Implement shutdown and exit RPCs per LSP specification (#102)

VS Code LSP client was failing with `No such method shutdown` when
stopping the server. The server lacked implementation of the required
lifecycle RPCs.

## Changes

- **Added shutdown request handler**: Returns null response, sets
`shutdown_received` flag
- **Added exit notification handler**: Exits with code 0 after proper
shutdown, code 1 otherwise per LSP spec
- **Added state tracking**: `shutdown_received: bool` field in
`ProtoLanguageServer` to determine exit behavior

## Implementation

```rust
pub(super) fn shutdown(&mut self, _params: ()) -> BoxFuture<'static, Result<(), ResponseError>> {
    info!("Received shutdown request");
    self.shutdown_received = true;
    Box::pin(async move { Ok(()) })
}

pub(super) fn exit(&mut self, _params: ()) -> ControlFlow<async_lsp::Result<()>> {
    if self.shutdown_received {
        info!("Received exit notification after shutdown, exiting with code 0");
        std::process::exit(0);
    } else {
        warn!("Received exit notification without shutdown, exiting with code 1");
        std::process::exit(1);
    }
}
```

The `LifecycleLayer` middleware handles state transitions; these
handlers provide the required lifecycle endpoints and exit code
semantics.

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Implement shutdown and exit RPCs for clean
exit</issue_title>
> <issue_description>For a clean exit,
[Shutdown](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#shutdown)
and
[Exit](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#exit)
notifications are sent by the client. Currently protols does not
implement these two rpcs on the server side.
> 
> VS Code built-in LSP client is failing with the following error when a
`stop()` command is given:
> 
> ```
> Error checking for protols updates: _ResponseError: No such method
shutdown {code: -32601, data: null, stack: 'Error: No such method
shutdown
> at handleResp…Trampoline (node:internal/async_hooks:130:17)', message:
'No such method shutdown'}
> ```
> 
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes #101

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Co-authored-by: coder3101 <22212259+coder3101@users.noreply.github.com>

Author: Copilot

src/lsp.rs

@@ -131,6 +131,15 @@ impl ProtoLanguageServer {
         Box::pin(async move { Ok(response) })
     }
 
+    pub(super) fn shutdown(
+        &mut self,
+        _params: (),
+    ) -> BoxFuture<'static, Result<(), ResponseError>> {
+        info!("Received shutdown request");
+        self.shutdown_received = true;
+        Box::pin(async move { Ok(()) })
+    }
+
     pub(super) fn hover(
         &mut self,
         param: HoverParams,
@@ -564,6 +573,16 @@ impl ProtoLanguageServer {
         }
         ControlFlow::Continue(())
     }
+
+    pub(super) fn exit(&mut self, _params: ()) -> ControlFlow<async_lsp::Result<()>> {
+        if self.shutdown_received {
+            info!("Received exit notification after shutdown, exiting with code 0");
+            std::process::exit(0);
+        } else {
+            warn!("Received exit notification without shutdown, exiting with code 1");
+            std::process::exit(1);
+        }
+    }
 }
 
 /// Parse include_paths from initialization options

src/server.rs

@@ -4,11 +4,11 @@ use async_lsp::{
         NumberOrString, ProgressParams, ProgressParamsValue,
         notification::{
             DidChangeTextDocument, DidCreateFiles, DidDeleteFiles, DidOpenTextDocument,
-            DidRenameFiles, DidSaveTextDocument,
+            DidRenameFiles, DidSaveTextDocument, Exit,
         },
         request::{
             Completion, DocumentSymbolRequest, Formatting, GotoDefinition, HoverRequest,
-            Initialize, PrepareRenameRequest, RangeFormatting, References, Rename,
+            Initialize, PrepareRenameRequest, RangeFormatting, References, Rename, Shutdown,
             WorkspaceSymbolRequest,
         },
     },
@@ -29,6 +29,7 @@ pub struct ProtoLanguageServer {
     pub counter: i32,
     pub state: ProtoLanguageState,
     pub configs: WorkspaceProtoConfigs,
+    pub shutdown_received: bool,
 }
 
 impl ProtoLanguageServer {
@@ -42,6 +43,7 @@ impl ProtoLanguageServer {
             counter: 0,
             state: ProtoLanguageState::new(),
             configs: WorkspaceProtoConfigs::new(cli_include_paths, fallback_include_path),
+            shutdown_received: false,
         });
 
         router.event::<TickEvent>(|st, _| {
@@ -57,6 +59,7 @@ impl ProtoLanguageServer {
 
         // Handling request
         router.request::<Initialize, _>(|st, params| st.initialize(params));
+        router.request::<Shutdown, _>(|st, params| st.shutdown(params));
         router.request::<HoverRequest, _>(|st, params| st.hover(params));
         router.request::<Completion, _>(|st, params| st.completion(params));
         router.request::<PrepareRenameRequest, _>(|st, params| st.prepare_rename(params));
@@ -75,6 +78,7 @@ impl ProtoLanguageServer {
         router.notification::<DidCreateFiles>(|st, params| st.did_create_files(params));
         router.notification::<DidRenameFiles>(|st, params| st.did_rename_files(params));
         router.notification::<DidDeleteFiles>(|st, params| st.did_delete_files(params));
+        router.notification::<Exit>(|st, params| st.exit(params));
 
         router
     }

src/workspace/workspace_symbol.rs

@@ -13,20 +13,20 @@ mod test {
             "file://{}/src/workspace/input/a.proto",
             current_dir.to_str().unwrap()
         )
-            .parse()
-            .unwrap();
+        .parse()
+        .unwrap();
         let b_uri = format!(
             "file://{}/src/workspace/input/b.proto",
             current_dir.to_str().unwrap()
         )
-            .parse()
-            .unwrap();
+        .parse()
+        .unwrap();
         let c_uri = format!(
             "file://{}/src/workspace/input/c.proto",
             current_dir.to_str().unwrap()
         )
-            .parse()
-            .unwrap();
+        .parse()
+        .unwrap();
 
         let a = include_str!("input/a.proto");
         let b = include_str!("input/b.proto");