diff --git a/.claude/settings.json b/.claude/settings.json
index db5172b..200bba3 100644
--- a/.claude/settings.json
+++ b/.claude/settings.json
@@ -2,6 +2,7 @@
   "permissions": {
     "allow": [
       "Bash(node -e *)",
+      "Bash(python3 *)",
       "Bash(node --input-type=module)",
       "Bash(2>&1)",
       "Bash(pnpm *)"
diff --git a/apps/api/prisma/migrations/20260507000000_initial_schema/migration.sql b/apps/api/prisma/migrations/20260507000000_initial_schema/migration.sql
new file mode 100644
index 0000000..486bc9b
--- /dev/null
+++ b/apps/api/prisma/migrations/20260507000000_initial_schema/migration.sql
@@ -0,0 +1,91 @@
+-- CreateTable
+CREATE TABLE "users" (
+    "id" UUID NOT NULL,
+    "twitch_opaque_user_id" TEXT NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "users_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "survivors" (
+    "id" UUID NOT NULL,
+    "user_id" UUID NOT NULL,
+    "channel_id" TEXT NOT NULL,
+    "name" VARCHAR(32) NOT NULL,
+    "state" TEXT NOT NULL DEFAULT 'active',
+    "stats" JSONB NOT NULL,
+    "perk_slots" JSONB NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "survivors_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "missions" (
+    "id" UUID NOT NULL,
+    "group_id" UUID,
+    "channel_id" TEXT NOT NULL,
+    "difficulty" SMALLINT NOT NULL,
+    "status" TEXT NOT NULL DEFAULT 'active',
+    "encounter_library_version" TEXT NOT NULL,
+    "started_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "ended_at" TIMESTAMP(3),
+    "tick_index" INTEGER NOT NULL DEFAULT 0,
+    "next_tick_at" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "missions_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "mission_participants" (
+    "id" UUID NOT NULL,
+    "mission_id" UUID NOT NULL,
+    "survivor_id" UUID NOT NULL,
+    "state" TEXT NOT NULL DEFAULT 'active',
+    "hook_count" SMALLINT NOT NULL DEFAULT 0,
+
+    CONSTRAINT "mission_participants_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "mission_logs" (
+    "id" UUID NOT NULL,
+    "mission_id" UUID NOT NULL,
+    "tick_index" INTEGER NOT NULL,
+    "encounter_key" TEXT NOT NULL,
+    "rendered_text" TEXT NOT NULL,
+    "seed" TEXT NOT NULL,
+    "modifiers_applied" JSONB NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "mission_logs_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "users_twitch_opaque_user_id_key" ON "users"("twitch_opaque_user_id");
+
+-- CreateIndex
+CREATE INDEX "missions_channel_id_idx" ON "missions"("channel_id");
+
+-- CreateIndex
+CREATE INDEX "missions_status_next_tick_at_idx" ON "missions"("status", "next_tick_at");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "mission_participants_mission_id_survivor_id_key" ON "mission_participants"("mission_id", "survivor_id");
+
+-- CreateIndex
+CREATE INDEX "mission_logs_mission_id_tick_index_idx" ON "mission_logs"("mission_id", "tick_index");
+
+-- AddForeignKey
+ALTER TABLE "survivors" ADD CONSTRAINT "survivors_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "users"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "mission_participants" ADD CONSTRAINT "mission_participants_mission_id_fkey" FOREIGN KEY ("mission_id") REFERENCES "missions"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "mission_participants" ADD CONSTRAINT "mission_participants_survivor_id_fkey" FOREIGN KEY ("survivor_id") REFERENCES "survivors"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "mission_logs" ADD CONSTRAINT "mission_logs_mission_id_fkey" FOREIGN KEY ("mission_id") REFERENCES "missions"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
diff --git a/apps/api/prisma/schema.prisma b/apps/api/prisma/schema.prisma
new file mode 100644
index 0000000..edbaeb1
--- /dev/null
+++ b/apps/api/prisma/schema.prisma
@@ -0,0 +1,80 @@
+generator client {
+  provider = "prisma-client-js"
+  output   = "../../../node_modules/.prisma/client"
+}
+
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+model User {
+  id           String     @id @default(uuid()) @db.Uuid
+  opaqueUserId String     @unique @map("twitch_opaque_user_id")
+  createdAt    DateTime   @default(now()) @map("created_at")
+  survivors    Survivor[]
+
+  @@map("users")
+}
+
+model Survivor {
+  id           String               @id @default(uuid()) @db.Uuid
+  userId       String               @map("user_id") @db.Uuid
+  user         User                 @relation(fields: [userId], references: [id])
+  channelId    String               @map("channel_id")
+  name         String               @db.VarChar(32)
+  state        String               @default("active")
+  stats        Json
+  perkSlots    Json                 @map("perk_slots")
+  createdAt    DateTime             @default(now()) @map("created_at")
+  participants MissionParticipant[]
+
+  @@map("survivors")
+}
+
+model Mission {
+  id                      String               @id @default(uuid()) @db.Uuid
+  groupId                 String?              @map("group_id") @db.Uuid
+  channelId               String               @map("channel_id")
+  difficulty              Int                  @db.SmallInt
+  status                  String               @default("active")
+  encounterLibraryVersion String               @map("encounter_library_version")
+  startedAt               DateTime             @default(now()) @map("started_at")
+  endedAt                 DateTime?            @map("ended_at")
+  tickIndex               Int                  @default(0) @map("tick_index")
+  nextTickAt              DateTime             @map("next_tick_at")
+  participants            MissionParticipant[]
+  logs                    MissionLog[]
+
+  @@index([channelId])
+  @@index([status, nextTickAt])
+  @@map("missions")
+}
+
+model MissionParticipant {
+  id         String   @id @default(uuid()) @db.Uuid
+  missionId  String   @map("mission_id") @db.Uuid
+  mission    Mission  @relation(fields: [missionId], references: [id])
+  survivorId String   @map("survivor_id") @db.Uuid
+  survivor   Survivor @relation(fields: [survivorId], references: [id])
+  state      String   @default("active")
+  hookCount  Int      @default(0) @map("hook_count") @db.SmallInt
+
+  @@unique([missionId, survivorId])
+  @@map("mission_participants")
+}
+
+model MissionLog {
+  id               String   @id @default(uuid()) @db.Uuid
+  missionId        String   @map("mission_id") @db.Uuid
+  mission          Mission  @relation(fields: [missionId], references: [id])
+  tickIndex        Int      @map("tick_index")
+  encounterKey     String   @map("encounter_key")
+  renderedText     String   @map("rendered_text")
+  seed             String
+  modifiersApplied Json     @map("modifiers_applied")
+  createdAt        DateTime @default(now()) @map("created_at")
+
+  @@index([missionId, tickIndex])
+  @@map("mission_logs")
+}
diff --git a/apps/api/src/app/app.module.ts b/apps/api/src/app/app.module.ts
index f6ed546..6b5d887 100644
--- a/apps/api/src/app/app.module.ts
+++ b/apps/api/src/app/app.module.ts
@@ -1,13 +1,23 @@
 import { Module } from '@nestjs/common';
+import { APP_GUARD } from '@nestjs/core';
 import { ScheduleModule } from '@nestjs/schedule';
+import { ThrottlerGuard, ThrottlerModule } from '@nestjs/throttler';
 import { MissionsModule } from './missions/missions.module';
+import { PrismaModule } from './prisma/prisma.module';
 import { TickEngineModule } from './tick-engine/tick-engine.module';
 
 @Module({
   imports: [
     ScheduleModule.forRoot(),
+    ThrottlerModule.forRoot({
+      throttlers: [{ ttl: 10000, limit: 30 }],
+    }),
+    PrismaModule,
     MissionsModule,
     TickEngineModule,
   ],
+  providers: [
+    { provide: APP_GUARD, useClass: ThrottlerGuard },
+  ],
 })
 export class AppModule {}
diff --git a/apps/api/src/app/missions/missions.controller.ts b/apps/api/src/app/missions/missions.controller.ts
index d1f9601..08645d5 100644
--- a/apps/api/src/app/missions/missions.controller.ts
+++ b/apps/api/src/app/missions/missions.controller.ts
@@ -1,13 +1,14 @@
 import {
   Body,
   Controller,
+  ForbiddenException,
   Get,
   HttpCode,
   HttpStatus,
-  NotFoundException,
   Post,
   UseGuards,
 } from '@nestjs/common';
+import { Throttle } from '@nestjs/throttler';
 import {
   MissionStateResponse,
   MissionStateResponseSchema,
@@ -26,6 +27,7 @@ export class MissionsController {
   ) {}
 
   @Get('state')
+  @Throttle({ default: { limit: 10, ttl: 10000 } })
   async getState(
     @TwitchClaims() claims: TwitchJwtPayload
   ): Promise<MissionStateResponse> {
@@ -38,9 +40,9 @@ export class MissionsController {
   async startMission(
     @TwitchClaims() claims: TwitchJwtPayload,
     @Body() body: unknown
-  ): Promise<MissionStateResponse> {
+  ): Promise<NonNullable<MissionStateResponse>> {
     if (!claims.opaque_user_id.startsWith('U')) {
-      throw new NotFoundException('Anonymous viewers cannot start missions');
+      throw new ForbiddenException('Anonymous viewers cannot start missions');
     }
     const { difficulty } = StartMissionRequestSchema.parse(body);
     return this.missions.startMission(claims, difficulty);
diff --git a/apps/api/src/app/missions/missions.module.ts b/apps/api/src/app/missions/missions.module.ts
index b26ff7a..48e75ba 100644
--- a/apps/api/src/app/missions/missions.module.ts
+++ b/apps/api/src/app/missions/missions.module.ts
@@ -15,6 +15,6 @@ import { MissionsService } from './missions.service';
     EncounterService,
     GroupSynergyService,
   ],
-  exports: [MissionStoreService, EncounterService],
+  exports: [MissionStoreService, EncounterService, GroupSynergyService],
 })
 export class MissionsModule {}
diff --git a/apps/api/src/app/missions/missions.service.ts b/apps/api/src/app/missions/missions.service.ts
index c3b57f0..d91dd68 100644
--- a/apps/api/src/app/missions/missions.service.ts
+++ b/apps/api/src/app/missions/missions.service.ts
@@ -7,6 +7,7 @@ import type {
 } from '@fog-explorer/api-interfaces';
 import { getLibraryVersion } from '@fog-explorer/encounter-library';
 import { TwitchJwtPayload } from '../auth/twitch-jwt.guard';
+import { PrismaService } from '../prisma/prisma.service';
 import { MissionStoreService } from './mission-store.service';
 
 const TICK_BASE_INTERVAL_MS = 60_000;
@@ -14,7 +15,10 @@ const TICK_JITTER_MS = 5_000;
 
