diff --git a/.cargo/config.toml b/.cargo/config.toml
index 7cef5a32e2..3f62e06197 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -1,10 +1,16 @@
 # Supply-chain soak for cargo's own dependency resolution — the same
 # soak-window rule the npm side applies via minimumReleaseAge /
 # min-release-age: crate versions younger than the window are skipped by
-# the resolver unless already in Cargo.lock. min-publish-age is an
-# [unstable] cargo feature, so these keys bite only under a nightly
-# toolchain; on perry's stable toolchain they are inert and the automated
-# window rides dependabot's cooldown (.github/dependabot.yml) instead.
+# the resolver unless already in Cargo.lock. min-publish-age is nightly-
+# only, which is why every workflow pins `dtolnay/rust-toolchain`'s
+# `toolchain:` input to a dated nightly (external-tools.json's `rust`
+# entry) instead of stable — this block is LIVE only on that pin.
+#
+# TEMPORARY: move to a stable pin once min-publish-age stabilizes —
+# targets Rust 1.100.0 (late September 2026), per
+# https://github.com/rust-lang/cargo/pull/17335 (open) and
+# https://github.com/rust-lang/cargo/issues/17009. Same condition
+# socket-wheelhouse's canonical rust-toolchain.toml is waiting on.
 # Managed by scripts/soak/soak.mts (`npm run soak` / `npm run soak:fix`).
 [unstable]
 min-publish-age = true
diff --git a/.github/workflows/auto-opt-app-patterns.yml b/.github/workflows/auto-opt-app-patterns.yml
index 7d23283db1..3deeebf15a 100644
--- a/.github/workflows/auto-opt-app-patterns.yml
+++ b/.github/workflows/auto-opt-app-patterns.yml
@@ -138,6 +138,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index 18a8310f2c..cdef58b02c 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -48,6 +48,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo
@@ -270,6 +272,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo
@@ -368,6 +372,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Measure clean-build time
diff --git a/.github/workflows/container-tests.yml b/.github/workflows/container-tests.yml
index 549e9ac2ea..f413a731ca 100644
--- a/.github/workflows/container-tests.yml
+++ b/.github/workflows/container-tests.yml
@@ -97,6 +97,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo registry
@@ -171,6 +173,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo registry
@@ -213,6 +217,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo registry
@@ -257,6 +263,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo registry
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 3bcdc86df8..a5946af769 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -37,6 +37,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: 'nightly-2026-08-20'
           components: llvm-tools-preview
       - uses: ./.github/actions/setup-llvm22
 
diff --git a/.github/workflows/eh-transport.yml b/.github/workflows/eh-transport.yml
index 557a1242a6..d22a4f704a 100644
--- a/.github/workflows/eh-transport.yml
+++ b/.github/workflows/eh-transport.yml
@@ -116,6 +116,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Setup Node.js
diff --git a/.github/workflows/ext-link.yml b/.github/workflows/ext-link.yml
index fb010a828c..e1e4dc7f65 100644
--- a/.github/workflows/ext-link.yml
+++ b/.github/workflows/ext-link.yml
@@ -114,6 +114,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.scope.outputs.pkgs != ''
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - if: steps.scope.outputs.pkgs != ''
         uses: ./.github/actions/setup-llvm22
 
diff --git a/.github/workflows/feature-matrix.yml b/.github/workflows/feature-matrix.yml
index 12d53a196e..3d2d718a9b 100644
--- a/.github/workflows/feature-matrix.yml
+++ b/.github/workflows/feature-matrix.yml
@@ -39,6 +39,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/gc-moving-witnesses.yml b/.github/workflows/gc-moving-witnesses.yml
index f3b4aec393..c65a715886 100644
--- a/.github/workflows/gc-moving-witnesses.yml
+++ b/.github/workflows/gc-moving-witnesses.yml
@@ -225,6 +225,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/gc-native-roots.yml b/.github/workflows/gc-native-roots.yml
index 55e2765f96..2c6206e20f 100644
--- a/.github/workflows/gc-native-roots.yml
+++ b/.github/workflows/gc-native-roots.yml
@@ -278,6 +278,8 @@ jobs:
         with:
           node-version-file: .node-version
       - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
       - uses: Swatinem/rust-cache@v2
         with:
diff --git a/.github/workflows/gc-parse-churn-gate.yml b/.github/workflows/gc-parse-churn-gate.yml
index 252cbf4102..b51afea87f 100644
--- a/.github/workflows/gc-parse-churn-gate.yml
+++ b/.github/workflows/gc-parse-churn-gate.yml
@@ -182,6 +182,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
         if: steps.relevance.outputs.run == 'true'
 
diff --git a/.github/workflows/gc-ptr-shape-off-witness.yml b/.github/workflows/gc-ptr-shape-off-witness.yml
index 48ca612ec8..36430bd26c 100644
--- a/.github/workflows/gc-ptr-shape-off-witness.yml
+++ b/.github/workflows/gc-ptr-shape-off-witness.yml
@@ -169,6 +169,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
         if: steps.relevance.outputs.run == 'true'
 
diff --git a/.github/workflows/gc-ratchet.yml b/.github/workflows/gc-ratchet.yml
index c556535e82..51d3610f59 100644
--- a/.github/workflows/gc-ratchet.yml
+++ b/.github/workflows/gc-ratchet.yml
@@ -179,6 +179,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Cache cargo
diff --git a/.github/workflows/gc-root-dominance.yml b/.github/workflows/gc-root-dominance.yml
index 6c87339ed5..0255c8a2df 100644
--- a/.github/workflows/gc-root-dominance.yml
+++ b/.github/workflows/gc-root-dominance.yml
@@ -217,6 +217,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       # ★ The dependency-scale corpus needs the dependency.
@@ -499,6 +501,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       # This also puts a matched LLVM 22 `opt` on disk and exports
       # LLVM_SYS_221_PREFIX, which is how the corpus script finds it. The
       # native corpus is `--trace llvm` output PLUS the production statepoint
diff --git a/.github/workflows/next-app-route.yml b/.github/workflows/next-app-route.yml
index f8467e8d02..d9d9a57044 100644
--- a/.github/workflows/next-app-route.yml
+++ b/.github/workflows/next-app-route.yml
@@ -40,6 +40,8 @@ jobs:
           persist-credentials: false
 
       - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: mozilla-actions/sccache-action@v0.0.11
diff --git a/.github/workflows/node-compat-matrix.yml b/.github/workflows/node-compat-matrix.yml
index ead4229ca1..8f04a9e0b8 100644
--- a/.github/workflows/node-compat-matrix.yml
+++ b/.github/workflows/node-compat-matrix.yml
@@ -62,6 +62,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Start sccache
diff --git a/.github/workflows/node-core-subset.yml b/.github/workflows/node-core-subset.yml
index 761733d544..df37ec2b77 100644
--- a/.github/workflows/node-core-subset.yml
+++ b/.github/workflows/node-core-subset.yml
@@ -74,6 +74,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/node-suite-guard.yml b/.github/workflows/node-suite-guard.yml
index 336f65e9d4..26728a8ef1 100644
--- a/.github/workflows/node-suite-guard.yml
+++ b/.github/workflows/node-suite-guard.yml
@@ -50,6 +50,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Start sccache
diff --git a/.github/workflows/npm-package-sweep.yml b/.github/workflows/npm-package-sweep.yml
index 6c8766bce1..07b2b75183 100644
--- a/.github/workflows/npm-package-sweep.yml
+++ b/.github/workflows/npm-package-sweep.yml
@@ -45,6 +45,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/release-packages.yml b/.github/workflows/release-packages.yml
index 1f74aa995c..86aae485dd 100644
--- a/.github/workflows/release-packages.yml
+++ b/.github/workflows/release-packages.yml
@@ -359,6 +359,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: 'nightly-2026-08-20'
           targets: ${{ matrix.target }}
       # The old-sysroot image carries LLVM 22 under /usr/lib/llvm-22.
       # Its host-side GTK4 build does not depend on perry-codegen, so avoid
@@ -411,22 +412,14 @@ jobs:
       # the canonical _ios suffix (`libperry_ui_ios.a`); simulator libs use
       # `_ios_sim` (`libperry_ui_ios_sim.a`) so they don't collide in the
       # bottle's flat lib dir. library_search.rs's cross-compile branch
-      # picks the right variant per --target. tier-3 tvOS/visionOS/watchOS
-      # are still a follow-up (need nightly + -Zbuild-std).
+      # picks the right variant per --target. tvOS/visionOS/watchOS
+      # (Rust Tier-3, needed -Zbuild-std) are no longer built here — that
+      # unstable-cargo-feature build is dropped entirely, independent of
+      # which channel the toolchain step above pins.
       - name: Install iOS Rust targets (macOS)
         if: runner.os == 'macOS'
         run: rustup target add aarch64-apple-ios aarch64-apple-ios-sim
 
-      # Closes #396 / #397 / #398: tvOS, visionOS, and watchOS are Rust Tier-3
-      # targets — no prebuilt std, so we install nightly + rust-src and use
-      # `-Zbuild-std=core,std,panic_abort` below to compile the standard library
-      # from source for each (device, sim) triple. Stable stays the default
-      # toolchain; we only invoke nightly explicitly via `cargo +nightly` for
-      # the Tier-3 cross-builds.
-      - name: Install Rust nightly + rust-src for Tier-3 Apple targets (macOS)
-        if: runner.os == 'macOS'
-        run: rustup toolchain install nightly --component rust-src --profile minimal
-
       - name: Install GTK4 development libraries (Linux glibc)
         if: runner.os == 'Linux' && !endsWith(matrix.target, '-musl')
         # libgstreamer1.0-dev added in v0.5.456 — perry-ui-gtk4 pulls in
@@ -563,7 +556,8 @@ jobs:
       # filenames are disambiguated in the staging step — device libs keep
       # the canonical `_ios` name, simulator libs get a `_sim` variant
       # suffix so the bottle can ship both side-by-side. tvOS/visionOS/
-      # watchOS are Tier-3 (need nightly + -Zbuild-std) and out of scope.
+      # watchOS (Rust Tier-3, needed -Zbuild-std) are no longer built —
+      # that unstable-cargo-feature build is dropped entirely.
       - name: Build iOS cross-compile libraries (macOS)
         # Only on the arm64 mac job. These iOS/Apple cross-libs are aarch64 and
         # identical regardless of host, so building them on the x86_64 mac runner
@@ -579,74 +573,6 @@ jobs:
             cargo build --profile dist --target "$triple" -p perry-ui-ios
           done
 
