diff --git a/.github/workflows/checks.yml b/.github/workflows/checks.yml
index 9f423b07..335db6ae 100644
--- a/.github/workflows/checks.yml
+++ b/.github/workflows/checks.yml
@@ -40,6 +40,12 @@ jobs:
       - name: Setup image (Linux)
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-checks
@@ -62,6 +68,12 @@ jobs:
       - name: Setup image (Linux)
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-checks
@@ -84,6 +96,12 @@ jobs:
       - name: Setup image (Linux)
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-checks
@@ -132,6 +150,12 @@ jobs:
       - name: Setup image (Linux)
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-checks
@@ -168,6 +192,12 @@ jobs:
       - name: Setup image (Linux)
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-checks
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index aec1f747..0d8c2d9f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -94,6 +94,12 @@ jobs:
         if: ${{ contains(matrix.os, 'ubuntu') }}
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-test
@@ -131,6 +137,12 @@ jobs:
             "$env:USERPROFILE\.cargo", `
             "$env:USERPROFILE\.rustup" -ErrorAction SilentlyContinue
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-test
diff --git a/.github/workflows/validate-examples.yml b/.github/workflows/validate-examples.yml
index 8e5b6595..13dcb353 100644
--- a/.github/workflows/validate-examples.yml
+++ b/.github/workflows/validate-examples.yml
@@ -52,6 +52,12 @@ jobs:
         if: ${{ contains(matrix.os, 'ubuntu') }}
         run: ./.github/scripts/provision-linux-build.sh
 
+      # rust-cache hashes all installed toolchains; the runner image's `stable`
+      # drifts as the image updates, which moves the cache key and causes misses.
+      # Remove it so only the rust-toolchain.toml-pinned version remains.
+      - name: Remove the runner's bundled Rust toolchain
+        run: rustup toolchain remove stable 2>/dev/null || true
+
       - uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache-shared-key: ${{ runner.os }}-validate