diff --git a/crates/epiphany-bundle/src/ids.rs b/crates/epiphany-bundle/src/ids.rs
index d010cb3..723d8f9 100644
--- a/crates/epiphany-bundle/src/ids.rs
+++ b/crates/epiphany-bundle/src/ids.rs
@@ -191,8 +191,16 @@ impl SchemaVersion {
     /// Schema major 3 — the third data-model expansion major (Binary Format
     /// companion §"Schema Major 3", Push 4b tranche 3b-i): `ScoreTuningContext`
     /// gains `smufl` and `overrides` on the wire. Stamped on the acceleration
-    /// full-`Score` snapshot only — no operation payload embeds the tuning
-    /// context, so `OperationEnvelopeBlock`'s accept-set is untouched.
+    /// full-`Score` snapshot **and** on any operation-envelope block carrying a
+    /// `SetTuningContext` payload.
+    ///
+    /// **Genesis tranche G2b raised `OperationEnvelopeBlock`'s accept-set to
+    /// `[0, 3]`** (`spec/CONTRACT_GENESIS_G2B_TUNING.md`). This comment
+    /// previously said major 3 was snapshot-only because no operation payload
+    /// embedded the tuning context; `SetTuningContext` (kind/tag 34) is exactly
+    /// that payload, carrying `epiphany_core::TuningContextSettings`, so the
+    /// claim no longer holds. See `max_supported_major` in `bundle.rs`, which
+    /// carried the same falsehood.
     pub const V3: SchemaVersion = SchemaVersion { major: 3, minor: 0 };
 
     /// Constructs a schema version.
diff --git a/crates/epiphany-ops/src/payload.rs b/crates/epiphany-ops/src/payload.rs
index e5d7a76..d73e75a 100644
--- a/crates/epiphany-ops/src/payload.rs
+++ b/crates/epiphany-ops/src/payload.rs
@@ -2470,6 +2470,9 @@ mod tests {
             (OperationKindTag::CreateInstrument, 8),
             (OperationKindTag::SetCanvasLayoutDefaults, 9),
             (OperationKindTag::SetSpellingPrecedence, 9),
+            // Genesis G2b. Kept in step with pin 1's table; an epoch omitted
+            // here is an epoch this test cannot see go wrong.
+            (OperationKindTag::SetTuningContext, 10),
         ] {
             assert_eq!(
                 tag.introduced_minor(),
diff --git a/crates/epiphany-ops/src/textproj_kind.rs b/crates/epiphany-ops/src/textproj_kind.rs
index 911b51a..281addb 100644
--- a/crates/epiphany-ops/src/textproj_kind.rs
+++ b/crates/epiphany-ops/src/textproj_kind.rs
@@ -89,7 +89,7 @@ fn parse_bytes(s: &Sexp) -> Result<Vec<u8>, TextError> {
     }
 }
 
