[GrischaE1]

Two items from the agent desktop's open list (docs/agent-desktop-draft.md §7): the frame rate now adapts to a slow network, and files can be dropped on the tab.

Frame rate on a slow network

Until now only the quality adapted. When the acks come late (a quarter of a 2 s window spent waiting), the device now takes one step every 2 s:

1. quality by 10, down to 50 – text stays readable,
2. then the frame rate by a third, down to 5 fps,
3. then quality by 10, down to 20.

When the acks keep up, it goes back up in the reverse order. The encoder keeps the frame rate that was asked for, so a step doesn't force a key frame. Stats carry frameRateLimit, and RemoteHub's connection info says "Slow network: the device sends at most N fps to keep the picture sharp."

The existing slow-link case D-VID-05 (quality drops below 80) still holds.

Drag and drop onto the tab

Files and folders dragged onto the agent desktop tab are saved on the device's Desktop, in From RemoteHub. When a dropped name already exists there, they go into a dated folder inside it, so nothing is overwritten.

• Protocol: a new transfer kind drop, behind the feature dropFiles. It is sent right away and never offered for pasting. The device never sends one, and an offer of one is refused.
• Rights: the same as copying files (DesktopClipboard 3). Like the clipboard, it is closed while the lock screen is up. The service and the helper both check.
• Written as the user: the helper finds the Desktop as LocalSystem (a redirected one too) but writes with the signed-in user's rights. A junction the user puts in the folder's place can only lead where they may write anyway.
• Unfinished drops: a drop that doesn't finish removes only the files and folders it created (TransferReceiver with ownsFolder: false). Until now, a failed transfer deleted its whole target folder, which here would have taken earlier files with it.
• Audit: a new agent event, 1108 DesktopFilesSaved, records the count, size and folder, but no file names.
• In the tab: while dragging, a panel says where the files go or why they can't. Afterwards it says "Saved 3 files on the device's Desktop, in “From RemoteHub”."

Tests

• Unit:
  • the quality and frame-rate steps (18 cases), and an end-to-end slow-ack run whose stats show the limit only once quality is at 50
  • the info line
  • drops end to end against an in-process agent: saved, a dated folder, a refused offer, refused by policy
  • an unfinished drop keeps earlier files; the folder choice; the tab's texts and drag state
• Lab: a new harness step dropFiles, and new cases D-VID-14 and D-DROP-01 to 04 (drop, same names, planted junction, policy).
  • They passed on Server 2025 and Windows 11, together with D-VID-05 (runs 20261023-152043 and 20261023-153302).
  • D-DROP-01 first failed because of a bug in the test (the newest event comes first); I fixed the test and the case passed on the rerun.
• Also fixed: JumpHostTests read the diagnostic log while other tests were writing to it and failed now and then. It now reads with sharing allowed.
• Before this rebase onto main, the full unit suite had 2 failures: that flaky JumpHostTests test, and HelperClipboardFilesTests.A_reader_that_fails_or_hangs…, a timing test this PR doesn't touch, which most likely failed because the machine was busy with the lab.

Docs

• agent-desktop-draft.md: §4.4, §4.7, the audit table, and the open list. I removed the items in it that are already done: ADMX templates, AllowAgentDesktop, the resume issue.
• README, the lab case sheet and the test document.

[github-actions]

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