A right click on a diff line opens the place it names: its file, the hunk's new line, the line itself

In a diff pane (a .diff/.patch file, or a command pane's diff output), the
look's own expansion, which its hover shows, takes a whole line for a
`diff --git`, `---`, `+++` or `@@` line wherever the pointer is on it,
markers included, and for a hunk line when the pointer is on its `+`, `-`
or space. Then the look opens the file (a/ b/ dropped, timestamps cut) at
the line from the hunk header and the lines above it: `@@` the hunk's
first new line, context and added lines their own, a removed line the new
line now where it was. `diff --git` and `+++` open the new file; `---` the
old one, unless the `+++` under it names another. On a hunk line's code
the expansion is its words, the prefix never one of them, and looks as
ever. Other panes are untouched.

Paths resolve in the repository (walking up to `.git` or `.jj` from the
diff's directory, or a command pane's), then that directory. A file not
here opens nothing and says `Look: b/x: no such file here`, or `deleted by
this diff`. A 9P look writing a whole line of the diff does the same.

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

1 files changed, 29 insertions, 0 deletions

diff --git a/test/snapshots/diffview.golden b/test/snapshots/diffview.golden
index 2da9f6e3..9e171fd8 100644
--- a/test/snapshots/diffview.golden
+++ b/test/snapshots/diffview.golden
@@ -54,6 +54,21 @@
 |28: 0-0 d,#608269, 1-99 d,#0d1410,
 |29: 0-0 d,#608269, 1-99 d,#0d1410,
 |30: 0-0 d,#608269, 1-99 d,#0d1410,
+== snap look-added-line grid=100x31 cursor=55,22
+|16:    /tmp/pardes-snap/diffview/cwd/src/shape.zig Save Tty Collapse Del TreeContext
+|17:      1 const std = @import("std");
+|18:      2
+|19:      3 pub const Shape = union(enum) {
+|20:      4     circle: f32,
+|21:      5     square: f32,
+|22:      6     triangle: struct { base: f32, height: f32 },
+|23:      7
+|24:      8     const note =
+|25:      9         \\areas, defer
+|26:     10         \\summed
+|27:     11     ;
+|28:     12 };
+|29:     13
 == snap command-pane grid=100x31 cursor=7,3
 |Newcol Joincol Find Grep Help Changelog Tutor Dump Themes Config Debug Exit
 |   New Tty Find Grep Joincol Delcol
@@ -117,3 +132,17 @@
 |28: 0-0 d,#608269, 1-2 d,#0d1410, 3-99 #e5eee5,#0d1410,
 |29: 0-0 d,#608269, 1-1 d,#0d1410, 2-99 #e5eee5,#0d1410,
 |30: 0-0 d,#152019, 1-99 d,#0d1410,
+== snap command-look grid=100x31 cursor=23,10
+|3:      1 cat change.diff
+|5:    /tmp/pardes-snap/diffview/cwd/src/shape.zig Save Tty Collapse Del TreeContext
+|6:      1 const std = @import("std");
+|7:      2
+|8:      3 pub const Shape = union(enum) {
+|9:      4     circle: f32,
+|10:      5     square: f32,
+|11:      6     triangle: struct { base: f32, height: f32 },
+|12:      7
+|13:      8     const note =
+|14:      9         \\areas, defer
+|15:     10         \\summed
+|16:     11     ;