Module subvolume_migrate 

Converting a main checkout into a btrfs subvolume, resumably. What: Convert a main checkout into a btrfs subvolume at the same path, in process, resumably. Why: The steps are those of the proven script (doc/handover/cli-git-subvolume-migration-script.md), without any program started: create <root>.subvol-new as a subvolume; create the linked worktrees inside it as nested subvolumes; copy the tree with cloned data; repeat the copy as a delta; hold .git/index.lock, run the last delta and swap the two directories in one atomic step; rename the old tree aside; carry over files newer in the old tree; rewrite the Git index stat fields; verify. Each step is recorded in the journal (subvolume_journal.rs), so a rerun after a kill at any point resumes: a finished step is skipped and an unfinished one is repeated, and all of them are idempotent. The old tree is never deleted here.

In TS you’d write (pseudocode):

const verdict = await migrate({ platform, root, options, interrupt, say });

Structs

MigrateOptions

What: What the person asked for the migration to do. Why: The two switches are the script’s --no-nested-worktrees and --no-refresh-indexes; the dry run previews.

Enums

Verdict

What: How a migration command ended, when it did not fail. Why: The command maps each to an exit status and the closing text.

Functions

migrate

What: Run the whole migration command: preflight, preview or steps. say receives progress lines as they happen. Why: A refusal returns before anything is created. A finished migration or a plain subvolume with no journal returns AlreadyDone. Any failure after the first step leaves the journal so a rerun resumes, and the error says so.