-      # Closes #396 / #397 / #398: cross-compile runtime + stdlib + UI for the
-      # Tier-3 Apple platforms (tvOS, visionOS, watchOS). Both device and
-      # simulator triples per platform; nightly + `-Zbuild-std=...` builds std
-      # from source. Note watchOS device uses the unusual `arm64_32` triple
-      # (32-bit pointers, 64-bit registers) — the only non-`aarch64-*` device
-      # triple in this set, so we keep the device/sim pairs explicit instead
-      # of deriving them. Library filenames are disambiguated in the staging
-      # step (device → `_<plat>.a`, sim → `_<plat>_sim.a`); library_search.rs's
-      # `apple_class_lib_name` already maps each `--target` to the correct
-      # variant (covered by the `handles_other_class_suffixes` unit test).
-      - name: Build tvOS/visionOS/watchOS cross-compile libraries (macOS)
-        # arm64 mac job only — same rationale as the iOS step above.
-        if: runner.os == 'macOS' && matrix.target == 'aarch64-apple-darwin'
-        run: |
-          set -e
-          # Format: "<platform>:<device-triple>:<sim-triple>"
-          #
-          # watchOS is back (v0.5.888 dropped it). The drop reason was real but
-          # narrower than the old note claimed: ring 0.17.14's pointer-size
-          # assertion fails for `arm64_32-apple-watchos` — 32-bit pointers with
-          # 64-bit registers. That is ILP32-specific. `aarch64-apple-watchos` is
-          # LP64 and ring builds for it fine, as does `perry-ui-watchos`, so the
-          # LP64 device triple and its simulator are restored here. The ILP32
-          # `arm64_32` triple stays out until ring is fixed or pinned.
-          for entry in \
-            "tvos:aarch64-apple-tvos:aarch64-apple-tvos-sim" \
-            "visionos:aarch64-apple-visionos:aarch64-apple-visionos-sim" \
-            "watchos:aarch64-apple-watchos:aarch64-apple-watchos-sim"; do
-            plat="${entry%%:*}"
-            rest="${entry#*:}"
-            dev="${rest%%:*}"
-            sim="${rest#*:}"
-            # watchOS and visionOS cannot build `dyn-eval` today, and it is in
-            # `default`. The feature reaches `psm` three crates down
-            # (dyn-eval -> perry-parser -> swc_ecma_parser -> stacker -> psm),
-            # whose Mach-O guard enumerates darwin/macos/ios/tvos and omits
-            # watchos/visionos — so both fall through to psm's ELF branch and
-            # emit `.type`/`.size`, which the Mach-O assembler rejects. Nothing
-            # in Perry is involved. Fix filed upstream as rust-lang/stacker#152;
-            # DELETE this branch and the feature list when it lands.
-            #
-            # The cost is scoped and worth stating: these two platforms ship
-            # without runtime `new Function` over a string body. Everything else
-            # in `default` is present — the list below is `default` minus
-            # `dyn-eval`, nothing more.
-            runtime_features=""
-            case "$plat" in
-              watchos|visionos)
-                runtime_features="--no-default-features --features full,regex-engine,temporal,url-engine,string-normalize,intl-segmenter,intl-namespace,global-math,global-json,global-reflect,global-atomics,global-url,global-text,global-websocket,global-webcrypto,global-webfetch,proc-ipc,intl-locale,intl-datetime,diagnostics,mod-dgram,mod-http2-constants,keepalive-anchors,alloc-mimalloc"
-                ;;
-            esac
-            for triple in "$dev" "$sim"; do
-              echo "::group::$plat $triple"
-              # Runtime first, with the per-platform feature set; stdlib and UI
-              # keep `default` (neither reaches psm).
-              cargo +nightly build --profile dist \
-                -Z build-std=core,std,panic_abort \
-                --target "$triple" \
-                $runtime_features \
-                -p perry-runtime -p perry-runtime-static
-              cargo +nightly build --profile dist \
-                -Z build-std=core,std,panic_abort \
-                --target "$triple" \
-                -p perry-stdlib -p perry-stdlib-static "-p" "perry-ui-${plat}"
-              echo "::endgroup::"
-            done
-          done
-
       - name: Build UI library (Linux glibc)
         if: runner.os == 'Linux' && !endsWith(matrix.target, '-musl')
         run: cargo build --profile dist --target ${{ matrix.target }} -p perry-ui-gtk4
@@ -785,44 +711,6 @@ jobs:
             if [ -f "$sim_dir/libperry_ui_ios.a" ]; then
               cp "$sim_dir/libperry_ui_ios.a" "staging/libperry_ui_ios_sim.a"
             fi
-            # Closes #396 / #397 / #398: same pattern as iOS for the Tier-3
-            # Apple platforms. Driven from an explicit triple list so the
-            # device/sim pairs stay visible rather than derived.
-            #
-            # watchOS uses `aarch64-apple-watchos`, NOT the ILP32
-            # `arm64_32-apple-watchos` an earlier note here assumed. That
-            # distinction is the whole reason it can ship again: ring 0.17.14's
-            # pointer-size assertion is ILP32-specific, so the LP64 triple was
-            # never affected. Keep them in step with the build step above.
-            for entry in \
-              "tvos:aarch64-apple-tvos:aarch64-apple-tvos-sim" \
-              "visionos:aarch64-apple-visionos:aarch64-apple-visionos-sim" \
-              "watchos:aarch64-apple-watchos:aarch64-apple-watchos-sim"; do
-              plat="${entry%%:*}"
-              rest="${entry#*:}"
-              dev_triple="${rest%%:*}"
-              sim_triple="${rest#*:}"
-              dev_dir="target/${dev_triple}/dist"
-              sim_dir="target/${sim_triple}/dist"
-              if [ -f "$dev_dir/libperry_runtime.a" ]; then
-                cp "$dev_dir/libperry_runtime.a" "staging/libperry_runtime_${plat}.a"
-              fi
-              if [ -f "$dev_dir/libperry_stdlib.a" ]; then
-                cp "$dev_dir/libperry_stdlib.a" "staging/libperry_stdlib_${plat}.a"
-              fi
-              if [ -f "$dev_dir/libperry_ui_${plat}.a" ]; then
-                cp "$dev_dir/libperry_ui_${plat}.a" "staging/libperry_ui_${plat}.a"
-              fi
-              if [ -f "$sim_dir/libperry_runtime.a" ]; then
-                cp "$sim_dir/libperry_runtime.a" "staging/libperry_runtime_${plat}_sim.a"
-              fi
-              if [ -f "$sim_dir/libperry_stdlib.a" ]; then
-                cp "$sim_dir/libperry_stdlib.a" "staging/libperry_stdlib_${plat}_sim.a"
-              fi
-              if [ -f "$sim_dir/libperry_ui_${plat}.a" ]; then
-                cp "$sim_dir/libperry_ui_${plat}.a" "staging/libperry_ui_${plat}_sim.a"
-              fi
-            done
           fi
           cd staging
           tar czf ../${{ matrix.artifact }}.tar.gz *
@@ -1104,8 +992,8 @@ jobs:
   build-cross:
     needs: await-tests
     strategy:
-      # Each leg is independent; let one Tier-3 failure not cancel the
-      # other targets so we still ship the bundles that did build.
+      # Each leg is independent; let one cross-target failure not cancel
+      # the other targets so we still ship the bundles that did build.
       fail-fast: false
       matrix:
         include:
@@ -1114,65 +1002,23 @@ jobs:
             target: aarch64-apple-darwin
             ui_crate: perry-ui-macos
             ui_lib: libperry_ui_macos.a
-            tier3: false
           - os: macos-15
             target: x86_64-apple-darwin
             ui_crate: perry-ui-macos
             ui_lib: libperry_ui_macos.a
-            tier3: false
           - os: macos-14
             target: aarch64-apple-ios
             ui_crate: perry-ui-ios
             ui_lib: libperry_ui_ios.a
-            tier3: false
           - os: macos-14
             target: aarch64-apple-ios-sim
             ui_crate: perry-ui-ios
             ui_lib: libperry_ui_ios.a
-            tier3: false
-          # --- Apple, Tier-3 (nightly + build-std) --------------------------
-          # tvOS / visionOS / watchOS are Rust Tier-3: no prebuilt std, so we
-          # install nightly + rust-src and pass `-Zbuild-std=core,std,panic_abort`
-          # in the build step below. Mirrors the existing `build:` job.
-          #
-          # watchOS is restored here on `aarch64-apple-watchos`. The v0.5.888
-          # drop was for ring 0.17.14's pointer-size assertion, which is
-          # specific to the ILP32 `arm64_32-apple-watchos` triple; the LP64
-          # triple builds ring and `perry-ui-watchos` fine. `arm64_32` stays
-          # out until ring is fixed or pinned.
-          #
-          # watchOS and visionOS need `dyn-eval` excluded — see the long note
-          # in `build:` and rust-lang/stacker#152.
-          - os: macos-14
-            target: aarch64-apple-tvos
-            ui_crate: perry-ui-tvos
-            ui_lib: libperry_ui_tvos.a
-            tier3: true
-          - os: macos-14
-            target: aarch64-apple-tvos-sim
-            ui_crate: perry-ui-tvos
-            ui_lib: libperry_ui_tvos.a
-            tier3: true
-          - os: macos-14
-            target: aarch64-apple-visionos
-            ui_crate: perry-ui-visionos
-            ui_lib: libperry_ui_visionos.a
-            tier3: true
-          - os: macos-14
-            target: aarch64-apple-visionos-sim
-            ui_crate: perry-ui-visionos
-            ui_lib: libperry_ui_visionos.a
-            tier3: true
-          - os: macos-14
-            target: aarch64-apple-watchos
-            ui_crate: perry-ui-watchos
-            ui_lib: libperry_ui_watchos.a
-            tier3: true
-          - os: macos-14
-            target: aarch64-apple-watchos-sim
-            ui_crate: perry-ui-watchos
-            ui_lib: libperry_ui_watchos.a
-            tier3: true
+          # tvOS/visionOS/watchOS (Rust Tier-3, needed -Zbuild-std) are no
+          # longer built here — that unstable-cargo-feature build is
+          # dropped entirely, along with the matrix's `tier3` field and its
+          # two build-step branches; if Tier-3 support returns, re-add both
+          # rather than reviving a dead flag.
           # --- Android (NDK on Linux runner) --------------------------------
           # perry-ui-android requires the NDK clang++ wrapper and JNI; the
           # existing test.yml leg already cross-compiles it on ubuntu-24.04,
@@ -1182,12 +1028,10 @@ jobs:
             target: aarch64-linux-android
             ui_crate: perry-ui-android
             ui_lib: libperry_ui_android.a
-            tier3: false
           - os: ubuntu-24.04
             target: x86_64-linux-android
             ui_crate: perry-ui-android
             ui_lib: libperry_ui_android.a
-            tier3: false
           # --- Windows MSVC (native runner) ---------------------------------
           # Both native Windows architectures use their matching hosted runner
           # so Rust, LLVM, MSVC, and the packaged executable all agree.
@@ -1195,12 +1039,10 @@ jobs:
             target: x86_64-pc-windows-msvc
             ui_crate: perry-ui-windows
             ui_lib: perry_ui_windows.lib
-            tier3: false
           - os: windows-11-arm
             target: aarch64-pc-windows-msvc
             ui_crate: perry-ui-windows
             ui_lib: perry_ui_windows.lib
-            tier3: false
 
