Add particle effects / atmosphere panel design spec

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/superpowers/specs/2026-04-10-particle-effects-design.md

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+# Particle Effects / Atmosphere Panel
+
+**Date:** 2026-04-10  
+**Status:** Approved
+
+## Summary
+
+Replace the single fog toggle button in the campaign header with an atmosphere panel that supports four effects: fog (CSS, existing), fire, rain, and embers (tsParticles). Effects stack independently. Each effect has an on/off toggle and an intensity slider (0–100).
+
+## Library
+
+`@tsparticles/react` + `@tsparticles/slim`
+
+- Slim engine includes all shapes and movers needed for fire, rain, embers
+- Intensity maps directly onto particle config params (count, speed)
+- FogOverlay stays as CSS — no library change for fog
+
+## Components
+
+### `AtmospherePanel.tsx` (new)
+
+Button trigger in the campaign header, replacing the existing fog `<button>`. When one or more effects are active the button shows their icons (e.g. `🌫🔥`). Clicking opens a popover panel anchored below the button. Clicking outside closes it.
+
+Panel contains one row per effect (Fog, Fire, Rain, Embers):
+- Label with emoji
+- Toggle switch (on/off)
+- Intensity slider (0–100), dimmed when effect is off
+
+On any toggle or slider change, the component calls an `onAtmosphereChange(newAtmosphere)` callback. CampaignView owns the socket; its handler calls `setAtmosphere(next)` and `socket.emit("atmosphere:update", { campaignId, ...next })`. AtmospherePanel receives only `atmosphere` state and `onAtmosphereChange` as props — no direct socket access.
+
+Fog intensity slider is rendered but has no mechanical effect in v1 (CSS fog doesn't have an intensity param). It will not be wired until the fog overlay supports it.
+
+### `ParticleOverlay.tsx` (new)
+
+Full-screen fixed canvas, `pointer-events: none`, z-index 9997 (just below FogOverlay at 9998). Receives the full `atmosphere` state. For each of fire, rain, embers: if `active === true`, renders a tsParticles instance with a config generated from `getXxxConfig(intensity)`. Each effect is a separate tsParticles instance so they layer independently.
+
+### `particleConfigs.ts` (new)
+
+Pure functions — no side effects, no imports from React. Each takes `intensity: number` (0–100) and returns a tsParticles `ISourceOptions` config.
+
+| Effect | Count range | Speed range | Particle style |
+|--------|-------------|-------------|----------------|
+| Fire   | 20–200      | 2–8 upward  | Small circles, orange/red/yellow gradient, fade as they rise, emitter along bottom edge |
+| Rain   | 50–500      | 5–20 downward | Thin elongated lines, ~70° angle, slight opacity, full-width emitter at top |
+| Embers | 5–80        | 0.2–1.5 drift | Small dots, warm amber, slow random drift, gentle fade-out |
+
+### `FogOverlay.tsx` (unchanged)
+
+Props unchanged: `active: boolean`. CampaignView passes `atmosphere.fog.active`.
+
+## State
+
+In `CampaignView.tsx`, replace `fogActive: boolean` with:
+
+```typescript
+const [atmosphere, setAtmosphere] = useState({
+  fog:    { active: false, intensity: 50 },
+  fire:   { active: false, intensity: 50 },
+  rain:   { active: false, intensity: 50 },
+  embers: { active: false, intensity: 50 },
+});
+```
+
+## Socket
+
+### Payload change
+
+`atmosphere:update` payload changes from `{ fog: boolean }` to:
+
+```typescript
+{
+  fog:    { active: boolean; intensity: number };
+  fire:   { active: boolean; intensity: number };
+  rain:   { active: boolean; intensity: number };
+  embers: { active: boolean; intensity: number };
+}
+```
+
+### Server (`server/src/socket.ts`)
+
+Update the TypeScript type for the `atmosphere:update` handler to accept and rebroadcast the new payload shape. No persistence — server is a pure relay.
+
+### Client (`CampaignView.tsx`)
+
+The `atmosphere:update` listener replaces the entire `atmosphere` state with the received payload, keeping all clients in sync including intensity values.
+
+## File Checklist
+
+| File | Action |
+|------|--------|
+| `client/src/components/AtmospherePanel.tsx` | Create |
+| `client/src/components/AtmospherePanel.module.css` | Create |
+| `client/src/components/ParticleOverlay.tsx` | Create |
+| `client/src/lib/particleConfigs.ts` | Create |
+| `client/src/components/FogOverlay.tsx` | No change |
+| `client/src/components/FogOverlay.module.css` | No change |
+| `client/src/pages/CampaignView.tsx` | Update state, socket listener, JSX |
+| `server/src/socket.ts` | Update TypeScript type |
+| `client/package.json` | Add @tsparticles/react, @tsparticles/slim |
+
+## Out of Scope
+
+- Fog intensity wiring (slider exists, does nothing in v1)
+- Moving atmosphere control to App-level header (deferred to DM view redesign)
+- Snow or other effects beyond fog/fire/rain/embers
+- Per-effect configuration beyond intensity (e.g. wind direction for rain)