Inline mode renders the diff grouped: all old-side content
(before-context, then deletions) is printed before all new-side content
(additions, then after-context), rather than interleaved like a unified
diff. Attach the same per-line OSC records here -- the old-side passes
emit the left-column record, the new-side passes the right-column one.

Because the records carry the file and new/old line numbers explicitly,
a host can reconstruct each line's identity despite the grouping: a
modification's d (in the deletions group) and a (in the additions group)
are emitted far apart in the output yet both reference the same new-file
line, with the d also carrying the old-file line. A positional or
structural re-parse of inline output could not pair them; the metadata
makes each line self-describing.

The line type is the row's patch-space type, from comparing the aligned
lines' contents (as in side-by-side) rather than the all-or-nothing
novelty the display colors hunk rows with -- so a context line that
happens to fall inside a hunk is tagged c, not a/d, while a line changed
only by added tokens (nothing highlighted on its old side) is still the
d half of its modification. In the context passes, an old line with no
new-side counterpart is a deletion even though this display files it
under context (a deleted blank line has no tokens to be novel), and the
mirrored new-side line is an addition; an aligned context row stays c
even if its sides differ in whitespace, since only one side of it is
ever rendered here and a d would hand the host a deletion whose addition
it can never show. A pure deletion's new-file line is derived from the
previous new-file line carried through the old-side passes, as in
side-by-side.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

A host can already learn difftastic's per-line diff metadata, but only
from the records emitted before content lines — so a diff with no
content (a binary file, or the empty diff a host would use to probe)
emits nothing, and "speaks the protocol" is indistinguishable from
"unsupported pager".

Emit a version-only OSC 1717 record (no further fields) once, as
difftastic's first output, whenever a version is negotiated. It's
content-independent, so a host can probe difftastic on an empty diff and
get a conclusive answer. Flushed explicitly because difftastic exits via
process::exit, which skips the implicit stdout flush — without it the
lone handshake of an empty probe could be lost.

See the diff-line-metadata OSC spec, §4.4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

difftastic renders no `@@`/`diff --git` rows; its only structural row
is one banner per hunk (`path --- N/total --- Format`) announcing both
the file and the hunk. Annotate it with the header records so a host
can anchor file and hunk navigation on the banners themselves and can
see files with no content lines: every banner carries its hunk's `h`
record with the hunk's first new-file line, and the first hunk's
banner -- the only row announcing the file -- additionally carries the
file's `f` record before the `h`, per the spec's combined-header rule
(§5.5). `f` never carries a line number; the spec fixes each header
type's payload rather than leaving it to the renderer (a streaming
renderer like delta cannot know the first-hunk line at its file
header).

Unlike delta, difftastic builds the whole diff before rendering, so
the hunk's first new-file line is in hand when the banner is printed:
the first aligned row with a new-file line provides it, falling back
to the position the next new line would occupy for a hunk with none
(a pure deletion), mirroring the deletion convention. In inline mode
the banner print moves below the context calculation for the same
reason. A whole-file add/delete renders through the single-column
path as one hunk, so its banner carries `f` plus an `h` at line 1
(addition) or 0 (deletion, matching its `d` records). A rename's
two-row banner repeats the records on each row (spec §6.4).

With OSC1717 unset, output remains byte-for-byte identical to stock
difftastic.