Port AOT-safe SetForegroundSessionRequest and COPILOT_HOME env var from reference implementation

- Add SetForegroundSessionRequest record in json package for typed serialization
- Update setForegroundSessionId() to use SetForegroundSessionRequest instead of Map.of()
  (port of c63feb2: fix(dotnet): Add AOT-safe SetForegroundSessionRequest)
- Add COPILOT_HOME env variable to E2ETestContext.getEnvironment()
  (port of test harness fix from E2ETestContext.cs)

Co-authored-by: edburns <75821+edburns@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/copilot/sdk/CopilotClient.java

@@ -744,18 +744,15 @@ public CompletableFuture<String> getForegroundSessionId() {
      *             if the operation fails
      */
     public CompletableFuture<Void> setForegroundSessionId(String sessionId) {
-        return ensureConnected()
-                .thenCompose(
-                        connection -> connection.rpc
-                                .invoke("session.setForeground", Map.of("sessionId", sessionId),
-                                        com.github.copilot.sdk.json.SetForegroundSessionResponse.class)
-                                .thenAccept(response -> {
-                                    if (!response.success()) {
-                                        throw new RuntimeException(response.error() != null
-                                                ? response.error()
-                                                : "Failed to set foreground session");
-                                    }
-                                }));
+        return ensureConnected().thenCompose(connection -> connection.rpc
+                .invoke("session.setForeground", new com.github.copilot.sdk.json.SetForegroundSessionRequest(sessionId),
+                        com.github.copilot.sdk.json.SetForegroundSessionResponse.class)
+                .thenAccept(response -> {
+                    if (!response.success()) {
+                        throw new RuntimeException(
+                                response.error() != null ? response.error() : "Failed to set foreground session");
+                    }
+                }));
     }
 
     /**

src/main/java/com/github/copilot/sdk/json/SetForegroundSessionRequest.java

@@ -0,0 +1,20 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+package com.github.copilot.sdk.json;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+/**
+ * Request for session.setForeground RPC call.
+ * <p>
+ * This is only available when connecting to a server running in TUI+server mode
+ * (--ui-server).
+ *
+ * @since 1.0.0
+ */
+public record SetForegroundSessionRequest(
+        /** The ID of the session to bring to the foreground. */
+        @JsonProperty("sessionId") String sessionId) {
+}

src/test/java/com/github/copilot/sdk/E2ETestContext.java

@@ -249,6 +249,7 @@ public List<Map<String, Object>> getExchanges() throws IOException, InterruptedE
     public Map<String, String> getEnvironment() {
         Map<String, String> env = new HashMap<>(System.getenv());
         env.put("COPILOT_API_URL", proxyUrl);
+        env.put("COPILOT_HOME", homeDir.toString());
         env.put("XDG_CONFIG_HOME", homeDir.toString());
         env.put("XDG_STATE_HOME", homeDir.toString());
         return env;