Fix InProcess test parity: respect explicit subprocess options over env var

- resolveDefaultConnection: when cliUrl, cliPath, or port are explicitly
  set, fall back to subprocess transport even if COPILOT_SDK_DEFAULT_CONNECTION
  is 'inprocess'. Explicit options take precedence over the env var default.
- validateEnvironmentOptions: check isEmpty() in addition to null, since
  setEnvironment(null) clears the map rather than nulling the field.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: d7a38160-a65e-4d0c-9087-4f28da2a51b8

Author: edburns

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

@@ -259,6 +259,16 @@ private static RuntimeConnection resolveDefaultConnection(CopilotClientOptions o
     static RuntimeConnection resolveDefaultConnection(CopilotClientOptions options, String envValue) {
         if (envValue != null && !envValue.isEmpty()) {
             if ("inprocess".equalsIgnoreCase(envValue)) {
+                // Explicit subprocess options take precedence over the env var default.
+                if (options.getCliUrl() != null && !options.getCliUrl().isEmpty()) {
+                    return inferConnectionFromOptions(options);
+                }
+                if (options.getCliPath() != null && !options.getCliPath().isEmpty()) {
+                    return inferConnectionFromOptions(options);
+                }
+                if (options.getPort() != 0) {
+                    return inferConnectionFromOptions(options);
+                }
                 return RuntimeConnection.forInProcess();
             }
             if (!"stdio".equalsIgnoreCase(envValue)) {
@@ -390,7 +400,7 @@ private static void validateEnvironmentOptions(CopilotClientOptions options, Run
             return;
         }
 
-        rejectInProcessOption("Environment", options.getEnvironment() != null,
+        rejectInProcessOption("Environment", options.getEnvironment() != null && !options.getEnvironment().isEmpty(),
                 "set the variables on the host process environment instead");
         rejectInProcessOption("Telemetry", options.getTelemetry() != null,
                 "configure telemetry through the host process environment instead");