* fix(checkout): check Extract's safety before replacing vfile (#230)

Extract called LoadVFile(rid, clear=true) first and only then checked for local work. A refusal therefore returned with the current version's rows already gone: pending adds, renames and merge state were lost, and vvar still named the old version while vfile held only the new one, so Status saw an empty checkout. The check also compared disk against the target version, so switching a clean checkout to any version that changed a file was refused.

Extract now follows fossil's checkout command, before touching anything: the current version must have no unsaved changes, and no file the current version does not track may sit where the target would write different content (fossil prompts there; a library refuses). Force skips both, as before.

The safety scan runs through a new refreshChanged, the observer-free core of ScanChanges, so an Extract does not report a scan of its own. Extract is split into extractRows, checkinTime and extractRow to bring it under 70 lines; behavior of the write loop is unchanged.

* fix(checkout): let Extract proceed when no change would be lost (#230)

Create records the tip as checked out before any file is written, so Create followed by Extract of an older version, into a directory that already holds it, saw every file differing from the tip as an unsaved edit and refused. That is EdgeSync's ExtractTo pattern.

The safety check now refuses only changes the extract would lose: a plain edit whose content already equals what the target writes is not lost, so it no longer blocks. Adds, removals, renames, merge states and edits to files the target does not write still refuse. The edit check and the untracked-file check share wouldClobber, and the target manifest is read once and walked in manifest order.

* fix(checkout): never relax Extract's check while a merge is pending (#230)

A vmerge row is unsaved work on its own. With every merged file already matching the target, the previous commit let Extract switch versions, dropping the merge and leaving the stale vmerge row to give a later commit a bogus merge parent. The content-equality relaxation now applies only when no merge is pending. check-in: c9d97efb90 user: [email protected] tags: trunk