 @Injectable()
 export class MissionsService {
-  constructor(private readonly store: MissionStoreService) {}
+  constructor(
+    private readonly store: MissionStoreService,
+    private readonly prisma: PrismaService
+  ) {}
 
   async startMission(
     claims: TwitchJwtPayload,
@@ -22,11 +26,50 @@ export class MissionsService {
   ): Promise<NonNullable<MissionStateResponse>> {
     const missionId = crypto.randomUUID();
     const survivorId = crypto.randomUUID();
-    const now = new Date().toISOString();
+    const now = new Date();
     const jitter = Math.floor(Math.random() * TICK_JITTER_MS);
-    const nextTickAt = new Date(Date.now() + TICK_BASE_INTERVAL_MS + jitter).toISOString();
+    const nextTickAt = new Date(now.getTime() + TICK_BASE_INTERVAL_MS + jitter);
+    const stats: SurvivorStats = { objectives: 5, survival: 5, altruism: 5 };
 
-    const stats: SurvivorStats = defaultStats();
+    // Upsert user and create survivor + mission in one transaction.
+    await this.prisma.$transaction(async (tx) => {
+      const user = await tx.user.upsert({
+        where: { opaqueUserId: claims.opaque_user_id },
+        create: { id: crypto.randomUUID(), opaqueUserId: claims.opaque_user_id },
+        update: {},
+      });
+
+      await tx.survivor.create({
+        data: {
+          id: survivorId,
+          userId: user.id,
+          channelId: claims.channel_id,
+          name: defaultName(claims.opaque_user_id),
+          state: 'active',
+          stats,
+          perkSlots: [],
+        },
+      });
+
+      await tx.mission.create({
+        data: {
+          id: missionId,
+          channelId: claims.channel_id,
+          difficulty,
+          status: 'active',
+          encounterLibraryVersion: getLibraryVersion(),
+          nextTickAt,
+          participants: {
+            create: {
+              id: crypto.randomUUID(),
+              survivorId,
+              state: 'active',
+              hookCount: 0,
+            },
+          },
+        },
+      });
+    });
 
     const survivor: Survivor = {
       id: survivorId,
@@ -36,7 +79,7 @@ export class MissionsService {
       state: 'active',
       stats,
       perkSlots: [],
-      createdAt: now,
+      createdAt: now.toISOString(),
     };
 
     const mission: Mission = {
@@ -46,9 +89,9 @@ export class MissionsService {
       difficulty,
       status: 'active',
       encounterLibraryVersion: getLibraryVersion(),
-      nextTickAt,
+      nextTickAt: nextTickAt.toISOString(),
       tickIndex: 0,
-      startedAt: now,
+      startedAt: now.toISOString(),
       endedAt: null,
     };
 
@@ -60,16 +103,12 @@ export class MissionsService {
 
     await this.store.setActiveMission(state);
     await this.store.setChannelMissionId(claims.channel_id, missionId);
-    await this.store.scheduleTick(missionId, new Date(nextTickAt).getTime());
+    await this.store.scheduleTick(missionId, nextTickAt.getTime());
 
     return state;
   }
 }
 
-function defaultStats(): SurvivorStats {
-  return { objectives: 5, survival: 5, altruism: 5 };
-}
-
 function defaultName(opaqueUserId: string): string {
   return `Survivor ${opaqueUserId.slice(-4)}`;
 }
diff --git a/apps/api/src/app/prisma/prisma.module.ts b/apps/api/src/app/prisma/prisma.module.ts
new file mode 100644
index 0000000..7207426
--- /dev/null
+++ b/apps/api/src/app/prisma/prisma.module.ts
@@ -0,0 +1,9 @@
+import { Global, Module } from '@nestjs/common';
+import { PrismaService } from './prisma.service';
+
+@Global()
+@Module({
+  providers: [PrismaService],
+  exports: [PrismaService],
+})
+export class PrismaModule {}
diff --git a/apps/api/src/app/prisma/prisma.service.ts b/apps/api/src/app/prisma/prisma.service.ts
new file mode 100644
index 0000000..829d52f
--- /dev/null
+++ b/apps/api/src/app/prisma/prisma.service.ts
@@ -0,0 +1,13 @@
+import { Injectable, OnModuleDestroy, OnModuleInit } from '@nestjs/common';
+import { PrismaClient } from '@prisma/client';
+
+@Injectable()
+export class PrismaService extends PrismaClient implements OnModuleInit, OnModuleDestroy {
+  async onModuleInit(): Promise<void> {
+    await this.$connect();
+  }
+
+  async onModuleDestroy(): Promise<void> {
+    await this.$disconnect();
+  }
+}
diff --git a/apps/api/src/app/tick-engine/tick-engine.module.ts b/apps/api/src/app/tick-engine/tick-engine.module.ts
index 16b1fe2..8cc8128 100644
--- a/apps/api/src/app/tick-engine/tick-engine.module.ts
+++ b/apps/api/src/app/tick-engine/tick-engine.module.ts
@@ -1,9 +1,10 @@
 import { Module } from '@nestjs/common';
 import { MissionsModule } from '../missions/missions.module';
 import { TickService } from './tick.service';
+import { TwitchPubSubService } from './twitch-pubsub.service';
 
 @Module({
   imports: [MissionsModule],
-  providers: [TickService],
+  providers: [TickService, TwitchPubSubService],
 })
 export class TickEngineModule {}
diff --git a/apps/api/src/app/tick-engine/tick.service.ts b/apps/api/src/app/tick-engine/tick.service.ts
index 11cf957..59b1b9d 100644
--- a/apps/api/src/app/tick-engine/tick.service.ts
+++ b/apps/api/src/app/tick-engine/tick.service.ts
@@ -1,7 +1,9 @@
 import { Injectable, Logger } from '@nestjs/common';
 import { Cron, CronExpression } from '@nestjs/schedule';
-import { MissionStoreService } from '../missions/mission-store.service';
+import { PrismaService } from '../prisma/prisma.service';
 import { EncounterService } from '../missions/encounter.service';
+import { MissionStoreService } from '../missions/mission-store.service';
+import { TwitchPubSubService } from './twitch-pubsub.service';
 
 @Injectable()
 export class TickService {
@@ -9,7 +11,9 @@ export class TickService {
 
   constructor(
     private readonly store: MissionStoreService,
-    private readonly encounters: EncounterService
+    private readonly encounters: EncounterService,
+    private readonly prisma: PrismaService,
+    private readonly pubsub: TwitchPubSubService
   ) {}
 
   @Cron(CronExpression.EVERY_10_SECONDS)
@@ -24,7 +28,7 @@ export class TickService {
 
   private async processMission(missionId: string): Promise<void> {
     const token = await this.store.acquireLock(missionId);
-    if (!token) return; // Another worker has the lock
+    if (!token) return;
 
     try {
       const state = await this.store.getActiveMission(missionId);
@@ -34,13 +38,57 @@ export class TickService {
       }
 
       const updated = this.encounters.processTick(state);
+      const newLogs = updated.recentLog.slice(
+        0,
+        updated.recentLog.length - state.recentLog.length
+      );
 
+      // Write to Postgres in a transaction.
+      await this.prisma.$transaction(async (tx) => {
+        await tx.mission.update({
+          where: { id: missionId },
+          data: {
+            tickIndex: updated.mission.tickIndex,
+            nextTickAt: new Date(updated.mission.nextTickAt),
+            status: updated.mission.status,
+            endedAt: updated.mission.endedAt ? new Date(updated.mission.endedAt) : null,
+          },
+        });
+
+        for (const survivor of updated.survivors) {
+          const participant = updated.mission.participants.find(
+            (p) => p.survivorId === survivor.id
+          );
+          if (!participant) continue;
+          await tx.missionParticipant.updateMany({
+            where: { missionId, survivorId: survivor.id },
+            data: { state: participant.state, hookCount: participant.hookCount },
+          });
+          await tx.survivor.update({
+            where: { id: survivor.id },
+            data: { state: survivor.state },
+          });
+        }
+
+        if (newLogs.length > 0) {
+          await tx.missionLog.createMany({
+            data: newLogs.map((log) => ({
+              id: crypto.randomUUID(),
+              missionId,
+              tickIndex: log.tickIndex,
+              encounterKey: log.encounterKey,
+              renderedText: log.logText,
+              seed: log.seed,
+              modifiersApplied: log.modifiersApplied,
+            })),
+          });
+        }
+      });
+
+      // Update Redis cache.
       await this.store.setActiveMission(updated);
 
