A diff look names a file as the repository does: git's side prefix dropped by git's rules, a plain diff's names as written

In a git section (one with a `diff --git` line) the one-letter side prefix
git writes, `a/`/`b/` or with diff.mnemonicPrefix `c/`, `i/`, `w/`, `o/`,
is dropped from its paths only when both paths of that line carry one,
different ones: `--no-prefix` writes none, so its `a/x a/x` is a real
directory `a` and is kept. A plain `diff -u` never strips: its names are
used as written, past the timestamp. `/dev/null` stays itself.

The walker does this once (diff.Walk.side, diff.gitHeader), so the path a
look resolves, and the one a miss says, are the repository's name:
`Look: src/x.zig: no such file here`, `Look: lib/old.zig: deleted by this
diff`. The look no longer tries a stripped name beside the written one.

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

1 files changed, 13 insertions, 7 deletions

diff --git a/docs/tags.md b/docs/tags.md
index 51977390..ec454bb8 100644
--- a/docs/tags.md
+++ b/docs/tags.md
@@ -97,13 +97,19 @@ opens the new file at line c. On a hunk line, the `+`, `-` or space in its
 first column takes the whole line and opens the new file at that line; for
 a removed line, at the new line now standing where it was (the one after
 it, or the hunk's last when it went from the end of the file). The code
-after it is words, looked at as ever. Paths are the repository's: pardes
-walks up from the diff's directory (a command pane's own) to a `.git` or
-`.jj` and drops git's `a/`/`b/`, else takes them from that directory as
-written; `diff -u`'s timestamps are cut. A file that is not here (a branch
-not checked out) opens nothing and says so: `Look: b/x.zig: no such file
-here`, or `deleted by this diff` for a deleted one. A 9P `look` of a whole
-line of the diff does the same.
+after it is words, looked at as ever.
+
+A path is the repository's name for the file. In a git section (one with a
+`diff --git` line) git's side prefix is dropped when both paths on that
+line carry one, different ones: `a/`/`b/`, or with `diff.mnemonicPrefix`
+`c/`, `i/`, `w/`, `o/`. `--no-prefix` writes none, so there `a/x a/x` is a
+real directory `a`, kept. A plain `diff -u`'s names are used as written,
+past the timestamp. The file is looked for from the repository's root
+(pardes walks up from the diff's directory, a command pane's own, to a
+`.git` or `.jj`), else from that directory. A file that is not here (a
+branch not checked out) opens nothing and says so by that name: `Look:
+src/x.zig: no such file here`, or `deleted by this diff` for a deleted one.
+A 9P `look` of a whole line of the diff does the same.
 
 ## Editing tags