diff --git a/rust/crates/du-db/src/grid/digest.rs b/rust/crates/du-db/src/grid/digest.rs
index 3dbcdbb..2c12836 100644
--- a/rust/crates/du-db/src/grid/digest.rs
+++ b/rust/crates/du-db/src/grid/digest.rs
@@ -84,6 +84,30 @@ impl Comparable {
     }
 }
 
+impl Comparable {
+    /// Whether this digest carries **no** comparable call at all.
+    ///
+    /// Two such digests agree with each other, because every field is absent on both sides. That is
+    /// correct as a comparison and disastrous as a quorum: two nodes whose analysis failed would
+    /// agree on nothing, canonicalize a unit with no content, and be paid for it.
+    ///
+    /// So validation refuses to canonicalize on an empty digest. The node is expected to fail its
+    /// unit rather than submit one, but the AppView cannot rely on that — a node is untrusted by
+    /// construction, and that is the whole premise of adaptive replication.
+    pub fn is_empty(&self) -> bool {
+        self.sex.is_none()
+            && self.y_terminal.is_none()
+            && self.ancestry_superpop_argmax.is_none()
+            && self.coverage_bucket.is_none()
+            && self.callable_bucket.is_none()
+    }
+}
+
+/// Whether a digest carries anything a quorum could be about.
+pub fn has_content(digest: &Value) -> bool {
+    !Comparable::from_digest(digest).is_empty()
+}
+
 /// The major component of a semver-ish stack version: `"1.7.0"` → `"1"`.
 ///
 /// Only submissions from a compatible major are compared. A minor release that refactors a walker
@@ -203,6 +227,19 @@ mod tests {
         );
     }
 
+    /// …and "equally uninformative" is exactly why agreement is not enough on its own. Two nodes
+    /// whose analysis failed submit two empty digests, which agree. Without this check they would
+    /// canonicalize a unit with no content and be credited for it.
+    #[test]
+    fn an_empty_digest_has_no_content_to_agree_about() {
+        assert!(!has_content(&json!({"unexpected": true})));
+        assert!(!has_content(&json!(null)));
+        assert!(!has_content(&json!({"calls": {}})));
+        assert!(has_content(&d("XY", "R-A", "EUR", 30.0, 0.94)));
+        // One discrete call is enough to be about something.
+        assert!(has_content(&json!({"calls": {"sex": "XX"}})));
+    }
+
     /// The cross-repo byte contract: key order in the source JSON must not change the hash, or a
     /// node and the AppView would disagree about what was signed.
     #[test]
diff --git a/rust/crates/du-db/src/grid/mod.rs b/rust/crates/du-db/src/grid/mod.rs
index 5860bf1..6a61888 100644
--- a/rust/crates/du-db/src/grid/mod.rs
+++ b/rust/crates/du-db/src/grid/mod.rs
@@ -419,6 +419,12 @@ pub struct CurationCandidate {
 /// With `only_new`, samples that already have a work unit are skipped. That is the nightly path.
 /// Passing `false` re-projects everything, which refreshes manifests after a re-crawl.
 ///
+/// **The manifest carries the instrument**, because the node can not choose a mapper without it.
+/// A read set with no mate can be a long read or a single-end short read, and those two need
+/// different presets. A long read mapped under a short-read preset does not fail — it gives
+/// alignments that look correct and are wrong. `crawl_project` already stores the instrument model
+/// of ENA on the library, so this only carries a value that we hold.
+///
 /// **`est_bases` prefers the measured `base_count`** that ENA publishes on `read_run`, and falls
 /// back to `reads × read_length` where a row predates that column. The fallback is only ever a
 /// mean-length approximation and is wrong outright for variable-length long reads, so it is a
@@ -460,7 +466,8 @@ pub async fn curation_candidates(
                     'index_url',     sf.http_locations->0->>'file_index_url', \
                     'md5',           sf.checksums->0->>'checksum', \
                     'bytes',         sf.file_size_bytes, \
-                    'format',        sf.file_format \
+                    'format',        sf.file_format, \
+                    'instrument',    sl.instrument \
                 )) ORDER BY sl.id, sf.id) AS manifest, \
                 ( SELECT SUM(COALESCE(l2.base_count, l2.reads::bigint * l2.read_length::bigint))::bigint \
                     FROM genomics.sequence_library l2 WHERE l2.sample_guid = s.sample_guid ) AS est_bases, \
diff --git a/rust/crates/du-db/tests/grid.rs b/rust/crates/du-db/tests/grid.rs
index 7011c43..cd2dff7 100644
--- a/rust/crates/du-db/tests/grid.rs
+++ b/rust/crates/du-db/tests/grid.rs
@@ -570,6 +570,10 @@ async fn curation_projects_crawled_samples_into_work_units() {
         "ftp.sra.ebi.ac.uk/vol1/run/ERR200/s1.cram.crai"
     );
     assert_eq!(cram.manifest[0]["md5"], "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
+    assert_eq!(
+        cram.manifest[0]["instrument"], "Illumina NovaSeq 6000",
+        "the node needs the instrument to choose a mapper preset"
+    );
     assert_eq!(cram.total_bytes, Some(12_000_000_000));
     assert_eq!(
         cram.est_bases,
diff --git a/rust/crates/du-jobs/src/grid_validate.rs b/rust/crates/du-jobs/src/grid_validate.rs
index 894cfe9..7e86616 100644
--- a/rust/crates/du-jobs/src/grid_validate.rs
+++ b/rust/crates/du-jobs/src/grid_validate.rs
@@ -141,6 +141,20 @@ pub async fn validate(pool: &PgPool, spot_check_rate: f64) -> anyhow::Result<Val
         let clusters = cluster(&subs);
         let winner = &clusters[0];
 
+        // A digest with no comparable call agrees with every other such digest, because every
+        // field is absent on both sides. Two nodes whose analysis failed would therefore reach a
+        // quorum on nothing and be paid for it. The node is expected to fail its unit instead of
+        // sending an empty digest, and the AppView must not depend on that: a node is untrusted by
+        // construction, which is the premise adaptive replication rests on.
+        if !digest::has_content(&subs[winner[0]].digest) {
+            tracing::warn!(
+                unit = %unit.sample_accession,
+                submissions = winner.len(),
+                "grid-validate: the agreeing digests carry no calls; not canonical"
+            );
+            continue;
+        }
+
         // Distinct DIDs, not distinct rows. The unique index already makes them the same thing;
         // relying on it silently would leave this correct only by coincidence.
         let dids: HashSet<&str> = winner.iter().map(|&i| subs[i].did.as_str()).collect();