sl0ppty: a wrapped line is one line when you copy it

Select a line too long for the pane and the clipboard came back with a `\n` in
the middle of it, at whatever column the pane happened to end. Paste that into a
shell and it runs half a path.

`pane_selection_text` set `trim` and left `unwrap` at whatever a zeroed struct
gives, which is false. lib-vt's header names the exact trio the clipboard wants --
plain output with `unwrap` and `trim` both true, matching Ghostty's own
`Screen.selectionString()` -- and we had two of the three. A row boundary in the
grid is not a newline in the text: a long line occupies two rows and is still one
line, and where it breaks is a fact about how wide the pane is rather than about
what was copied.

Hard newlines are untouched, which is the half a fix for this could easily have
broken: lib-vt joins only the rows that are continuations, so three separate lines
still come back as three lines. Both directions are now asserted, because "copy
joins everything" would be a worse bug than the one being fixed and would look
identical from the inside.

`emit` is now set explicitly as well, to `GHOSTTY_FORMATTER_FORMAT_PLAIN`. It is
already zero, so this changes nothing today -- but this is the API where a zeroed
field means "whatever the enum happens to start with" (DESIGN.md's note on
`ghostty_terminal_set`), and a silently defaulted field is how the wrap flag came
to be missing. There is one call site, checked.

Verified: three checks in `tests/test_clipboard.py` -- a 50-character line printed
into a 40-column pane, dragged across the row boundary, arrives as the string that
was printed with no newline in it; three short lines keep their two newlines; and a
double-click on a word in a wrapped line brings back no newline either. 46 checks in
that file, 1795 overall, all green.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/pane.c b/src/pane.c
index 9f39a0b..860806f 100644
--- a/src/pane.c
+++ b/src/pane.c
@@ -1026,6 +1026,22 @@ bool pane_select_word(pane_t *p, uint16_t x, uint16_t y, const char *seps) {
 char *pane_selection_text(pane_t *p) {
   GhosttyTerminalSelectionFormatOptions opts =
       GHOSTTY_INIT_SIZED(GhosttyTerminalSelectionFormatOptions);
+  /* Plain text, and both flags on: lib-vt documents this exact trio as the
+   * clipboard behaviour, and getting it wrong is invisible until somebody pastes.
+   *
+   * `unwrap` is the one that matters. A row boundary in the grid is not a
+   * newline in the text -- a line too long for the pane occupies two rows and is
+   * still one line -- so without this, copying a wrapped path or a wrapped URL
+   * pasted a `\n` into the middle of it. The newline came from how wide the pane
+   * happened to be, which is not a fact about what was copied. Hard newlines are
+   * untouched: lib-vt joins only the rows that are continuations.
+   *
+   * `emit` is set rather than left zero even though PLAIN *is* zero. This is the
+   * API where a zero means "whatever the enum happens to start with" (see
+   * DESIGN.md on ghostty_terminal_set), and a silent default is how the wrap flag
+   * came to be missing in the first place. */
+  opts.emit = GHOSTTY_FORMATTER_FORMAT_PLAIN;
+  opts.unwrap = true;
   opts.trim = true;
   uint8_t *ptr = NULL;
   size_t len = 0;