a new file splits the doc column you were last working in

placeDoc picked its source by SLOT INDEX — it scanned panes from 0 and took the
first doc it found — so which column your file landed in depended on internal
id allocation, not on where you had been. It now walks the jump stack backwards
to the newest live doc pane.

No new state: jumps already IS the record of where the keyboard has been, and
Pane.serial is already the "this slot was reused" test. The slot-order scan
stays as the fallback, deliberately: a restored dump has one jump entry, and if
that pane is a shell the stack knows no doc — without the fallback the next
file would claim a second column with docs already open.

lookpanes moved: a file now lands under the doc that was actually last read
rather than under whichever doc happened to hold the lowest pane id. New
golden doccol pins the case the line exists for, and it fails at exactly one
capture with the walk disabled.

1 files changed, 155 insertions, 0 deletions

diff --git a/test/snapshots/doccol.golden b/test/snapshots/doccol.golden
new file mode 100644
index 00000000..a1508b9f
--- /dev/null
+++ b/test/snapshots/doccol.golden
@@ -0,0 +1,155 @@
+== snap boot grid=100x30 cursor=7,2
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/doccol/cwd/a.txt Save Del    NOR /tmp/pardes-snap/doccol/cwd Del
+|     1 AAA
+|                                                    a.txt  b.txt  c.txt
+|
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+== snap two-docs grid=100x30 cursor=7,17
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/doccol/cwd/a.txt Save Del    NOR /tmp/pardes-snap/doccol/cwd Del
+|     1 AAA
+|                                                    a.txt  b.txt  c.txt
+|
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+|  NOR /tmp/pardes-snap/doccol/cwd/b.txt Save Del
+|     1 BBB
+|     2 B-TWO
+|
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+|
+|
+|
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+|
+|
+== snap moved grid=100x30 cursor=57,20
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/doccol/cwd/a.txt Save Del    NOR /tmp/pardes-snap/doccol/cwd Del
+|     1 AAA
+|                                                    a.txt  b.txt  c.txt
+|
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+|                                                    NOR /tmp/pardes-snap/doccol/cwd/b.txt Save Del
+|                                                       1 BBB
+|                                                       2 B-TWO
+|
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+|
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+== snap worked grid=100x30 cursor=59,21
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/doccol/cwd/a.txt Save Del    NOR /tmp/pardes-snap/doccol/cwd Del
+|     1 AAA
+|                                                    a.txt  b.txt  c.txt
+|
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+|                                                    NOR /tmp/pardes-snap/doccol/cwd/b.txt Save Del
+|                                                       1 BBB
+|                                                       2 B-TWO
+|
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+== snap third grid=100x30 cursor=57,26
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/doccol/cwd/a.txt Save Del    NOR /tmp/pardes-snap/doccol/cwd Del
+|     1 AAA
+|                                                    a.txt  b.txt  c.txt
+|
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+|                                                    NOR /tmp/pardes-snap/doccol/cwd/b.txt Save Del
+|                                                       1 BBB
+|                                                       2 B-TWO
+|
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+|                                                    NOR /tmp/pardes-snap/doccol/cwd/c.txt Save Del
+|                                                       1 CCC
+|
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+|