Add versioned host settings API for plugins

crates/ocs_plugin_api/ARCHITECTURE.md

@@ -44,12 +44,14 @@ The host and each plugin run in separate OS processes. The host re-executes itse
 
 ## Versioning and ABI stability
 
-- `API_VERSION` (currently `5`) is the host's advertised major.
+- `API_VERSION` (currently `6`) is the host's advertised major.
 - `API_VERSION_MIN_SUPPORTED` (currently `2`) is the oldest plugin major the host loads.
-- `OCS_PLUGIN_MAX_API_VERSION` can cap the accepted major at runtime (e.g. `4` to disable V5).
+- `OCS_PLUGIN_MAX_API_VERSION` can cap the accepted major at runtime (e.g. `5` to disable V6).
 - A plugin built against major `N` runs on a host whose major is `>= N` because new vtable entries and enum variants are appended at the end.
 - V4 introduces the **acadrust gate**: plugins targeting API v4 or later must resolve the same `acadrust` source as the host (see [`src/version_info.rs`](src/version_info.rs)).
 - V5 introduces `BuiltinPlugin::on_load` and tab-keyed document paths.
+- V6 appends typed system-variable access to `HostApi`; the fork currently
+  supports `CLAYER` and `SNAPANG`.
 
 The runtime enforces three gates:
 

crates/ocs_plugin_api/README.md

@@ -9,7 +9,7 @@ cheaply. The runtime host surface is enabled by the `host` feature.
 ## Plugin Architecture
 
 OCS is scriptable and extensible through a versioned plugin API. The API
-supports four major generations: **V2**, **V3**, **V4**, and **V5**. Each
+supports five major generations: **V2**, **V3**, **V4**, **V5**, and **V6**. Each
 generation keeps the previous ABI stable by appending new vtable entries and new
 enum variants at the end, so older plugins continue to load on newer hosts.
 
@@ -19,10 +19,11 @@ enum variants at the end, so older plugins continue to load on newer hosts.
 | **V3** | Out-of-process runner | Local cached `document()`/`document_mut()` + shared-memory `DocumentReader`/`document_view` for large reads | New vtable entries appended; new `PluginRequest`/`PluginResponse` variants appended |
 | **V4** | Out-of-process runner over a multiplexed local socket | Full-duplex notifications + asynchronous REPL `ExecuteCode` | New `HostToPluginV4`/`PluginToHostV4` frame layer; `BuiltinPlugin::on_notification` and `start_execute_code` appended to trait |
 | **V5** | V4 multiplexed runner | One-shot initialization + tab-keyed document paths | `BuiltinPlugin::on_load` and `HostApi::document_path` appended to the traits |
+| **V6** | V4 multiplexed runner | Read and write supported host system variables | `HostApi::system_variable` and `HostApi::set_system_variable` appended to the trait; request/response variants appended |
 
 The host controls which generations are accepted at runtime through
-`OCS_PLUGIN_MAX_API_VERSION` (e.g. `2` for V2-only mode, `4` to disable V5). The
-current host advertises [`API_VERSION = 5`](src/manifest.rs) and supports plugins
+`OCS_PLUGIN_MAX_API_VERSION` (e.g. `2` for V2-only mode, `5` to disable V6). The
+current host advertises [`API_VERSION = 6`](src/manifest.rs) and supports plugins
 back to `API_VERSION_MIN_SUPPORTED = 2`.
 
 V5 calls `BuiltinPlugin::on_load` once after the runner connects and before the
@@ -30,6 +31,10 @@ first user command. Plugins can cache `HostApi::plugin_request_sender()` there
 for worker-thread access. A panic in the callback fails plugin loading.
 `HostApi::document_path(tab_id)` returns the saved path for a document tab.
 