     runs-on: ${{ matrix.os }}
     env:
@@ -1211,16 +1053,13 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - name: Install Rust stable + cross target
+      - name: Install Rust toolchain + cross target
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: 'nightly-2026-08-20'
           targets: ${{ matrix.target }}
       - uses: ./.github/actions/setup-llvm22
 
-      - name: Install Rust nightly + rust-src (Tier-3 only)
-        if: matrix.tier3
-        run: rustup toolchain install nightly --component rust-src --profile minimal
-
       # Same cache shape as `build:` so the cross legs share crate compiles
       # across release cycles. Keyed on (target, Cargo.lock) — first run on a
       # new target is cold, but every subsequent release-tag reuses the
@@ -1301,8 +1140,7 @@ jobs:
       # ships clang-cl + lib.exe through Visual Studio.
 
       # --- Build the three (or two, when UI is N/A) static libs ------------
-      - name: Build runtime + stdlib + UI (stable, Tier-2)
-        if: ${{ !matrix.tier3 }}
+      - name: Build runtime + stdlib + UI
         shell: bash
         run: |
           set -euo pipefail
@@ -1313,34 +1151,6 @@ jobs:
           # already on windows-latest. Both go through plain `cargo build`.
           cargo build --profile dist --target ${{ matrix.target }} -p ${{ matrix.ui_crate }}
 
-      - name: Build runtime + stdlib + UI (nightly + build-std, Tier-3)
-        if: matrix.tier3
-        shell: bash
-        run: |
-          set -euo pipefail
-          # watchOS and visionOS cannot build `dyn-eval`, which is in `default`:
-          # it reaches `psm` via perry-parser -> swc_ecma_parser -> stacker, and
-          # psm's Mach-O guard omits watchos/visionos so both fall through to
-          # its ELF branch and emit directives the Mach-O assembler rejects.
-          # Upstream fix: rust-lang/stacker#152 — delete this branch when it
-          # lands. The list is `default` minus `dyn-eval`, nothing else, so the
-          # only capability these two lose is runtime `new Function`.
-          runtime_features=""
-          case "${{ matrix.target }}" in
-            *-apple-watchos|*-apple-watchos-sim|*-apple-visionos|*-apple-visionos-sim)
-              runtime_features="--no-default-features --features full,regex-engine,temporal,url-engine,string-normalize,intl-segmenter,intl-namespace,global-math,global-json,global-reflect,global-atomics,global-url,global-text,global-websocket,global-webcrypto,global-webfetch,proc-ipc,intl-locale,intl-datetime,diagnostics,mod-dgram,mod-http2-constants,keepalive-anchors,alloc-mimalloc"
-              ;;
-          esac
-          cargo +nightly build --profile dist \
-            -Z build-std=core,std,panic_abort \
-            --target ${{ matrix.target }} \
-            $runtime_features \
-            -p perry-runtime -p perry-runtime-static
-          cargo +nightly build --profile dist \
-            -Z build-std=core,std,panic_abort \
-            --target ${{ matrix.target }} \
-            -p perry-stdlib -p perry-stdlib-static -p ${{ matrix.ui_crate }}
-
       # #4856 — defense in depth behind the cache eviction above: a stale
       # cached runtime archive fails the release here instead of breaking
       # every consumer executable link on the build workers.
@@ -1510,8 +1320,8 @@ jobs:
   # ---------------------------------------------------------------------------
   create-release:
     needs: [preflight, build, build-cross]
-    # Strict by design: in tag-last mode a red Tier-3 cross leg blocks the tag
-    # too (nothing is public yet, so "fix or rerun-to-green, then the skipped
+    # Strict by design: in tag-last mode a red cross leg blocks the tag too
+    # (nothing is public yet, so "fix or rerun-to-green, then the skipped
     # downstream jobs rerun via `gh run rerun <id> --failed`" is cheap).
     if: >
       !cancelled() &&
@@ -1571,7 +1381,7 @@ jobs:
   # cut-release to the one create-release just made. Host archives are a hard
   # requirement; cross bundles are best-effort on the legacy paths (workers
   # rebuild from source when a bundle is missing), matching the old per-leg
-  # upload semantics where a red Tier-3 leg didn't sink the release.
+  # upload semantics where a red cross leg didn't sink the release.
   # ---------------------------------------------------------------------------
   publish-assets:
     needs: [preflight, build, build-cross, create-release]
diff --git a/.github/workflows/security-audit.yml b/.github/workflows/security-audit.yml
index 05a4206d8b..8c97262a3e 100644
--- a/.github/workflows/security-audit.yml
+++ b/.github/workflows/security-audit.yml
@@ -49,6 +49,8 @@ jobs:
         with:
           persist-credentials: false
       - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
       - uses: Swatinem/rust-cache@v2
         with:
@@ -199,6 +201,8 @@ jobs:
         with:
           persist-credentials: false
       - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
       - uses: Swatinem/rust-cache@v2
         with:
diff --git a/.github/workflows/simctl-tests.yml b/.github/workflows/simctl-tests.yml
index e4d2510faa..6e586e64ee 100644
--- a/.github/workflows/simctl-tests.yml
+++ b/.github/workflows/simctl-tests.yml
@@ -33,6 +33,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install iOS simulator Rust target
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f59a1efbeb..454959388f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -227,6 +227,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: 'nightly-2026-08-20'
           components: rustfmt, clippy
       - uses: ./.github/actions/setup-llvm22
 
@@ -711,6 +712,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: 'nightly-2026-08-20'
           components: clippy
       - uses: ./.github/actions/setup-llvm22
 
@@ -796,6 +798,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install sccache
@@ -908,6 +912,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install sccache
@@ -1212,6 +1218,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.scope.outputs.rust_work == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
         if: steps.scope.outputs.rust_work == 'true'
 
@@ -1392,6 +1400,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Setup Node.js
@@ -1495,6 +1505,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Set up ARM64 MSVC environment
@@ -1605,6 +1617,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -1724,6 +1738,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install sccache
@@ -1920,6 +1936,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install sccache
@@ -2092,6 +2110,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Install sccache
@@ -2203,6 +2223,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -2318,6 +2340,8 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
       - uses: Swatinem/rust-cache@v2
         with:
@@ -2479,6 +2503,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -2869,6 +2895,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -2931,6 +2959,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -2998,6 +3028,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -3052,6 +3084,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
@@ -3203,6 +3237,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - name: Set up MSVC environment (Windows)
@@ -3358,6 +3394,8 @@ jobs:
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
 