-      if (
-        updated.mission.status === 'active' ||
-        updated.mission.status === 'lobby'
-      ) {
+      if (updated.mission.status === 'active') {
         const nextMs = new Date(updated.mission.nextTickAt).getTime();
         await this.store.scheduleTick(missionId, nextMs);
       } else {
@@ -52,10 +100,22 @@ export class TickService {
           tickIndex: updated.mission.tickIndex,
         });
       }
+
+      await this.pubsub.broadcast(state.mission.participants[0]
+        ? await this.getChannelId(missionId)
+        : null, updated);
     } catch (err) {
       this.logger.error({ message: 'tick failed', missionId, err });
     } finally {
       await this.store.releaseLock(missionId, token);
     }
   }
+
+  private async getChannelId(missionId: string): Promise<string | null> {
+    const mission = await this.prisma.mission.findUnique({
+      where: { id: missionId },
+      select: { channelId: true },
+    });
+    return mission?.channelId ?? null;
+  }
 }
diff --git a/apps/api/src/app/tick-engine/twitch-pubsub.service.ts b/apps/api/src/app/tick-engine/twitch-pubsub.service.ts
new file mode 100644
index 0000000..121c74d
--- /dev/null
+++ b/apps/api/src/app/tick-engine/twitch-pubsub.service.ts
@@ -0,0 +1,72 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { createHmac } from 'crypto';
+import type { MissionStateResponse } from '@fog-explorer/api-interfaces';
+
+const PUBSUB_URL = 'https://api.twitch.tv/extensions/message';
+const TOKEN_TTL_SECONDS = 60;
+
+@Injectable()
+export class TwitchPubSubService {
+  private readonly logger = new Logger(TwitchPubSubService.name);
+
+  async broadcast(
+    channelId: string | null,
+    state: NonNullable<MissionStateResponse>
+  ): Promise<void> {
+    if (!channelId) return;
+
+    const clientId = process.env['TWITCH_CLIENT_ID'];
+    const secret = process.env['TWITCH_EXTENSION_SECRET'];
+    if (!clientId || !secret) return;
+
+    const token = buildServerToken(clientId, secret);
+    const payload = JSON.stringify({
+      content_type: 'application/json',
+      message: JSON.stringify(state),
+      targets: ['broadcast'],
+    });
+
+    if (Buffer.byteLength(payload, 'utf8') > 5000) {
+      this.logger.warn({ message: 'pubsub payload too large, skipping', channelId });
+      return;
+    }
+
+    try {
+      const res = await fetch(`${PUBSUB_URL}/${channelId}`, {
+        method: 'POST',
+        headers: {
+          'Authorization': `Bearer ${token}`,
+          'Client-Id': clientId,
+          'Content-Type': 'application/json',
+        },
+        body: payload,
+      });
+
+      if (!res.ok) {
+        this.logger.warn({
+          message: 'pubsub broadcast failed',
+          channelId,
+          status: res.status,
+        });
+      }
+    } catch (err) {
+      this.logger.error({ message: 'pubsub broadcast error', channelId, err });
+    }
+  }
+}
+
+function buildServerToken(clientId: string, secretB64: string): string {
+  const secretBytes = Buffer.from(secretB64, 'base64');
+  const exp = Math.floor(Date.now() / 1000) + TOKEN_TTL_SECONDS;
+
+  const header = Buffer.from(JSON.stringify({ alg: 'HS256', typ: 'JWT' })).toString('base64url');
+  const payload = Buffer.from(
+    JSON.stringify({ exp, user_id: clientId, role: 'external' })
+  ).toString('base64url');
+
+  const sig = createHmac('sha256', secretBytes)
+    .update(`${header}.${payload}`)
+    .digest('base64url');
+
+  return `${header}.${payload}.${sig}`;
+}
diff --git a/libs/encounter-library/src/lib/encounters.json b/libs/encounter-library/src/lib/encounters.json
index d1f93f2..5a500d3 100644
--- a/libs/encounter-library/src/lib/encounters.json
+++ b/libs/encounter-library/src/lib/encounters.json
@@ -9,12 +9,26 @@
       "flavorSuccess": [
         "The generator sputters to life. Light floods the area.",
         "Sparks fly, then hum — the generator catches.",
-        "Wires connected. The machine breathes again."
+        "Wires connected. The machine breathes again.",
+        "A deep mechanical thrum. Progress.",
+        "The gauge climbs. Another generator done.",
+        "Hands steady, heart racing. The engine turns over.",
+        "The generator shudders, then roars. One less in the dark.",
+        "Circuit reconnected. The hum is its own small victory.",
+        "It takes longer than expected, but the light comes.",
+        "The generator protests, then yields."
       ],
       "flavorFailure": [
         "The generator kicks back. Too many watchers in the dark.",
         "The mechanism jams. Footsteps echo nearby.",
-        "A noise betrays the position. The generator goes cold."
+        "A noise betrays the position. The generator goes cold.",
+        "Something shifts in the fog. The work abandoned.",
+        "The wiring resists every attempt. No progress tonight.",
+        "A shadow crosses the generator. Not now.",
+        "The tool slips. The noise is too loud.",
+        "The generator sparks wrong. An alarm of sorts.",
+        "Patience runs out before the generator does.",
+        "A nearby sound. The repair will have to wait."
       ]
     },
     {
@@ -25,12 +39,26 @@
       "flavorSuccess": [
         "The totem crumbles. Its curse lifts from the fog.",
         "Bones scatter. The hex dissolves into smoke.",
-        "The ritual unravels. Something distant screams."
+        "The ritual unravels. Something distant screams.",
+        "The totem falls apart like it was never solid.",
+        "Ash and splinter. The hex breaks.",
+        "A soft crack — the bones give way. Something changes.",
+        "The skull shatters. Whatever watched through it is gone.",
+        "The cleansing takes. The fog feels thinner.",
+        "The totem offers no resistance. It was waiting to fall.",
+        "One less curse in the trial."
       ],
       "flavorFailure": [
         "The totem resists. Its pull is stronger than expected.",
         "A presence drives the survivor back before the cleanse completes.",
-        "The hex holds. Dread thickens the air."
+        "The hex holds. Dread thickens the air.",
+        "Fingers close on the totem — then something warns away.",
+        "The totem hums with malice. Not today.",
+        "The ritual is interrupted. The hex burns brighter.",
+        "The bones refuse to break. Wrong approach.",
+        "The totem feels wrong. Leave it for now.",
+        "Whatever keeps the totem standing isn't done yet.",
+        "The cleanse stalls halfway. The hex endures."
       ]
     },
     {
@@ -41,12 +69,26 @@
       "flavorSuccess": [
         "The chest yields a worn medkit. Small mercies.",
         "A flashlight, still charged. The fog recedes slightly.",
-        "A useful tool among the debris."
+        "A useful tool among the debris.",
+        "Something worth having. The chest wasn't empty after all.",
+        "Buried under detritus — a working toolbox.",
+        "A medkit, half-depleted but still viable.",
+        "The chest creaks open. Something useful inside.",
+        "Luck, this time.",
+        "Not everything in the fog is hostile. The chest provides.",
+        "A find. The supplies won't last, but they'll help."
       ],
       "flavorFailure": [
         "The chest is empty. Only rust and regret.",
         "The lid splinters — nothing useful inside.",
-        "A noise nearby cuts the search short."
+        "A noise nearby cuts the search short.",
+        "Someone got here first.",
+        "The chest is locked. No time to force it.",
+        "Debris, nothing more.",
+        "Whatever was here is long gone.",
+        "The chest yields nothing. Time wasted.",
+        "Empty. The trial takes without giving.",
+        "Nothing. Move on."
       ]
     },
     {
@@ -57,12 +99,26 @@
       "flavorSuccess": [
         "With grim determination, the survivor slips free.",
         "Arms aching, the hook releases. Freedom, for now.",
-        "A desperate push — the chains give way."
+        "A desperate push — the chains give way.",
+        "The hook yields to persistence.",
+        "Blood and effort. The barb comes free.",
+        "The survivor drops to the ground, gasping.",
+        "Will wins where strength falls short. Free.",
+        "The hook's grip loosens. A precious second of clarity.",
+        "Every instinct says stop. The survivor doesn't.",
+        "The chains snap. Unlikely. Necessary."
       ],
       "flavorFailure": [
         "The struggle exhausts. The hook holds.",
         "Every movement drives the barb deeper. Stay still.",
-        "The fog presses in. The hook remains."
+        "The fog presses in. The hook remains.",
+        "The attempt fails. The chains don't care.",
+        "No leverage. No escape. Not yet.",
+        "The energy spent is wasted. Still trapped.",
+        "The hook was designed for this. It holds.",
+        "Patience isn't a luxury here — but neither is panic.",
+        "The barb shifts but doesn't release.",
+        "The struggle ends. The hook wins this round."
       ]
     },
     {
@@ -73,12 +129,26 @@
       "flavorSuccess": [
         "The gate grinds open. Cold air rushes in.",
         "Generators humming, the lock gives. Almost there.",
-        "The exit yields. Light from outside cuts the fog."
+        "The exit yields. Light from outside cuts the fog.",
+        "The switch holds down. The gate obeys.",
+        "A long, agonising second — then the gate opens.",
+        "The exit panel responds. The way out is clear.",
+        "The gate was always going to open. Tonight it does.",
+        "The outside world, briefly visible through iron.",
+        "The switch trips. The gate moves.",
+        "One last obstacle overcome."
       ],
       "flavorFailure": [
         "The gate mechanism is jammed. Precious seconds lost.",
         "A shadow falls across the panel. The attempt abandoned.",
-        "The switch is stuck. The gate stays shut."
+        "The switch is stuck. The gate stays shut.",
+        "The gate won't cooperate. Not now.",
+        "The panel sparks and resets. Try again.",
+        "Something holds the gate. Not mechanical — worse.",
+        "The generator noise covers the gate's resistance.",
+        "The lock mechanism fails. The gate holds.",
+        "Too slow. The gate doesn't open in time.",
+        "Pressure on the switch, nothing. Wrong timing."
       ]
     },
     {
@@ -89,12 +159,26 @@
       "flavorSuccess": [
         "Still as stone. The threat passes without noticing.",
         "A breath held long — then silence. Safe.",
-        "The fog swallows the survivor whole. Unseen."
+        "The fog swallows the survivor whole. Unseen.",
+        "The patrol route is predictable. Predictable is avoidable.",
+        "Close. Too close. But not close enough to matter.",
+        "The survivor becomes scenery. The patrol sees nothing.",
+        "A narrow gap in the patrol. Taken.",
+        "The killer's attention is elsewhere. Move.",
+        "Footsteps near, then receding. Safe.",
+        "The locker is cold and cramped and perfect."
       ],
       "flavorFailure": [
         "A twig snaps. Eye contact — then the chase begins.",
         "The survivor misjudges the angle. Spotted.",
-        "Heartbeat too loud. Presence too close."
+        "Heartbeat too loud. Presence too close.",
+        "The patrol's route changed. A fatal assumption.",
+        "No cover. The survivor is seen.",
+        "A shadow where there should be none. Detected.",
+        "The instinct to run is wrong. It happens anyway.",
+        "The fog offers no protection here.",
+        "Spotted. The trial shifts.",
+        "The killer turns at the wrong moment."
       ]
     },
     {
@@ -105,12 +189,26 @@
       "flavorSuccess": [
         "Bandages tight, the wound closes. Pain recedes.",
         "The medkit does its job. The survivor steadies.",
-        "A few tense minutes — injuries tended."
+        "A few tense minutes — injuries tended.",
+        "Not good as new, but functional. Good enough.",
+        "The bleeding stops. The fog feels slightly less hostile.",
+        "Clinical precision in a place with no clinics.",
+        "The medkit is emptied wisely. The injury yields.",
+        "Hands that shake still heal.",
+        "The wound is dressed. One less liability.",
+        "Recovery, however temporary, is still recovery."
       ],
       "flavorFailure": [
         "Supplies exhausted before the job is done.",
         "Shaking hands fumble the medkit. Time runs out.",
-        "The wound is worse than it looked. Supplies fall short."
+        "The wound is worse than it looked. Supplies fall short.",
+        "The medkit can't do what it wasn't built for.",
+        "Partial healing is still an open wound.",
+        "The medkit empties wrong. Wasted.",
+        "Not enough supplies. Not enough time.",
+        "A noise ends the attempt prematurely.",
+        "The injury resists treatment.",
+        "The medkit fails the survivor. Move anyway."
       ]
     },
     {
@@ -121,12 +219,26 @@
       "flavorSuccess": [
         "The pallet crashes down. A moment bought.",
         "Timber splinters between them. Distance gained.",
-        "The drop lands true. The chase falters."
+        "The drop lands true. The chase falters.",
+        "A calculated throw. The pallet does its job.",
+        "The killer staggers. A few precious seconds.",
+        "The pallet drops at the right instant.",
+        "An obstacle placed. The chase interrupted.",
+        "The wood holds. That's all it needs to do.",
+        "A roar of frustration behind the pallet. Run.",
+        "The drop lands. The gap widens."
       ],
       "flavorFailure": [
         "The pallet drops wide. No gap created.",
         "Too slow — the obstacle proves useless.",
-        "The throw miscalculated. The pursuit continues."
+        "The throw miscalculated. The pursuit continues.",
+        "The pallet falls too early. Used for nothing.",
+        "The killer vaults before the drop lands.",
+        "The angle was wrong. The pallet wasted.",
+        "The swing comes before the pallet hits.",
+        "Not enough distance to matter.",
+        "The throw panics. The pallet means nothing.",
+        "A wasted pallet. The chase doesn't stop."
       ]
     },
     {
@@ -137,12 +249,26 @@
       "flavorSuccess": [
         "The basement yields rare supplies. Worth the risk.",
         "A pristine toolbox — almost worth dying for.",
-        "The gamble paid off. The survivor emerges with something valuable."
+        "The gamble paid off. The survivor emerges with something valuable.",
+        "The basement gives up its best. A full medkit.",
+        "Down there and back. The best supplies in the trial.",
+        "The risk calculates out. Everything needed, found.",
+        "The stairs back up feel like a victory.",
+        "The basement held back something good tonight.",
+        "A rare find. The fog occasionally provides.",
+        "Against instinct, into the basement. Worth it."
       ],
       "flavorFailure": [
         "The basement was a trap. Retreat costs dearly.",
         "The stairwell offers no escape. A mistake made clear.",
-        "The risk was not worth the reward found — nothing."
+        "The risk was not worth the reward found — nothing.",
+        "The basement is empty. And now time is lost.",
+        "Going down is easy. Coming back is not.",
+        "The killer knows about the basement.",
+        "Nothing down here but dread.",
+        "The search finds nothing. The stairs up feel longer.",
+        "An empty chest in a dangerous room.",
+        "The basement takes more than it gives tonight."
       ]
     },
     {
@@ -153,12 +279,326 @@
       "flavorSuccess": [
         "The hatch sighs open. One last mercy from the fog.",
         "A sound — familiar, haunting. The hatch, just ahead.",
-        "Against all odds, the escape route reveals itself."
+        "Against all odds, the escape route reveals itself.",
