context_store: Refactor state management (#29910)

Because we instantiated `ContextServerManager` both in `agent` and
`assistant-context-editor`, and these two entities track the running MCP
servers separately, we were effectively running every MCP server twice.

This PR moves the `ContextServerManager` into the project crate (now
called `ContextServerStore`). The store can be accessed via a project
instance. This ensures that we only instantiate one `ContextServerStore`
per project.

Also, this PR adds a bunch of tests to ensure that the
`ContextServerStore` behaves correctly (Previously there were none).

Closes #28714
Closes #29530

Release Notes:

- N/A

crates/project/src/project_settings.rs

@@ -1,5 +1,6 @@
 use anyhow::Context as _;
 use collections::HashMap;
+use context_server::ContextServerCommand;
 use dap::adapters::DebugAdapterName;
 use fs::Fs;
 use futures::StreamExt as _;
@@ -51,6 +52,10 @@ pub struct ProjectSettings {
     #[serde(default)]
     pub dap: HashMap<DebugAdapterName, DapSettings>,
 
+    /// Settings for context servers used for AI-related features.
+    #[serde(default)]
+    pub context_servers: HashMap<Arc<str>, ContextServerConfiguration>,
+
     /// Configuration for Diagnostics-related features.
     #[serde(default)]
     pub diagnostics: DiagnosticsSettings,
@@ -78,6 +83,19 @@ pub struct DapSettings {
     pub binary: Option<String>,
 }
 
+#[derive(Deserialize, Serialize, Clone, PartialEq, Eq, JsonSchema, Debug, Default)]
+pub struct ContextServerConfiguration {
+    /// The command to run this context server.
+    ///
+    /// This will override the command set by an extension.
+    pub command: Option<ContextServerCommand>,
+    /// The settings for this context server.
+    ///
+    /// Consult the documentation for the context server to see what settings
+    /// are supported.
+    pub settings: Option<serde_json::Value>,
+}
+
 #[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema)]
 pub struct NodeBinarySettings {
     /// The path to the Node binary.
@@ -376,6 +394,40 @@ impl Settings for ProjectSettings {
             }
         }
 
+        #[derive(Deserialize)]
+        struct VsCodeContextServerCommand {
+            command: String,
+            args: Option<Vec<String>>,
+            env: Option<HashMap<String, String>>,
+            // note: we don't support envFile and type
+        }
+        impl From<VsCodeContextServerCommand> for ContextServerCommand {
+            fn from(cmd: VsCodeContextServerCommand) -> Self {
+                Self {
+                    path: cmd.command,
+                    args: cmd.args.unwrap_or_default(),
+                    env: cmd.env,
+                }
+            }
+        }
+        if let Some(mcp) = vscode.read_value("mcp").and_then(|v| v.as_object()) {
+            current
+                .context_servers
+                .extend(mcp.iter().filter_map(|(k, v)| {
+                    Some((
+                        k.clone().into(),
+                        ContextServerConfiguration {
+                            command: Some(
+                                serde_json::from_value::<VsCodeContextServerCommand>(v.clone())
+                                    .ok()?
+                                    .into(),
+                            ),
+                            settings: None,
+                        },
+                    ))
+                }));
+        }
+
         // TODO: translate lsp settings for rust-analyzer and other popular ones to old.lsp
     }
 }