-/// Projects and strictly parses all 31 `kind` productions from
+/// Projects and strictly parses all 35 `kind` productions from
 /// `spec/text_projection.tex`.
 impl TextValue for OperationKind {
     fn project(&self) -> Sexp {
diff --git a/crates/epiphany-testkit/src/generators.rs b/crates/epiphany-testkit/src/generators.rs
index 588f939..3bf90ed 100644
--- a/crates/epiphany-testkit/src/generators.rs
+++ b/crates/epiphany-testkit/src/generators.rs
@@ -1837,7 +1837,9 @@ mod tests {
     /// where that set's ceiling sits.
     ///
     /// The accept-set ceiling itself (`max_supported_major(
-    /// OperationEnvelopeBlock) == 2`) is **already** asserted in a compiled
+    /// OperationEnvelopeBlock)`, raised from 2 to **3** by genesis tranche
+    /// G2b, which introduced the first operation payload born at major 3)
+    /// is **already** asserted in a compiled
     /// test inside `epiphany-bundle` (`bundle.rs:1322`), which predates this
     /// packet and which this packet leaves untouched. An earlier draft of
     /// this comment claimed that half of s6 was unassertable because
@@ -1910,6 +1912,7 @@ mod tests {
         let mut rng = Rng::new(17);
         let (mut saw_transpose_interval, mut saw_create_instrument) = (false, false);
         let (mut saw_canvas_layout_defaults, mut saw_spelling_precedence) = (false, false);
+        let mut saw_tuning_context = false;
         for _ in 0..2000 {
             let OperationPayload::Primitive(kind) = operation_payload(&mut rng, 8, 8) else {
                 continue;
@@ -1919,6 +1922,7 @@ mod tests {
                 OperationKind::CreateInstrument(_) => saw_create_instrument = true,
                 OperationKind::SetCanvasLayoutDefaults(_) => saw_canvas_layout_defaults = true,
                 OperationKind::SetSpellingPrecedence(_) => saw_spelling_precedence = true,
+                OperationKind::SetTuningContext(_) => saw_tuning_context = true,
                 _ => {}
             }
         }
@@ -1938,6 +1942,10 @@ mod tests {
             saw_spelling_precedence,
             "SetSpellingPrecedence (kind 33) never drawn in 2000 samples"
         );
+        assert!(
+            saw_tuning_context,
+            "SetTuningContext (kind 34, G2b debt) never drawn in 2000 samples"
+        );
     }
 
     #[test]
diff --git a/crates/epiphany-testkit/src/roundtrip.rs b/crates/epiphany-testkit/src/roundtrip.rs
index 35a05c9..ff40d54 100644
--- a/crates/epiphany-testkit/src/roundtrip.rs
+++ b/crates/epiphany-testkit/src/roundtrip.rs
@@ -683,6 +683,52 @@ mod tests {
         assert_eq!(blocks, vec![env.to_canonical_bytes()]);
     }
 
+    /// (G2b, t3+t4 as an integration) A **real** `SetTuningContext` envelope,
+    /// staged through the production writer path and reopened, must stamp
+    /// `{3, 10}` and be admitted **read-write**.
+    ///
+    /// The unit-level t3/t4 did not prove this. t3 computed
+    /// `max(schema_major())` over bare `OperationKind`s — never building a
+    /// block — and t4 only asserted the ceiling constant. Both would stay
+    /// green if `stage_operation_block` mis-derived the stamp or if the
+    /// accept-set gate rejected the block it now admits. This test is the one
+    /// that actually crosses ops → testkit → bundle.
+    #[test]
+    fn a_set_tuning_context_block_stamps_3_10_and_reopens_read_write() {
+        use epiphany_core::{OperationId, ReplicaId, WallClockTime};
+        use epiphany_ops::{
+            valuegen, AuthorId, CausalContext, HybridLogicalClock, OperationEnvelope,
+            OperationKind, OperationPayload, OperationStamp, SetTuningContextOp,
+        };
+
+        let id = OperationId::new(ReplicaId(1), 1);
+        let env = OperationEnvelope {
+            id,
+            author: AuthorId(0xAB),
+            stamp: OperationStamp::new(HybridLogicalClock::new(WallClockTime(100), 0), id),
+            causal_context: CausalContext::new(),
+            transaction: None,
+            payload: OperationPayload::Primitive(OperationKind::SetTuningContext(
+                SetTuningContextOp {
+                    settings: valuegen::tuning_context_settings(3),
+                },
+            )),
+        };
+
+        let staged = crate::bundle_harness::stage_operation_block(&[env]);
+        assert_eq!(
+            staged.schema_version,
+            SchemaVersion::new(3, 10),
+            "a block carrying SetTuningContext stamps major 3 (the payload is              born at v3) and minor 10 (its ratified G2b epoch)"
+        );
+
+        let reopened = reopen_with_op_block(0xD2_0003, staged);
+        assert!(
+            !reopened.is_read_only(),
+            "major 3 is inside the raised op-block accept-set [0, 3], so the              bundle must open read-write"
+        );
+    }
+
     #[test]
     fn op_block_beyond_the_accept_set_opens_read_only() {
         use epiphany_bundle::IntegrityAnomaly;
diff --git a/crates/epiphany-textproj/src/vectors.rs b/crates/epiphany-textproj/src/vectors.rs
index 30fa27c..2f4cca0 100644
--- a/crates/epiphany-textproj/src/vectors.rs
+++ b/crates/epiphany-textproj/src/vectors.rs
@@ -24,7 +24,7 @@ use epiphany_bundle::{
 use epiphany_core::{OperationId, RegionId, ReplicaId, WallClockTime};
 use epiphany_ops::{
     AuthorId, CausalContext, DeleteRegionOp, HybridLogicalClock, OperationEnvelope, OperationKind,
-    OperationPayload, OperationStamp,
+    OperationPayload, OperationStamp, SetTuningContextOp,
 };
 
