build: only redistribute the orig tarball on new upstream (-si)

dpkg-genchanges includes the upstream tarballs in the .changes only when
the upload brings a new upstream: no previous changelog entry, a changed
upstream version or a renamed source. On a plain revision bump the
tarball already sits in the archive, and dpkg strips it (and its .asc)
from the distribution set.

pkh's native source pipeline listed every .dsc-referenced tarball
unconditionally, making every upload re-ship the orig. Implement the
dpkg source styles as --orig auto|always|never (auto being the -si
default; always/never are -sa/-sd), stripping the tarballs out of the
changes, buildinfo-free checksum set and artifact list like dpkg, with
the explicit 'never' ignored for native packages. Comparison uses the
epoch-less upstream version, exactly like dpkg's version().

Differential tests against real dpkg cover revision bumps, new upstream
versions and both forced styles.

src/build/changes.rs

@@ -4,10 +4,58 @@
 
 use std::path::Path;
 
+use super::OrigSourceMode;
+use crate::debian::changelog::ChangelogEntry;
 use crate::debian::checksums::FileChecksums;
 use crate::debian::control::{Paragraph, write_paragraph};
 use crate::debian::files::FilesList;
 
+/// Compression suffixes dpkg recognizes on source tarballs.
+const TARBALL_COMPRESSIONS: &[&str] = &[".gz", ".bz2", ".xz", ".lzma", ".zst"];
+
+/// Whether this `.dsc`-listed file is an upstream orig tarball
+/// (`*.orig.tar.<ext>` or a component tarball `*.orig-<c>.tar.<ext>`),
+/// mirroring dpkg-genchanges' strip pattern `\.orig(-.+)?\.tar\.$ext`.
+pub fn is_orig_tarball(name: &str) -> bool {
+    TARBALL_COMPRESSIONS.iter().any(|ext| {
+        name.strip_suffix(ext)
+            .and_then(|s| s.strip_suffix(".tar"))
+            .is_some_and(|stem| stem.ends_with(".orig") || stem.contains(".orig-"))
+    })
+}
+
+/// Whether this `.dsc`-listed file is the Debian part of the source package
+/// (`*.debian.tar.<ext>` for the 3.0 formats, `*.diff.<ext>` for 1.0).
+pub fn is_debian_tarball_or_diff(name: &str) -> bool {
+    TARBALL_COMPRESSIONS.iter().any(|ext| {
+        name.ends_with(&format!(".debian.tar{ext}")) || name.ends_with(&format!(".diff{ext}"))
+    })
+}
+
+/// Whether the upload redistributes the upstream tarballs, mirroring the
+/// dpkg-genchanges source styles: `Always`/`Never` are the forced
+/// `-sa`/`-sd`, while `Auto` is the default `-si` — include them only when
+/// there is no previous changelog entry (first upload) or the source name or
+/// upstream version changed since it. Like dpkg, the comparison uses the
+/// epoch-less upstream version: a plain revision bump reuses the tarball
+/// already in the archive.
+pub fn include_orig_tarball(
+    mode: OrigSourceMode,
+    current: &ChangelogEntry,
+    previous: Option<&ChangelogEntry>,
+) -> bool {
+    match mode {
+        OrigSourceMode::Always => true,
+        OrigSourceMode::Never => false,
+        OrigSourceMode::Auto => match previous {
+            None => true,
+            Some(prev) => {
+                prev.source != current.source || prev.version.upstream != current.version.upstream
+            }
+        },
+    }
+}
+
 /// Everything needed to render a `.changes` file.
 #[derive(Debug, Clone)]
 pub struct ChangesInput {
@@ -159,6 +207,91 @@ pub fn save_changes(path: &Path, paragraph: &Paragraph) -> Result<(), Box<dyn st
 mod tests {
     use super::*;
 
+    #[test]
+    fn orig_tarball_detection() {
+        assert!(is_orig_tarball("pkg_1.0.orig.tar.gz"));
+        assert!(is_orig_tarball("pkg_1.0.orig.tar.xz"));
+        assert!(is_orig_tarball("pkg_1.0.orig.tar.zst"));
+        assert!(is_orig_tarball("pkg_1.0~rc1.orig.tar.bz2"));
+        // Component tarballs.
+        assert!(is_orig_tarball("pkg_1.0.orig-docs.tar.xz"));
+        assert!(is_orig_tarball("pkg_1.0.orig-vendor.tar.gz"));
+        // Not orig tarballs.
+        assert!(!is_orig_tarball("pkg_1.0.debian.tar.xz"));
+        assert!(!is_debian_tarball_or_diff("pkg_1.0.orig.tar.xz"));
+        assert!(!is_orig_tarball("pkg_1.0.tar.xz")); // native tarball
+        assert!(!is_orig_tarball("pkg_1.0.dsc"));
+        assert!(!is_orig_tarball("pkg_1.0.orig.tar")); // no compression suffix
+    }
+
+    #[test]
+    fn debian_tarball_detection() {
+        assert!(is_debian_tarball_or_diff("pkg_1.0.debian.tar.xz"));
+        assert!(is_debian_tarball_or_diff("pkg_1.0.diff.gz"));
+        assert!(!is_debian_tarball_or_diff("pkg_1.0.orig.tar.xz"));
+        assert!(!is_debian_tarball_or_diff("pkg_1.0.tar.xz"));
+    }
+
+    /// Build a minimal changelog entry for one source/version pair.
+    fn entry(src: &str, ver: &str) -> ChangelogEntry {
+        crate::debian::changelog::parse_changelog_entries_from_str(
+            &format!(
+                "{src} ({ver}) unstable; urgency=medium\n\n * x\n\n \
+                 -- A B <a@b.c>  Thu, 01 Jan 2026 00:00:00 +0000\n"
+            ),
+            Some(1),
+        )
+        .unwrap()
+        .remove(0)
+    }
+
+    #[test]
+    fn orig_inclusion_matrix() {
+        let cur = entry("pkg", "1.4-2");
+        let prev_same_upstream = entry("pkg", "1.4-1");
+        let prev_new_upstream = entry("pkg", "2.0-1");
+        let prev_renamed = entry("renamed", "1.4-1");
+
+        // -sa / -sd force the outcome.
+        assert!(include_orig_tarball(
+            OrigSourceMode::Always,
+            &cur,
+            Some(&prev_same_upstream)
+        ));
+        assert!(!include_orig_tarball(
+            OrigSourceMode::Never,
+            &cur,
+            Some(&prev_new_upstream)
+        ));
+
+        // -si: first upload includes; a revision bump excludes; a new
+        // upstream version or a renamed source includes.
+        assert!(include_orig_tarball(OrigSourceMode::Auto, &cur, None));
+        assert!(!include_orig_tarball(
+            OrigSourceMode::Auto,
+            &cur,
+            Some(&prev_same_upstream)
+        ));
+        assert!(include_orig_tarball(
+            OrigSourceMode::Auto,
+            &cur,
+            Some(&prev_new_upstream)
+        ));
+        assert!(include_orig_tarball(
+            OrigSourceMode::Auto,
+            &cur,
+            Some(&prev_renamed)
+        ));
+
+        // The epoch is not part of the comparison, like dpkg's version().
+        let cur_epoch = entry("pkg", "2:1.4-2");
+        assert!(!include_orig_tarball(
+            OrigSourceMode::Auto,
+            &cur_epoch,
+            Some(&prev_same_upstream)
+        ));
+    }
+
     #[test]
     fn description_formatting() {
         assert_eq!(