Let the idle timings know whether you are plugged in

An idle screen costs a screen on wall power and the rest of your
afternoon on battery, so they should not be the same number. hypridle
has no concept of a power source -- one config, one set of timeouts --
so rather than maintaining two configs and swapping them, panama-idle
builds the single config from whichever key set applies, and IdleLock
rebuilds it when the charger comes or goes. That runs through the same
400ms debounce a settings change uses, so a loose charger cannot
restart hypridle in a loop.

The battery keys fall back to their AC counterparts rather than to the
schema defaults. Without that, unplugging would silently override a
deliberately long timing with a shipped short one, which is the kind
of thing you would notice only by losing work.

A machine with no battery reads none of it and generates exactly what
it generated before. The contract pins that alongside the two obvious
directions, and was checked by sabotaging the detection to confirm it
fails rather than passing vacuously.

tests/hypr/idle-config-contract

@@ -77,6 +77,84 @@ status="$(XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" "$helper"
 jq -e '.managed == false and .blankMinutes == 5 and .lockMinutes == 10' <<<"$status" >/dev/null \
     || fail "status did not report the generated values: $status"
 
+# ── Power source ─────────────────────────────────────────────────────────────
+#
+# hypridle has no concept of AC versus battery, so there is one config and it
+# is rebuilt from the other set of keys when the charger comes or goes. Three
+# things must hold, and the third is the one that protects every existing
+# desktop:
+#
+#   1. On battery, the battery keys win.
+#   2. A battery key that was never written falls back to its AC counterpart,
+#      not to the schema's shorter shipped default -- otherwise unplugging
+#      would silently override a deliberately long setting.
+#   3. A machine with no battery reads none of them, and generates exactly
+#      what it generated before any of this existed.
+#
+# panama-hw is stubbed rather than the sysfs tree, because this is testing
+# which keys panama-idle chooses, not how the hardware is detected. That is
+# the hardware predicates contract's job.
+
+stub_hw() {
+    mkdir -p "$work/fake/bin"
+    cat >"$work/fake/bin/panama-hw" <<STUB
+#!/usr/bin/env bash
+case "\$1" in
+    battery) exit $1 ;;
+    ac)      exit $2 ;;
+    *)       exit 1 ;;
+esac
+STUB
+    chmod +x "$work/fake/bin/panama-hw"
+}
+
+run_powered() {
+    mkdir -p "$work/config/panama"
+    printf '%s' "$1" >"$work/config/panama/settings.json"
+    XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" \
+        PANAMA_PATH="$work/fake" "$helper" apply
+}
+
+settings='{"screenBlankMinutes":30,"lockMinutes":45,"suspendMinutes":0,
+           "screenBlankMinutesBattery":2,"lockMinutesBattery":5,"suspendMinutesBattery":20}'
+
+# On battery: battery keys.
+stub_hw 0 1
+run_powered "$settings"
+grep -q 'timeout = 120' "$generated" || fail 'on battery, the battery blank timing was not used'
+grep -q 'timeout = 300' "$generated" || fail 'on battery, the battery lock timing was not used'
+grep -q 'systemctl suspend' "$generated" || fail 'on battery, the battery suspend listener is missing'
+grep -q 'Power source at generation: battery' "$generated" \
+    || fail 'the generated config does not record that it was built for battery'
+
+# Plugged in: AC keys, and no suspend, even though the battery set has one.
+stub_hw 0 0
+run_powered "$settings"
+grep -q 'timeout = 1800' "$generated" || fail 'on wall power, the AC blank timing was not used'
+grep -q 'timeout = 2700' "$generated" || fail 'on wall power, the AC lock timing was not used'
+grep -q 'systemctl suspend' "$generated" && fail 'on wall power, a battery-only suspend listener was written'
+
+# A battery key that was never written falls back to its AC counterpart.
+stub_hw 0 1
+run_powered '{"screenBlankMinutes":30,"lockMinutes":45}'
+grep -q 'timeout = 1800' "$generated" \
+    || fail 'an unset battery blank did not fall back to the AC value, so unplugging would override a deliberate setting'
+grep -q 'timeout = 2700' "$generated" \
+    || fail 'an unset battery lock did not fall back to the AC value'
+
+# No battery at all: the battery keys are never consulted, even when present.
+stub_hw 1 0
+run_powered "$settings"
+grep -q 'timeout = 1800' "$generated" || fail 'a machine with no battery did not use the AC blank timing'
+grep -q 'timeout = 120' "$generated" && fail 'a machine with no battery read the battery keys'
+grep -q 'Power source at generation: wall power' "$generated" \
+    || fail 'a machine with no battery did not record wall power'
+
+status="$(XDG_CONFIG_HOME="$work/config" XDG_STATE_HOME="$work/state" \
+    PANAMA_PATH="$work/fake" "$helper" status)"
+jq -e '.powerSource == "ac"' <<<"$status" >/dev/null \
+    || fail "status did not report the power source: $status"
+
 trap - EXIT
 cleanup
 printf 'idle config contract: PASS\n'