+V6 adds a typed system-variable interface. This fork currently implements
+`CLAYER` (current drawing layer) and `SNAPANG` (snap-angle degrees). Unknown
+variables return an error rather than silently accepting a value.
+
 ### High-level layout
 
 ```mermaid

crates/ocs_plugin_api/build.rs

@@ -908,7 +908,7 @@ fn generate_version_info(out_dir: &Path) {
         "acadrust_version": acadrust.version.to_string(),
         "acadrust_source": acadrust.source.as_ref().map(|s| s.to_string()),
         "rustc_version": rustc_version,
-        "api_version": 5,
+        "api_version": 6,
         "api_version_min_supported": 2,
         "build_timestamp": build_timestamp,
     });

crates/ocs_plugin_api/src/host.rs

@@ -60,6 +60,13 @@ pub enum LogLevel {
     Error,
 }
 
+/// Value of a host-managed drafting or document setting exposed to plugins.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum HostSettingValue {
+    Text(String),
+    Number(f64),
+}
+
 /// A notification the host sends to a plugin. These are best-effort,
 /// full-duplex messages correlated with an optional `command_id`.
 #[derive(Debug, Clone, PartialEq)]
@@ -552,6 +559,22 @@ pub trait HostApi {
         let _ = tab_id;
         None
     }
+
+    /// Read a named host setting without invoking the command dispatcher.
+    /// Names are case-insensitive. Hosts may support only a subset.
+    fn system_variable(&self, _name: &str) -> Option<HostSettingValue> {
+        None
+    }
+
+    /// Set a named host setting without re-entering command dispatch.
+    /// Returns the effective value after validation and normalization.
+    fn set_system_variable(
+        &mut self,
+        _name: &str,
+        _value: HostSettingValue,
+    ) -> Result<HostSettingValue, String> {
+        Err("system variable is not supported by this host".to_owned())
+    }
 }
 
 /// Simplified, read-only entity kind exposed by [`DocumentReader`].

crates/ocs_plugin_api/src/ipc/client.rs

@@ -11,7 +11,7 @@ use acadrust::{CadDocument, EntityType, Handle};
 use interprocess::local_socket::traits::Stream as StreamTrait;
 use interprocess::local_socket::{GenericNamespaced, Stream, ToNsName};
 
-use crate::host::{DocumentReader, HostApi, InteractiveCommand, ReaderEntity};
+use crate::host::{DocumentReader, HostApi, HostSettingValue, InteractiveCommand, ReaderEntity};
 use crate::ipc::protocol::{
     HostResponse, HostToPlugin, PluginRequest, PluginResponse, PluginToHost, RunnerHandshake,
 };
@@ -416,6 +416,34 @@ impl HostApi for PluginHostApi {
             }
         }
     }
+
+    fn system_variable(&self, name: &str) -> Option<HostSettingValue> {
+        match self.client.request(PluginRequest::GetSystemVariable { name: name.to_owned() }) {
+            Ok(PluginResponse::SystemVariable(value)) => value,
+            _ => None,
+        }
+    }
+
+    fn set_system_variable(
+        &mut self,
+        name: &str,
+        value: HostSettingValue,
+    ) -> Result<HostSettingValue, String> {
+        match self.client.request(PluginRequest::SetSystemVariable {
+            name: name.to_owned(),
+            value,
+        }) {
+            Ok(PluginResponse::SystemVariableResult(result)) => {
+                if result.is_ok() {
+                    self.document_cache = OnceCell::new();
+                }
+                result
+            }
+            Ok(PluginResponse::Error(error)) => Err(error),
+            Ok(other) => Err(format!("unexpected system variable response: {other:?}")),
+            Err(error) => Err(error.to_string()),
+        }
+    }
 }
 
 /// Sentinel reader used when the shared-memory view could not be initialized.

crates/ocs_plugin_api/src/ipc/protocol.rs

@@ -17,7 +17,7 @@
 
 use serde::{Deserialize, Serialize};
 
-use crate::host::{CommandSource, CommandStep};
+use crate::host::{CommandSource, CommandStep, HostSettingValue};
 use crate::manifest::ApiVersion;
 use crate::ribbon::owned::{OwnedPluginManifest, OwnedRibbonGroup};
 
@@ -138,6 +138,10 @@ pub enum PluginRequest {
