Merge the promisor-style bulk blob fetch

GitHub will not answer a bare blob id through plain fetch --stdin in a
blob:none clone; Git's own lazy fetch shape does. Proven against
GameCult/CultLib on Yggdrasil for partial and full clones.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/drivers.rs

@@ -1133,6 +1133,10 @@ impl GitSourceDriver {
     /// in depth: Git itself refuses a fetched tree with duplicate names
     /// before any of it reaches disk, independent of the explicit `fsck`
     /// call S1 added around the revision this bulk fetch serves.
+    /// The noop negotiation, `--recurse-submodules=no` and explicit
+    /// `--filter=blob:none` are the arguments Git's own lazy fetch uses for a
+    /// promisor remote; without them a hosted origin omits the wanted blob and
+    /// Git's connectivity check fails on the bare blob id.
     fn bulk_fetch_objects(&self, repository: &Path, objects: &[String]) -> Result<()> {
         if objects.is_empty() {
             return Ok(());
@@ -1155,11 +1159,15 @@ impl GitSourceDriver {
         let mut command = self.git_command([
             OsString::from("-c"),
             OsString::from("transfer.fsckObjects=true"),
+            OsString::from("-c"),
+            OsString::from("fetch.negotiationAlgorithm=noop"),
             OsString::from("-C"),
             repository.as_os_str().to_owned(),
             OsString::from("fetch"),
             OsString::from("--no-tags"),
             OsString::from("--no-write-fetch-head"),
+            OsString::from("--recurse-submodules=no"),
+            OsString::from("--filter=blob:none"),
             OsString::from("--stdin"),
             OsString::from("origin"),
         ])?;
@@ -10554,6 +10562,90 @@ Content-Le".to_vec()), |_| {}),
             bulk_fetches, 1,
             "expected exactly one bulk --stdin fetch; invocations:\n{log_text}"
         );
+        // Git's own lazy fetch for a promisor remote sends exactly these; a
+        // hosted origin (GitHub) omits an explicitly wanted blob, and Git's
+        // connectivity check then fails, without them. A file:// origin
+        // delivers the blob either way, so only the arguments can pin this.
+        let bulk_line = log_text
+            .lines()
+            .find(|line| line.contains("fetch") && line.contains("--stdin"))
+            .unwrap_or_default();
+        for required in [
+            "fetch.negotiationAlgorithm=noop",
+            "--recurse-submodules=no",
+            "--filter=blob:none",
+        ] {
+            assert!(
+                bulk_line.contains(required),
+                "bulk fetch lacks {required}: {bulk_line}"
+            );
+        }
+        Ok(())
+    }
+
+    /// A real partial clone: the origin advertises `uploadpack.allowFilter`,
+    /// so `--filter=blob:none` is honoured and the checkout holds no blobs.
+    /// Every other fixture's origin ignores the filter and clones in full,
+    /// so `bulk_fetch_objects` never had a missing blob to fetch and never
+    /// met Git's post-fetch connectivity check on a bare blob id. The blob
+    /// is checked with `GIT_NO_LAZY_FETCH=1`, so only the bulk fetch itself
+    /// can have delivered it.
+    #[cfg(unix)]
+    #[test]
+    fn bulk_fetch_objects_delivers_a_blob_into_a_blob_none_partial_clone() -> Result<()> {
+        let temp = tempfile::tempdir()?;
+        let origin_repo = temp.path().join("origin");
+        fs::create_dir(&origin_repo)?;
+        git_at(&origin_repo, &["init", "--initial-branch=main"])?;
+        git_at(&origin_repo, &["config", "user.name", "Idunn Test"])?;
+        git_at(
+            &origin_repo,
+            &["config", "user.email", "idunn-test@example.invalid"],
+        )?;
+        git_at(&origin_repo, &["config", "uploadpack.allowFilter", "true"])?;
+        git_at(&origin_repo, &["config", "uploadpack.allowAnySHA1InWant", "true"])?;
+        fs::write(origin_repo.join("payload.txt"), b"partial clone payload\n")?;
+        git_at(&origin_repo, &["add", "--all"])?;
+        git_at(&origin_repo, &["commit", "-m", "fixture"])?;
+        let blob = git_at(&origin_repo, &["rev-parse", "HEAD:payload.txt"])?;
+
+        let source_cache_root = temp.path().join("source-cache");
+        fs::create_dir(&source_cache_root)?;
+        let driver = GitSourceDriver::new(
+            source_cache_root.clone(),
+            temp.path().join("frozen"),
+            None,
+        );
+        let checkout = source_cache_root.join("checkout");
+        driver.git([
+            OsString::from("clone"),
+            OsString::from("--filter=blob:none"),
+            OsString::from("--no-checkout"),
+            OsString::from(format!("file://{}", origin_repo.display())),
+            checkout.as_os_str().to_owned(),
+        ])?;
+
+        let blob_present = || -> Result<bool> {
+            Ok(Command::new("/usr/bin/git")
+                .arg("-C")
+                .arg(&checkout)
+                .args(["cat-file", "-t", &blob])
+                .env_clear()
+                .env("PATH", "/usr/bin:/bin")
+                .env("GIT_NO_LAZY_FETCH", "1")
+                .output()?
+                .status
+                .success())
+        };
+        ensure!(
+            !blob_present()?,
+            "fixture is not a partial clone: the blob is already local"
+        );
+        driver.bulk_fetch_objects(&checkout, std::slice::from_ref(&blob))?;
+        assert!(
+            blob_present()?,
+            "bulk fetch succeeded but did not deliver the blob"
+        );
         Ok(())
     }