@@ -1416,6 +1416,67 @@ async fn vendor_check_fails_after_hatch_dependency_reset() {
     assert_check_catches_relock(&root, files);
 }
 
+/// #1120: a `requirements.txt` exported beside `uv.lock` pins the
+/// package from PyPI, so the uv-only wiring leaves installs from it
+/// unpatched. `uv export > requirements.txt` in Windows PowerShell 5.1
+/// writes it as UTF-16 with a byte-order mark, which pip and uv read like
+/// its UTF-8 twin, so `vendor` must name it (`pypi_multiple_lockfiles`)
+/// and `vendor --check` must fail on the contested wiring in every
+/// encoding, not pass as if the file were absent.
+#[tokio::test]
+async fn uv_requirements_export_contests_the_wiring_in_any_encoding() {
+    let text = "six==1.16.0\r\n";
+    let le: Vec<u8> = [0xFF, 0xFE]
+        .into_iter()
+        .chain(text.encode_utf16().flat_map(u16::to_le_bytes))
+        .collect();
+    let be: Vec<u8> = [0xFE, 0xFF]
+        .into_iter()
+        .chain(text.encode_utf16().flat_map(u16::to_be_bytes))
+        .collect();
+    for (case, bytes) in [
+        ("utf-8", text.as_bytes().to_vec()),
+        ("utf-16 le", le),
+        ("utf-16 be", be),
+    ] {
+        let (_tmp, root) = project();
+        stage_uv(&root);
+        std::fs::write(root.join("requirements.txt"), &bytes).unwrap();
+        stage_manifest(&root);
+        let (code, env) = run_cli(&root, &["vendor"], &[]);
+        assert_eq!(code, 0, "{case}: {env:#}");
+        assert!(
+            std::fs::read_to_string(root.join("uv.lock"))
+                .unwrap()
+                .contains(&format!(".socket/vendor/pypi/{UUID}/")),
+            "{case}: uv.lock is wired: {env:#}"
+        );
+        assert!(
+            env.to_string().contains("pypi_multiple_lockfiles"),
+            "{case}: vendor names requirements.txt as an unpatched install source: {env:#}"
+        );
+
+        let (code, env) = run_cli(&root, &["vendor", "--check"], &[]);
+        assert_eq!(
+            code, 1,
+            "{case}: requirements.txt installs unpatched: {env:#}"
+        );
+        let event = &env["events"][0];
+        assert_eq!(event["errorCode"], "vendor_check_failed", "{case}: {env:#}");
+        let reason = event["reason"].as_str().unwrap_or_default();
+        assert!(
+            reason.contains("wiring contested") && reason.contains("requirements.txt"),
+            "{case}: {env:#}"
+        );
+        // The vendored file is left as the user wrote it.
+        assert_eq!(
+            std::fs::read(root.join("requirements.txt")).unwrap(),
+            bytes,
+            "{case}"
+        );
+    }
+}
+
 /// #699: hosted mode rewrites only the ROOT `requirements.txt`, while
 /// vendored mode also wires a pin in a `-r` include or appends a managed
 /// `(transitive)` line. A vendored → hosted takeover of such a pin used to
 
@@ -8,6 +8,8 @@
 //! * #412: pins reached through in-root `-r` includes;
 //! * #721: a UTF-16 file with a BOM (Windows PowerShell 5.1's
 //!   `pip freeze >` output), which pip decodes.
+//! * #1119: a file pip decodes through a PEP 263 coding line
+//!   (`# -*- coding: latin-1 -*-`), as the root file or an include.
 //! * #994: include targets pip unquotes (`-r "dev reqs.txt"`,
 //!   `--requirement="dev.txt"`, `-r dev\ reqs.txt`) or expands
 //!   (`-r ${REQDIR}/dev.txt`);
@@ -209,6 +211,35 @@ async fn lock_only_scan_discovers_utf16_pins() {
     }
 }
 
+/// #1119: with no BOM, pip decodes a requirements file through a PEP 263
+/// coding line, so a Latin-1 file with a non-ASCII comment is discovered,
+/// as the root file and as a `-r` include, instead of reading as
+/// "No packages found".
+#[tokio::test]
+async fn lock_only_scan_discovers_pep_263_pins() {
+    let latin1 =
+        b"# -*- coding: latin-1 -*-\n# Maintainer: Jos\xe9\nsp-fixture-six==1.16.0\n".to_vec();
+    assert_lock_only_discovers_bytes(
+        &[("requirements.txt", &latin1[..])],
+        &["pkg:pypi/sp-fixture-six@1.16.0"],
+    )
+    .await;
+    assert_lock_only_discovers_bytes(
+        &[
+            (
+                "requirements.txt",
+                &b"-r dev.txt\nsp-fixture-idna==3.7\n"[..],
+            ),
+            ("dev.txt", &latin1[..]),
+        ],
+        &[
+            "pkg:pypi/sp-fixture-idna@3.7",
+            "pkg:pypi/sp-fixture-six@1.16.0",
+        ],
+    )
+    .await;
+}
+
 /// #994: pip `shlex`-splits an include line's options, so a quoted or
 /// backslash-escaped target names the file without its quotes, and a
 /// target with a space is one path, not two words.
 
@@ -14,17 +14,20 @@
 //! `--hash=sha256:ab#cd` are data. Exactly one leading BOM is encoding, not
 //! data (pip decodes with utf-8-sig; uv strips it too).
 
-use crate::formats::text::strip_bom;
+use crate::formats::text::{strip_bom, strip_bom_bytes};
 
 /// Decode a requirements file the way pip's `auto_decode` does: a UTF-16
-/// or UTF-32 byte-order mark selects that encoding and is dropped; anything
+/// or UTF-32 byte-order mark selects that encoding and is dropped; a
+/// mark-less file with a PEP 263 coding line (`# -*- coding: latin-1 -*-`)
+/// in its first two lines is decoded in that encoding (#1119); anything
 /// else is UTF-8, its one leading BOM kept for [`logical_lines`] to drop.
 /// Windows PowerShell 5.1 writes `pip freeze > requirements.txt` as UTF-16
 /// LE with a BOM, and pip installs from it (#721). pip tries the UTF-16
 /// marks first, so a UTF-32 LE mark (`FF FE 00 00`) reads as UTF-16 LE, as
-/// it does for pip. `None` when the bytes are not valid in that encoding.
-/// (pip's last resort, the locale's encoding for a mark-less non-UTF-8
-/// file, is machine-dependent and not modelled.)
+/// it does for pip. `None` when the bytes are not valid in that encoding,
+/// or the coding line names a codec this reader does not model (see
+/// [`coding_line_codec`]). (pip's last resort, the locale's encoding for a
+/// mark-less non-UTF-8 file, is machine-dependent and not modelled.)
 pub(crate) fn decode(bytes: &[u8]) -> Option<String> {
     fn utf16(body: &[u8], unit: fn([u8; 2]) -> u16) -> Option<String> {
         if !body.len().is_multiple_of(2) {
@@ -49,9 +52,95 @@ pub(crate) fn decode(bytes: &[u8]) -> Option<String> {
             .map(|c| char::from_u32(u32::from_be_bytes([c[0], c[1], c[2], c[3]])))
             .collect();
     }
+    if strip_bom_bytes(bytes).len() == bytes.len() {
+        if let Some(name) = coding_line(bytes) {
+            return match coding_line_codec(&name)? {
+                Codec::Utf8 => String::from_utf8(bytes.to_vec()).ok(),
+                Codec::Ascii => bytes
+                    .is_ascii()
+                    .then(|| String::from_utf8_lossy(bytes).into_owned()),
+                Codec::Latin1 => Some(bytes.iter().map(|&b| char::from(b)).collect()),
+                Codec::Cp1252 => bytes.iter().map(|&b| cp1252_char(b)).collect(),
+            };
+        }
+    }
     String::from_utf8(bytes.to_vec()).ok()
 }
 
