Expose read-only device power info to mods

tests/modkit/cases/device_power_info.lua

@@ -0,0 +1,52 @@
+-- A sandboxed mod may read battery state without receiving love.system and
+-- its process-launching surface.
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+
+local FIXTURE = {
+  ["mods/power_probe/manifest.json"] = [[{
+    "id": "power_probe",
+    "name": "Power Probe",
+    "version": "1.0.0",
+    "entry": "main.lua",
+    "api": 2
+  }]],
+  ["mods/power_probe/main.lua"] = [[
+    local mod = ...
+    mod.exports.state, mod.exports.percent = mod.device:powerInfo()
+  ]],
+}
+
+local saved = T.love.system.getPowerInfo
+local calls = 0
+T.love.system.getPowerInfo = function()
+  calls = calls + 1
+  return "charging", 42, 900
+end
+
+local vanilla = T.sdk.loadNone({})
+T.eq(calls, 0, "no mod leaves the device power backend cold")
+vanilla.release()
+
+local run = T.sdk.loadMods({ "mods/power_probe" },
+  { fs = T.sdk.memfs(FIXTURE) })
+T.eq(#run.errors, 0,
+  "the sandboxed power probe loads clean (" .. tostring(run.errors[1]) .. ")")
+local out = run.loader.exports.power_probe or {}
+T.eq(out.state, "charging", "the public facade reports battery state")
+T.eq(out.percent, 42, "the public facade reports battery percentage")
+T.eq(calls, 1, "one facade read makes one platform call")
+run.release()
+
+T.love.system.getPowerInfo = nil
+local unavailable = T.sdk.loadMods({ "mods/power_probe" },
+  { fs = T.sdk.memfs(FIXTURE) })
+out = unavailable.loader.exports.power_probe or {}
+T.eq(out.state, "unknown", "a missing platform backend has a stable state")
+T.eq(out.percent, nil, "a missing platform backend has no invented percentage")
+unavailable.release()
+
+T.love.system.getPowerInfo = saved
+T.finish("device_power_info")

tests/modkit/cases/sandbox.lua

@@ -125,7 +125,8 @@ T.eq(type(out.requireSemver), "table",
 T.check(out.loveFilesystem and out.loveFilesystem:find("mod.storage", 1, true),
   "love.filesystem is refused and names the replacement")
 T.check(out.loveThread ~= false, "love.thread is refused: it opens a full Lua state")
-T.check(out.loveSystem ~= false, "love.system is refused: openURL launches anything")
+T.check(out.loveSystem and out.loveSystem:find("mod.device:powerInfo()", 1, true),
+  "love.system is refused and names the scoped power replacement")
 T.eq(out.loveGraphics, "table", "the rest of love passes through")
 T.check(out.loveAssign ~= false, "a mod cannot assign into the love facade")