fix(segmentation): preserve finality across process-exit teardown

[CodingInAVan]

Repair and salvage final segment windows without losing immutable metadata, track writer ownership on drain timeouts, and prevent the Windows sampler thread from leaking a per-iteration segment lease when ExitProcess terminates it without stack unwinding. Preserve synthetic lifecycle provenance and add regression coverage for final-window recovery, segment writers, and sampler lease reuse.

Description

• Preserve immutable window metadata when repairing final segment artifacts.
• Track active segment-writer ownership for actionable drain-timeout diagnostics.
• Prevent Windows ExitProcess teardown from leaking the sampler’s per-iteration writer lease.
• Use a read-only segment snapshot for change detection while retaining one batch writer lease.
• Preserve synthetic lifecycle provenance during launcher repair.

Type of Change

• Bug fix
• New feature
• Documentation update

Testing

• Client suite: 515 passed, 7 skipped.
• Reproduction before the sampler fix: 2 of 6 runs timed out.
• After the fix: 0 of 10 runs timed out.
• Localhost E2E produced two complete, non-synthetic segments.
• Agent ACK cleanup retained metadata/tombstones with no loss markers or .tmp files.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas