diff --git a/.github/workflows/book.yml b/.github/workflows/book.yml
index c66be0ce35..a5f821f06b 100644
--- a/.github/workflows/book.yml
+++ b/.github/workflows/book.yml
@@ -35,6 +35,8 @@ jobs:
 
       - name: Install Rust nightly
         uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: nightly-2026-02-21
 
       - uses: mozilla-actions/sccache-action@v0.0.9
 
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 864643e859..e81229c81d 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -26,6 +26,9 @@ jobs:
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@clippy
         with:
+          # Pin nightly to avoid breakage from str::as_str() stabilization
+          # which breaks shellexpand 3.1.1 method resolution.
+          toolchain: nightly-2026-02-21
           components: clippy
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: Swatinem/rust-cache@v2
@@ -49,6 +52,9 @@ jobs:
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@nightly
         with:
+          # Pin nightly to avoid breakage from str::as_str() stabilization
+          # which breaks shellexpand 3.1.1 method resolution.
+          toolchain: nightly-2026-02-21
           components: clippy
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: Swatinem/rust-cache@v2
@@ -141,6 +147,8 @@ jobs:
       - uses: actions/checkout@v6
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: nightly-2026-02-21
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: Swatinem/rust-cache@v2
         with:
@@ -160,6 +168,7 @@ jobs:
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@nightly
         with:
+          toolchain: nightly-2026-02-21
           components: rustfmt
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Run fmt
@@ -173,6 +182,8 @@ jobs:
       - uses: actions/checkout@v6
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: nightly-2026-02-21
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: Swatinem/rust-cache@v2
         with:
@@ -188,6 +199,8 @@ jobs:
       - uses: actions/checkout@v6
       - uses: rui314/setup-mold@v1
       - uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: nightly-2026-02-21
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: Swatinem/rust-cache@v2
         with: