diff --git a/spec/CONTRACT_GENESIS_G2B_TUNING.md b/spec/CONTRACT_GENESIS_G2B_TUNING.md
index fcb8b84..fab1c76 100644
--- a/spec/CONTRACT_GENESIS_G2B_TUNING.md
+++ b/spec/CONTRACT_GENESIS_G2B_TUNING.md
@@ -99,8 +99,9 @@ test (`codec.rs:3725`, `textvalue_graph.rs:1092`). The **text projection drops
 it too** (`textvalue_graph.rs:1123`), so it already survives no persistence
 surface at all. The subset type ratifies the status quo rather than changing it.
 
-**Open for ratification:** the type's **name**. `TuningContextSettings` is the
-default. It must not be named so as to imply it is the whole context.
+**RATIFIED 2026-07-28:** the subset design, and the type's name and path —
+**`epiphany_core::TuningContextSettings`**. It lives in `epiphany-core`
+alongside the type it narrows, and is publicly exported at that exact path.
 
 ---
 
@@ -140,18 +141,43 @@ G-minor's `introduced_minor()` is **exhaustive with no wildcard arm**, so
 kind/tag 34 **cannot compile** without an epoch. That is the control working as
 designed — do not defeat it.
 
-**Epoch 10, for the genesis G2b event.** This extends the ratified ladder
-(`PLAN_GMINOR_SCHEMA_MINOR.md` §4, minors 2–9) by one, monotonically. **This
-addition requires ratification** alongside this contract; it is the first
-exercise of the ladder's own growth path.
+**Epoch 10, for the genesis G2b event — RATIFIED 2026-07-28** and already
+recorded in the authoritative ladder (`PLAN_GMINOR_SCHEMA_MINOR.md` §4).
+**Transcribe it; do not edit that plan.** This is the first exercise of the
+ladder's own growth path, and it stayed monotonic and prefix-closed.
 
-### Pin 5 — undo must distinguish never-authored from authored-to-default
+### Pin 5 — undo restores the **seeded base**, and the never-authored /
+authored-to-default distinction must stay **unobservable**
 
-`Score::empty` seeds `tuning_context` with a **default value**, so the
-`WriteChain` cannot treat "no base" and "base equals default" alike. Follow
-G2a's chain shape (`reduce.rs`), and note the chain's value type is the
-**subset type**, not `ScoreTuningContext` — `accidental_extensions` never
-participates in undo because no operation ever writes it.
+**An earlier draft of this contract had this backwards.** It required undo to
+distinguish "never authored" from "authored to the default value".
+`spec/PLAN_GENESIS_OPS.md` §5 trap 5 **withdrew** that on 2026-07-28, and
+`SetMetadata` is the disproof: `Score::empty` seeds `metadata` exactly as it
+seeds `tuning_context` (`graph.rs:1749`, `:1757`), and base ingest then runs
+`metadata_chain.seed(score.metadata.clone())` (`reduce.rs:1385`) precisely so a
+value-restoring undo of the *first* operational write restores the
+pre-operational state.
+
+**The rule:**
+
+* From-empty reduces **onto** `Score::empty` (via `reduce_operation_set_onto`),
+  so **the seed runs**. Undoing the first write yields
+  `Restore(Some(Predecessor::Base(seeded)))`.
+* **Undo restores the seeded base settings — default or non-default alike.**
+  Restoring the seeded value is correct in *both* cases, so the distinction is
+  unobservable, **and this contract must keep it so.** Writing code that can
+  tell them apart is a defect, not a safeguard.
+* **`Predecessor::Base` vs `::Write` earns its keep only for the canonical
+  bookkeeping families** (`spellings`, `breaks`, `page_breaks`,
+  `reduce.rs:707`), where a base predecessor returns a **map key to absence**.
+  `ScoreTuningContext` is an **always-valued** `Score` field, like `metadata`:
+  **there is no absent state to return to.**
+* **Copy `set_metadata` structurally**, as all three G2 setters do. Do not
+  invent a chain shape for this field.
+
+The chain's value type is the **subset type**, not `ScoreTuningContext`:
+`accidental_extensions` never participates in undo, because no operation ever
+writes it and undo must leave it exactly as it found it.
 
