File the tag code into tagline.zig and draw tags beside bodies

With tags reduced to Texts, what is left of them is the computed prefix, the
default and saved tails, entering and leaving a tag and the headers: that goes
to tagline.zig, as acme keeps the tag half of a window in wind.c. Tag and
header drawing moves next to body drawing in body_layer.zig, and the tag hit
helpers go to tag_layer.zig with the Hit they read, where sameCell now also
tells the lines of a taller tag apart. The docs describe the tag as a Text.

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

1 files changed, 6 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index da4f4e68..c43034f6 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -180,7 +180,12 @@ back evaluates it, which is what acme(4) promises of its own `addr`.
 The three flag files `dirty`, `mark` and `scroll` read `0` or `1` and take
 `0` or `1`: whether the buffer differs from its file, whether a write pushes
 an undo point (writing `1` pushes one now), and whether a write scrolls the
-pane. Truncating `tag` clears the part of the tag you may edit.
+pane.
+
+`tag` reads the whole tag as the pane shows it: the computed path, dirty
+marker or PDF page, then the text you may edit. A write appends to that text,
+newlines included, and a tag with more than one line takes a row per line on
+screen; truncating `tag` clears it, as acme's `cleartag` does.
 
 Stats report real lengths for `index`, `status`, `look`, `exec`, `listeners`,
 `name`, `body`, `tag`, `sel`, `ctl`, the range files and the flag files, and