+        "The hatch was always here. It waited.",
+        "The fog breaks once. That's enough.",
+        "The survivor finds it before the killer does.",
+        "One last door. It opens.",
+        "The hatch glows faintly. Run.",
+        "The sound of it — an invitation.",
+        "Found. The trial ends here."
       ],
       "flavorFailure": [
         "The hatch is nowhere. Only fog and silence.",
         "Close — so close. Then it closes.",
-        "The sound was something else entirely."
+        "The sound was something else entirely.",
+        "The hatch stays hidden.",
+        "Searching costs time that isn't there.",
+        "The killer finds the hatch first.",
+        "The fog gives nothing freely.",
+        "The sound led nowhere. A trick of the trial.",
+        "No hatch. No escape. Not this way.",
+        "The trial isn't done with the survivor yet."
+      ]
+    },
+    {
+      "key": "window_vault",
+      "baseProbability": 0.60,
+      "tags": ["escape", "survival"],
+      "tier": 1,
+      "flavorSuccess": [
+        "The window frame holds. Through and clear.",
+        "A clean vault. Momentum kept.",
+        "The opening is tight but usable.",
+        "Through the gap before the killer closes.",
+        "The vault buys distance. Use it.",
+        "A practiced move. The window yields.",
+        "Landing clean on the other side.",
+        "The window is a door when you need it.",
+        "Fast enough. The gap widens.",
+        "Through. The chase resets."
+      ],
+      "flavorFailure": [
+        "The window is boarded shut.",
+        "The vault is too slow. Caught.",
+        "The frame splinters. Not a clean exit.",
+        "Misjudged the height. A costly stumble.",
+        "The window closes the gap but not the killer.",
+        "Too narrow. No good.",
+        "The vault fails at the worst moment.",
+        "The opening was an illusion. Dead end.",
+        "A bad angle kills the attempt.",
+        "The window doesn't help tonight."
+      ]
+    },
+    {
+      "key": "locker_hide",
+      "baseProbability": 0.65,
+      "tags": ["stealth", "survival"],
+      "tier": 1,
+      "flavorSuccess": [
+        "The locker closes. Footsteps pass. Breathe.",
+        "Darkness and rust — perfect cover.",
+        "The killer walks past the locker without a glance.",
+        "Still. Quiet. Safe.",
+        "The locker is old and cold and hiding works.",
+        "In and out before the threat turns around.",
+        "The locker holds its occupant safe.",
+        "A long minute of nothing. Then clear.",
+        "The hiding spot works. The patrol moves on.",
+        "The locker door stays closed. The killer moves on."
+      ],
+      "flavorFailure": [
+        "The locker door rattles. Discovered.",
+        "The killer yanks it open. No hiding here.",
+        "The locker was already checked.",
+        "The sound of breathing gives the position away.",
+        "The killer knows these lockers too well.",
+        "A squeak of the hinge. Fatal.",
+        "The hiding spot chosen is the wrong one.",
+        "The killer's instinct is correct tonight.",
+        "Spotted entering. No time.",
+        "The locker offers nothing. Pulled out."
+      ]
+    },
+    {
+      "key": "trap_disarm",
+      "baseProbability": 0.50,
+      "tags": ["objectives", "altruistic"],
+      "tier": 2,
+      "flavorSuccess": [
+        "The trap clicks disarmed. One less hazard.",
+        "Patient work. The mechanism yields.",
+        "The snap of metal, controlled this time.",
+        "Disarmed without triggering. Clean.",
+        "The trap comes apart safely.",
+        "A moment of focus. The trap poses no more threat.",
+        "The floor is safer now.",
+        "The mechanism was elegant. Now it's inert.",
+        "One trap gone. Onwards.",
+        "The disarm holds. The path is clear."
+      ],
+      "flavorFailure": [
+        "The trap snaps. A brutal reminder.",
+        "One wrong move. The trap wins.",
+        "The mechanism was subtler than expected.",
+        "The disarm attempt triggers it.",
+        "Fingers too slow. The trap bites.",
+        "The trap was set with someone capable in mind.",
+        "Miscalculation. The mechanism triggers.",
+        "The trap holds and catches.",
+        "The attempt fails. Pain follows.",
+        "The trap wasn't meant to be disarmed easily."
+      ]
+    },
+    {
+      "key": "survivor_rescue",
+      "baseProbability": 0.45,
+      "tags": ["altruistic", "hook"],
+      "tier": 2,
+      "flavorSuccess": [
+        "Off the hook. Both survivors run.",
+        "The unhook is clean. No one watching.",
+        "A teammate freed. The trial continues.",
+        "Quick hands, lucky timing. The rescue holds.",
+        "The hook releases. Time to move.",
+        "Pulled free before the killer returns.",
+        "The rescue works. Move fast.",
+        "A window of opportunity, taken.",
+        "The teammate drops free. The trial has two again.",
+        "Freed. Both running now."
+      ],
+      "flavorFailure": [
+        "The killer turns back too soon. Retreat.",
+        "The rescue fails. Both caught.",
+        "The timing was wrong.",
+        "The unhook attempted — the killer was watching.",
+        "No safe window. The rescue abandoned.",
+        "The hook held on.",
+        "The approach was spotted.",
+        "The teammate is hooked again. Worse now.",
+        "The rescue was a trap.",
+        "The killer was closer than it looked."
+      ]
+    },
+    {
+      "key": "ruin_destroy",
+      "baseProbability": 0.45,
+      "tags": ["totem", "objectives", "altruistic"],
+      "tier": 2,
+      "flavorSuccess": [
+        "The ruin totem falls. Generator speed returns to normal.",
+        "The hex breaks. The pressure lifts.",
+        "Ruin destroyed. The generators are finally cooperating.",
+        "The totem crumbles. Something screams.",
+        "The ruin is gone. Work can continue properly.",
+        "The corrupting influence ends here.",
+        "Ruin undone. A meaningful contribution.",
+        "The hex shattered. Every generator benefits.",
+        "Ruin falls. The trial shifts.",
+        "The cleansing removes one of the fog's advantages."
+      ],
+      "flavorFailure": [
+        "Ruin holds. The generators resist every effort.",
+        "The totem is guarded.",
+        "Ruin endures. Progress is a trickle.",
+        "The hex is stronger than expected.",
+        "The cleanse fails. Ruin stays.",
+        "Guarded or cursed — the totem won't fall.",
+        "The approach to ruin is cut off.",
+        "Ruin watches everything. No safe approach.",
+        "The hex survives the attempt.",
+        "Ruin stands. The generators punish every mistake."
+      ]
+    },
+    {
+      "key": "noise_check",
+      "baseProbability": 0.70,
+      "tags": ["stealth", "survival", "objectives"],
+      "tier": 1,
+      "flavorSuccess": [
+        "The area is clear. Work continues.",
+        "A careful sweep — nothing here.",
+        "All quiet. Safe to proceed.",
+        "The check takes seconds. Worth every one.",
+        "Nothing threatening nearby. Focus returned.",
+        "The perimeter is clean. Move on.",
+        "A slow look around — all clear.",
+        "The survivor's instincts were right. Safe.",
+        "No danger. The noise was nothing.",
+        "The area is empty. Continue."
+      ],
+      "flavorFailure": [
+        "The check reveals what was feared.",
+        "Not clear. Danger is close.",
+        "The area isn't empty.",
+        "The sound was not nothing.",
+        "A presence, sensed too late.",
+        "The check confirms the worst.",
+        "Not safe. Move now.",
+        "The area is watched.",
+        "The noise was a warning.",
+        "Something is here."
+      ]
+    },
+    {
+      "key": "map_find",
+      "baseProbability": 0.40,
+      "tags": ["item", "objectives"],
+      "tier": 1,
+      "flavorSuccess": [
+        "A map of the trial grounds. The generators are marked.",
+        "Routes, exits — everything useful on one piece of paper.",
+        "The map provides context. Decisions improve.",
+        "A schematic of the realm. Useful.",
+        "The map shows what couldn't be known otherwise.",
+        "A rare find. The trial becomes navigable.",
+        "Totem locations, hooks — the map tells all.",
+        "The map is accurate. That's not guaranteed here.",
+        "A clearer picture of the trial grounds.",
+        "The map is old but correct. It will help."
+      ],
+      "flavorFailure": [
+        "Nothing useful found.",
+        "The map, if it existed, is gone.",
+        "The search yields no information.",
+        "Fog and confusion. No map here.",
+        "The grounds give nothing away.",
+        "The trial keeps its layout to itself.",
+        "No orientation gained.",
+        "Blind as before.",
+        "The realm offers no guide tonight.",
+        "No map. Trust instinct."
+      ]
+    },
+    {
+      "key": "scratch_marks",
+      "baseProbability": 0.55,
+      "tags": ["stealth", "altruistic"],
+      "tier": 1,
+      "flavorSuccess": [
+        "The trail read correctly. The survivor is found.",
+        "Scratch marks, followed. Another survivor located.",
+        "The signs in the fog tell a story.",
+        "The trail is fresh. Someone was here recently.",
+        "The marks lead somewhere useful.",
+        "Reading the ground pays off.",
+        "The scratch marks don't lie.",
+        "A teammate's path, followed to its source.",
+        "The signs are legible. The survivor is found.",
+        "The trail ends at something worth finding."
+      ],
+      "flavorFailure": [
+        "The trail goes cold.",
+        "The marks lead nowhere useful.",
+        "Misread. The path was wrong.",
+        "The trail circles back. Disorienting.",
+        "The signs in the fog are misleading.",
+        "Too old. The trail is gone.",
+        "The scratch marks weren't recent.",
+        "The trail led somewhere dangerous.",
+        "The signs can't be read clearly.",
+        "The trail ends without resolution."
+      ]
+    },
+    {
+      "key": "bone_chill",
+      "baseProbability": 0.35,
+      "tags": ["high-risk", "survival"],
+      "tier": 3,
+      "flavorSuccess": [
+        "The presence recedes. The survivor is not chosen.",
+        "Whatever stalks the fog passes over.",
+        "The terror subsides. Not tonight.",
+        "The entity considers — then moves on.",
+        "The survivor is overlooked. Lucky.",
+        "The cold lifts. The entity chose elsewhere.",
+        "The fog's attention moves away.",
+        "Stillness. The presence is gone.",
+        "Not taken. Not yet.",
+        "The chill passes. The trial continues."
+      ],
+      "flavorFailure": [
+        "The fog thickens. Something approaches.",
+        "The presence locks on. There is no outrunning this.",
+        "The entity's attention does not waver.",
+        "Noticed. The trial changes.",
+        "The chill deepens. The entity is here.",
+        "No escape from something this deliberate.",
+        "The fog moves with purpose.",
+        "The survivor is seen by something that doesn't forget.",
+        "The presence descends.",
+        "Chosen. The hardest part begins."
+      ]
+    },
+    {
+      "key": "killer_instinct",
+      "baseProbability": 0.30,
+      "tags": ["high-risk", "stealth"],
+      "tier": 3,
+      "flavorSuccess": [
+        "The instinct passes harmlessly. Not found.",
+        "The killer's sense of where to look is wrong tonight.",
+        "The prediction fails. Safe.",
+        "The killer checks elsewhere.",
+        "Instinct misfires. The survivor is still hidden.",
+        "Wrong corner checked. The survivor breathes.",
+        "The killer's certainty was misplaced.",
+        "Not there. Not tonight.",
+        "The instinct was wrong. Move quickly.",
+        "The killer's focus breaks elsewhere."
+      ],
+      "flavorFailure": [
+        "The killer knows exactly where to look.",
+        "Instinct and experience. The survivor is found.",
+        "No hiding from something this certain.",
+        "The killer's read was correct.",
+        "The position is given away before the search begins.",
+        "Exactly where expected. No luck tonight.",
+        "The killer's certainty was earned.",
+        "Found before the search starts.",
+        "The instinct is right.",
+        "The killer walks directly to the survivor."
       ]
     }
   ]
diff --git a/libs/mission-logic/src/index.ts b/libs/mission-logic/src/index.ts
index 8b54e17..f461982 100644
--- a/libs/mission-logic/src/index.ts
+++ b/libs/mission-logic/src/index.ts
@@ -1 +1,2 @@
 export * from './lib/encounter-resolver';
+export * from './lib/perk-math';
diff --git a/libs/mission-logic/src/lib/encounter-resolver.spec.ts b/libs/mission-logic/src/lib/encounter-resolver.spec.ts
index a023626..70dddc2 100644
--- a/libs/mission-logic/src/lib/encounter-resolver.spec.ts
+++ b/libs/mission-logic/src/lib/encounter-resolver.spec.ts
@@ -198,6 +198,69 @@ describe('resolveEncounter', () => {
       expect(result.logText.length).toBeGreaterThan(0);
     }
   });
+
+  // Edge cases: modifier overflow / degenerate inputs
+  it('massive positive perk modifier clamps probability to 1 — never throws', () => {
+    const perk: Perk = {
+      id: '00000000-0000-4000-a000-000000000003',
+      key: 'overpowered',
+      name: '',
+      description: '',
+      tags: [],
+      modifiers: [{ target: 'successChance', type: 'additive', amount: 100 }],
+    };
+    const result = resolveEncounter(
+      makeInput({ encounter: { key: 'gen', baseProbability: 0.5, tags: [] },
+        survivor: { id: '00000000-0000-4000-a000-000000000002', state: 'active',
+          stats: { objectives: 5, survival: 5, altruism: 5 }, perkSlots: [perk], hookCount: 0 } })
+    );
+    expect(result.success).toBe(true); // clamped to 1 → always succeeds
+  });
+
+  it('massive negative perk modifier clamps probability to 0 — never throws', () => {
+    const perk: Perk = {
+      id: '00000000-0000-4000-a000-000000000003',
+      key: 'cursed',
+      name: '',
+      description: '',
+      tags: [],
+      modifiers: [{ target: 'successChance', type: 'additive', amount: -100 }],
+    };
+    const result = resolveEncounter(
+      makeInput({ encounter: { key: 'gen', baseProbability: 0.5, tags: [] },
+        survivor: { id: '00000000-0000-4000-a000-000000000002', state: 'active',
+          stats: { objectives: 5, survival: 5, altruism: 5 }, perkSlots: [perk], hookCount: 0 } })
+    );
+    expect(result.success).toBe(false); // clamped to 0 → always fails
+  });
+
+  it('empty perkSlots array is handled without error', () => {
+    expect(() =>
+      resolveEncounter(makeInput({ survivor: {
+        id: '00000000-0000-4000-a000-000000000002', state: 'active',
+        stats: { objectives: 5, survival: 5, altruism: 5 }, perkSlots: [], hookCount: 0,
+      } }))
+    ).not.toThrow();
+  });
+
+  it('sacrificed survivor produces no state change on failure', () => {
+    const result = resolveEncounter(makeInput({
+      encounter: { key: 'gen', baseProbability: 0, tags: [] },
+      survivor: { id: '00000000-0000-4000-a000-000000000002', state: 'sacrificed',
+        stats: { objectives: 1, survival: 1, altruism: 1 }, perkSlots: [], hookCount: 2 },
+    }));
+    expect(result.success).toBe(false);
+    expect(result.survivorStateChange).toBeNull();
+  });
+
+  it('idle survivor produces no state change on failure', () => {
+    const result = resolveEncounter(makeInput({
+      encounter: { key: 'gen', baseProbability: 0, tags: [] },
+      survivor: { id: '00000000-0000-4000-a000-000000000002', state: 'idle',
+        stats: { objectives: 1, survival: 1, altruism: 1 }, perkSlots: [], hookCount: 0 },
+    }));
+    expect(result.survivorStateChange).toBeNull();
+  });
 });
 
