubclassBattleMaster,
+		Resource:    "superiority",
+		Description: "Add +d8 (≈+4) to your first attack roll this combat (consumes 1 superiority die).",
+		Apply: func(c *DnDCharacter, mods *CombatModifiers) {
+			mods.FirstAttackBonus += 4
+		},
+	}
+	dndActiveAbilities["trip_attack"] = DnDAbility{
+		ID:          "trip_attack",
+		Name:        "Tripping Attack",
+		Class:       ClassFighter,
+		Subclass:    SubclassBattleMaster,
+		Resource:    "superiority",
+		Description: "Trip the enemy on engagement: they skip their first attack (consumes 1 superiority die).",
+		Apply: func(c *DnDCharacter, mods *CombatModifiers) {
+			mods.SpellEnemySkipFirst = true
+		},
+	}
+	dndActiveAbilities["rally"] = DnDAbility{
+		ID:          "rally",
+		Name:        "Rally",
+		Class:       ClassFighter,
+		Subclass:    SubclassBattleMaster,
+		Resource:    "superiority",
+		Description: "Steel yourself for the fight: heal at low HP for d8 + CHA mod (consumes 1 superiority die).",
+		Apply: func(c *DnDCharacter, mods *CombatModifiers) {
+			mods.HealItem += 4 + abilityModifier(c.CHA)
+		},
+	}
 }
 
 // persistDnDPostCombatSubclass handles end-of-combat subclass bookkeeping.