[ccoventry]

Release note: Fixed: a disk mounted as a folder inside another drive now has its free space counted on its own, so capture and render don't treat it as the drive around it.

Closes #1041

What changes

• sys::disk::volume_key keys a drive-letter path by its Windows volume name (\\?\volume{guid}\): GetVolumePathNameW finds the mount point the path is under (its nearest existing folder decides, so a folder not made yet still keys by the volume it'll be on), then GetVolumeNameForVolumeMountPointW names that volume. So D:\Captures mounted from a second disk keys apart from D:. Two folders on one plain drive still share one key.
• Falls back to the old key (c:, \\server\share) when Windows has no volume name: a network share (deliberately not asked, since an offline share would wait on the network), a subst drive, or a drive letter that isn't there.
• Every place that grouped by drive now goes through it: build_batch_queue's per-drive budgets (group_by_volume), the render reservations (ledger_key), the Capture footer's pool total (export_pool_space), and the take cleanup's volume_of (Delete finished takes automatically: Recycle Bin or permanent, optionally only when space is needed (part of #644) #716), which had its own copy of the prefix rule.
• Free space itself already used the longest mount point a path is under (get_available_bytes), so it was right for a mounted folder; only the grouping was wrong.
• Not changed: the frontend's same-drive warning (refreshSameDriveWarning) still compares drive letters.

Test done

• New test a_drive_keys_by_its_volume_name: the system drive keys as \\?\volume{…}, a folder that doesn't exist on it keys the same, a missing drive letter keys as the letter. Updated the two tests that compared against the literal c:/d:.
• cargo test -p native -p desktop-studio pass; clippy 1.98.1 + fmt clean.
• Not tested with a real folder mount. This PC has none, and making one (mountvol/Disk Management) needs admin.

🤖 Generated with Claude Code

[ccoventry]

Results of the overnight check (unattended pass, 2026-10-29)

Merged origin/dev in (b4d1607e): no conflicts.

Tests

• cargo test --workspace --locked --exclude goldsrc-hooks --exclude web-analyzer: the first full run had 2 failures in the native lib (912 pass) while I was also running vitest and a cargo build; they were not named in my filtered output, and a clean re-run of cargo test -p native --lib --locked passes (914, 12 ignored), including sys::disk::tests::a_drive_keys_by_its_volume_name. I take it for load flakiness but did not identify the two tests, so flagging it. CI's Rust workspace tests pass on this head.
• npm run test:unit: 1019 pass. Playwright e2e whole suite (CI=1): 433 pass, including app-boot.spec.js.
• CI on the merged head: Clippy, Rust workspace tests, Frontend e2e, Hooks 32-bit, Web analyzer all pass.

Live test with a real folder mount (debug build of this branch in a real Tauri window, own settings folder): the test volume is a VHD mounted at C:\mnt\test1104 with no drive letter (NTFS, 2,111,942,656 bytes free).

• Capture Destinations = C:\mnt\test1104\takes (I created the folder): the Capture footer says Capture Output Free: 2.0 GB, the VHD's own space, not C:'s (about 442 GiB).
• calculate_export_pool_space invoked in the live app: [VHD takes] = 2,111,938,560; [C: folder] = 474,324,717,568; [VHD, C:] and [C:, VHD] both = 476,436,656,128 (the sum of the two volumes, either order); two folders on C: = C: once (474,324,717,568); the VHD's takes plus its root C:\mnt\test1104 = the VHD once (2,111,938,560). The Render footer, with the VHD folder and a C: folder as export dirs, said "Export Pool Free: 445.1 GB" (about 442 + 2).
• Not run: the same checks on the old code (dev) to show the "before" number; by the PR's description it keyed both as c: and counted one of them. Not exercised live: the batch budget path (group_by_volume) and the render reservations, which are covered by the unit tests only.
• Screenshot: local\review-images\1104\capture-footer-vhd.png (a "Render Batch Interrupted" dialog from an earlier stop of my test Studio sits on top of it; unrelated).

Verdict: ready to merge.