 // ── Property-based tests ──────────────────────────────────────────────────────
diff --git a/libs/mission-logic/src/lib/encounter-resolver.ts b/libs/mission-logic/src/lib/encounter-resolver.ts
index 9055121..b30d6a3 100644
--- a/libs/mission-logic/src/lib/encounter-resolver.ts
+++ b/libs/mission-logic/src/lib/encounter-resolver.ts
@@ -2,11 +2,11 @@ import seedrandom = require('seedrandom');
 import type {
   EncounterDefinition,
   EncounterResult,
-  ModifierApplication,
   Perk,
   SurvivorState,
   SurvivorStats,
 } from '@fog-explorer/api-interfaces';
+import { applyPerkModifiers } from './perk-math';
 
 export interface ResolverInput {
   seed: string;
@@ -23,15 +23,10 @@ export interface ResolverInput {
   };
 }
 
-// Probability adjustments per stat point and per difficulty level.
 const OBJECTIVES_BONUS = 0.02;
 const ALTRUISM_BONUS = 0.02;
 const DIFFICULTY_PENALTY = 0.12;
-
-// Tag that enables the altruism stat bonus.
 const ALTRUISM_TAG = 'altruistic';
-
-// Injury probability floor/ceiling when active survivor fails.
 const INJURY_CHANCE_BASE = 0.8;
 const INJURY_CHANCE_FLOOR = 0.2;
 const SURVIVAL_INJURY_REDUCTION = 0.05;
@@ -40,25 +35,28 @@ export function resolveEncounter(input: ResolverInput): EncounterResult {
   const rng = seedrandom(input.seed);
 
   let probability = input.encounter.baseProbability;
-
   probability -= (input.difficulty - 1) * DIFFICULTY_PENALTY;
   probability += input.survivor.stats.objectives * OBJECTIVES_BONUS;
-
   if (input.encounter.tags.includes(ALTRUISM_TAG)) {
     probability += input.survivor.stats.altruism * ALTRUISM_BONUS;
   }
 
-  const modifiersApplied = applyPerkModifiers(probability, input);
-  probability = modifiersApplied.adjusted;
-  const appliedList = modifiersApplied.applied;
+  const { probability: finalProbability, applied } = applyPerkModifiers(
+    probability,
+    input.survivor.perkSlots,
+    input.encounter.tags
+  );
 
-  probability = Math.max(0, Math.min(1, probability));
-
-  const success = rng() < probability;
+  const success = rng() < finalProbability;
 
   const survivorStateChange = success
     ? null
-    : computeStateChange(rng, input.survivor.state, input.survivor.stats.survival, input.survivor.hookCount);
+    : computeStateChange(
+        rng,
+        input.survivor.state,
+        input.survivor.stats.survival,
+        input.survivor.hookCount
+      );
 
   return {
     missionId: input.missionId,
@@ -68,47 +66,11 @@ export function resolveEncounter(input: ResolverInput): EncounterResult {
     seed: input.seed,
     success,
     survivorStateChange,
-    modifiersApplied: appliedList,
+    modifiersApplied: applied,
     logText: buildLogText(input.encounter.key, success, survivorStateChange),
   };
 }
 
