[Hygge-Gezelligheid]

Add PUT /vm/dirty-memory-ranges/clear so external snapshot consumers can clear dirty records after committing a snapshot. The endpoint accepts {}, returns 204 on success, and supports only PUT.

With dirty tracking enabled, it clears KVM dirty logs and Firecracker bitmaps, then conservatively re-marks activated virtio queue pages as dirty. With dirty tracking disabled, it returns success without performing any clearing.

Usage constraints

• The VM must be started and paused. With dirty tracking enabled, keep it paused and coordinate other memory writers throughout state capture, export, commit, and CLEAR.
• Native snapshots and external exports share one dirty baseline. With dirty tracking enabled, subsequent Diffs must be applied to the complete image committed before CLEAR.
• With dirty tracking disabled, GET continues to use mincore to query page residency. CLEAR does not establish an incremental baseline or guarantee that the next export contains only new writes.
• CLEAR does not modify guest memory contents or pause state. A KVM failure may leave partially cleared logs, with no rollback. Recover from the last committed snapshot in a replacement instance rather than transparently retrying.

Validation

All 9 CLEAR unit tests passed on ARM64, covering:

• Request bodies, paths, response status, and preconditions, including rejection of GET and PATCH on /clear.
• Repeated CLEAR, unchanged guest memory contents and pause state, and tracking of subsequent writes.
• Errors in the first, middle, and last slots, with no subsequent reset of Firecracker bitmaps.
• Re-marking activated MMIO virtio queue pages and skipping unplugged slots.
• Success with dirty tracking disabled, without reading KVM dirty logs or resetting retained Firecracker dirty bits.

All 4 real-guest integration cases passed, testing the following flows with PCI both enabled and disabled:

• Tracking enabled: create a full external baseline; CLEAR without a preceding dirty GET; export changes A, commit S1, and CLEAR; write B and zero pages; directly create a native Diff; apply it to S1, restore, and verify the actual guest memory contents.
• Tracking disabled: CLEAR is rejected while the VM is running; after pausing, repeated calls return 204, with memory contents, GET results, and pause state unchanged; the VM can subsequently resume.

Swagger validation and relevant formatting and static checks passed. Historical full-suite runs on x86 and ARM additionally covered an incorrect S0 base, another CLEAR/Diff/restore cycle after restoration, external-only incremental recovery, and background I/O. These results are retained as one-off validation records. x86 was not rerun in this round.