language_extension: Hold LspStore weakly in LspAccess::ViaLspStore (#60558)

# Objective

Fix a Windows CI flake in `extension_host
extension_store_test::test_extension_store_with_test_extension`, which
panicked in GPUI's leak detector with three leaked `LspStore` handles
([example
run](https://github.com/zed-industries/zed/actions/runs/28871529605/job/85635418351)).

## Solution

`LspAccess::ViaLspStore` held a strong `Entity<LspStore>`, cloned into
three `ExtensionHostProxy` registrations by `language_extension::init`.
The proxy sits inside an `Arc` cycle (proxy →
`LanguageServerRegistryProxy` → `LanguageRegistry` →
`ExtensionLspAdapter` → `WasmExtension` → `WasmHost` → proxy), so
whenever an extension LSP adapter was registered at app-drop time, the
cycle pinned the `LspStore` entity after its owning `Project` dropped.
The flake was purely timing: extension reload toggles the adapter
registration, and an unclean LSP pipe shutdown on Windows shifted
teardown into the pinned window.

`ViaLspStore` now holds a `WeakEntity<LspStore>`, upgraded at its sole
use site (`remove_language_server`), skipping the stop task when the
store is gone — matching the existing `ViaWorkspaces` semantics. A dead
store is the expected terminal state after the owning project drops, so
no error is logged or propagated. `Project`/`HeadlessProject` remain the
sole long-term owners of `LspStore`, which is already the convention
everywhere else (e.g. `json_schema_store`, the `lsp_store` message
handlers).

## Testing

- Ran `cargo nextest run -p extension_host
extension_store_test::test_extension_store_with_test_extension` locally:
passes.
- The flake is timing-dependent (reproduced on Windows CI), so a local
pass doesn't prove absence; the fix removes the only strong non-owner
handle, which the leak detector reported.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

---

Release Notes:

- N/A

---------

Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>

crates/extension_host/src/extension_store_test.rs

@@ -769,7 +769,11 @@ async fn test_extension_store_with_test_extension(cx: &mut TestAppContext) {
     theme_extension::init(proxy.clone(), theme_registry.clone(), cx.executor());
     let language_registry = project.read_with(cx, |project, _cx| project.languages().clone());
     language_extension::init(
-        LspAccess::ViaLspStore(project.update(cx, |project, _| project.lsp_store())),
+        LspAccess::ViaLspStore(
+            project
+                .update(cx, |project, _| project.lsp_store())
+                .downgrade(),
+        ),
         proxy.clone(),
         language_registry.clone(),
     );

crates/language_extension/src/extension_lsp_adapter.rs

@@ -79,16 +79,19 @@ impl ExtensionLanguageServerProxy for LanguageServerRegistryProxy {
 
         let mut tasks = Vec::new();
         match &self.lsp_access {
-            LspAccess::ViaLspStore(lsp_store) => lsp_store.update(cx, |lsp_store, cx| {
-                let stop_task = lsp_store.stop_language_servers_for_buffers(
-                    Vec::new(),
-                    HashSet::from_iter([LanguageServerSelector::Name(
-                        language_server_name.clone(),
-                    )]),
-                    cx,
-                );
-                tasks.push(stop_task);
-            }),
+            LspAccess::ViaLspStore(lsp_store) => {
+                if let Ok(stop_task) = lsp_store.update(cx, |lsp_store, cx| {
+                    lsp_store.stop_language_servers_for_buffers(
+                        Vec::new(),
+                        HashSet::from_iter([LanguageServerSelector::Name(
+                            language_server_name.clone(),
+                        )]),
+                        cx,
+                    )
+                }) {
+                    tasks.push(stop_task);
+                }
+            }
             LspAccess::ViaWorkspaces(lsp_store_provider) => {
                 if let Ok(lsp_stores) = lsp_store_provider(cx) {
                     for lsp_store in lsp_stores {

crates/language_extension/src/language_extension.rs

@@ -5,13 +5,13 @@ use std::sync::Arc;
 
 use anyhow::Result;
 use extension::{ExtensionGrammarProxy, ExtensionHostProxy, ExtensionLanguageProxy};
-use gpui::{App, Entity};
+use gpui::{App, Entity, WeakEntity};
 use language::{LanguageMatcher, LanguageName, LanguageRegistry, LoadedLanguage};
 use project::LspStore;
 
 #[derive(Clone)]
 pub enum LspAccess {
-    ViaLspStore(Entity<LspStore>),
+    ViaLspStore(WeakEntity<LspStore>),
     ViaWorkspaces(Arc<dyn Fn(&mut App) -> Result<Vec<Entity<LspStore>>> + Send + Sync + 'static>),
     Noop,
 }

crates/remote_server/src/headless_project.rs

@@ -254,7 +254,7 @@ impl HeadlessProject {
 
         cx.subscribe(&lsp_store, Self::on_lsp_store_event).detach();
         language_extension::init(
-            language_extension::LspAccess::ViaLspStore(lsp_store.clone()),
+            language_extension::LspAccess::ViaLspStore(lsp_store.downgrade()),
             proxy.clone(),
             languages.clone(),
         );