[ChakraFusion]

The next standalone part of the play-sessions draft (#34), rebuilt on dev-public without save versions.

The problem. A game autosaves every few minutes, and each autosave was synced as it came. One afternoon, a device took eleven versions of one game in 26 minutes from the device it was being played on, each with its own "synced from another device" snapshot. The playing device snapshotted every autosave too. The gameplay guard only waits while save files are locked, and many games don't keep them locked. And a device took other devices' versions of a game running on it, writing a save under the game.

The change (syncengine/playing.go, daemon/sessions.go). While a game is being played on a device (the daemon's play sessions):

• it isn't synced either way there: SyncGame declines quietly (ErrPlayingHere, which counts as ErrHeld);
• another device asking for it, for its manifest or for deletions, is answered "playing". That device says so once per session instead of failing. The answer contains SettlingMessage, so an older build takes it as "busy, ask again";
• the watcher snapshots a change to it at most once per 30 minutes, so a crash still leaves a recent copy.

When the session ends, the existing "After playing" snapshot is taken and the save goes to the other devices in one sync.

A session must end when the game does (second commit), since it now holds the save. A process named like the game stayed behind for fifteen minutes after one closed, with under 1 MB and no processor time; a killed one left two that kept their memory and used none. On Windows, processes are now measured (memory and processor time). One holding under 32 MB that used no processor time since the last poll, or one that used none for a minute whatever it holds, is not the game. A game being played uses some all the time; a paused one still draws its menu. A process that can't be measured still counts.

Tests:

• syncengine: TestPlaying_NotSyncedWhilePlayedHere, TestPlaying_PeerPlayingIsWaitedFor
• daemon: checkpoint timing, TestSessionEndsWhenOnlyAStubIsLeft (fails without the idle filter), TestActiveProcesses_HoldingMemoryDoingNothing
• sessions: TestIdle

Left for a follow-up (P2): finding a running game wherever it is installed, and protected games whose path can't be read.

Checks: the full unit and e2e suites pass locally on today's dev-public.

🤖 Generated with Claude Code

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[Omar-VF]

Thanks, this reads well, and it fits with the Deck plugin's play sessions (#109). One question on idleFor: a game minimised in the background can throttle to almost nothing, and some suspend outright. If one used no processor time for a minute, its session would end while it's still running, and the save would be synced under it, which is the case this PR is there to stop. Would a longer quiet period (a few minutes) still catch the stubs you saw, which lingered for fifteen?