"Keep computer awake" was a boolean: off, or a machine-global power-save
blocker held for as long as Hermes Desktop is open. That is the wrong shape
for its own stated purpose. An unattended overnight run dies when the
machine sleeps unless the user predicted, before starting, that they would
need the toggle — and a user who did flip it leaves a laptop pinned awake
all week, including the idle hours after the run finished (#101991).
Main already knows, live, whether any turn is in flight:
`mergeActiveWork(activeWorkByWebContents.values()).count > 0` is the exact
expression that drives stream throttling. This change wires the blocker to
that same signal behind a three-way mode:
off never hold the blocker (unchanged default)
while-working hold it only while a turn is in flight; release at idle
always hold it whenever the app is open (what `on` used to mean)
Both persisted copies migrate in place. The renderer's localStorage boolean
(`hermes.desktop.keepAwake.v1`) and main's `keep-awake.json` `{ on }` are
read once and mapped `true -> always`, `false -> off`, so an existing user
sees exactly the behaviour they had. The IPC channel keeps its name and
accepts either the mode or the old boolean. An unrecognised saved value is
refused rather than trusted and falls back to `off`.
No new listener, timer, or IPC channel: `updateStreamThrottleFromActiveWork`
computes the merged picture once and hands it to both consumers, and the
cold-launch apply reads the mode instead of the flag. No trailing delay
between back-to-back turns — a sub-second release cannot let a machine
sleep, and `powerSaveBlocker` start/stop are cheap.
The policy is three pure functions in power-save.ts (parse, read, wanted)
so it is testable without the main process; main only wires them.
(cherry picked from commit c6dab931a2891ea7026eea2c07c271bcf48446b9)
3acd949217