feat(tools): add cargo-stow for Cargo.toml validation and enforcement (#2961)

## Summary

Introduces `cargo stow`, a workspace linting tool that validates and
fixes Cargo.toml files to enforce project conventions.

### Features

- **Validation Rules:**
  - Flat crate structure (no nested crates under `crates/`)
  - Crate naming conventions (`baml_<word>` or `baml_<prefix>_<word>`)
  - Test crate pairing (e.g., `baml_ide_tests` requires `baml_ide`)
  - Workspace dependency format (`{ workspace = true }`)
- Dependency restriction rules (e.g., `anyhow` only in CLI/test crates)
  - Dependency sorting (internal deps first, then external)

- **Auto-fix capability:** Run `cargo stow --fix` to automatically fix
sortable/formattable issues

- **Runtime configuration:** Configure via `stow.toml` or
`[workspace.metadata.stow]` in Cargo.toml - no recompilation needed to
change rules

### Integration

- Added `cargo-stow` CI job that runs on every PR
- Integrated into pre-commit hooks via `setup-hooks.sh`

### Usage

```bash
# Check for validation errors
cargo stow --check

# Automatically fix issues
cargo stow --fix

# Verbose output
cargo stow --check --verbose
```

## Test plan

- [x] `cargo stow --check` passes on the current workspace
- [x] Pre-commit hook runs stow check
- [x] CI workflow includes cargo-stow job

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: hellovai

.github/workflows/cargo-tests.reusable.yaml

@@ -70,7 +70,7 @@ jobs:
         working-directory: baml_language
 
       - name: "Clippy (wasm)"
-        run: cargo clippy --workspace --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --target wasm32-unknown-unknown --all-features --locked -- -D warnings
+        run: cargo clippy --workspace --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --exclude baml_tools_stow --target wasm32-unknown-unknown --all-features --locked -- -D warnings
         working-directory: baml_language
 
   cargo-test-linux:
@@ -204,8 +204,8 @@ jobs:
 
       - name: "Build for WASM"
         run: |
-          cargo build --workspace --target wasm32-unknown-unknown --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --no-default-features
-          cargo build --workspace --target wasm32-unknown-unknown --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --no-default-features --release
+          cargo build --workspace --target wasm32-unknown-unknown --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --exclude baml_tools_stow --no-default-features
+          cargo build --workspace --target wasm32-unknown-unknown --exclude baml_tools_onionskin --exclude baml_lsp --exclude baml_cli --exclude baml_tools_stow --no-default-features --release
         working-directory: baml_language
 
       - name: "Check WASM size"

.github/workflows/ci.yaml

@@ -200,6 +200,31 @@ jobs:
             echo "changed=true" >> "$GITHUB_OUTPUT"
           fi
 
+  # Lint checks
+  cargo-stow:
+    name: "Cargo Stow"
+    runs-on: ubuntu-latest
+    needs: determine_changes
+    if: needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' || github.ref == 'refs/heads/canary'
+    timeout-minutes: 10
+    steps:
+      - name: "Checkout Branch"
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: "baml_language -> target"
+
+      - name: "Install Rust toolchain"
+        run: rustup show
+        working-directory: baml_language
+
+      - name: "Run cargo stow --check"
+        run: cargo run -p baml_tools_stow --release -- stow --check
+        working-directory: baml_language
+
   # Call reusable workflows
   cargo-tests:
     name: "Cargo Tests"
@@ -300,6 +325,7 @@ jobs:
     runs-on: ubuntu-latest
     if: always()
     needs:
+      - cargo-stow
       - cargo-tests
       - wasm-pack-tests
       - beps
@@ -309,6 +335,11 @@ jobs:
     steps:
       - name: "Check test results"
         run: |
+          if [[ "${{ needs.cargo-stow.result }}" != "success" && "${{ needs.cargo-stow.result }}" != "skipped" ]]; then
+            echo "::error::Cargo stow check failed"
+            exit 1
+          fi
+
           if [[ "${{ needs.cargo-tests.result }}" != "success" && "${{ needs.cargo-tests.result }}" != "skipped" ]]; then
             echo "::error::Cargo tests failed"
             exit 1

baml_language/.claude/settings.local.json

@@ -20,7 +20,9 @@
       "Bash(cargo clippy:*)",
       "WebSearch",
       "Bash(cargo run:*)",
-      "Bash(cargo check:*)"
+      "Bash(cargo check:*)",
+      "Bash(git add:*)",
+      "Bash(git commit -m \"$\\(cat <<''EOF''\nfeat\\(tools\\): add cargo-stow for Cargo.toml validation and enforcement\n\nIntroduces `cargo stow`, a workspace linting tool that validates and fixes\nCargo.toml files to enforce project conventions:\n\n- Flat crate structure \\(no nested crates\\)\n- Crate naming conventions \\(baml_* with approved prefixes\\)\n- Test crate pairing requirements\n- Workspace dependency format enforcement\n- Dependency restriction rules \\(e.g., anyhow only in CLI crates\\)\n- Dependency sorting \\(internal deps first, then external\\)\n\nConfiguration via stow.toml or [workspace.metadata.stow] in Cargo.toml\nallows changing rules without recompilation.\n\nIntegrated into:\n- CI workflow \\(cargo-stow job\\)\n- Pre-commit hooks \\(via setup-hooks.sh\\)\nEOF\n\\)\")"
     ]
   }
 }