-function applyPerkModifiers(
-  startProbability: number,
-  input: ResolverInput
-): { adjusted: number; applied: ModifierApplication[] } {
-  let probability = startProbability;
-  const applied: ModifierApplication[] = [];
-
-  for (const perk of input.survivor.perkSlots) {
-    for (const mod of perk.modifiers) {
-      if (mod.target !== 'successChance') continue;
-
-      if (mod.condition) {
-        const tagMatch = mod.condition.encounterTags.some((t) =>
-          input.encounter.tags.includes(t)
-        );
-        if (!tagMatch) continue;
-      }
-
-      if (mod.type === 'additive') {
-        probability += mod.amount;
-      } else {
-        probability *= 1 + mod.amount;
-      }
-
-      applied.push({
-        perkKey: perk.key,
-        target: mod.target,
-        type: mod.type,
-        effectiveAmount: mod.amount,
-      });
-    }
-  }
-
-  return { adjusted: probability, applied };
-}
-
 function computeStateChange(
   rng: seedrandom.PRNG,
   currentState: SurvivorState,
diff --git a/libs/mission-logic/src/lib/monte-carlo.spec.ts b/libs/mission-logic/src/lib/monte-carlo.spec.ts
new file mode 100644
index 0000000..5f69d88
--- /dev/null
+++ b/libs/mission-logic/src/lib/monte-carlo.spec.ts
@@ -0,0 +1,305 @@
+import { resolveEncounter } from './encounter-resolver';
+import type {
+  EncounterDefinition,
+  Perk,
+  SurvivorState,
+  SurvivorStats,
+} from '@fog-explorer/api-interfaces';
+
+// ── Constants ─────────────────────────────────────────────────────────────────
+
+const TICKS_PER_MISSION = 20;
+const MISSIONS_PER_SCENARIO = 2000; // 5 scenarios × 2000 = 10 000 total
+
+// ── Types ─────────────────────────────────────────────────────────────────────
+
+interface SimScenario {
+  readonly name: string;
+  readonly difficulty: number;
+  readonly encounter: EncounterDefinition;
+  readonly stats: SurvivorStats;
+  readonly perks: Perk[];
+}
+
+interface MissionOutcome {
+  readonly successCount: number;
+  readonly wasInjured: boolean;
+  readonly wasSacrificed: boolean;
+}
+
+interface DistributionSnapshot {
+  successRate: number;
+  injuryRate: number;
+  sacrificeRate: number;
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makePerk(
+  key: string,
+  amount: number,
+  type: 'additive' | 'multiplicative'
+): Perk {
+  return {
+    id: '00000000-0000-4000-a000-000000000001',
+    key,
+    name: key,
+    description: '',
+    tags: [],
+    modifiers: [{ target: 'successChance', type, amount }],
+  };
+}
+
+function simulateMission(
+  scenario: SimScenario,
+  missionIndex: number
+): MissionOutcome {
+  let state: SurvivorState = 'active';
+  let hookCount = 0;
+  let successCount = 0;
+  let wasInjured = false;
+  let wasSacrificed = false;
+
+  for (let tick = 0; tick < TICKS_PER_MISSION; tick++) {
+    const result = resolveEncounter({
+      seed: `mc-${scenario.name}-${missionIndex}-${tick}`,
+      missionId: `mc-mission-${missionIndex}`,
+      tickIndex: tick,
+      difficulty: scenario.difficulty,
+      encounter: scenario.encounter,
+      survivor: {
+        id: '00000000-0000-4000-a000-000000000002',
+        state,
+        stats: scenario.stats,
+        perkSlots: scenario.perks,
+        hookCount,
+      },
+    });
+
+    if (result.survivorStateChange) {
+      const sc = result.survivorStateChange;
+      if (sc.to === 'injured') {
+        state = 'injured';
+        wasInjured = true;
+      } else if (sc.to === 'downed') {
+        // Stay downed for the next tick so downed+hookCount≥2 → sacrifice can fire.
+        hookCount++;
+        state = 'downed';
+        wasInjured = true;
+      } else if (sc.to === 'sacrificed') {
+        wasSacrificed = true;
+        break;
+      }
+    } else {
+      // No state change: success, or failure with no consequence (e.g. downed+hookCount<2).
+      // If currently downed (and not sacrificed), the encounter resolves without harm — rescued.
+      if (state === 'downed') {
+        state = 'active';
+      }
+      if (result.success) {
+        successCount++;
+      }
+    }
+  }
+
+  return { successCount, wasInjured, wasSacrificed };
+}
+
+function runScenario(scenario: SimScenario): DistributionSnapshot {
+  let totalSuccess = 0;
+  let injuredCount = 0;
+  let sacrificedCount = 0;
+
+  for (let i = 0; i < MISSIONS_PER_SCENARIO; i++) {
+    const { successCount, wasInjured, wasSacrificed } = simulateMission(
+      scenario,
+      i
+    );
+    totalSuccess += successCount;
+    if (wasInjured) injuredCount++;
+    if (wasSacrificed) sacrificedCount++;
+  }
+
+  const round = (n: number): number => Math.round(n * 1000) / 1000;
+  return {
+    successRate: round(totalSuccess / (MISSIONS_PER_SCENARIO * TICKS_PER_MISSION)),
+    injuryRate: round(injuredCount / MISSIONS_PER_SCENARIO),
+    sacrificeRate: round(sacrificedCount / MISSIONS_PER_SCENARIO),
+  };
+}
+
+// ── Scenarios ─────────────────────────────────────────────────────────────────
+
+const STANDARD_ENCOUNTER: EncounterDefinition = {
+  key: 'generator',
+  baseProbability: 0.6,
+  tags: [],
+};
+
+const BASE_STATS: SurvivorStats = { objectives: 5, survival: 5, altruism: 5 };
+
+const SCENARIOS = {
+  baseline: {
+    name: 'baseline',
+    difficulty: 1,
+    encounter: STANDARD_ENCOUNTER,
+    stats: BASE_STATS,
+    perks: [],
+  },
+  hard: {
+    name: 'hard',
+    difficulty: 3,
+    encounter: STANDARD_ENCOUNTER,
+    stats: BASE_STATS,
+    perks: [],
+  },
+  objectivesPerk: {
+    name: 'objectives-perk',
+    difficulty: 1,
+    encounter: STANDARD_ENCOUNTER,
+    stats: BASE_STATS,
+    perks: [makePerk('objectives-boost', 0.15, 'additive')],
+  },
+  survivalPerk: {
+    name: 'survival-perk',
+    difficulty: 1,
+    encounter: STANDARD_ENCOUNTER,
+    stats: { ...BASE_STATS, survival: 10 },
+    perks: [],
+  },
+  stacked: {
+    // objectives=7 → +0.14, add +0.05, mul ×1.10 → ~87% final probability.
+    // Represents a well-optimised build that is strong but not degenerate.
+    name: 'stacked',
+    difficulty: 1,
+    encounter: STANDARD_ENCOUNTER,
+    stats: { objectives: 7, survival: 7, altruism: 5 },
+    perks: [
+      makePerk('add-boost', 0.05, 'additive'),
+      makePerk('mul-boost', 0.1, 'multiplicative'),
+    ],
+  },
+} satisfies Record<string, SimScenario>;
+
+// ── Distribution snapshot tests ───────────────────────────────────────────────
+// Seeds are deterministic strings → results are reproducible across runs.
+// On first run, vitest writes the inline snapshots; CI then guards regressions.
+
+describe('Monte Carlo balance harness — distribution snapshots', () => {
+  let results: Record<keyof typeof SCENARIOS, DistributionSnapshot>;
+
+  beforeAll(() => {
+    results = {
+      baseline: runScenario(SCENARIOS.baseline),
+      hard: runScenario(SCENARIOS.hard),
+      objectivesPerk: runScenario(SCENARIOS.objectivesPerk),
+      survivalPerk: runScenario(SCENARIOS.survivalPerk),
+      stacked: runScenario(SCENARIOS.stacked),
+    };
+  });
+
+  it('baseline distribution', () => {
+    expect(results.baseline).toMatchInlineSnapshot(`
+      {
+        "injuryRate": 0.973,
+        "sacrificeRate": 0.194,
+        "successRate": 0.67,
+      }
+    `);
+  });
+
+  it('hard difficulty distribution', () => {
+    expect(results.hard).toMatchInlineSnapshot(`
+      {
+        "injuryRate": 0.999,
+        "sacrificeRate": 0.72,
+        "successRate": 0.341,
+      }
+    `);
+  });
+
+  it('objectives-perk distribution', () => {
+    expect(results.objectivesPerk).toMatchInlineSnapshot(`
+      {
+        "injuryRate": 0.815,
+        "sacrificeRate": 0.018,
+        "successRate": 0.849,
+      }
+    `);
+  });
+
+  it('survival-perk distribution', () => {
+    expect(results.survivalPerk).toMatchInlineSnapshot(`
+      {
+        "injuryRate": 0.846,
+        "sacrificeRate": 0.093,
+        "successRate": 0.686,
+      }
+    `);
+  });
+
+  it('stacked perk loadout distribution', () => {
+    expect(results.stacked).toMatchInlineSnapshot(`
+      {
+        "injuryRate": 0.711,
+        "sacrificeRate": 0.007,
+        "successRate": 0.866,
+      }
+    `);
+  });
+});
+
+// ── Balance envelope assertions ───────────────────────────────────────────────
+// These fire on top of snapshots to catch degenerate configurations even if
+// a snapshot was accidentally committed with broken numbers.
+
+describe('Monte Carlo balance harness — balance envelopes', () => {
+  let results: Record<keyof typeof SCENARIOS, DistributionSnapshot>;
+
+  beforeAll(() => {
+    results = {
+      baseline: runScenario(SCENARIOS.baseline),
+      hard: runScenario(SCENARIOS.hard),
+      objectivesPerk: runScenario(SCENARIOS.objectivesPerk),
+      survivalPerk: runScenario(SCENARIOS.survivalPerk),
+      stacked: runScenario(SCENARIOS.stacked),
+    };
+  });
+
+  it('hard difficulty has lower success rate than baseline', () => {
+    expect(results.hard.successRate).toBeLessThan(results.baseline.successRate);
+  });
+
+  it('hard difficulty has higher sacrifice rate than baseline', () => {
+    expect(results.hard.sacrificeRate).toBeGreaterThan(
+      results.baseline.sacrificeRate
+    );
+  });
+
+  it('objectives perk increases success rate over baseline', () => {
+    expect(results.objectivesPerk.successRate).toBeGreaterThan(
+      results.baseline.successRate
+    );
+  });
+
+  it('stacked loadout does not produce degenerate success rate (>0.95)', () => {
+    expect(results.stacked.successRate).toBeLessThan(0.95);
+  });
+
+  it('baseline sacrifice rate is meaningful (>1%) and not excessive (<25%)', () => {
+    expect(results.baseline.sacrificeRate).toBeGreaterThan(0.01);
+    expect(results.baseline.sacrificeRate).toBeLessThan(0.25);
+  });
+
+  it('every scenario produces some successes (not locked out)', () => {
+    for (const dist of Object.values(results)) {
+      expect(dist.successRate).toBeGreaterThan(0);
+    }
+  });
+
+  it('every scenario has a chance of injury (game has stakes)', () => {
+    for (const dist of Object.values(results)) {
+      expect(dist.injuryRate).toBeGreaterThan(0);
+    }
+  });
+});
diff --git a/libs/mission-logic/src/lib/perk-math.spec.ts b/libs/mission-logic/src/lib/perk-math.spec.ts
new file mode 100644
index 0000000..25a4ea2
--- /dev/null
+++ b/libs/mission-logic/src/lib/perk-math.spec.ts
@@ -0,0 +1,225 @@
+import * as fc from 'fast-check';
+import { applyPerkModifiers } from './perk-math';
+import type { Perk } from '@fog-explorer/api-interfaces';
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makePerk(overrides: Partial<Perk> & { amount: number; type?: 'additive' | 'multiplicative'; tags?: string[] }): Perk {
+  return {
+    id: '00000000-0000-4000-a000-000000000001',
+    key: overrides.key ?? 'test-perk',
+    name: 'Test Perk',
+    description: '',
+    tags: [],
+    modifiers: [
+      {
+        target: 'successChance',
+        type: overrides.type ?? 'additive',
+        amount: overrides.amount,
+        condition: overrides.tags ? { encounterTags: overrides.tags } : undefined,
+      },
+    ],
+  };
+}
+
+// ── Unit tests ────────────────────────────────────────────────────────────────
+
+describe('applyPerkModifiers', () => {
+  it('returns baseProbability unchanged with no perks', () => {
+    const { probability, applied } = applyPerkModifiers(0.5, [], []);
+    expect(probability).toBe(0.5);
+    expect(applied).toHaveLength(0);
+  });
+
+  it('applies a single additive modifier', () => {
+    const { probability } = applyPerkModifiers(0.4, [makePerk({ amount: 0.2 })], []);
+    expect(probability).toBeCloseTo(0.6);
+  });
+
+  it('applies a single multiplicative modifier', () => {
+    const { probability } = applyPerkModifiers(0.5, [makePerk({ amount: 0.2, type: 'multiplicative' })], []);
+    expect(probability).toBeCloseTo(0.6);
+  });
+
+  it('additives sum before multiplicatives apply', () => {
+    const perks: Perk[] = [
+      makePerk({ key: 'a', amount: 0.1 }),                              // additive +0.1
+      makePerk({ key: 'b', amount: 0.1 }),                              // additive +0.1
