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+# Fan-Profile "Auto" Mode Design
+
+**Date:** 2026-05-01
+**Status:** Approved
+
+## Summary
+
+Add a virtual `auto` strategy to the waybar fan-profile module. When auto is on, `scripts/fan-profile.sh` keeps `fw-fanctrl` in sync with the active `power-profiles-daemon` profile — `power-saver` → `lazy`, `balanced` → `medium`, `performance` → `agile`. Reconciliation rides waybar's existing 5 s poll; no new daemon, no udev hooks, no fw-fanctrl strategy edits.
+
+## Current Behaviour
+
+`scripts/fan-profile.sh` is invoked by waybar's `custom/fan-profile` module on a 5 s interval and on click:
+
+- **Status emit:** runs `fw-fanctrl print`, parses out the active strategy and current speed, prints a JSON line with an icon and tooltip.
+- **`--menu`:** runs `fw-fanctrl print list`, pipes the strategy names through wofi, calls `fw-fanctrl use <choice>`, signals `pkill -RTMIN+9 waybar` so the bar refreshes.
+
+The strategy list is whatever `fw-fanctrl print list` returns: `laziest, lazy, medium, agile, very-agile, deaf, aeolus`. There is currently no notion of an automatic mode.
+
+## Target Behaviour
+
+### Wofi menu
+
+A new entry `auto` is prepended to the strategy list before passing it to wofi. Selecting it:
+
+1. Touches the state file `~/.local/state/fan-profile-auto`.
+2. Resolves the current power profile and calls `fw-fanctrl use <mapped>` once.
+3. Signals waybar to refresh.
+
+Selecting any non-`auto` strategy:
+
+1. Removes the state file (if it exists).
+2. Calls `fw-fanctrl use <choice>` (current behaviour, unchanged).
+3. Signals waybar to refresh.
+
+### Status emit (every 5 s)
+
+```
+state file exists?
+├── yes → read powerprofilesctl get
+│         ├── ok       → resolve mapped strategy
+│         │              ├── differs from fw-fanctrl's active → fw-fanctrl use <mapped>
+│         │              └── matches → no-op
+│         │              emit JSON: text="auto", tooltip="auto → <mapped>", class="auto"
+│         └── error    → emit JSON: text="auto (?)", tooltip="auto: power-profiles-daemon unreachable", class="auto"
+└── no  → existing behaviour: emit fw-fanctrl's active strategy
+```
+
+### Mapping
+
+| power-profiles-daemon | fw-fanctrl |
+|---|---|
+| `power-saver` | `lazy` |
+| `balanced` | `medium` |
+| `performance` | `agile` |
+
+Hardcoded in the script — small, stable, doesn't need a config file. If a profile name comes back unrecognized (e.g. a custom profile), the script falls into the error branch above (`auto (?)`).
+
+## Implementation
+
+### `scripts/fan-profile.sh` (only file changed)
+
+Three additions to the existing script:
+
+1. **State path constant** at top:
+   ```bash
+   STATE_FILE="${XDG_STATE_HOME:-$HOME/.local/state}/fan-profile-auto"
+   ```
+
+2. **Mapping function**:
+   ```bash
+   map_profile_to_strategy() {
+     case "$1" in
+       power-saver) echo lazy ;;
+       balanced)    echo medium ;;
+       performance) echo agile ;;
+       *)           return 1 ;;
+     esac
+   }
+   ```
+
+3. **Menu branch** — prepend `auto` and route the choice:
+   ```bash
+   if [ "$1" = "--menu" ]; then
+     STRATS=$(fw-fanctrl print list 2>/dev/null | grep "^-" | sed 's/^- //')
+     CHOICE=$(printf 'auto\n%s\n' "$STRATS" | wofi --dmenu --prompt "Fan Strategy:" \
+                  --width 260 --height 320 --hide-scroll --no-actions --insensitive)
+     [ -z "$CHOICE" ] && exit
+     if [ "$CHOICE" = "auto" ]; then
+       mkdir -p "$(dirname "$STATE_FILE")"
+       touch "$STATE_FILE"
+       PROFILE=$(powerprofilesctl get 2>/dev/null) && \
+         MAPPED=$(map_profile_to_strategy "$PROFILE") && \
+         fw-fanctrl use "$MAPPED"
+     else
+       rm -f "$STATE_FILE"
+       fw-fanctrl use "$CHOICE"
+     fi
+     pkill -RTMIN+9 waybar
+     exit
+   fi
+   ```
+
+4. **Status branch** — wrap the existing emit with auto-mode handling:
+   ```bash
+   if [ -f "$STATE_FILE" ]; then
+     PROFILE=$(powerprofilesctl get 2>/dev/null)
+     MAPPED=$(map_profile_to_strategy "$PROFILE" 2>/dev/null)
+     if [ -n "$MAPPED" ]; then
+       ACTIVE=$(fw-fanctrl print 2>/dev/null | awk -F"'" '/^Strategy:/{print $2}')
+       [ "$ACTIVE" != "$MAPPED" ] && fw-fanctrl use "$MAPPED" >/dev/null 2>&1
+       printf '{"text": "󰈐  auto", "tooltip": "Auto fan strategy\\nProfile: %s → %s\\nClick to change", "class": "auto"}\n' "$PROFILE" "$MAPPED"
+     else
+       printf '{"text": "󰈐  auto (?)", "tooltip": "Auto: power-profiles-daemon unreachable or unknown profile\\nClick to change", "class": "auto"}\n'
+     fi
+     exit
+   fi
+   # ... existing status emit (fw-fanctrl print → icon/level → JSON) ...
+   ```
+
+### Reconciliation cadence
+
+Waybar polls `custom/fan-profile` every 5 s (`"interval": 5` in `waybar/config.jsonc`). Each poll runs the script, which reads the state file and reconciles. No additional daemon, signal, or hook is needed. Worst-case desync: 5 s after a power-profile change.
+
+The existing `pkill -RTMIN+9 waybar` from `power-profile.sh --menu` will trigger an immediate refresh when the user changes profile via the bar — so in the common case, the fan strategy switches within waybar's render cycle, not 5 s later.
+
+### Persistence
+
+State file lives at `$XDG_STATE_HOME/fan-profile-auto` (default `~/.local/state/fan-profile-auto`). XDG state dir survives reboot, so auto stays on across sessions. Removing the file (or selecting any non-auto strategy) disables auto mode.
+
+## Files Touched
+
+- `scripts/fan-profile.sh` — three additions (state constant, mapping function, two new branches in menu and status handlers).
+
+No CSS, no waybar config, no install.sh changes.
+
+## Out of Scope
+
+- Syncing the auto-on state across machines (would require moving the state file into `~/.config/` and tracking it in the dotfiles repo).
+- Mapping to strategies other than `lazy`/`medium`/`agile`. The user can edit the mapping function inline if they want different curves later.
+- Reacting to anything other than power-profiles-daemon (CPU temp, AC vs battery, etc.). Those were rejected during brainstorming in favour of the cleaner power-profile coupling.
+- A separate icon for auto mode. Reuses the existing `󰈐` glyph; the `auto` text in the bar is the differentiator.
+- Tracking `/etc/fw-fanctrl/config.json` in the dotfiles repo (raised during clarifications, not adopted — auto doesn't need any new fw-fanctrl strategies).