       - uses: Swatinem/rust-cache@v2
diff --git a/.github/workflows/tls-budget.yml b/.github/workflows/tls-budget.yml
index 6ee339e64b..f52a9bc2c7 100644
--- a/.github/workflows/tls-budget.yml
+++ b/.github/workflows/tls-budget.yml
@@ -164,6 +164,8 @@ jobs:
       - name: Install Rust toolchain
         if: steps.relevance.outputs.run == 'true'
         uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: 'nightly-2026-08-20'
       - uses: ./.github/actions/setup-llvm22
         if: steps.relevance.outputs.run == 'true'
 
diff --git a/CLAUDE.md b/CLAUDE.md
index 5e23d062ab..40049ccc69 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -172,7 +172,7 @@ Values cross threads via `SerializedValue` deep-copy. Each thread has independen
 
 ## Native UI (`perry/ui`)
 
-Declarative TypeScript compiles to AppKit/UIKit calls. Handle-based widget system (1-based i64 handles, NaN-boxed with POINTER_TAG). `--target ios-simulator`/`--target ios`/`--target tvos-simulator`/`--target tvos` for cross-compilation.
+Declarative TypeScript compiles to AppKit/UIKit calls. Handle-based widget system (1-based i64 handles, NaN-boxed with POINTER_TAG). `--target ios-simulator`/`--target ios`/`--target tvos-simulator`/`--target tvos` for cross-compilation. **`release-packages.yml` no longer builds or ships tvOS/visionOS/watchOS artifacts**: they're Rust Tier-3 (no prebuilt std, needed `-Z build-std`, still unstable), and that leg is dropped from the release workflow entirely. The compiler itself still supports them: `perry compile --target tvos-simulator` (etc.) auto-rebuilds via `cargo +nightly -Z build-std` using whatever nightly the caller has installed (`crates/perry/src/commands/compile/link/build_and_run.rs`, `crates/perry/src/commands/compile/optimized_libs/driver.rs`), and `test.yml` still exercises that path for tvOS-sim doc-tests.
 
 **To add a new widget** — change 4 places:
 1. Runtime: `crates/perry-ui-macos/src/widgets/` — create widget, `register_widget(view)`
diff --git a/changelog.d/8550-rust-1.98.0-pin.md b/changelog.d/8550-rust-1.98.0-pin.md
new file mode 100644
index 0000000000..af9694cf85
--- /dev/null
+++ b/changelog.d/8550-rust-1.98.0-pin.md
@@ -0,0 +1,3 @@
+Pinned the Rust toolchain to an exact `nightly-2026-08-20` across every CI workflow (was floating on `dtolnay/rust-toolchain@stable`). Nightly, not stable 1.98.0, because `-Zmin-publish-age` -- the cargo dependency-resolution soak feature `.cargo/config.toml` already configures -- is still nightly-only (verified directly: stable 1.98.0 silently ignores the config with a warning; [rust-lang/cargo#17009](https://github.com/rust-lang/cargo/issues/17009) is still open); the pin is recorded via a `soakBypass`-adopted `rust` entry in `external-tools.json`. Dropped the tvOS/visionOS/watchOS Rust Tier-3 build legs from `release-packages.yml` -- the `-Z build-std` those needed is unstable regardless of channel, so the removal is independent of which channel this pin uses. The `perry-ui-tvos`/`perry-ui-visionos`/`perry-ui-watchos` crates remain in the workspace for a manual `-Z build-std` build; CI just no longer builds or ships them. Also applied 1.98.0's newly-stabilized `{f32,f64}::algebraic_*` methods to `perry-runtime`'s `perf_hooks` `Histogram.stddev()`, an internal HdrHistogram statistic where reassociation is safe.
+
+The newer pinned nightly surfaced two classes of pre-existing issues invisible under the previous floating stable: `Atomic::fetch_update` was renamed to `try_update` (8 call sites fixed), and an expanded unused-import lint now catches a redundant `use super::super::*;` sitting alongside `use super::*;` (33 files fixed). Both were required for the `warnings` CI job to pass under the new pin.
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/assert.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/assert.rs
index 16ee5fdf32..4dfff47220 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/assert.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/assert.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_ASSERT_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/dgram_fs_os.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/dgram_fs_os.rs
index ad53365f83..c21ed41d2e 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/dgram_fs_os.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/dgram_fs_os.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_DGRAM_FS_OS_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/inspector_vm.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/inspector_vm.rs
index fe742081dd..c7aac3f5fb 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/inspector_vm.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/inspector_vm.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_INSPECTOR_VM_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/module_sea_tls_test.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/module_sea_tls_test.rs
index 933bb24c9b..af72ab5d09 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/module_sea_tls_test.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/module_sea_tls_test.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_MODULE_SEA_TLS_TEST_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/url_punycode_console.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/url_punycode_console.rs
index 14f528f595..1db5622960 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/url_punycode_console.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/url_punycode_console.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_URL_PUNYCODE_CONSOLE_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-codegen/src/lower_call/native_table/node_core/util_buffer.rs b/crates/perry-codegen/src/lower_call/native_table/node_core/util_buffer.rs
index 74f4093a42..2bc34f1653 100644
--- a/crates/perry-codegen/src/lower_call/native_table/node_core/util_buffer.rs
+++ b/crates/perry-codegen/src/lower_call/native_table/node_core/util_buffer.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) const NODE_CORE_UTIL_BUFFER_ROWS: &[NativeModSig] = &[
diff --git a/crates/perry-runtime/src/arena/block.rs b/crates/perry-runtime/src/arena/block.rs
index 630fb9d1d9..0258036d47 100644
--- a/crates/perry-runtime/src/arena/block.rs
+++ b/crates/perry-runtime/src/arena/block.rs
@@ -163,7 +163,7 @@ fn block_pool_process_bytes_sub(bytes: usize) {
         return;
     }
     BLOCK_POOL_PROCESS_BYTES
-        .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |current| {
+        .try_update(Ordering::Relaxed, Ordering::Relaxed, |current| {
             current.checked_sub(bytes)
         })
         .unwrap_or_else(|current| {
@@ -181,7 +181,7 @@ pub(super) fn block_pool_counter_try_reserve(
     cap: usize,
 ) -> bool {
     counter
-        .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |current| {
+        .try_update(Ordering::Relaxed, Ordering::Relaxed, |current| {
             current.checked_add(size).filter(|&next| next <= cap)
         })
         .is_ok()
diff --git a/crates/perry-runtime/src/gc/barrier/mod.rs b/crates/perry-runtime/src/gc/barrier/mod.rs
index 243fb325bb..067becd4fa 100644
--- a/crates/perry-runtime/src/gc/barrier/mod.rs
+++ b/crates/perry-runtime/src/gc/barrier/mod.rs
@@ -775,7 +775,7 @@ pub(super) fn incremental_mark_barrier_disable() {
     });
     if was_active {
         super::instruments::note_mark_barrier_disarmed();
-        let _ = PERRY_INCREMENTAL_MARK_BARRIER_ACTIVE_COUNT.fetch_update(
+        let _ = PERRY_INCREMENTAL_MARK_BARRIER_ACTIVE_COUNT.try_update(
             Ordering::SeqCst,
             Ordering::SeqCst,
             |count| count.checked_sub(1),
@@ -1038,7 +1038,7 @@ pub extern "C" fn js_gc_write_barriers_emitted(active: u32) {
     if active != 0 {
         GENERATED_WRITE_BARRIERS_EMITTED.fetch_add(1, Ordering::AcqRel);
     } else {
-        let _ = GENERATED_WRITE_BARRIERS_EMITTED.fetch_update(
+        let _ = GENERATED_WRITE_BARRIERS_EMITTED.try_update(
             Ordering::AcqRel,
             Ordering::Acquire,
             |count| count.checked_sub(1),
diff --git a/crates/perry-runtime/src/gc/layout_tables.rs b/crates/perry-runtime/src/gc/layout_tables.rs
index d1f5af7760..8a0eb1b551 100644
--- a/crates/perry-runtime/src/gc/layout_tables.rs
+++ b/crates/perry-runtime/src/gc/layout_tables.rs
@@ -426,7 +426,7 @@ pub static PERRY_PER_OBJECT_LAYOUTS_ANY: std::sync::atomic::AtomicU32 =
 fn per_object_layouts_global_arm() {
     use std::sync::atomic::Ordering;
     PERRY_PER_OBJECT_LAYOUTS_ANY
-        .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |count| {
+        .try_update(Ordering::SeqCst, Ordering::SeqCst, |count| {
             count.checked_add(1)
         })
         .expect("per-object layout thread count overflow");
@@ -443,7 +443,7 @@ fn per_object_layouts_global_disarm_with_hook(
 ) {
     use std::sync::atomic::Ordering;
     armed_threads
-        .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |count| {
+        .try_update(Ordering::SeqCst, Ordering::SeqCst, |count| {
             count.checked_sub(1)
         })
         .expect("per-object layout thread count underflow");
diff --git a/crates/perry-runtime/src/gc/poll_arm.rs b/crates/perry-runtime/src/gc/poll_arm.rs
index e9405329b8..7005945621 100644
--- a/crates/perry-runtime/src/gc/poll_arm.rs
+++ b/crates/perry-runtime/src/gc/poll_arm.rs
@@ -109,7 +109,7 @@ fn arm_counters(armed: &AtomicU32, events: &AtomicU64) {
 /// See [`disarm_poll`] for why this saturates instead of wrapping.
 #[inline]
 fn disarm_counter(armed: &AtomicU32) {
-    let _ = armed.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |armed| {
+    let _ = armed.try_update(Ordering::Relaxed, Ordering::Relaxed, |armed| {
         (armed > 0).then(|| armed - 1)
     });
 }
diff --git a/crates/perry-runtime/src/gc/roots/stack_maps.rs b/crates/perry-runtime/src/gc/roots/stack_maps.rs
index 942e888406..0fb0bdd46d 100644
--- a/crates/perry-runtime/src/gc/roots/stack_maps.rs
+++ b/crates/perry-runtime/src/gc/roots/stack_maps.rs
@@ -164,7 +164,7 @@ impl StackMapIndexStore {
         // is also the minimum loader recency each rebuild must preserve.
         let generation = self
             .next_generation
-            .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |generation| {
+            .try_update(Ordering::Relaxed, Ordering::Relaxed, |generation| {
                 generation.checked_add(1)
             })
             .unwrap_or_else(|_| panic!("perry: stack-map rebuild generation overflow"))
diff --git a/crates/perry-runtime/src/node_stream_constructors/builders.rs b/crates/perry-runtime/src/node_stream_constructors/builders.rs
index 503b94e2ba..f5d4f96f18 100644
--- a/crates/perry-runtime/src/node_stream_constructors/builders.rs
+++ b/crates/perry-runtime/src/node_stream_constructors/builders.rs
@@ -1,7 +1,6 @@
 //! node:stream — the `js_node_stream_*_new` / `*_subclass_init` constructors
 //! and `Readable.from` factory (split out of node_stream_constructors.rs for
 //! the 2000-line file-size gate, #1987).
-use super::super::*;
 use super::*;
 use crate::closure::ClosureHeader;
 use crate::object::{js_object_get_field_by_name_f64, js_object_set_field_by_name, ObjectHeader};
diff --git a/crates/perry-runtime/src/node_stream_constructors/introspection.rs b/crates/perry-runtime/src/node_stream_constructors/introspection.rs
index 671a2d2161..5ff0495066 100644
--- a/crates/perry-runtime/src/node_stream_constructors/introspection.rs
+++ b/crates/perry-runtime/src/node_stream_constructors/introspection.rs
@@ -3,7 +3,6 @@
 //! `_isArrayBufferView` type predicates), default-highWaterMark accessors and
 //! abort-signal wiring (split out of node_stream_constructors.rs for the
 //! 2000-line file-size gate, #1987).
-use super::super::*;
 use super::*;
 use crate::closure::{js_closure_alloc, js_closure_set_capture_ptr};
 use crate::value::JSValue;
diff --git a/crates/perry-runtime/src/node_stream_constructors/pipeline.rs b/crates/perry-runtime/src/node_stream_constructors/pipeline.rs
index 5bb157094f..893064dc8a 100644
--- a/crates/perry-runtime/src/node_stream_constructors/pipeline.rs
+++ b/crates/perry-runtime/src/node_stream_constructors/pipeline.rs
@@ -1,7 +1,6 @@
 //! node:stream — `Duplex.from`, `compose`, `finished`, `pipeline` and
 //! `duplexPair` (split out of node_stream_constructors.rs for the 2000-line
 //! file-size gate, #1987).
-use super::super::*;
 use super::*;
 use crate::closure::{
     js_closure_alloc, js_closure_get_capture_f64, js_closure_set_capture_f64, ClosureHeader,
diff --git a/crates/perry-runtime/src/node_stream_constructors/web_adapter.rs b/crates/perry-runtime/src/node_stream_constructors/web_adapter.rs
index cc653bd900..e5f1b6535c 100644
--- a/crates/perry-runtime/src/node_stream_constructors/web_adapter.rs
+++ b/crates/perry-runtime/src/node_stream_constructors/web_adapter.rs
@@ -1,7 +1,6 @@
 //! node:stream — WHATWG Web-stream interop (`Readable.toWeb`/`fromWeb`, the
 //! adapter pumps, and the fallback stub) split out of
 //! node_stream_constructors.rs for the 2000-line file-size gate, #1987.
-use super::super::*;
 use super::*;
 use crate::closure::{
     js_closure_alloc, js_closure_get_capture_f64, js_closure_set_capture_f64, ClosureHeader,
diff --git a/crates/perry-runtime/src/object/global_this/array_error.rs b/crates/perry-runtime/src/object/global_this/array_error.rs
index b95ce57e0f..4409d209bb 100644
--- a/crates/perry-runtime/src/object/global_this/array_error.rs
+++ b/crates/perry-runtime/src/object/global_this/array_error.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) fn global_this_rest_array_values(rest: f64) -> Vec<f64> {
diff --git a/crates/perry-runtime/src/object/global_this/ctor_thunks.rs b/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
index 6713de0db7..60430e6619 100644
--- a/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
+++ b/crates/perry-runtime/src/object/global_this/ctor_thunks.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(crate) fn normalize_eval_this_body(body: &str) -> Option<String> {
diff --git a/crates/perry-runtime/src/object/global_this/fetch_globals.rs b/crates/perry-runtime/src/object/global_this/fetch_globals.rs
index 1b3817fd5b..fadf21b9f5 100644
--- a/crates/perry-runtime/src/object/global_this/fetch_globals.rs
+++ b/crates/perry-runtime/src/object/global_this/fetch_globals.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 crate::perry_thread_local! {
diff --git a/crates/perry-runtime/src/object/global_this/generator.rs b/crates/perry-runtime/src/object/global_this/generator.rs
index 9aeb679524..31da8fea3a 100644
--- a/crates/perry-runtime/src/object/global_this/generator.rs
+++ b/crates/perry-runtime/src/object/global_this/generator.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 /// Distinguishes plain vs async generator closures for the intrinsic-tower
diff --git a/crates/perry-runtime/src/object/global_this/install_static.rs b/crates/perry-runtime/src/object/global_this/install_static.rs
index 78019b6189..2c2cf65811 100644
--- a/crates/perry-runtime/src/object/global_this/install_static.rs
+++ b/crates/perry-runtime/src/object/global_this/install_static.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 #[no_mangle]
diff --git a/crates/perry-runtime/src/object/global_this/math_temporal.rs b/crates/perry-runtime/src/object/global_this/math_temporal.rs
index d334f46b88..d6ad2f1072 100644
--- a/crates/perry-runtime/src/object/global_this/math_temporal.rs
+++ b/crates/perry-runtime/src/object/global_this/math_temporal.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 // Math.* thunks live in the sibling `builtin_thunks` module (split out of
 // `global_this`); pull them in directly so `install_math_namespace` resolves
diff --git a/crates/perry-runtime/src/object/global_this/populate.rs b/crates/perry-runtime/src/object/global_this/populate.rs
index aeb36ef1a0..37fdfb2b48 100644
--- a/crates/perry-runtime/src/object/global_this/populate.rs
+++ b/crates/perry-runtime/src/object/global_this/populate.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 /// Populate the freshly-allocated globalThis singleton with built-in
diff --git a/crates/perry-runtime/src/object/global_this/proto_methods.rs b/crates/perry-runtime/src/object/global_this/proto_methods.rs
index 0cdb8f8b4d..4e09f6adb6 100644
--- a/crates/perry-runtime/src/object/global_this/proto_methods.rs
+++ b/crates/perry-runtime/src/object/global_this/proto_methods.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 // Array.prototype thunks live in the sibling `array_error` module (split out of
 // `global_this`); pull them in directly so the prototype-install tables resolve
diff --git a/crates/perry-runtime/src/object/global_this/typed_array.rs b/crates/perry-runtime/src/object/global_this/typed_array.rs
index beeb82047d..252bca14b3 100644
--- a/crates/perry-runtime/src/object/global_this/typed_array.rs
+++ b/crates/perry-runtime/src/object/global_this/typed_array.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 fn array_buffer_receiver_addr() -> Option<usize> {
diff --git a/crates/perry-runtime/src/object/native_call_method/collection_methods.rs b/crates/perry-runtime/src/object/native_call_method/collection_methods.rs
index 55583c355c..bbfffbde1a 100644
--- a/crates/perry-runtime/src/object/native_call_method/collection_methods.rs
+++ b/crates/perry-runtime/src/object/native_call_method/collection_methods.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 /// Whether `method` is a backing-store collection method for a `class … extends
diff --git a/crates/perry-runtime/src/object/native_call_method/common_methods.rs b/crates/perry-runtime/src/object/native_call_method/common_methods.rs
index c0d1b4b868..a59a065384 100644
--- a/crates/perry-runtime/src/object/native_call_method/common_methods.rs
+++ b/crates/perry-runtime/src/object/native_call_method/common_methods.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::object_proto::*;
 use super::proto_dispatch::*;
 use super::*;
diff --git a/crates/perry-runtime/src/object/native_call_method/disposal.rs b/crates/perry-runtime/src/object/native_call_method/disposal.rs
index a391583521..39efdd6a6d 100644
--- a/crates/perry-runtime/src/object/native_call_method/disposal.rs
+++ b/crates/perry-runtime/src/object/native_call_method/disposal.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 /// #4795: resolve `obj[Symbol.dispose]` / `obj[Symbol.asyncDispose]` for the
diff --git a/crates/perry-runtime/src/object/native_call_method/handle_methods.rs b/crates/perry-runtime/src/object/native_call_method/handle_methods.rs
index a73ab195e8..7b4a1e5b9b 100644
--- a/crates/perry-runtime/src/object/native_call_method/handle_methods.rs
+++ b/crates/perry-runtime/src/object/native_call_method/handle_methods.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::typed_array::*;
 use super::*;
 