+      makePerk({ key: 'c', amount: 0.5, type: 'multiplicative' }),     // ×1.5
+    ];
+    // base 0.4 + 0.2 additive = 0.6 → × 1.5 = 0.9
+    const { probability } = applyPerkModifiers(0.4, perks, []);
+    expect(probability).toBeCloseTo(0.9);
+  });
+
+  it('clamps overflow above 1.0 to 1.0', () => {
+    const perks = [makePerk({ amount: 5.0 })]; // base 0.5 + 5 = 5.5 → clamped
+    const { probability } = applyPerkModifiers(0.5, perks, []);
+    expect(probability).toBe(1);
+  });
+
+  it('clamps underflow below 0 to 0', () => {
+    const perks = [makePerk({ amount: -5.0 })];
+    const { probability } = applyPerkModifiers(0.5, perks, []);
+    expect(probability).toBe(0);
+  });
+
+  it('negative multiplicative modifier reduces probability', () => {
+    const { probability } = applyPerkModifiers(0.6, [makePerk({ amount: -0.5, type: 'multiplicative' })], []);
+    expect(probability).toBeCloseTo(0.3);
+  });
+
+  it('skips modifier when condition tag not in encounter tags', () => {
+    const perk = makePerk({ amount: 0.3, tags: ['totem'] });
+    const { probability, applied } = applyPerkModifiers(0.5, [perk], ['generator']);
+    expect(probability).toBeCloseTo(0.5);
+    expect(applied).toHaveLength(0);
+  });
+
+  it('applies modifier when condition tag matches', () => {
+    const perk = makePerk({ amount: 0.3, tags: ['generator'] });
+    const { probability } = applyPerkModifiers(0.5, [perk], ['generator', 'objectives']);
+    expect(probability).toBeCloseTo(0.8);
+  });
+
+  it('unconditional modifier applies regardless of encounter tags', () => {
+    const perk = makePerk({ amount: 0.2 }); // no condition
+    const { probability } = applyPerkModifiers(0.5, [perk], []);
+    expect(probability).toBeCloseTo(0.7);
+  });
+
+  it('non-successChance target modifiers are ignored', () => {
+    const perk: Perk = {
+      id: '00000000-0000-4000-a000-000000000001',
+      key: 'stat-perk',
+      name: '',
+      description: '',
+      tags: [],
+      modifiers: [{ target: 'objectives', type: 'additive', amount: 2 }],
+    };
+    const { probability } = applyPerkModifiers(0.5, [perk], []);
+    expect(probability).toBe(0.5);
+  });
+
+  it('records one applied entry per modifier', () => {
+    const perks = [
+      makePerk({ key: 'a', amount: 0.1 }),
+      makePerk({ key: 'b', amount: 0.2 }),
+    ];
+    const { applied } = applyPerkModifiers(0.4, perks, []);
+    expect(applied).toHaveLength(2);
+    expect(applied.map((a) => a.perkKey)).toEqual(expect.arrayContaining(['a', 'b']));
+  });
+
+  it('applied entries record preApply and postApply probabilities', () => {
+    const perk = makePerk({ amount: 0.2 });
+    const { applied } = applyPerkModifiers(0.4, [perk], []);
+    expect(applied[0].preApplyProbability).toBeCloseTo(0.4);
+    expect(applied[0].postApplyProbability).toBeCloseTo(0.6);
+  });
+});
+
+// ── Property-based tests ──────────────────────────────────────────────────────
+
+describe('applyPerkModifiers — property-based', () => {
+  const arbAmount = fc.float({ min: Math.fround(-1), max: Math.fround(1), noNaN: true });
+
+  const arbPerk: fc.Arbitrary<Perk> = fc.record({
+    id: fc.uuid(),
+    key: fc.string({ minLength: 1, maxLength: 20 }),
+    name: fc.string({ minLength: 1 }),
+    description: fc.string(),
+    tags: fc.constant([]),
+    modifiers: fc.array(
+      fc.record({
+        target: fc.constantFrom('successChance' as const),
+        type: fc.constantFrom('additive' as const, 'multiplicative' as const),
+        amount: arbAmount,
+        condition: fc.option(
+          fc.record({ encounterTags: fc.array(fc.constantFrom('generator', 'totem'), { minLength: 1 }) }),
+          { nil: undefined }
+        ),
+      }),
+      { maxLength: 3 }
+    ),
+  });
+
+  it('result probability is always in [0, 1]', () => {
+    fc.assert(
+      fc.property(
+        fc.float({ min: 0, max: 1, noNaN: true }),
+        fc.array(arbPerk, { maxLength: 4 }),
+        fc.array(fc.constantFrom('generator', 'totem', 'exit'), { maxLength: 3 }),
+        (base, perks, tags) => {
+          const { probability } = applyPerkModifiers(base, perks, tags);
+          expect(probability).toBeGreaterThanOrEqual(0);
+          expect(probability).toBeLessThanOrEqual(1);
+        }
+      )
+    );
+  });
+
+  it('every applied modifier references a perk in the input', () => {
+    fc.assert(
+      fc.property(
+        fc.float({ min: 0, max: 1, noNaN: true }),
+        fc.array(arbPerk, { maxLength: 4 }),
+        (base, perks) => {
+          const { applied } = applyPerkModifiers(base, perks, []);
+          const keys = new Set(perks.map((p) => p.key));
+          for (const mod of applied) {
+            expect(keys.has(mod.perkKey)).toBe(true);
+          }
+        }
+      )
+    );
+  });
+
+  it('no perks never changes base probability (within [0,1])', () => {
+    fc.assert(
+      fc.property(fc.float({ min: 0, max: 1, noNaN: true }), (base) => {
+        const { probability, applied } = applyPerkModifiers(base, [], []);
+        expect(probability).toBeCloseTo(base);
+        expect(applied).toHaveLength(0);
+      })
+    );
+  });
+
+  it('additive modifiers with large positive amounts still clamp to 1', () => {
+    fc.assert(
+      fc.property(
+        fc.float({ min: 0, max: 1, noNaN: true }),
+        fc.array(
+          fc.float({ min: Math.fround(0.1), max: Math.fround(10), noNaN: true }),
+          { minLength: 1, maxLength: 5 }
+        ),
+        (base, amounts) => {
+          const perks = amounts.map((amount, i) =>
+            makePerk({ key: `p${i}`, amount })
+          );
+          const { probability } = applyPerkModifiers(base, perks, []);
+          expect(probability).toBeLessThanOrEqual(1);
+        }
+      )
+    );
+  });
+
+  it('additive modifiers with large negative amounts still clamp to 0', () => {
+    fc.assert(
+      fc.property(
+        fc.float({ min: 0, max: 1, noNaN: true }),
+        fc.array(
+          fc.float({ min: Math.fround(-10), max: Math.fround(-0.1), noNaN: true }),
+          { minLength: 1, maxLength: 5 }
+        ),
+        (base, amounts) => {
+          const perks = amounts.map((amount, i) =>
+            makePerk({ key: `p${i}`, amount })
+          );
+          const { probability } = applyPerkModifiers(base, perks, []);
+          expect(probability).toBeGreaterThanOrEqual(0);
+        }
+      )
+    );
+  });
+});
diff --git a/libs/mission-logic/src/lib/perk-math.ts b/libs/mission-logic/src/lib/perk-math.ts
new file mode 100644
index 0000000..111a1c3
--- /dev/null
+++ b/libs/mission-logic/src/lib/perk-math.ts
@@ -0,0 +1,101 @@
+import type { ModifierApplication, Perk, PerkModifierTarget } from '@fog-explorer/api-interfaces';
+
+export interface AppliedModifier extends ModifierApplication {
+  readonly preApplyProbability: number;
+  readonly postApplyProbability: number;
+}
+
+export interface PerkMathResult {
+  readonly probability: number;
+  readonly applied: AppliedModifier[];
+}
+
+const P_MIN = 0;
+const P_MAX = 1;
+
+/**
+ * Applies all perk modifiers targeting `successChance` from the given perk
+ * slots, filtered by encounter tags. Additives are summed first, then
+ * multiplicatives applied in order. Result is clamped to [0, 1].
+ *
+ * Separating this from the resolver keeps the probability pipeline testable
+ * independently and makes modifier-overflow edge cases visible.
+ */
+export function applyPerkModifiers(
+  baseProbability: number,
+  perks: Perk[],
+  encounterTags: string[],
+  target: PerkModifierTarget = 'successChance'
+): PerkMathResult {
+  let probability = baseProbability;
+  const applied: AppliedModifier[] = [];
+
+  // Two-pass: collect additive sum, then apply multiplicatives.
+  // This matches standard RPG convention: add-then-multiply prevents
+  // multiplicative stacking from compounding excessively.
+  let additiveSum = 0;
+  const multiplicativePerks: Array<{ perk: Perk; amount: number }> = [];
+
+  for (const perk of perks) {
+    for (const mod of perk.modifiers) {
+      if (mod.target !== target) continue;
+      if (!conditionMatches(mod.condition, encounterTags)) continue;
+
+      if (mod.type === 'additive') {
+        additiveSum += mod.amount;
+      } else {
+        multiplicativePerks.push({ perk, amount: mod.amount });
+      }
+    }
+  }
+
+  // Apply additive sum in one step.
+  if (additiveSum !== 0) {
+    const pre = probability;
+    probability += additiveSum;
+
+    // Record one entry per contributing perk.
+    for (const perk of perks) {
+      for (const mod of perk.modifiers) {
+        if (mod.target !== target || mod.type !== 'additive') continue;
+        if (!conditionMatches(mod.condition, encounterTags)) continue;
+        applied.push({
+          perkKey: perk.key,
+          target: mod.target,
+          type: mod.type,
+          effectiveAmount: mod.amount,
+          preApplyProbability: pre,
+          postApplyProbability: probability,
+        });
+      }
+    }
+  }
+
+  // Apply multiplicatives individually so each can be logged.
+  for (const { perk, amount } of multiplicativePerks) {
+    const pre = probability;
+    probability *= 1 + amount;
+    applied.push({
+      perkKey: perk.key,
+      target,
+      type: 'multiplicative',
+      effectiveAmount: amount,
+      preApplyProbability: pre,
+      postApplyProbability: probability,
+    });
+  }
+
+  return { probability: clamp(probability, P_MIN, P_MAX), applied };
+}
+
+function conditionMatches(
+  condition: { encounterTags: string[] } | undefined,
+  encounterTags: string[]
+): boolean {
+  if (!condition) return true;
+  return condition.encounterTags.some((t) => encounterTags.includes(t));
+}
+
+function clamp(value: number, min: number, max: number): number {
+  return Math.max(min, Math.min(max, value));
+}
diff --git a/package.json b/package.json
index e50407c..880d928 100644
--- a/package.json
+++ b/package.json
@@ -52,6 +52,7 @@
     "jsonc-eslint-parser": "^2.1.0",
     "nx": "22.7.1",
     "prettier": "~3.6.2",
+    "prisma": "^5.22.0",
     "ts-jest": "^29.4.0",
     "ts-node": "10.9.1",
     "tslib": "^2.3.0",
@@ -72,11 +73,29 @@
     "@nestjs/core": "^11.0.0",
     "@nestjs/platform-express": "^11.0.0",
     "@nestjs/schedule": "^6.1.3",
+    "@nestjs/throttler": "^6.5.0",
+    "@prisma/client": "^5.22.0",
     "axios": "^1.6.0",
     "ioredis": "^5.10.1",
     "reflect-metadata": "^0.1.13",
     "rxjs": "^7.8.0",
     "seedrandom": "^3.0.5",
     "zod": "^4.4.3"
+  },
+  "pnpm": {
+    "onlyBuiltDependencies": [
+      "@nestjs/core",
+      "@parcel/watcher",
+      "@prisma/client",
+      "@prisma/engines",
+      "@swc/core",
+      "esbuild",
+      "less",
+      "lmdb",
+      "msgpackr-extract",
+      "nx",
+      "prisma",
+      "unrs-resolver"
+    ]
   }
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index a33d8ec..ed5b7a4 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -38,6 +38,12 @@ importers:
       '@nestjs/schedule':
         specifier: ^6.1.3
         version: 6.1.3(@nestjs/common@11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2))(@nestjs/core@11.1.19)
+      '@nestjs/throttler':
+        specifier: ^6.5.0
+        version: 6.5.0(@nestjs/common@11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2))(@nestjs/core@11.1.19)(reflect-metadata@0.1.14)
+      '@prisma/client':
+        specifier: ^5.22.0
+        version: 5.22.0(prisma@5.22.0)
       axios:
         specifier: ^1.6.0
         version: 1.15.0
@@ -198,6 +204,9 @@ importers:
       prettier:
         specifier: ~3.6.2
         version: 3.6.2
+      prisma:
+        specifier: ^5.22.0
+        version: 5.22.0
       ts-jest:
         specifier: ^29.4.0
         version: 29.4.9(@babel/core@7.29.0)(@jest/transform@30.3.0)(@jest/types@30.3.0)(babel-jest@30.3.0(@babel/core@7.29.0))(esbuild@0.27.3)(jest-util@30.3.0)(jest@30.3.0(@types/node@20.19.9)(babel-plugin-macros@3.1.0)(ts-node@10.9.1(@swc/core@1.15.33(@swc/helpers@0.5.21))(@types/node@20.19.9)(typescript@5.9.3)))(typescript@5.9.3)
@@ -2188,6 +2197,13 @@ packages:
       '@nestjs/platform-express':
         optional: true
 
