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, 7 insertions, 5 deletions

diff --git a/src/exec.zig b/src/exec.zig
index c673aab2..ea20f969 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -170,8 +170,9 @@ pub fn pointerOperand(p: *Pardes, pane: *Pane, clicked: Pane.Sel) PointerOperand
         return result;
     }
     // In a diff, a file or hunk header, and a hunk line pointed at on its
-    // `+`/`-`/` ` prefix, are looked at whole: the place the line names
-    // (look.diffLook). A hunk line's code is words, looked at as ever:
+    // `+`/`-`/` ` prefix, expand to the whole line (the hover shows it) and
+    // the look is of the address it names (look.diffAddress), a regular
+    // look from there. A hunk line's code is words, looked at as ever:
     // the code's, the prefix never one of them.
     var word_from: usize = 0;
     if (clicked.r0 >= pane.tag_rows and clicked.r0 == clicked.r1 and clicked.c0 == clicked.c1 and row >= 0) diff: {
@@ -179,7 +180,9 @@ pub fn pointerOperand(p: *Pardes, pane: *Pane, clicked: Pane.Sel) PointerOperand
         const at: usize = @intCast(row);
         if (at >= lines.len) break :diff;
         const line = lines[at];
-        const target = @import("diff.zig").targetAt(lines, at, pane.file == null) orelse break :diff;
+        var address_buf: [4096 + 32]u8 = undefined;
+        const address = look.diffAddress(pane, lines, at, &address_buf) orelse break :diff;
+        const target = @import("diff.zig").targetAt(lines, at, pane.file == null).?;
         const on_prefix = col == 0 and line.len > 0 and std.mem.indexOfScalar(u8, "+- ", line[0]) != null;
         switch (target.kind) {
             .context, .added, .removed => if (!on_prefix) {
@@ -188,8 +191,7 @@ pub fn pointerOperand(p: *Pardes, pane: *Pane, clicked: Pane.Sel) PointerOperand
             },
             else => {},
         }
-        result.text = line;
-        p.diff_look = .{ .serial = pane.serial, .row = at };
+        result.text = p.scratch.allocator().dupe(u8, address) catch break :diff;
         const hi = std.math.cast(i32, line.len) orelse return result;
         if (hi == 0) return result;
         var expanded = clicked;