diff --git a/crates/perry-runtime/src/object/native_call_method/object_proto.rs b/crates/perry-runtime/src/object/native_call_method/object_proto.rs
index 02c6cc928c..218df09375 100644
--- a/crates/perry-runtime/src/object/native_call_method/object_proto.rs
+++ b/crates/perry-runtime/src/object/native_call_method/object_proto.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 pub(super) unsafe fn object_has_null_proto_flag(object: *const ObjectHeader) -> bool {
diff --git a/crates/perry-runtime/src/object/native_call_method/primitive_methods.rs b/crates/perry-runtime/src/object/native_call_method/primitive_methods.rs
index 58d4501632..87c2907ed0 100644
--- a/crates/perry-runtime/src/object/native_call_method/primitive_methods.rs
+++ b/crates/perry-runtime/src/object/native_call_method/primitive_methods.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::typed_array::*;
 use super::*;
 
diff --git a/crates/perry-runtime/src/object/native_call_method/proto_dispatch.rs b/crates/perry-runtime/src/object/native_call_method/proto_dispatch.rs
index 516f5ba16b..2345646d70 100644
--- a/crates/perry-runtime/src/object/native_call_method/proto_dispatch.rs
+++ b/crates/perry-runtime/src/object/native_call_method/proto_dispatch.rs
@@ -1,4 +1,3 @@
-use super::super::*;
 use super::*;
 
