Make a pane's tag a Text edited with the body's own keys

The tag was a fixed buffer with its own one-line editor, a cursor measured
across the path, and a hijack of the body's mode while it was typed into.
It is now the pane's second Text: its own characters after the computed
prefix (path, dirty marker, PDF page), which is never stored in it, so a
rename or a dirty marker never moves its cursor. Normal and insert mode are
the body's, undo included; `:` moves the keyboard between body and tag, the
tag remembers its cursor and starts on Save, and executing a word from it
hands the keyboard back. The mouse still sees the prefix: a sweep selects
across it and a click on the path drafts a new name.

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

1 files changed, 7 insertions, 2 deletions

diff --git a/test/snapshots/tagalign.snap b/test/snapshots/tagalign.snap
index 9df22f57..a77415d9 100644
--- a/test/snapshots/tagalign.snap
+++ b/test/snapshots/tagalign.snap
@@ -22,9 +22,14 @@ press left 12 3
 release left 12 3
 stable 400 5000
 snap clicked
-# End reveals the complete command suffix; a scrolled Del still executes.
+# The click was on the path, so it drafted a name; Esc drops the draft. `:`
+# then `A` puts the caret after the tag's end, which reveals the complete
+# command suffix; a scrolled Del still executes.
 resize 31 70
-key end
+key esc
+settle 100
+key :
+key A
 stable 400 5000
 snap revealed
 press middle @Del 3