focus history is a stack of locations, and the Jumplist is that same stack

One container, not two: focus_hist (a stack of pane ids rebuilt every sync) is
now jumps[] + a current pointer, and the +Jumps buffer is a RENDERING of that
array — nothing copies it, nothing shadows it. prevFocus, Toggleterm, Look's
directory order, Back/Forward, Last and Jumplist all walk the one list.

A pane id is reused, so a location that only remembered an id would retarget
after a respawn: panes now carry a monotonic serial and an entry whose slot
holds a different serial is dead. trackJump compacts those out and fixes the
pointer in the same pass.

The push rule lives in ONE place and says: a location is worth remembering
when you cannot see it any more — a different pane, or more than a bodyful of
rows away in the same one. So hjkl never grows the list and 100G, a search hit
and a goto-definition do.

Ctrl-o/Ctrl-i walk it, SPC j j toggles the last two, SPC j l lists them.
Ctrl-i IS Tab on a legacy host, where the binding simply never fires and
Tab-executes is untouched; kitty reports them apart. SPC j o/i work anywhere.

Two goldens moved, both the SPC ? Help listing gaining four rows.

1 files changed, 85 insertions, 0 deletions

diff --git a/test/snapshots/jumps.snap b/test/snapshots/jumps.snap
new file mode 100644
index 00000000..900b63a1
--- /dev/null
+++ b/test/snapshots/jumps.snap
@@ -0,0 +1,85 @@
+# RULE: there is ONE focus history and it is a stack of LOCATIONS — a pane and
+# a spot in it. Ctrl-o walks it back, Ctrl-i walks it forward again, `SPC j j`
+# (Last) hops to the newest OTHER pane, and `SPC j l` (Jumplist) writes the
+# same stack out as an output buffer whose rows are ordinary look targets, so
+# n/N step them. What gets ONTO the stack is decided in one place (trackJump):
+# focus ended the update in a different pane, or more than a bodyful of rows
+# away in the same one — which is why `100G` below leaves a location behind
+# and the j/k that follow it do not.
+#
+# Focus and position both show in the golden's `cursor=` header: that is the
+# ACTIVE pane's cursor, so each snap is named by where it should land.
+lines big.txt 200
+start 30 150 big.txt
+wait 8000 big.txt
+stable 700 20000
+# left column = big.txt, right column = the launch shell; the file has focus
+snap start
+# two focus moves, so the stack is file -> shell -> file
+key space w l
+stable 400 5000
+snap to-shell
+key space w h
+stable 400 5000
+snap to-file
+# a FAR motion inside one pane: 100G is a jump, so the line we left is
+# remembered and Ctrl-o can come back to it
+text 100
+key G
+stable 400 5000
+snap goto-100
+# Ctrl-o: back to line 1 of the same pane — a stack of panes could not do this
+key c-o
+stable 400 5000
+snap back-in-file
+# ...and back again into the shell
+key c-o
+stable 400 5000
+snap back-to-shell
+# Ctrl-i forward, twice: the shell entry, then line 100 again. Sent as the
+# kitty-protocol CSI u (`CSI 105;5u`) because on the wire Ctrl-i IS Tab —
+# see config.jump_keys.
+send \e[105;5u
+stable 400 5000
+snap forward-file
+send \e[105;5u
+stable 400 5000
+snap forward-100
+# SPC j j — the newest OTHER pane, and pressing it again comes straight back
+key space j j
+stable 400 5000
+snap last
+key space j j
+stable 400 5000
+snap last-back
+# SPC j l — the stack as text: `location text` rows, the file naming itself
+# and the shell spelled @pN because it has no path
+key space j l
+stable 700 15000
+snap jumplist
+# n/N step the rows and look them, exactly as they do a +Search: the stepped
+# row is selected in the buffer (snapstyle) and the pane it names follows.
+# Row 1 is the file at line 1, row 2 the shell (no path, so `@pN`), row 4 the
+# file at line 100 — so the body visibly rides the list.
+key n
+stable 700 15000
+snap step1
+snapstyle step1
+key n
+stable 700 15000
+snap step2-shell
+key n
+stable 700 15000
+key n
+stable 700 15000
+snap step4-line100
+key N
+stable 700 15000
+snap step-back
+# and an ordinary LOOK on a row goes there too — the leading word IS a
+# location, so the right-click look resolves it like any other path. Row 4
+# again, this time by clicking it.
+press right 16 28
+release right 16 28
+stable 700 15000
+snap look-row