 /// #3716: a built-in *prototype method* read off its prototype and called *as
diff --git a/crates/perry-runtime/src/object/object_ops/accessors.rs b/crates/perry-runtime/src/object/object_ops/accessors.rs
index 4bc8ea5480..99eea60469 100644
--- a/crates/perry-runtime/src/object/object_ops/accessors.rs
+++ b/crates/perry-runtime/src/object/object_ops/accessors.rs
@@ -1,6 +1,5 @@
 //! Annex B accessor methods (`__defineGetter__`/`__lookupSetter__` etc.) and
 //! the raw own-field read `js_object_get_own_field_or_undef`.
-use super::super::*;
 use super::*;
 // Disambiguate the two in-scope `value_is_callable` globs (object_ops'
 // `descriptor_helpers` via `super::*` and `object`'s `instanceof` via
diff --git a/crates/perry-runtime/src/object/object_ops/define_property.rs b/crates/perry-runtime/src/object/object_ops/define_property.rs
index 5ba09e966e..e3d38a03b0 100644
--- a/crates/perry-runtime/src/object/object_ops/define_property.rs
+++ b/crates/perry-runtime/src/object/object_ops/define_property.rs
@@ -1,5 +1,4 @@
 //! `Object.defineProperty` and its class-prototype-method installation helper.
-use super::super::*;
 use super::*;
 
 /// #2159 helper: install a `target_cid.method` entry from an
diff --git a/crates/perry-runtime/src/object/object_ops/descriptor_helpers.rs b/crates/perry-runtime/src/object/object_ops/descriptor_helpers.rs
index 1637dece5a..431aefce77 100644
--- a/crates/perry-runtime/src/object/object_ops/descriptor_helpers.rs
+++ b/crates/perry-runtime/src/object/object_ops/descriptor_helpers.rs
@@ -1,6 +1,5 @@
 //! Descriptor validation + throw helpers backing `Object.defineProperty` /
 //! `Object.create` / `Object.defineProperties` (moved out of `object_ops.rs`).
-use super::super::*;
 use super::*;
 /// Throw a `TypeError` with the given UTF-8 message bytes. Used by the
 /// `Object.defineProperty` / `Object.create` descriptor + invariant validation
diff --git a/crates/perry-runtime/src/object/object_ops/from_entries.rs b/crates/perry-runtime/src/object/object_ops/from_entries.rs
index 4e242c0deb..577b87f054 100644
--- a/crates/perry-runtime/src/object/object_ops/from_entries.rs
+++ b/crates/perry-runtime/src/object/object_ops/from_entries.rs
@@ -1,5 +1,4 @@
 //! `Object.fromEntries` and its iterable-materialization helpers.
-use super::super::*;
 use super::*;
 
 fn throw_from_entries_type_error(message: &[u8]) -> ! {
diff --git a/crates/perry-runtime/src/object/object_ops/has_own.rs b/crates/perry-runtime/src/object/object_ops/has_own.rs
index 62044704e7..c6125dca3a 100644
--- a/crates/perry-runtime/src/object/object_ops/has_own.rs
+++ b/crates/perry-runtime/src/object/object_ops/has_own.rs
@@ -1,5 +1,4 @@
 //! `Object.is`, `Object.hasOwn`, and `Object.prototype.propertyIsEnumerable`.
-use super::super::*;
 use super::*;
 
 /// Object.is(a, b) — SameValue algorithm
diff --git a/crates/perry-runtime/src/object/object_ops/keys_array.rs b/crates/perry-runtime/src/object/object_ops/keys_array.rs
index f33f875115..c4796d9017 100644
--- a/crates/perry-runtime/src/object/object_ops/keys_array.rs
+++ b/crates/perry-runtime/src/object/object_ops/keys_array.rs
@@ -1,6 +1,5 @@
 //! keys_array maintenance helpers shared by the descriptor-define paths:
 //! `ensure_key_in_keys_array`, `install_builtin_getter`, `own_key_present`.
-use super::super::*;
 use super::*;
 
 /// Ensure a key appears in the object's keys_array. Used by `Object.defineProperty`
diff --git a/crates/perry-runtime/src/object/object_ops/prototype.rs b/crates/perry-runtime/src/object/object_ops/prototype.rs
index 189bab2b6a..5f463af7f0 100644
--- a/crates/perry-runtime/src/object/object_ops/prototype.rs
+++ b/crates/perry-runtime/src/object/object_ops/prototype.rs
@@ -1,5 +1,4 @@
 //! `Object.create`, `Object.getPrototypeOf`, and the globalThis-builtin lookup.
-use super::super::*;
 use super::*;
 
 /// Look up the canonical NaN-boxed value of a built-in constructor /
diff --git a/crates/perry-runtime/src/perf_histogram.rs b/crates/perry-runtime/src/perf_histogram.rs
index d86a923c6e..0492a61458 100644
--- a/crates/perry-runtime/src/perf_histogram.rs
+++ b/crates/perry-runtime/src/perf_histogram.rs
@@ -269,8 +269,14 @@ impl Histogram {
         let mut it = self.iter();
         while it.step() {
             if it.count != 0 {
-                let dev = self.median_equivalent(it.value) as f64 - mean;
-                geometric_dev_total += dev * dev * it.count as f64;
+                // Rust 1.98's algebraic_* float methods let LLVM reassociate
+                // and vectorize this reduction (Node's own HdrHistogram-based
+                // stddev is already a bucketed approximation, not a value
+                // any spec requires bit-exact, so reordering is safe here).
+                let dev = self.median_equivalent(it.value) as f64;
+                let dev = dev.algebraic_sub(mean);
+                let sq = dev.algebraic_mul(dev).algebraic_mul(it.count as f64);
+                geometric_dev_total = geometric_dev_total.algebraic_add(sq);
             }
         }
         (geometric_dev_total / self.total_count as f64).sqrt()
diff --git a/external-tools.json b/external-tools.json
index 7795f0eaae..8d8fbe5445 100644
--- a/external-tools.json
+++ b/external-tools.json
@@ -1,5 +1,24 @@
 {
   "tools": {
+    "rust": {
+      "description": "Rust toolchain (rustc + cargo) — pinned exact version for every workflow, instead of floating on whatever `dtolnay/rust-toolchain@stable` resolves to at run time.",
+      "version": "nightly-2026-08-20",
+      "release": "rustup-toolchain",
+      "repository": "github:rust-lang/rust",
+      "notes": [
+        "Pinned via `toolchain:` on every `dtolnay/rust-toolchain@stable` step in .github/workflows/*.yml. Bump by editing tools.rust.version here and re-running the same substitution across every workflow file.",
+        "Integrity is rustup's own signed-manifest verification, not a second SRI hash — this entry just records the adopted version for the soak gate.",
+        "Nightly, not stable, because -Zmin-publish-age (.cargo/config.toml) is nightly-only on 1.98.0 — verified directly, not assumed.",
+        "Transition-to-stable target: Rust 1.100.0, late September 2026, per the min-publish-age stabilization PR (https://github.com/rust-lang/cargo/pull/17335, open) and tracking issue (https://github.com/rust-lang/cargo/issues/17009). Same target as socket-wheelhouse's canonical rust-toolchain.toml.",
+        "Already carries the algebraic_* float methods used in crates/perry-runtime/src/perf_histogram.rs — stable since 1.98.0, unrelated to the nightly pin above.",
+        "Adopted 1 day after this nightly's cut, via soakBypass below."
+      ],
+      "soakBypass": {
+        "version": "nightly-2026-08-20",
+        "published": "2026-08-20",
+        "removable": "2026-08-27"
+      }
+    },
     "node": {
       "description": "Node.js — the pinned oracle for the builtin-module compatibility matrix (scripts/node_compat_matrix.mjs).",
       "version": "26.5.1",