+/// The codecs a PEP 263 coding line may select that [`decode`] models.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Codec {
+    Utf8,
+    Ascii,
+    Latin1,
+    Cp1252,
+}
+
+/// The encoding name of pip's PEP 263 check: the first of the file's first
+/// two lines that starts with `#` and matches `coding[:=]\s*([-\w.]+)`.
+fn coding_line(bytes: &[u8]) -> Option<String> {
+    bytes.split(|&b| b == b'\n').take(2).find_map(|line| {
+        if line.first() != Some(&b'#') {
+            return None;
+        }
+        line.windows(6)
+            .enumerate()
+            .filter(|(_, w)| *w == b"coding")
+            .find_map(|(at, _)| {
+                let rest = &line[at + 6..];
+                let rest = rest
+                    .strip_prefix(b":")
+                    .or_else(|| rest.strip_prefix(b"="))?;
+                let start = rest.iter().position(|b| !b.is_ascii_whitespace())?;
+                let name: Vec<u8> = rest[start..]
+                    .iter()
+                    .copied()
+                    .take_while(|&b| b.is_ascii_alphanumeric() || matches!(b, b'-' | b'_' | b'.'))
+                    .collect();
+                (!name.is_empty()).then(|| String::from_utf8_lossy(&name).into_owned())
+            })
+    })
+}
+
+/// Python's codec lookup for the names [`decode`] models: case-folded,
+/// `-` and ` ` read as `_`, then Python's alias table for UTF-8, ASCII,
+/// Latin-1 and cp1252. Any other codec (pip would use it) is `None`, so
+/// the file reads as undecodable rather than being guessed at.
+fn coding_line_codec(name: &str) -> Option<Codec> {
+    let name = name.to_ascii_lowercase().replace(['-', ' '], "_");
+    Some(match name.as_str() {
+        "utf_8" | "utf8" | "u8" | "utf" | "utf8_ucs2" | "utf8_ucs4" | "cp65001" | "utf_8_sig" => {
+            Codec::Utf8
+        }
+        "ascii" | "646" | "us_ascii" | "us" | "cp367" | "csascii" | "ibm367" | "iso646_us"
+        | "iso_ir_6" | "ansi_x3.4_1968" | "ansi_x3_4_1968" | "ansi_x3.4_1986"
+        | "iso_646.irv_1991" => Codec::Ascii,
+        "latin_1" | "latin1" | "latin" | "l1" | "8859" | "cp819" | "csisolatin1" | "ibm819"
+        | "iso8859" | "iso8859_1" | "iso_8859_1" | "iso_8859_1_1987" | "iso_ir_100" => {
+            Codec::Latin1
+        }
+        "cp1252" | "windows_1252" | "1252" => Codec::Cp1252,
+        _ => return None,
+    })
+}
+
+/// One cp1252 byte as Python decodes it: Latin-1 outside `0x80..=0x9F`,
+/// Windows punctuation inside it, and five bytes Python leaves undefined.
+fn cp1252_char(b: u8) -> Option<char> {
+    const HIGH: [u16; 32] = [
+        0x20AC, 0, 0x201A, 0x0192, 0x201E, 0x2026, 0x2020, 0x2021, 0x02C6, 0x2030, 0x0160, 0x2039,
+        0x0152, 0, 0x017D, 0, 0, 0x2018, 0x2019, 0x201C, 0x201D, 0x2022, 0x2013, 0x2014, 0x02DC,
+        0x2122, 0x0161, 0x203A, 0x0153, 0, 0x017E, 0x0178,
+    ];
+    match b {
+        0x80..=0x9F => match HIGH[usize::from(b - 0x80)] {
+            0 => None,
+            unit => char::from_u32(u32::from(unit)),
+        },
+        _ => Some(char::from(b)),
+    }
+}
+
 /// One logical requirements line.
 pub(crate) struct LogicalLine {
     /// 0-based index of the first physical line.
@@ -393,6 +482,48 @@ mod tests {
         assert_eq!(decode(&[b's', 0xC3, 0x28]), None);
     }
 
