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, 40 insertions, 20 deletions

diff --git a/docs/tags.md b/docs/tags.md
index f299c859..ecca046a 100644
--- a/docs/tags.md
+++ b/docs/tags.md
@@ -44,34 +44,54 @@ asks; there bare `Del` gives the rows to the nearest document above, as it
 always has. A collapsed pane is never asked about, and collapsed neighbors
 are passed over: they only keep a weight for later.
 
-Left-click a tag to place its caret; drag to select text, then type to
-replace it. Arrow keys, Home, End, Backspace and Delete edit the line.
-Tags reveal the caret horizontally when text is wider than their column.
-Escape returns to the body, keeping command-text edits. The existing Exec
-and Look gestures still apply; the workspace tag is no longer an inert
-left-click target. Pasted text goes to the focused tag, not to the file or
-embedded shell beneath it.
+A tag is a text like a pane's body: pane tags, column tags and the
+workspace tag all edit with the body's own normal and insert modes, undo
+included, and may hold more than one line. A tag with a newline in it takes
+a row per line, up to eight: a pane's tag leaves its body at least one row
+and a collapsed pane shows only the first line; the column and workspace
+tags take no more than a third of the screen, and the panes below move down
+to make room. The path, the dirty marker and a PDF's page at the start of a
+pane tag are computed, never stored: the tag's cursor, selections and undo
+live in the text after them, so a rename or a save never moves the cursor.
+The mouse still sees the whole line -- a sweep selects across the path and
+the commands, and Look and Exec work on either -- but the keyboard moves only
+in the tag's own text: `0` goes to its start, not the path's.
 
-Keyboard entry returns to the tag's last cursor position. The first entry into
-a pane tag starts at its commands; clicking always chooses a new position.
-Each pane, column and workspace tag remembers its own position during the
-session. Shortened text clamps the saved cursor to a valid character boundary.
+Left-click a tag or a header to type into it at the click, in insert mode;
+tags reveal the caret horizontally when text is wider than their column.
+Esc is normal mode, where everything a body's normal mode does works, and
+Enter looks up and Tab executes the word under the cursor (or an explicit
+selection), in either mode. Executing gives the keyboard back to the body
+first, so `Del`, `Kill` and `Restore` never return into a tag that is gone.
+Pasted text goes to the focused tag, not to the file or embedded shell
+beneath it.
 
-In normal mode, `h` and `l` move within the tag, `k` stays on the single line,
-and `j` returns to the panel like Escape. Uppercase `HJKL` move between pane
-tags. From the top pane's `:` tag, `K` reaches the column and another `K` reaches
-the workspace; `J` walks back down. Enter or Tab on a header command in
-normal mode executes it, as before. `i`/`a`/`I`/`A` switch to editing the
-header. In insert mode, letters type normally, Enter is Look and Tab is Exec,
-as in pane tags.
+`:` is the one key a tag and a body do not share: in the body's normal mode
+it focuses the pane's tag in normal mode, and in the tag's normal mode it
+goes back to the body; in a column or workspace tag it goes back to the
+active pane. Each pane, column and workspace tag remembers its own cursor
+during the session; the first `:` into a pane tag starts on its `Save`. A
+tag's text changing under it (a 9P write, a shorter tag) pulls the cursor
+back inside it.
+
+Moving between tags is the window keys' job, as it is between bodies
+(`Ctrl-w` or `SPC w` with `h/j/k/l`): they move to the neighbouring pane's
+body. Up from a pane with nothing above it reaches its column's tag, then
+the workspace's; Down comes back the same way, and Left and Right walk the
+column tags.
+
+Search (`/`), pipe (`|`) and Save's path prompt are not typed into the tag:
+each gets a line of its own on the pane's notice band, with the body's
+insert-mode keys, and leaves the tag as it was.
 
 Pane filenames and commands now have a single separator space rather than
 generated right-alignment padding. Intentionally customized spacing is kept.
 
 ## File names
 
-Editing a file pane's name creates a draft. Enter confirms the new buffer
-name; Escape or leaving the tag cancels the draft. Confirmation changes the
+Clicking a file pane's name starts a draft of it, typed into at the click.
+Enter or Tab confirms the new buffer name; Escape or leaving the pane
+cancels the draft. Confirmation changes the
 buffer's save target and marks it unsaved. It does **not** rename, create or
 overwrite a disk file. A subsequent explicit `Save` writes the buffer to its
 committed name. Executing a pane-tag command confirms a valid name draft