A diff line looks up the path and line it names, as any look does

The look on a diff line was its own resolver: a walk up to .git/.jj from
the diff's directory, its own "no such file here" and "deleted by this
diff". A review tool's cached patch, in no repository, missed every file
though the session's terminals sat in the checkout.

Now a diff line only expands and transforms. Its expansion (what the hover
shows) is the whole line for a header, a `@@` line, or a hunk line
pointed at on its prefix, and its text is the look address the line names
(look.diffAddress): `path` for `diff --git`/`---`/`+++`, `path:c` for
`@@ -a,b +c,d @@`, `path:N` for a hunk line's new line (a removed line's,
the new line now where it was). That text goes through the regular look
exactly as if selected by hand: same resolution, placement and errors. A
9P look of a whole diff line takes the same transform.

Kept: the line classification, hunk arithmetic, git prefix stripping and
timestamp cutting (diff.zig). Gone: the repo-root walk, its messages,
Target.old_side and deletesAhead, and the click's row stash
(Pardes.diff_look). A test compares a B3 on a cached patch's line with a
look of the hand-selected `entry/src/entry.rs:2` in the same session.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 3 insertions, 2 deletions

diff --git a/docs/fs.md b/docs/fs.md
index 7fa33a02..6b73a124 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -222,8 +222,9 @@ go. An `exec` line's blanks at either end are trimmed.
   too.
 - a directory types `ls` into a terminal idle there, else opens one there.
 - a URL opens in the browser.
-- in a diff pane, a whole line of the diff opens the place it names, as a
-  right click on its first column does ([tags.md](tags.md#reviewing-diffs)).
+- in a diff pane, a whole line of the diff is a look at the `path:line` it
+  names, as a right click on its first column is
+  ([tags.md](tags.md#reviewing-diffs)).
 - a plain word selects its next place after dot, wrapping (`LookWord list`
   on the root ctl lists every place in a `+Search` pane instead). In a
   terminal a word is always listed, rows spelled `@p3:12:5-9`.