fix: an absent battery reading is an absent KEY, not undefined (MX-835)

[MGrin]

bb plugin list on mgrin's Mac reads, whenever it is plugged in:

system@0.1.0  running  (rpc current failed: rpc result at $result.sample.battery.minutesRemaining is not a JSON value (undefined))

The System panel renders nothing at all.

Cause

si.battery() returns timeRemaining: 65535 (IOKit's "no estimate") on AC power. asMinutes correctly refuses it — and the refusal was then assigned, as minutesRemaining: undefined. bb's RPC serialiser refuses undefined and fails the whole current call, not the field.

JSON.stringify drops such keys, so encodeBattery/decodeBattery round-trip clean and the persisted path never saw it. Only the live object carries the key — which is why this reached a running machine.

Fix

"No reading" now means the key is absent, everywhere on the RPC surface:

• presentBattery() writes only the optional readings that have a value (pct, minutesRemaining, cycleCount, healthPct) — used by both batteryFromSi and batteryFromRemote.
• withBattery() does the same one level up: sample.battery is optional too, so { battery: undefined } fails identically. All three Sample constructors (local sample, persisted row, remote sampler) go through it.

Those are the only optional fields reachable from current/history; procShape and machineShape are all-required. No frontend change — app.tsx already tests !== undefined, which an absent key satisfies.

Tests

This repo had none, so typecheck was the whole story and a type-correct undefined sailed through it. Adds node --test --experimental-strip-types over lib/*.test.ts (the pattern bb-plugin-cf-tunnel uses, no framework) and a Test CI job.

The assertion is assertJsonValue — bb's own rule walked over the whole result — rather than a spot check on one field name, because the next optional field added is the next outage.

Falsified: on the old construction 4 of 12 fail, the first with the verbatim production message $result.sample.battery.minutesRemaining is not a JSON value (undefined). On this branch 12/12 pass.

Gates

gate	result
npm test	12 passed, 0 failed
npm run typecheck	rc=0
bb plugin build .	rc=0, all six artifacts

No pre-existing failures; there was nothing to be pre-existing.

MX-835

🤖 Generated with Claude Code