     GetTabId,
     /// V5: ask the host for the filesystem path of the document in `tab_id`.
     DocumentPath { tab_id: u64 },
+    /// Read a host-managed setting without nested command dispatch.
+    GetSystemVariable { name: String },
+    /// Change a host-managed setting without nested command dispatch.
+    SetSystemVariable { name: String, value: HostSettingValue },
 }
 
 /// Responses the host sends back for `PluginRequest`.
@@ -164,6 +168,8 @@ pub enum PluginResponse {
     TabId(u64),
     /// V5: filesystem path of the document in the requested tab, if any.
     DocumentPath(Option<std::ffi::OsString>),
+    SystemVariable(Option<HostSettingValue>),
+    SystemVariableResult(Result<HostSettingValue, String>),
 }
 
 /// Messages sent from the host to the plugin runner.

crates/ocs_plugin_api/src/ipc/server.rs

@@ -77,5 +77,11 @@ pub fn handle_plugin_request(
         DocumentPath { tab_id } => PluginResponse::DocumentPath(
             host.document_path(tab_id).map(|path| path.into_os_string()),
         ),
+        GetSystemVariable { name } => {
+            PluginResponse::SystemVariable(host.system_variable(&name))
+        }
+        SetSystemVariable { name, value } => {
+            PluginResponse::SystemVariableResult(host.set_system_variable(&name, value))
+        }
     }
 }

crates/ocs_plugin_api/src/ipc/v4/client.rs

@@ -17,7 +17,7 @@ use interprocess::TryClone;
 
 use crate::host::{
     DocumentReader, ExecutionResult, HostApi, HostNotification, InteractiveCommand,
-    PluginNotification, PluginRequestSender, PluginRequestError, ReaderEntity,
+    PluginNotification, PluginRequestSender, PluginRequestError, ReaderEntity, HostSettingValue,
 };
 use crate::ipc::protocol::{
     HostRequest, HostResponse, PluginRequest, PluginResponse, RunnerHandshake,
@@ -730,6 +730,34 @@ impl HostApi for V4PluginHostApi {
             }
         }
     }
+
+    fn system_variable(&self, name: &str) -> Option<HostSettingValue> {
+        match self.request(PluginRequest::GetSystemVariable { name: name.to_owned() }) {
+            Ok(PluginResponse::SystemVariable(value)) => value,
+            _ => None,
+        }
+    }
+
+    fn set_system_variable(
+        &mut self,
+        name: &str,
+        value: HostSettingValue,
+    ) -> Result<HostSettingValue, String> {
+        match self.request(PluginRequest::SetSystemVariable {
+            name: name.to_owned(),
+            value,
+        }) {
+            Ok(PluginResponse::SystemVariableResult(result)) => {
+                if result.is_ok() {
+                    self.document_cache = OnceCell::new();
+                }
+                result
+            }
+            Ok(PluginResponse::Error(error)) => Err(error),
+            Ok(other) => Err(format!("unexpected system variable response: {other:?}")),
+            Err(error) => Err(error.to_string()),
+        }
+    }
 }
 
 #[cfg(test)]

crates/ocs_plugin_api/src/manifest.rs

@@ -19,8 +19,9 @@
 /// vtable so API v2 plugins keep working. v4 adds full-duplex notifications on
 /// a multiplexed socket while leaving the V2/V3 ABI and protocol untouched. v5
 /// adds the `BuiltinPlugin::on_load` lifecycle callback and
-/// `HostApi::document_path`.
-pub const API_VERSION: u32 = 5;
+/// `HostApi::document_path`. v6 appends generic host system-variable access
+/// (`HostApi::system_variable` / `set_system_variable`).
+pub const API_VERSION: u32 = 6;
 
 /// Oldest plugin API major the current host still loads. This keeps previously
 /// compiled cdylibs usable as long as their vtable layout is a prefix of the
@@ -28,7 +29,7 @@ pub const API_VERSION: u32 = 5;
 pub const API_VERSION_MIN_SUPPORTED: u32 = 2;
 
 /// Environment variable that caps the API major accepted by the host at
-/// runtime. Set to `4` to disable V5 plugins, `3` to disable V4, or `2` for
+/// runtime. Set to `5` to disable V6 plugins, `4` to disable V5, or `2` for
 /// V2-only mode.
 pub const MAX_API_VERSION_ENV: &str = "OCS_PLUGIN_MAX_API_VERSION";