 ### Pin 6 — P13-S13 closes here
 
@@ -189,7 +215,25 @@ Five non-compiler-checked sites (`layout_stub`'s is now derived):
 Plus `editor-core/src/barriers.rs`'s `subjects_of`, which the compiler forces.
 **Prefer deriving over extending** wherever the site allows it.
 
-### Pin 9 — P13-S15 stays open
+### Pin 9 — explicit non-goal: G2b authorizes **no** pruning or compaction
+
+**G2b does not authorize pruning or compaction of the canonical operation
+log**, and nothing in this packet may implement, enable, or prepare either.
+
+`spec/PLAN_GENESIS_OPS.md` §3 requires this stated outright, and the reason is
+that G2b **sharpens** the standing prohibition rather than relaxing it. Before
+this rung, pruning was a performance concern: it would have discarded
+re-derivable state. **The moment G2b lands, pruning would discard *authored
+genesis state*** — the tuning context exists canonically only in the op log,
+because the canonical base embeds no graph values for any field.
+
+The prohibition remains blocked on **disposition C** (the canonical base
+carrying graph values). There is no `fn prune` in the tree today, which is
+exactly why the prohibition is free now and would be catastrophic later. **If
+the implementation finds itself wanting a prune or compaction step for any
+reason, that is a finding to report, not a feature to add.**
+
+### Pin 10 — P13-S15 stays open
 
 The golden lock ends at 29 and **this rung must not extend it**. Adding 34 while
 30–33 remain unlocked would make the table look maintained while the gap
@@ -197,7 +241,88 @@ persists. S15 lands as its own rung with its own mutation evidence.
 