+    /// #1119: with no BOM, pip honours a PEP 263 coding line in the
+    /// file's first two lines (`auto_decode`), so a Latin-1 file with a
+    /// non-ASCII comment installs. Codecs this reader does not model stay
+    /// unreadable instead of guessed.
+    #[test]
+    fn decode_follows_pips_pep_263_coding_line() {
+        let latin1 = b"# -*- coding: latin-1 -*-\n# Maintainer: Jos\xe9\nsix==1.16.0\n";
+        assert_eq!(
+            decode(latin1).as_deref(),
+            Some("# -*- coding: latin-1 -*-\n# Maintainer: Jos\u{e9}\nsix==1.16.0\n")
+        );
+        // The second line counts; every alias spelling Python accepts.
+        for coding in ["ISO-8859-1", "iso8859_1", "latin1", "L1", "cp819"] {
+            let text = format!("# deps\n# vim: set fileencoding={coding} :\nsix==1.16.0 # Jos");
+            let mut bytes = text.into_bytes();
+            bytes.push(0xE9);
+            assert!(
+                decode(&bytes).is_some_and(|t| t.ends_with("Jos\u{e9}")),
+                "{coding}"
+            );
+        }
+        // cp1252's Windows punctuation, and its bytes Python leaves undefined.
+        assert_eq!(
+            decode(b"# coding=cp1252\n# \x93six\x94\nsix==1.16.0\n").as_deref(),
+            Some("# coding=cp1252\n# \u{201c}six\u{201d}\nsix==1.16.0\n")
+        );
+        assert_eq!(decode(b"# coding: windows-1252\n# \x81\n"), None);
+        // A UTF-8 coding line still requires UTF-8.
+        assert_eq!(decode(b"# coding: utf-8\n# Jos\xe9\n"), None);
+        assert_eq!(decode(b"# coding: ascii\n# Jos\xe9\n"), None);
+        // A coding line on the third line, or not in a comment, is data.
+        assert_eq!(decode(b"# a\n# b\n# coding: latin-1\n# \xe9\n"), None);
+        assert_eq!(decode(b"six==1.16.0  # coding: latin-1 \xe9\n"), None);
+        // A codec this reader does not model is unreadable, never guessed.
+        assert_eq!(decode(b"# coding: koi8-r\n# \xe9\n"), None);
+        // A BOM wins over a coding line, as in pip.
+        assert_eq!(
+            decode(b"\xef\xbb\xbf# coding: latin-1\nsix==1.16.0\n").as_deref(),
+            Some("\u{feff}# coding: latin-1\nsix==1.16.0\n")
+        );
+    }
+
     #[test]
     fn requires_hashes_reads_pip_hash_checking_mode() {
         for hashed in [
 
@@ -3608,6 +3608,56 @@ async fn requirements_utf16_files_are_inventoried() {
     }
 }
 
+/// #1119: with no BOM, pip decodes a requirements file through a PEP 263
+/// coding line, so a Latin-1 root file and a Latin-1 include are
+/// inventoried on a fresh checkout instead of reading as "no requirements",
+/// on disk and in memory.
+#[tokio::test]
+async fn requirements_pep_263_files_are_inventoried() {
+    let latin1 = |pins: &str| {
+        let mut bytes = b"# -*- coding: latin-1 -*-\n# Maintainer: Jos\xe9\n".to_vec();
+        bytes.extend_from_slice(pins.as_bytes());
+        bytes
+    };
+    for (root_bytes, base_bytes) in [
+        // The root file itself.
+        (
+            latin1("-r requirements/base.txt\nidna==3.7\n"),
+            b"six==1.16.0\n".to_vec(),
+        ),
+        // Only the include.
+        (
+            b"-r requirements/base.txt\nidna==3.7\n".to_vec(),
+            latin1("six==1.16.0\n"),
+        ),
+    ] {
+        let tmp = tempfile::tempdir().unwrap();
+        std::fs::create_dir_all(tmp.path().join("requirements")).unwrap();
+        std::fs::write(tmp.path().join("requirements.txt"), &root_bytes).unwrap();
+        std::fs::write(tmp.path().join("requirements/base.txt"), &base_bytes).unwrap();
+        let entries = inventory_pypi_locks(tmp.path()).await.unwrap();
+        assert_eq!(
+            sorted_pairs(&entries),
+            vec![
+                ("idna".to_string(), "3.7".to_string()),
+                ("six".to_string(), "1.16.0".to_string()),
+            ],
+            "{entries:?}"
+        );
+
+        let mut project = MemoryProject::new();
+        project.insert("requirements.txt", MemoryEntry::Binary(root_bytes.into()));
+        project.insert(
+            "requirements/base.txt",
+            MemoryEntry::Binary(base_bytes.into()),
+        );
+        let in_memory = super::pypi::inventory_pypi_locks_in(&ProjectView::Memory(&project))
+            .await
+            .unwrap();
+        assert_eq!(sorted_pairs(&in_memory), sorted_pairs(&entries));
+    }
+}
+
 /// pip applies an index option from ANY file of the tree globally, so an
 /// `--index-url` inside an include keeps the root file's hashed pins
 /// unverifiable too (the `public_index` rule spans the whole tree).