feat(plugins): expose document path to plugins via HostApi

OpenCADStudio/plugins#901 (comment)

- Add HostApi::document_path(tab_id) returning Option<PathBuf>.
- Add PluginRequest::DocumentPath and PluginResponse::DocumentPath for
  out-of-process plugins.
- Implement the request in the IPC server and in both V3/V4 plugin-side
  HostApi proxies.
- Implement HostSession::document_path by looking up the tab by id and
  returning its current_path.

crates/ocs_plugin_api/src/ipc/client.rs

@@ -401,6 +401,21 @@ impl HostApi for PluginHostApi {
             None => Box::new(EmptyDocumentReader),
         }
     }
+
+    fn document_path(&self, tab_id: u64) -> Option<std::path::PathBuf> {
+        match self.client.request(PluginRequest::DocumentPath { tab_id }) {
+            Ok(PluginResponse::DocumentPath(Some(path))) => Some(std::path::PathBuf::from(path)),
+            Ok(PluginResponse::DocumentPath(None)) => None,
+            Ok(other) => {
+                eprintln!("[plugin] unexpected DocumentPath response: {other:?}");
+                None
+            }
+            Err(e) => {
+                eprintln!("[plugin] DocumentPath request failed: {e}");
+                None
+            }
+        }
+    }
 }
 
 /// Sentinel reader used when the shared-memory view could not be initialized.

crates/ocs_plugin_api/src/ipc/protocol.rs

@@ -136,6 +136,8 @@ pub enum PluginRequest {
     CloseDocumentViewV4 { tab_id: u64 },
     /// V4: ask the host for the stable tab identifier of the active tab.
     GetTabId,
+    /// V4: ask the host for the filesystem path of the document in `tab_id`.
+    DocumentPath { tab_id: u64 },
 }
 
 /// Responses the host sends back for `PluginRequest`.
@@ -160,6 +162,8 @@ pub enum PluginResponse {
     },
     /// V4: stable tab identifier of the active tab.
     TabId(u64),
+    /// V4: filesystem path of the document in the requested tab, if any.
+    DocumentPath(Option<String>),
 }
 
 /// Messages sent from the host to the plugin runner.

crates/ocs_plugin_api/src/ipc/server.rs

@@ -74,5 +74,8 @@ pub fn handle_plugin_request(
             PluginResponse::Ok
         }
         GetTabId => PluginResponse::TabId(host.tab_id()),
+        DocumentPath { tab_id } => {
+            PluginResponse::DocumentPath(host.document_path(tab_id).map(|p| p.to_string_lossy().to_string()))
+        }
     }
 }

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

@@ -715,6 +715,21 @@ impl HostApi for V4PluginHostApi {
             view.take();
         }
     }
+
+    fn document_path(&self, tab_id: u64) -> Option<std::path::PathBuf> {
+        match self.request(PluginRequest::DocumentPath { tab_id }) {
+            Ok(PluginResponse::DocumentPath(Some(path))) => Some(std::path::PathBuf::from(path)),
+            Ok(PluginResponse::DocumentPath(None)) => None,
+            Ok(other) => {
+                eprintln!("[plugin] unexpected DocumentPath response: {other:?}");
+                None
+            }
+            Err(e) => {
+                eprintln!("[plugin] DocumentPath request failed: {e}");
+                None
+            }
+        }
+    }
 }
 
 #[cfg(test)]