 ---
 
-## 3. Tests — each with the mutation that must kill it
+## 3. Touch table
+
+**Derived from G2a's actual footprint** (`git show 7df5ca1 --name-only`, thirty
+files) plus G1's one extra, then extended for what G2b does that neither did.
+It is a **floor, not a ceiling** — a touch outside it is a finding to report,
+but a file here that turns out not to need changing is fine, said plainly.
+
+### Core — the new type
+
+| # | File | Change |
+|---|---|---|
+| 1 | `core/src/graph.rs` | **new `TuningContextSettings`** (the five wire-bearing fields, in codec order); doc it as the authored subset of `ScoreTuningContext` and say why `accidental_extensions` is absent |
+| 2 | `core/src/lib.rs` | **public export** `epiphany_core::TuningContextSettings` (the ratified path) |
+| 3 | `core/src/codec.rs` | its `Codec` — **byte-identical to `ScoreTuningContext`'s existing five-field walk**; add the assertion that the two encodings agree |
+| 4 | `core/DECISIONS.md` | the subset ruling and its rationale |
+
+### Ops — the operation
+
+| # | File | Change |
+|---|---|---|
+| 5 | `ops/src/payload.rs` | `SetTuningContext` **kind 34** in the enum, the hand-written `discriminant()` match, `schema_major()` → **3** (pin 2), `tag()`, tag **34** inside `operation_kind_tag_vocabulary!`, and **`introduced_minor()` → epoch 10 in both spaces** (pin 4) |
+| 6 | `ops/src/reduce.rs` | the `WriteChain<TuningContextSettings>` — decl, snapshot, init, **seed**, setter, undo verdict, restoration apply, working-snapshot save/restore. **Copy `set_metadata` structurally** (pin 5) |
+| 7 | `ops/src/envdecode.rs` | envelope decode arm |
+| 8 | `ops/src/migrate.rs` | migration arm |
+| 9 | `ops/src/v0.rs` | v0-catalog arm |
+| 10 | `ops/src/valuegen.rs` | a generator for the payload |
+| 11 | `ops/src/vectors.rs` | **decode vectors pinned to literal bytes, not round-trip** (plan trap 4: a self-consistent reorder passed 1283 tests and 8/8) |
+| 12 | `ops/src/fuzz.rs` | fuzz arm |
+| 13 | `ops/src/textproj_kind.rs` | the kind **count** — hand-maintained (pin 8) |
+| 14 | `ops/src/lib.rs` | public exports |
+| 15 | `ops/DECISIONS.md` | the rung's decisions |
+
+### Bundle — the accept-set raise (**new to G2b; G2a touched no bundle file**)
+
+| # | File | Change |
+|---|---|---|
+| 16 | `bundle/src/bundle.rs` | `max_supported_major(OperationEnvelopeBlock)` **2 → 3** (:69) **and the rewritten rationale at :53-58** whose current text this rung falsifies (pin 3) |
+| 17 | `bundle/DECISIONS.md` | why the raise is charged to this surface alone |
+
+### Boundary crossings — budgeted up front (pin 8)
+
+| # | File | Change |
+|---|---|---|
+| 18 | `editor-core/src/barriers.rs` | `subjects_of` arm — **compiler-forced**; without it the workspace does not build and the gate cannot run at all |
+| 19 | `layout-ir/src/barrier.rs` | the "one past the vocabulary" literal → 35 |
+| 20 | `testkit/src/generators.rs` | the `rng.below(N)` bound |
+| 21 | `testkit/src/layout_stub.rs` | confirm the derived `PAYLOAD_FREE` path still holds — **prefer deriving over extending** |
+| 22 | `testkit/tests/text_projection_grammar.rs` | the kind **count** |
+
+### Text projection
+
+| # | File | Change |
+|---|---|---|
+| 23 | `textproj/src/parse.rs` | the kind production |
+| 24 | `textproj/src/project.rs` | the projection arm (G1 touched this; G2a did not — **check, don't assume**) |
+| 25 | `textproj/src/vectors.rs` | vector coverage for the new kind |
+| 26 | `textproj/src/lib.rs` | **`COMPANION_VERSION` 0.10.0 → 0.11.0** |
+
+### Normative documents — the four-document ritual (pin 7)
+
+| # | File | Change |
+|---|---|---|
+| 27 | `spec/binary_format.tex` | payload-layout row, tag row, the **accept-set/major-3 text**, the §2373 minor-additive history (kind 34 / epoch 10), version, Revision History row |
+| 28 | `spec/operation_catalog.tex` | a `\section{SetTuningContext}`, version, changelog |
+| 29 | `spec/core_spec.tex` | the **normative `OperationKind` *and* `OperationKindTag` listings**, plus any spelled-out payload count |
+| 30 | `spec/text_projection.tex` | kind production, companion 0.11.0, changelog |
+| 31–34 | `spec/binary_format.pdf`, `operation_catalog.pdf`, `core_spec.pdf`, `text_projection.pdf` | **all four regenerate and are committed** — every `.tex` source changes here |
+
+### Vectors and tracking
+
+| # | File | Change |
+|---|---|---|
+| 35 | `spec/vectors/decode_vectors.txt` | regenerate |
+| 36 | `spec/vectors/textproj_document_vectors.txt` | regenerate |
+| 37 | `spec/PASS13_CANDIDATES.md` | **close P13-S13**, citing this rung and the `metadata` precedent (pin 6) |
+| 38 | `spec/PLAN_GENESIS_OPS.md` | mark G2b complete; ladder advances to G3 |
+
+**Already done by the ratification, do NOT redo:** epoch 10 is recorded in
+`spec/PLAN_GMINOR_SCHEMA_MINOR.md` §4. Transcribe it into code; do not edit that
+plan.
+
+## 4. Tests — each with the mutation that must kill it
 
 | # | Test | Required mutation |
 |---|---|---|
@@ -207,14 +332,14 @@ persists. S15 lands as its own rung with its own mutation evidence.
 | t4 | That block is **admitted** by the accept-set | Revert the cap to 2; must fail |
 | t5 | **The subset pin holds**: an op authored live and the same op reloaded from bytes produce **identical** graph states, with a pre-existing non-empty `accidental_extensions` **preserved across both** | Make the payload carry the full `ScoreTuningContext`; must fail — this is the pin's whole reason for existing |
 | t6 | Undo restores the previous five-field value | Restore the default instead of the predecessor; must fail |
-| t7 | Undo of the **first** authoring returns to never-written, distinguished from authored-to-default | Treat the `Score::empty` seed as a base write; must fail |
+| t7 | Undo of the **first** authoring restores the **seeded base** settings, and does so identically whether the seed was the default or a non-default value — with `accidental_extensions` untouched throughout | Skip `seed()` on the tuning chain during base ingest, so the first undo yields `NotWritten` instead of `Restore(Base)`; must fail. **Assert the two cases are indistinguishable**, not that they differ |
 | t8 | Kind 34 carries **epoch 10** and a block containing it stamps minor 10 | Assign epoch 9; must fail |
 | t9 | The from-empty spine still reaches a note, now with a tuning context authored | — regression guard; mutation is t2's |
 | t10 | The accept-set prose no longer claims no payload embeds the tuning context | Grep-assert the stale sentence is absent; restore it to see the test fail |
 
 ---
 
-## 4. Gate
+## 5. Gate
 
 `cargo fmt --check`; `cargo clippy --workspace --all-targets` **0 warnings**;
 `cargo test --workspace` green with the count; conformance suites with counts
@@ -223,10 +348,10 @@ vectors regenerated; **all four PDFs at 0 undefined references**, committing
 `binary_format.pdf`, `operation_catalog.pdf`, `core_spec.pdf` and
 `text_projection.pdf` (**all four `.tex` sources change here**, unlike G-minor);
 and `git status --short` **before and after**, whose only differences may be
-this contract's own touch set — the editor track's dirt must appear unchanged
+the §3 touch table — the editor track's dirt must appear unchanged
 in both.
 
-## 5. Report
+## 6. Report
 
 The gate outputs; every mutation with the failure actually observed; any touch
 outside this contract; and **any place where this contract's own assumptions
diff --git a/spec/PLAN_GMINOR_SCHEMA_MINOR.md b/spec/PLAN_GMINOR_SCHEMA_MINOR.md
index a4816fe..2c48b12 100644
--- a/spec/PLAN_GMINOR_SCHEMA_MINOR.md
+++ b/spec/PLAN_GMINOR_SCHEMA_MINOR.md
@@ -177,6 +177,14 @@ numbering spaces are unrelated and must not be cross-read.
 | 7 | Push 4a | `OperationKind`/`OperationKindTag` 30; `PreconditionFailureReason` 14–15 |
 | 8 | Genesis G1 | `OperationKind`/`OperationKindTag` 31 |
 | 9 | Genesis G2a | `OperationKind`/`OperationKindTag` 32–33 |
+| 10 | Genesis G2b | `OperationKind`/`OperationKindTag` 34 (`SetTuningContext`) |
+
+> **Epoch 10 ratified 2026-07-28**, with G2b as the event. This is the **first
+> exercise of the ladder's own growth path**: G-minor's `introduced_minor()` is
+> exhaustive with no wildcard arm, so kind/tag 34 *cannot compile* without an
+> epoch — the control working exactly as designed. The ladder stays monotonic
+> (G2b follows G2a) and prefix-closed. Epoch assignment remains a ratified
+> schema decision, never an implementer's choice.
 
 **The ladder is complete against the audit** — every post-baseline variant in
 `AUDIT_GMINOR_VOCABULARIES.md` appears exactly once: all ten kind/tag pairs,