Diffity stored all state under a hardcoded ~/.diffity. Add a
getDiffityHome() resolver that honors a DIFFITY_HOME environment
variable (falling back to ~/.diffity) and route the registry,
per-repo database/session paths, and prune through it.

This lets the home be pointed at a durable location (e.g. a mounted
volume) so review comments, tours, and sessions persist across
ephemeral environments.

Co-authored-by: [email protected] <[email protected]>

Viewed state was in-memory only, so it reset every time the diff was
reopened. Persist it server-side keyed by the comparison ref and a
content hash, so a file stays viewed across reloads and only resets when
its content actually changes — matching GitHub.

Co-authored-by: [email protected] <[email protected]>

The browser's native find only sees rendered DOM, so it misses lines
that the diff virtualizer hasn't mounted. This searches the parsed diff
model and scrolls matches into view, with Cmd/Ctrl+F focusing the box
(press again to fall through to native find).

Co-authored-by: [email protected] <[email protected]>

Files auto-collapse on load (generated paths, lock files, large or
deleted files) with no way to turn it off. Add a persisted setting so
users can disable auto-collapse entirely and have everything expanded.

Co-authored-by: [email protected] <[email protected]>

Marking a file viewed collapses it, and the virtualizer compensated for
the removed height by subtracting the file's entire height from the
scroll offset, yanking the view toward the top for large files. Pin the
collapsed file's header to the top of the viewport instead so the
reviewer stays oriented.

Co-authored-by: [email protected] <[email protected]>

The search input was fixed-width, so longer queries scrolled out of
view. It now grows to fit the query (clamped between the original width
and a max) using a hidden mirror element to measure the text.

[open
devspace](https://devspaces.int.canals.ai/workspaces/lucid-buffalo-pwzo)

Co-authored-by: [email protected] <[email protected]>

## Summary

The diff content on the right rendered files in raw git order, while the
sidebar file tree on the left sorted them (directories first, then
alphabetical, with single-child directories collapsed). The two
orderings didn't line up, so scrolling the diff didn't track the tree.

This reorders the diff files once, at the source, to match the tree:

- `sortFilesByTree` (in `file-tree.ts`) builds the same sorted tree the
sidebar uses and flattens it back to a `DiffFile[]`, preserving the
original file objects.
- `DiffPage` runs the diff from `useDiff` through `sortFilesByTree`
before anything consumes it.

Because every right-hand consumer keys off the single `diff.files` array
— the virtualizer, search match indices, file navigation, and
first-open-thread lookup — reordering at the source keeps them all
consistent while making the rendered order match the tree exactly. The
sidebar re-sorts internally, so it is unaffected.

Added tests covering the ordering (directories first / alphabetical,
including nested subtrees) and that the original file objects are
preserved.

[open
devspace](https://devspaces.int.canals.ai/workspaces/funny-flamingo-33t5)

Co-authored-by: [email protected] <[email protected]>

Adding a comment to one file re-expanded other files that had comments —
including files marked viewed, which yanked the viewport onto them — and
viewed files with pre-existing comments opened on load instead of
staying collapsed. The comment-surfacing effect now only expands a file
when it *newly* enters the commented set, and skips viewed files on the
initial load so an existing comment can't reopen them, while still
letting a comment that arrives later (e.g. from an AI review) surface
its file.

[open
devspace](https://devspaces.int.canals.ai/workspaces/eager-cheetah-4jcr)

Co-authored-by: [email protected] <[email protected]>

Adds a way to mark every file under a folder as viewed (or unviewed) in
one action, so reviewers don't have to check off each file individually.
It's reachable both by right-clicking a folder row and via a
hover-revealed menu button; the options shown adapt to how much of the
folder is already viewed, and the action cascades through nested
subfolders.

[open
devspace](https://devspaces.int.canals.ai/workspaces/happy-jaguar-jai4)

Co-authored-by: [email protected] <[email protected]>