fix(plugins): enforce rustc compatibility

BREAKING CHANGE: API v4+ plugin packages must declare the exact rustc version used to build the binary.

Refs #901

docs/plugin-architecture.md

@@ -99,10 +99,10 @@ affect whether a prebuilt plugin can safely be loaded:
 - `rustc_version` — the output of `rustc --version` for the compiler that built
   the host.
 
-A plugin's `plugin.toml` may declare the same values under `[opencad]`. When
-either is declared, the host refuses to load the plugin unless it matches the
-host exactly. This turns the current silent runner crash into a one-line
-diagnosis such as:
+A plugin's `plugin.toml` declares the same values under `[opencad]`. For API v4
+and later, `rustc_version` is required and the host refuses to load the plugin
+unless it matches exactly. This turns the current silent runner crash into a
+one-line diagnosis such as:
 
 ```
 Plugin built with rustc 1.96.0, host requires 1.98.0 - rebuild required
@@ -229,12 +229,12 @@ version = "0.1.0"
 description = "…"
 
 [opencad]
-api_version = 3
+api_version = 4
 ribbon_order = 50
 command_prefixes = ["EX_"]
 xdata_apps = []
-# For API v4+, also record the exact rustc used to build the release asset.
-# rustc_version = "rustc 1.98.0 (hash date)"
+# Filled with the exact compiler output while staging the release asset.
+rustc_version = "rustc 1.98.0 (hash date)"
 ```
 
 The full, buildable scaffold is in [`docs/plugin-template/`](plugin-template);

docs/plugin-template/.github/workflows/release.yml

@@ -36,7 +36,7 @@ jobs:
         run: |
           mkdir -p dist
           cp target/release/*.${{ matrix.ext }} "dist/${{ matrix.asset }}"
-          cp plugin.toml dist/plugin.toml
+          sed "s|__RUSTC_VERSION__|$(rustc --version)|" plugin.toml > dist/plugin.toml
       - uses: softprops/action-gh-release@v2
         with:
           files: |

docs/plugin-template/README.md

@@ -28,7 +28,8 @@ folder into a new repo and rename the placeholders.
 cargo build --release
 mkdir -p "<config>/OpenCADStudio/plugins/opencad.my_plugin"
 cp target/release/*my_plugin*.so "<config>/OpenCADStudio/plugins/opencad.my_plugin/"
-cp plugin.toml                    "<config>/OpenCADStudio/plugins/opencad.my_plugin/"
+sed "s|__RUSTC_VERSION__|$(rustc --version)|" plugin.toml > \
+  "<config>/OpenCADStudio/plugins/opencad.my_plugin/plugin.toml"
 ```
 
 Restart Open CAD Studio: the ribbon tab appears and `MP_` commands route to your

docs/plugin-template/plugin.toml

@@ -8,7 +8,8 @@ license = "GPL-3.0-only"
 repository = "your-account/your-plugin-repo"
 
 [opencad]
-api_version = 3
+api_version = 4
+rustc_version = "__RUSTC_VERSION__"
 ribbon_order = 60
 command_prefixes = ["MP_"]
 xdata_apps = ["MYPLUGIN_RECORD"]