+  '@nestjs/throttler@6.5.0':
+    resolution: {integrity: sha512-9j0ZRfH0QE1qyrj9JjIRDz5gQLPqq9yVC2nHsrosDVAfI5HHw08/aUAWx9DZLSdQf4HDkmhTTEGLrRFHENvchQ==}
+    peerDependencies:
+      '@nestjs/common': ^7.0.0 || ^8.0.0 || ^9.0.0 || ^10.0.0 || ^11.0.0
+      '@nestjs/core': ^7.0.0 || ^8.0.0 || ^9.0.0 || ^10.0.0 || ^11.0.0
+      reflect-metadata: ^0.1.13 || ^0.2.0
+
   '@noble/hashes@1.4.0':
     resolution: {integrity: sha512-V1JJ1WTRUqHHrOSh597hURcMqVKVGL/ea3kv0gSnEdsEZ0/+VyPghM1lMNGc00z7CIQorSvbKpuJkxvuHbvdbg==}
     engines: {node: '>= 16'}
@@ -2661,6 +2677,30 @@ packages:
     engines: {node: '>=18'}
     hasBin: true
 
+  '@prisma/client@5.22.0':
+    resolution: {integrity: sha512-M0SVXfyHnQREBKxCgyo7sffrKttwE6R8PMq330MIUF0pTwjUhLbW84pFDlf06B27XyCR++VtjugEnIHdr07SVA==}
+    engines: {node: '>=16.13'}
+    peerDependencies:
+      prisma: '*'
+    peerDependenciesMeta:
+      prisma:
+        optional: true
+
+  '@prisma/debug@5.22.0':
+    resolution: {integrity: sha512-AUt44v3YJeggO2ZU5BkXI7M4hu9BF2zzH2iF2V5pyXT/lRTyWiElZ7It+bRH1EshoMRxHgpYg4VB6rCM+mG5jQ==}
+
+  '@prisma/engines-version@5.22.0-44.605197351a3c8bdd595af2d2a9bc3025bca48ea2':
+    resolution: {integrity: sha512-2PTmxFR2yHW/eB3uqWtcgRcgAbG1rwG9ZriSvQw+nnb7c4uCr3RAcGMb6/zfE88SKlC1Nj2ziUvc96Z379mHgQ==}
+
+  '@prisma/engines@5.22.0':
+    resolution: {integrity: sha512-UNjfslWhAt06kVL3CjkuYpHAWSO6L4kDCVPegV6itt7nD1kSJavd3vhgAEhjglLJJKEdJ7oIqDJ+yHk6qO8gPA==}
+
+  '@prisma/fetch-engine@5.22.0':
+    resolution: {integrity: sha512-bkrD/Mc2fSvkQBV5EpoFcZ87AvOgDxbG99488a5cexp5Ccny+UM6MAe/UFkUC0wLYD9+9befNOqGiIJhhq+HbA==}
+
+  '@prisma/get-platform@5.22.0':
+    resolution: {integrity: sha512-pHhpQdr1UPFpt+zFfnPazhulaZYCUqeIcPpJViYoq9R+D/yw4fjE+CtnsnKzPYm0ddUbeXUzjGVGIRVgPDCk4Q==}
+
   '@rolldown/binding-android-arm64@1.0.0-rc.17':
     resolution: {integrity: sha512-s70pVGhw4zqGeFnXWvAzJDlvxhlRollagdCCKRgOsgUOH3N1l0LIxf83AtGzmb5SiVM4Hjl5HyarMRfdfj3DaQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -6637,6 +6677,11 @@ packages:
     resolution: {integrity: sha512-oG4T3wCbfeuvljnyAzhBvpN45E8iOTXCU/TD3zXW80HA3dQ4ahdqMkWGiPWZvjpQwlbyHrPTWUAqUzGzv4l1JQ==}
     engines: {node: ^18.14.0 || ^20.0.0 || ^22.0.0 || >=24.0.0}
 
+  prisma@5.22.0:
+    resolution: {integrity: sha512-vtpjW3XuYCSnMsNVBjLMNkTj6OZbudcPPTPYHqX0CJfpcdWciI1dM8uHETwmDxxiqEwCIE6WvXucWUetJgfu/A==}
+    engines: {node: '>=16.13'}
+    hasBin: true
+
   proc-log@6.1.0:
     resolution: {integrity: sha512-iG+GYldRf2BQ0UDUAd6JQ/RwzaQy6mXmsk/IzlYyal4A4SNFw54MeH4/tLkF4I5WoWG9SQwuqWzS99jaFQHBuQ==}
     engines: {node: ^20.17.0 || >=22.9.0}
@@ -10398,6 +10443,12 @@ snapshots:
     optionalDependencies:
       '@nestjs/platform-express': 11.1.19(@nestjs/common@11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2))(@nestjs/core@11.1.19)
 
+  '@nestjs/throttler@6.5.0(@nestjs/common@11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2))(@nestjs/core@11.1.19)(reflect-metadata@0.1.14)':
+    dependencies:
+      '@nestjs/common': 11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2)
+      '@nestjs/core': 11.1.19(@nestjs/common@11.1.19(reflect-metadata@0.1.14)(rxjs@7.8.2))(@nestjs/platform-express@11.1.19)(reflect-metadata@0.1.14)(rxjs@7.8.2)
+      reflect-metadata: 0.1.14
+
   '@noble/hashes@1.4.0': {}
 
   '@npmcli/agent@4.0.0':
@@ -11250,6 +11301,31 @@ snapshots:
     dependencies:
       playwright: 1.59.1
 
+  '@prisma/client@5.22.0(prisma@5.22.0)':
+    optionalDependencies:
+      prisma: 5.22.0
+
+  '@prisma/debug@5.22.0': {}
+
+  '@prisma/engines-version@5.22.0-44.605197351a3c8bdd595af2d2a9bc3025bca48ea2': {}
+
+  '@prisma/engines@5.22.0':
+    dependencies:
+      '@prisma/debug': 5.22.0
+      '@prisma/engines-version': 5.22.0-44.605197351a3c8bdd595af2d2a9bc3025bca48ea2
+      '@prisma/fetch-engine': 5.22.0
+      '@prisma/get-platform': 5.22.0
+
+  '@prisma/fetch-engine@5.22.0':
+    dependencies:
+      '@prisma/debug': 5.22.0
+      '@prisma/engines-version': 5.22.0-44.605197351a3c8bdd595af2d2a9bc3025bca48ea2
+      '@prisma/get-platform': 5.22.0
+
+  '@prisma/get-platform@5.22.0':
+    dependencies:
+      '@prisma/debug': 5.22.0
+
   '@rolldown/binding-android-arm64@1.0.0-rc.17':
     optional: true
 
@@ -15648,6 +15724,12 @@ snapshots:
       ansi-styles: 5.2.0
       react-is: 18.3.1
 
+  prisma@5.22.0:
+    dependencies:
+      '@prisma/engines': 5.22.0
+    optionalDependencies:
+      fsevents: 2.3.3
+
   proc-log@6.1.0: {}
 
   process-nextick-args@2.0.1: {}
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index 9f45815..d19b9c2 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -1,21 +1,25 @@
 allowBuilds:
   '@nestjs/core': true
   '@parcel/watcher': true
+  '@prisma/engines': true
   '@swc/core': true
   esbuild: true
   less: true
   lmdb: true
   msgpackr-extract: true
   nx: true
+  prisma: true
   unrs-resolver: true
 autoInstallPeers: true
 onlyBuiltDependencies:
   - '@nestjs/core'
   - '@parcel/watcher'
+  - '@prisma/engines'
   - '@swc/core'
   - esbuild
   - less
   - lmdb
   - msgpackr-extract
   - nx
+  - prisma
   - unrs-resolver