diff --git a/.cargo/config.toml b/.cargo/config.toml
new file mode 100644
index 000000000..33342ff82
--- /dev/null
+++ b/.cargo/config.toml
@@ -0,0 +1,12 @@
+# Guest-only build flags: the key is scoped to the guest target, so host builds
+# read this file and take nothing from it. Cargo joins `rustflags` across
+# ancestor configs, so each guest crate keeps its own flags and gains this one.
+[target.riscv64im-lambda-vm-elf]
+# `compiler_builtins` turns `mem-unaligned` on for x86, aarch64 and bpf only, so
+# on RISC-V `memcpy`/`memmove` reassemble every misaligned word by hand; this VM
+# does unaligned scalar accesses natively (#864). The cfg reaches every crate in
+# the guest graph, but only `compiler-builtins` reads that name, and it declares
+# the value in its own check-cfg. It lives in that crate's `build.rs` with no
+# stability guarantee: bumping the `nightly-2026-02-01` pin in the Makefile can
+# turn this into a silent no-op.
+rustflags = ["--cfg", "feature=\"mem-unaligned\""]
diff --git a/.github/workflows/hyperfine.yaml b/.github/workflows/hyperfine.yaml
index b52241fc2..70f99e1d2 100644
--- a/.github/workflows/hyperfine.yaml
+++ b/.github/workflows/hyperfine.yaml
@@ -40,7 +40,7 @@ jobs:
         id: cache
         with:
           path: ${{ matrix.branch }}_programs/*.elf
-          key: benchmarks-${{ matrix.branch }}-${{ hashFiles( 'executor/programs/bench/**', 'syscalls/**' ) }}
+          key: benchmarks-${{ matrix.branch }}-${{ hashFiles( 'executor/programs/bench/**', 'syscalls/**', '.cargo/config.toml' ) }}
           restore-keys: benchmarks-${{ matrix.branch }}-
 
       - name: Setup Rust Environment
@@ -56,7 +56,7 @@ jobs:
 
       - name: Export benchmark hashes
         id: export-hashes
-        run: echo "benchmark-hashes-${{ matrix.branch }}=${{ hashFiles( 'executor/programs/bench/**', 'syscalls/**' ) }}" >> "$GITHUB_OUTPUT"
+        run: echo "benchmark-hashes-${{ matrix.branch }}=${{ hashFiles( 'executor/programs/bench/**', 'syscalls/**', '.cargo/config.toml' ) }}" >> "$GITHUB_OUTPUT"
 
   build-binaries:
     strategy:
diff --git a/.github/workflows/pr_main.yaml b/.github/workflows/pr_main.yaml
index 89bff2b03..7fa77ba22 100644
--- a/.github/workflows/pr_main.yaml
+++ b/.github/workflows/pr_main.yaml
@@ -103,7 +103,7 @@ jobs:
           path: |
             executor/program_artifacts/rust
             executor/shared_target
-          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile') }}
+          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             rust-elf-artifacts-
 
@@ -275,7 +275,7 @@ jobs:
           path: |
             executor/program_artifacts/rust
             executor/shared_target
-          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile') }}
+          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             rust-elf-artifacts-
 
@@ -391,7 +391,7 @@ jobs:
           path: |
             executor/program_artifacts/rust
             executor/shared_target
-          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile') }}
+          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             rust-elf-artifacts-
 
@@ -409,7 +409,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: executor/program_artifacts/recursion
-          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile') }}
+          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             recursion-elf-artifacts-
 
@@ -480,7 +480,7 @@ jobs:
           path: |
             executor/program_artifacts/rust
             executor/shared_target
-          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile') }}
+          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             rust-elf-artifacts-
 
@@ -508,7 +508,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: executor/program_artifacts/recursion
-          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile') }}
+          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             recursion-elf-artifacts-
 
@@ -564,7 +564,7 @@ jobs:
           path: |
             executor/program_artifacts/rust
             executor/shared_target
-          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile') }}
+          key: rust-elf-artifacts-${{ hashFiles('executor/programs/rust/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'syscalls/**', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             rust-elf-artifacts-
 
@@ -581,7 +581,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: executor/program_artifacts/recursion
-          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile') }}
+          key: recursion-elf-artifacts-${{ hashFiles('bench_vs/lambda/**', 'prover/src/**', 'prover/Cargo.toml', 'crypto/**/src/**', 'crypto/**/Cargo.toml', 'executor/src/**', 'executor/Cargo.toml', 'syscalls/**', 'executor/programs/riscv64im-lambda-vm-elf.json', 'Makefile', '.cargo/config.toml') }}
           restore-keys: |
             recursion-elf-artifacts-