 use crate::parse::parse_document;
@@ -158,6 +158,25 @@ fn sample_envelope(counter: u64, physical_time: i64) -> OperationEnvelope {
     }
 }
 
+/// A `SetTuningContext` envelope (kind 34, genesis G2b). The committed corpus
+/// must contain a real `set-tuning-context` document: the typed all-kind
+/// round-trip test proves the *production* parses, but only a committed vector
+/// proves the emitted document text is stable across implementations, which is
+/// what this corpus exists for.
+fn tuning_context_envelope(counter: u64, physical_time: i64) -> OperationEnvelope {
+    let id = OperationId::new(ReplicaId(1), counter);
+    OperationEnvelope {
+        id,
+        author: AuthorId(0xAB),
+        stamp: OperationStamp::new(HybridLogicalClock::new(WallClockTime(physical_time), 0), id),
+        causal_context: CausalContext::new(),
+        transaction: None,
+        payload: OperationPayload::Primitive(OperationKind::SetTuningContext(SetTuningContextOp {
+            settings: epiphany_ops::valuegen::tuning_context_settings(7),
+        })),
+    }
+}
+
 fn profiles(custom: bool) -> Vec<ProfileDeclaration> {
     let mut profiles = vec![ProfileDeclaration::full()];
     if custom {
@@ -248,8 +267,22 @@ fn accept_documents() -> Vec<(&'static str, String)> {
         ],
     };
 
+    // Genesis G2b: kind 34 in the committed corpus, carried at minor 10 —
+    // the epoch a block containing this operation actually requires.
+    let tuning_context = TextDocument {
+        document_id: DocumentId([5; 16]),
+        manifest_schema_version: SchemaVersion::new(0, 10),
+        lineage_id: None,
+        profiles: profiles(false),
+        extensions: Vec::new(),
+        canonical_base: None,
+        blobs: Vec::new(),
+        envelopes: vec![tuning_context_envelope(7, 700)],
+    };
+
     vec![
         ("minimal", project_text_document(&minimal)),
+        ("set_tuning_context", project_text_document(&tuning_context)),
         (
             "lineage_custom_profile",
             project_text_document(&lineage_custom),
@@ -319,10 +352,23 @@ fn duplicate_first_line(text: &str, head: &str) -> String {
 /// Every whole-document vector in stable committed order.
 pub fn document_vectors() -> Vec<TextVector> {
     let accepts = accept_documents();
-    let minimal = &accepts[0].1;
-    let lineage_custom = &accepts[1].1;
-    let extension_base_multi = &accepts[2].1;
-    let rich = &accepts[3].1;
+    // Bound **by name, not by index**. These were positional (`accepts[0]`..
+    // `accepts[3]`), which silently coupled every negative vector to the
+    // insertion order of the accept list: adding the G2b
+    // `set_tuning_context` document shifted all four and made the reject
+    // builders operate on the wrong source text. By-name binding makes the
+    // accept list reorderable and extendable without touching this block.
+    let by_name = |name: &str| -> &String {
+        &accepts
+            .iter()
+            .find(|(n, _)| *n == name)
+            .unwrap_or_else(|| panic!("accept document is absent: {name}"))
+            .1
+    };
+    let minimal = by_name("minimal");
+    let lineage_custom = by_name("lineage_custom_profile");
+    let extension_base_multi = by_name("extension_base_two_envelopes");
+    let rich = by_name("rich_document");
 
     let mut vectors: Vec<TextVector> = accepts
         .iter()
@@ -659,7 +705,7 @@ mod tests {
     #[test]
     fn the_reference_implementation_agrees_with_every_vector() {
         match verify(COMMITTED) {
-            Ok(count) => assert_eq!(count, 13, "the corpus has unexpectedly thinned"),
+            Ok(count) => assert_eq!(count, 14, "the corpus has unexpectedly thinned"),
             Err(failures) => panic!(
                 "{} disagreement(s):\n{}",
                 failures.len(),
diff --git a/spec/vectors/textproj_document_vectors.txt b/spec/vectors/textproj_document_vectors.txt
index 0987071..6b7f00e 100644
--- a/spec/vectors/textproj_document_vectors.txt
+++ b/spec/vectors/textproj_document_vectors.txt
@@ -23,6 +23,7 @@
 
 # textproj.document
 textproj.document accept - minimal 28746578742d70726f6a656374696f6e202830203131203029290a28646f63756d656e7420237830313031303130313031303130313031303130313031303130313031303130312028736368656d612030203129290a2870726f66696c652066756c6c20283020312030292028636f6e73747261696e74732036373130383836342028726574656e74696f6e203120282920747275652929290a
+textproj.document accept - set_tuning_context 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
 textproj.document accept - lineage_custom_profile 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
 textproj.document accept - extension_base_two_envelopes 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
 textproj.document accept - rich_document 28746578742d70726f6a656374696f6e202830203131203029290a28646f63756d656e7420237830343034303430343034303430343034303430343034303430343034303430342028736368656d612030203129290a286c696e656167652023783134313431343134313431343134313431343134313431343134313431343134290a2870726f66696c652066756c6c20283020312030292028636f6e73747261696e74732036373130383836342028726574656e74696f6e203120282920747275652929290a2870726f66696c652028637573746f6d20237863636363636363636363636363636363636363636363636363636363636363632920283120322033292028636f6e73747261696e74732036373130383836342028726574656e74696f6e203120282920747275652929290a28657874656e73696f6e202378303130313031303130313031303130313031303130313031303130313031303120283120302031292066616c73652028286368756e6b20657874656e73696f6e2d646174612028736368656d61203020312920237830312920286368756e6b20657874656e73696f6e2d646174612028736368656d61203020312920237830322929202378303120237830313032290a28657874656e73696f6e202378303230323032303230323032303230323032303230323032303230323032303220283120302032292066616c73652028286368756e6b20657874656e73696f6e2d646174612028736368656d61203020312920237830332929202378303220237830323033290a2863616e6f6e6963616c2d62617365202378303430343034303430343034303430343034303430343034303430343034303420237830313032303420312066756c6c2028736368656d61203020312920237861303034290a28656e76656c6f70652023783030303030303030303030303030303130303030303030303030303030303034202378303030303030303030303030303030303030303030303030303030303030616220287374616d70203430302030202378303030303030303030303030303030313030303030303030303030303030303429202863617573616c2028292028292920282920287072696d6974697665202864656c6574652d726567696f6e20237830303030303030303030303030303031303030303030303030303030303030342929290a28656e76656c6f70652023783030303030303030303030303030303130303030303030303030303030303035202378303030303030303030303030303030303030303030303030303030303030616220287374616d70203530302030202378303030303030303030303030303030313030303030303030303030303030303529202863617573616c2028292028292920282920287072696d6974697665202864656c6574652d726567696f6e20237830303030303030303030303030303031303030303030303030303030303030352929290a28656e76656c6f70652023783030303030303030303030303030303130303030303030303030303030303036202378303030303030303030303030303030303030303030303030303030303030616220287374616d70203630302030202378303030303030303030303030303030313030303030303030303030303030303629202863617573616c2028292028292920282920287072696d6974697665202864656c6574652d726567696f6e20237830303030303030303030303030303031303030303030303030303030303030362929290a