chore: pin Rust toolchain, set MSRV 1.88.0, add MSRV guide

.github/workflows/ci.yml

@@ -18,9 +18,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
-        with:
-          components: clippy, rustfmt
+        run: rustup show
 
       - name: Install protoc
         # Issue #28: prost-build needs protoc to compile our internal
@@ -60,7 +58,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        run: rustup show
 
       - name: Install protoc
         # Issue #28: prost-build needs protoc; ubuntu-latest does not

Cargo.toml

@@ -17,6 +17,9 @@ default-members = [
     "crates/merutable",
 ]
 
+[workspace.package]
+rust-version = "1.88.0"
+
 [workspace.dependencies]
 # Parquet / Arrow (arrow-rs monorepo)
 parquet      = { version = "53", features = ["async"] }

DEVELOPER.md

@@ -2,10 +2,12 @@
 
 ## Prerequisites
 
-- **Rust stable** (1.80+): install via [rustup](https://rustup.rs/)
+- **Rust**: install via [rustup](https://rustup.rs/)
   ```
   curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
   ```
+  The exact toolchain version is pinned in `rust-toolchain.toml` at the workspace root.
+  `rustup` reads this file automatically — no manual version selection needed.
 - **Git**
 
 ## Python bindings (`merutable-python`)
@@ -131,3 +133,31 @@ modules with `pub` visibility (a follow-up sweep tightens to
 ## Adding a dependency
 
 All dependency versions are pinned in the workspace root `Cargo.toml` under `[workspace.dependencies]`. Individual crates reference them with `{ workspace = true }`. Never add version specs in crate-level `Cargo.toml` files.
+
+## MSRV (Minimum Supported Rust Version)
+
+The MSRV is set via `rust-version` in `[workspace.package]` in the root `Cargo.toml`.
+
+### Finding the MSRV
+
+```bash
+cargo install cargo-msrv
+cargo msrv find --min <version>
+```
+
+### Verifying after a dependency upgrade
+
+After bumping a dependency version, check that it still builds with the
+MSRV. The `+<version>` syntax tells cargo to use a specific toolchain
+instead of the default:
+
+```bash
+# Install the MSRV toolchain (one-time)
+rustup install <msrv>
+
+# Build against it
+cargo +<msrv> check
+```
+
+If the build fails, either pin the dependency to its last MSRV-compatible
+version or bump `rust-version` in the workspace root.

crates/merutable-python/Cargo.toml

@@ -2,6 +2,7 @@
 name    = "merutable-python"
 version = "0.1.0"
 edition = "2021"
+rust-version = { workspace = true }
 description = "Python bindings for merutable via PyO3"
 license = "Apache-2.0"
 publish = false

crates/merutable/Cargo.toml

@@ -2,6 +2,7 @@
 name          = "merutable"
 version       = "0.0.1"
 edition       = "2021"
+rust-version = { workspace = true }
 description   = "Embeddable single-table engine: row + columnar Parquet with Iceberg-compatible metadata"
 keywords      = ["embedded", "lsm", "iceberg", "parquet", "table"]
 license       = "Apache-2.0"

rust-toolchain.toml

@@ -0,0 +1,3 @@
+[toolchain]
+channel = "stable"
+components = ["clippy", "rustfmt"]