diff --git a/.claude/knowledge/abi-ownership-and-handles.md b/.claude/knowledge/abi-ownership-and-handles.md
index 460617b..7ceb250 100644
--- a/.claude/knowledge/abi-ownership-and-handles.md
+++ b/.claude/knowledge/abi-ownership-and-handles.md
@@ -66,3 +66,38 @@ the `Arena`/segment lifetime as nested *inside* the resource's own lifetime,
 so Java's own bookkeeping fails fast on a use-after-close even before the
 call reaches Rust (belt-and-braces, not a substitute for the Rust-side
 check).
+
+## Rust 1.99 (2026-10-10): what the C-ABI changes do and do not buy here
+
+MEASURED on 1.99.0 / LLVM 23. lgj-abi is clippy-clean with `-D warnings`. All
+four Java suites pass (`AllTests` 612, consumers 70 + 68 + 3 + 12) against a
+`liblgj_abi.so` built by 1.99. lgj-abi's graph contains no lance, lancedb or
+arrow, so the lance 13 move does not reach this crate.
+
+- **`UnsafeCell` contents may be accessed without `get` (newly guaranteed).**
+  This does NOT change the soundness of the writable mask lane.
+  - `lgj_mask_describe` hands Java the address of `MaskWords.words`. That is
+    a boxed heap buffer, not the inside of the lock's `UnsafeCell`. Java writes
+    to it through the segment, outside the lock.
+  - It is sound today because no Rust reference to those words is live while
+    Java writes. The one production writer, `RowStore.importRows`, writes a
+    mask whose handle has not been returned to anyone yet. Every Rust op
+    re-borrows through the lock.
+  - A concurrent Java writer would still be a data race, and the guarantee
+    does not make a race defined. That needs `AtomicU64` words plus a
+    documented protocol, which this ABI deliberately does not define.
+  - Possible hardening, not done: take the address under the write guard
+    (`as_mut_ptr`), so it carries write provenance. Not done because
+    `write_mask` also invalidates `resolved_carving`, so every describe would
+    drop the carving cache. That is a behaviour change for no reachable
+    defect.
+- **C-variadic definitions / `VaList` (stabilized):** not applicable. The ABI
+  is fixed-arity and bulk-only (`docs/abi.md` §6), and `no-c-ever.md` holds.
+- **`no_mangle` on generic items is now a hard error:** the 30 `#[no_mangle]`
+  exports are all non-generic.
+- **Extern statics no longer promoted:** none are referenced.
+- **`Box::into_non_null` / `Vec::from_parts`:** no site here. Handles are
+  registry ids, never raw boxes.
+
+REVISIT WHEN: the ABI grows a concurrent-writer protocol (then: atomic word
+lanes), or a Java writer other than `importRows` appears.
diff --git a/README.md b/README.md
index 558b6ed..54bcb75 100644
--- a/README.md
+++ b/README.md
@@ -71,7 +71,8 @@ no `cbindgen`, no `jextract`, no JNI. See `docs/abi.md` §1 and
 
 ## Toolchains
 
-- Rust: **1.97.1** stable, matching `ndarray`/`lance-graph`'s pin.
+- Rust: stable, pinned in `native/lgj-abi/rust-toolchain.toml` (the version
+  lives there only, matching `ndarray`/`lance-graph`'s pin).
 - Production JDK: **JDK 28** (`/opt/jdks/jdk-28+16`). Panama FFM is final
   there and needs no flag; Valhalla (JEP 401) is preview-gated and production
   uses it, so `--enable-preview` is required — for the value classes, never
diff --git a/native/lgj-abi/Cargo.toml b/native/lgj-abi/Cargo.toml
index ea6b8a6..4eba618 100644
--- a/native/lgj-abi/Cargo.toml
+++ b/native/lgj-abi/Cargo.toml
@@ -2,7 +2,7 @@
 name = "lgj-abi"
 version = "0.1.0"
 edition = "2021"
-rust-version = "1.98.1"
+rust-version = "1.99.0"
 license = "MIT OR Apache-2.0"
 publish = false
 description = "The lance-graph-java machine membrane: a self-describing, versioned, bulk-only psABI surface. No C, no JNI, no headers."
diff --git a/native/lgj-abi/rust-toolchain.toml b/native/lgj-abi/rust-toolchain.toml
index f19a0b1..ba52bec 100644
--- a/native/lgj-abi/rust-toolchain.toml
+++ b/native/lgj-abi/rust-toolchain.toml
@@ -2,7 +2,7 @@
 # Stable only. Matches ndarray / lance-graph / the rest of the AdaWorldAPI
 # stack. No nightly features anywhere in this crate — in particular no
 # `core::simd` / portable-simd (abi.md §8).
-channel = "1.98.1"
+channel = "1.99.0"
 components = ["clippy", "rustfmt"]
 
 # Bump log (append one line per bump; the version itself is the `channel`
@@ -11,6 +11,12 @@ components = ["clippy", "rustfmt"]
 #                     carried by ndarray / lance-graph / OGAR. Forced, not
 #                     optional: ndarray 0.17.2 now declares rustc 1.98, so
 #                     a 1.97.1 build of this crate fails to resolve at all.
+#   1.98.1 → 1.99.0   2026-10-10: workspace-wide sweep (lance-graph #1437).
+#                     Must merge BEFORE the ndarray / lance-graph bumps: CI
+#                     checks the siblings out at main, and once they declare
+#                     rust-version 1.99 a 1.98 build here no longer resolves.
+#                     Measured: clippy -D warnings clean; AllTests 612 +
+#                     consumers 153 green against a 1.99-built .so.
 #
 # This is THE toolchain file for this repo. A second one briefly existed at
 # the repository root; it was removed rather than kept in sync, because two