diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7ef5fce..0bb2afa 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -19,7 +19,7 @@ jobs:
     env:
       # CI runs no git hooks, so skip the cargo:hk source build (~3 min on every run).
       # node/bun are still provisioned from mise.toml for parity with local dev.
-      MISE_DISABLE_TOOLS: cargo:hk
+      MISE_DISABLE_TOOLS: cargo:hk,mr-boxington
     steps:
       - name: Checkout code
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 6bb87b3..5c9f80a 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -35,6 +35,8 @@ concurrency:
 jobs:
   build:
     runs-on: ubuntu-latest
+    env:
+      CARGO_INCREMENTAL: 0
     steps:
       - name: Checkout code
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
@@ -42,16 +44,25 @@ jobs:
           persist-credentials: false
 
       # The toolchain (and rustfmt/clippy components) is selected by
-      # rust-toolchain.toml via the runner's preinstalled rustup — no
-      # third-party action needed.
+      # rust-toolchain.toml via the runner's preinstalled rustup.
+      - name: Install pinned toolchain
+        run: rustup show active-toolchain || rustup toolchain install
+
+      # After the toolchain step: the cache key hashes the `rustc` on PATH.
+      - name: Set up mbx cache
+        uses: jdx/mr-boxington-action@88acf2bb50552c7c508cbac13e5f8c576b95b1de # v1.7.3
+        with:
+          version: 1.29.2
+          cache-generation: test-v1
+
       - name: Format check
         run: cargo fmt --all -- --check
 
       - name: Clippy
-        run: cargo clippy --all-targets --all-features -- -D warnings
+        run: mbx clippy --all-targets --all-features -- -D warnings
 
       - name: Test
-        run: cargo test --all-features --locked --workspace
+        run: mbx test --all-features --locked --workspace
 
   ignored-tests:
     # Network-gated: these tests download tree-sitter grammars from GitHub
@@ -60,11 +71,22 @@ jobs:
     # grammar-fetch / parser-compat regressions.
     if: github.event_name == 'workflow_dispatch' || github.event_name == 'schedule'
     runs-on: ubuntu-latest
+    env:
+      CARGO_INCREMENTAL: 0
     steps:
       - name: Checkout code
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
         with:
           persist-credentials: false
 
+      - name: Install pinned toolchain
+        run: rustup show active-toolchain || rustup toolchain install
+
+      - name: Set up mbx cache
+        uses: jdx/mr-boxington-action@88acf2bb50552c7c508cbac13e5f8c576b95b1de # v1.7.3
+        with:
+          version: 1.29.2
+          cache-generation: ignored-v1
+
       - name: Test (ignored / network-gated)
-        run: cargo test --all-features --locked --workspace -- --ignored
+        run: mbx test --all-features --locked --workspace -- --ignored
diff --git a/.github/workflows/sonar.yml b/.github/workflows/sonar.yml
index f745133..d85b276 100644
--- a/.github/workflows/sonar.yml
+++ b/.github/workflows/sonar.yml
@@ -19,6 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
+      CARGO_INCREMENTAL: 0
     steps:
       - name: Checkout code
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
@@ -27,11 +28,21 @@ jobs:
           fetch-depth: 0
 
       # --- Rust coverage (coverage/rust-lcov.info) ---
+      - name: Install pinned toolchain
+        run: rustup show active-toolchain || rustup toolchain install
+
       # rust-toolchain.toml uses `profile = "minimal"`, so the llvm-tools-preview
       # component (required by cargo-llvm-cov) is not present by default.
       - name: Add llvm-tools-preview component
         run: rustup component add llvm-tools-preview
 
+      # After the toolchain and llvm-tools steps: the cache key hashes the `rustc` on PATH.
+      - name: Set up mbx cache
+        uses: jdx/mr-boxington-action@88acf2bb50552c7c508cbac13e5f8c576b95b1de # v1.7.3
+        with:
+          version: 1.29.2
+          cache-generation: coverage-v1
+
       - name: Install cargo-llvm-cov
         uses: taiki-e/install-action@9e1e5806d4a4822de933115878265be9aaa786d9 # v2
         with:
@@ -42,7 +53,7 @@ jobs:
         # offline (see ADR-0004). --all-features mirrors the Rust CI gate.
         run: |
           mkdir -p coverage
-          cargo llvm-cov --workspace --locked --all-features --lcov --output-path coverage/rust-lcov.info
+          mbx llvm-cov --workspace --locked --all-features --lcov --output-path coverage/rust-lcov.info
 
       - name: Upload Rust coverage to Codecov
         uses: codecov/codecov-action@fb8b3582c8e4def4969c97caa2f19720cb33a72f # v7.0.0
diff --git a/.miserc.toml b/.miserc.toml
new file mode 100644
index 0000000..8f0b74b
--- /dev/null
+++ b/.miserc.toml
@@ -0,0 +1 @@
+auto_env = true
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1395ba7..021776b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -6,16 +6,16 @@ By participating, you agree to abide by our [Code of Conduct](./CODE_OF_CONDUCT.
 
 ## Getting started
 
-`csp` is Rust-first (the workspace under `crates/`) with a thin JS toolchain for the npm wrapper and repo tooling. [mise](https://mise.jdx.dev/) pins the tool versions (node, bun, and the `hk` git-hook manager); the Rust toolchain is pinned separately by `rust-toolchain.toml`.
+`csp` is Rust-first (the workspace under `crates/`) with a thin JS toolchain for the npm wrapper and repo tooling. [mise](https://mise.jdx.dev/) pins the tool versions (node, bun, the `hk` git-hook manager, and the `mbx` Cargo build cache); the Rust toolchain is pinned separately by `rust-toolchain.toml`.
 
 ```bash
 git clone https://github.com/pleaseai/code-search.git
 cd code-search
-mise install        # install pinned tool versions (node, bun, hk) and set up git hooks
+mise install        # install pinned tool versions (node, bun, hk, mbx) and set up git hooks
 bun install         # install JS dependencies
 ```
 
-If you do not use mise, install the versions listed in `mise.toml` and `rust-toolchain.toml` manually, then run `bun install`. Rust builds use the standard `cargo` toolchain.
+If you do not use mise, install the versions listed in `mise.toml` and `rust-toolchain.toml` manually, then run `bun install`. Rust builds use the standard `cargo` toolchain; `mbx` is optional (see [Faster local builds](#faster-local-builds-optional)).
 
 ## Development workflow
 
@@ -33,6 +33,30 @@ mise run check       # full pre-commit gate: JS lint/typecheck + Rust fmt/clippy
 
 For Rust changes, also run `cargo fmt --all` and `cargo clippy --all-targets --all-features -- -D warnings` (both are part of `mise run check`).
 
+### Faster local builds (optional)
+
+CI compiles Rust through [mbx (mr boxington)](https://mr-boxington.jdx.dev), a shared Cargo build
+cache, via `jdx/mr-boxington-action`. `mise install` also installs `mbx` locally (pinned in
+`mise.toml`), so a build in one worktree warms every other worktree. Run Cargo through it:
+
+```bash
+mise exec -- mbx build           # or: mise exec -- mbx test --all-features --locked --workspace
+mise exec -- mbx explain --last  # why a build did or did not hit the cache
+```
+
+mise's `mr_boxington` Rust option is deliberately not used: a `rust` entry in `mise.toml`
+needs a version, which would override `rust-toolchain.toml` (the sole owner of the Rust channel).
+So plain `cargo` is not routed through `mbx`; call `mbx` explicitly. Set
+`CARGO_INCREMENTAL=0` for the best hit rate.
+
+There is no prebuilt `mbx` for Intel macOS, so `mise.macos-x64.toml` (loaded through `auto_env` in
+`.miserc.toml`) builds it from crates.io via the `cargo:mbx` backend (Rust 1.91 or newer). Without
+mise, run `cargo install mbx --version 1.29.2 --locked`.
+
+`mbx` wraps `rustc` itself, so it **defers to any `RUSTC_WRAPPER` already set** (for example
+`RUSTC_WRAPPER=sccache` in a shell profile) and then caches nothing. Unset the wrapper before
+using it. The `mbx[cache]` summary line it prints shows the hit count.
+
 ## Commit messages
 
 We follow [Conventional Commits](https://www.conventionalcommits.org/): `type(scope): subject`, where `type` is one of `feat`, `fix`, `docs`, `refactor`, `test`, `chore`, etc. Breaking changes include a `BREAKING CHANGE:` footer. Versioning and the changelog are generated automatically from these messages, so accurate types matter.
diff --git a/mise.macos-x64.toml b/mise.macos-x64.toml
new file mode 100644
index 0000000..4b81b4b
--- /dev/null
+++ b/mise.macos-x64.toml
@@ -0,0 +1,6 @@
+# mr-boxington ships no darwin/x86_64 release archive, so build mbx from crates.io.
+[tools]
+mr-boxington = "1.29.2"
+
+[tool_alias]
+mr-boxington = "cargo:mbx"
diff --git a/mise.toml b/mise.toml
index be1f3f7..d9628be 100644
--- a/mise.toml
+++ b/mise.toml
@@ -4,7 +4,9 @@
 # This repo is Rust-first (crates/) with a thin JS toolchain for the npm/ wrapper and SDK.
 # - The Rust toolchain (channel, rustfmt, clippy) is owned solely by rust-toolchain.toml —
 #   do not double-pin it here.
-# - Only node/bun (JS lint + typecheck) and hk (the git hook manager) are pinned via mise.
+# - Only node/bun (JS lint + typecheck), hk (the git hook manager) and mbx (the Cargo build
+#   cache CLI) are pinned via mise. mise's `mr_boxington` Rust option is not used: a `rust`
+#   entry requires a version, which would override rust-toolchain.toml.
 
 [tools]
 node = "24"
@@ -15,6 +17,7 @@ bun = "1.3.14" # matches package.json packageManager
 # Pinned to match the v1.48.0 hk.pkl amends — keep the two in sync on upgrades.
 # Details: dev-tooling → references/git-hooks.md
 "cargo:hk" = "1.48.0"
+mr-boxington = "1.29.2"
 
 [env]
 # Wrap hooks in `mise x` so the mise-managed node/bun are on PATH