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+# Power-Profile → Fan-Profile Sync Trigger Design
+
+**Date:** 2026-05-11
+**Status:** Approved
+
+## Summary
+
+When the user changes power profile via `scripts/power-profile.sh --menu`, also nudge the waybar fan widget so `scripts/fan-profile.sh` immediately re-evaluates its auto-mode mapping. Without this nudge, the fan strategy follows the new power profile only on the next 5 s waybar poll; with it, the change is essentially instant. If fan auto mode is off (the `~/.local/state/fan-profile-auto` sentinel is absent), nothing changes — manual fan strategy is preserved.
+
+## Current Behaviour
+
+`scripts/power-profile.sh --menu` ends with:
+```bash
+[ -n "$CHOICE" ] && powerprofilesctl set "$CHOICE" && pkill -RTMIN+8 waybar
+```
+
+Signal `RTMIN+8` is the `signal:` value declared by waybar's `custom/power-profile` module — refreshes the power widget. The fan widget (`signal: 9`) is NOT refreshed; it only re-evaluates on its `interval: 5` poll.
+
+`scripts/fan-profile.sh` already has the coupling logic. When the auto sentinel exists, every status emit:
+1. Reads `powerprofilesctl get`
+2. Maps it via `map_profile_to_strategy`
+3. Calls `fw-fanctrl use <mapped>` if the active strategy differs
+
+So changing the power profile causes the fan strategy to follow within ≤5 s already — but only on the next poll. The user wants this to be instant.
+
+## Target Behaviour
+
+After the user picks a new power profile from the wofi menu:
+1. `powerprofilesctl set` applies the change.
+2. `pkill -RTMIN+8 waybar` refreshes the power widget.
+3. **`pkill -RTMIN+9 waybar` refreshes the fan widget**, which re-runs `fan-profile.sh`. If auto mode is on, fan-profile.sh notices the strategy mismatch and applies the new strategy via `fw-fanctrl use`. If auto mode is off, the script just re-renders the existing strategy (no functional change).
+
+End-to-end latency: well under a second.
+
+## Why This Implementation
+
+Reuses the existing single-source-of-truth mapping in `fan-profile.sh::map_profile_to_strategy`. Power-profile.sh doesn't need to know:
+- The mapping table (lives in fan-profile.sh)
+- The auto sentinel path (lives in fan-profile.sh)
+- The `fw-fanctrl use` command (lives in fan-profile.sh)
+
+It just sends a "hey, you should re-evaluate" signal. Zero duplication. Zero new files. One line.
+
+## Implementation
+
+### `scripts/power-profile.sh`
+
+Change line 13 from:
+```bash
+    [ -n "$CHOICE" ] && powerprofilesctl set "$CHOICE" && pkill -RTMIN+8 waybar
+```
+to:
+```bash
+    [ -n "$CHOICE" ] && powerprofilesctl set "$CHOICE" && pkill -RTMIN+8 waybar && pkill -RTMIN+9 waybar
+```
+
+The chained `&&` means the fan-widget refresh fires only if the power-widget refresh succeeded, which only fires if `powerprofilesctl set` succeeded. So a failure to apply the profile (e.g. dbus not running) skips both refreshes — the bar reflects the unchanged state on its next 5 s poll.
+
+## Files Touched
+
+- `scripts/power-profile.sh` — one-line change to line 13.
+
+## Out of Scope
+
+- **Power-profile changes via tools other than this script.** If the user runs `powerprofilesctl set X` from a terminal or via a GNOME settings panel, the fan still follows on fan-profile.sh's 5 s poll (auto mode). Making that path zero-lag would need a dbus listener for `org.freedesktop.UPower.PowerProfiles` — bigger architectural change, deferred.
+- **Changing the mapping** — `power-saver→lazy`, `balanced→medium`, `performance→agile` is locked from the original fan-profile auto spec.
+- **Making auto default-on** — auto sentinel still has to be created via the fan wofi menu choice; this spec doesn't change that opt-in.
+- **Race condition between powerprofilesctl set and fan-profile.sh re-read.** `powerprofilesctl set` is synchronous on dbus; by the time it returns, `powerprofilesctl get` reflects the new value. No race.