feat(xai): upgrade to Responses API, add TTS provider

Cherry-picked and trimmed from PR #10600 by Jaaneek.

- Switch xAI transport from openai_chat to codex_responses (Responses API)
- Add codex_responses detection for xAI in all runtime_provider resolution paths
- Add xAI api_mode detection in AIAgent.__init__ (provider name + URL auto-detect)
- Add extra_headers passthrough for codex_responses requests
- Add x-grok-conv-id session header for xAI prompt caching
- Add xAI reasoning support (encrypted_content include, no effort param)
- Move x-grok-conv-id from chat_completions path to codex_responses path
- Add xAI TTS provider (dedicated /v1/tts endpoint with Opus conversion)
- Add xAI provider aliases (grok, x-ai, x.ai) across auth, models, providers, auxiliary
- Trim xAI model list to agentic models (grok-4.20-reasoning, grok-4-1-fast-reasoning)
- Add XAI_API_KEY/XAI_BASE_URL to OPTIONAL_ENV_VARS
- Add xAI TTS config section, setup wizard entry, tools_config provider option
- Add shared xai_http.py helper for User-Agent string

Co-authored-by: Jaaneek <Jaaneek@users.noreply.github.com>

hermes_cli/setup.py

@@ -920,6 +920,7 @@ def _setup_tts_provider(config: dict):
         "edge": "Edge TTS",
         "elevenlabs": "ElevenLabs",
         "openai": "OpenAI TTS",
+        "xai": "xAI TTS",
         "minimax": "MiniMax TTS",
         "mistral": "Mistral Voxtral TTS",
         "neutts": "NeuTTS",
@@ -941,12 +942,13 @@ def _setup_tts_provider(config: dict):
             "Edge TTS (free, cloud-based, no setup needed)",
             "ElevenLabs (premium quality, needs API key)",
             "OpenAI TTS (good quality, needs API key)",
+            "xAI TTS (Grok voices, needs API key)",
             "MiniMax TTS (high quality with voice cloning, needs API key)",
             "Mistral Voxtral TTS (multilingual, native Opus, needs API key)",
             "NeuTTS (local on-device, free, ~300MB model download)",
         ]
     )
-    providers.extend(["edge", "elevenlabs", "openai", "minimax", "mistral", "neutts"])
+    providers.extend(["edge", "elevenlabs", "openai", "xai", "minimax", "mistral", "neutts"])
     choices.append(f"Keep current ({current_label})")
     keep_current_idx = len(choices) - 1
     idx = prompt_choice("Select TTS provider:", choices, keep_current_idx)
@@ -1012,6 +1014,23 @@ def _setup_tts_provider(config: dict):
                 print_warning("No API key provided. Falling back to Edge TTS.")
                 selected = "edge"
 
+    elif selected == "xai":
+        existing = get_env_value("XAI_API_KEY")
+        if not existing:
+            print()
+            api_key = prompt("xAI API key for TTS", password=True)
+            if api_key:
+                save_env_value("XAI_API_KEY", api_key)
+                print_success("xAI TTS API key saved")
+            else:
+                from hermes_constants import display_hermes_home as _dhh
+                print_warning(
+                    "No xAI API key provided for TTS. Configure XAI_API_KEY via "
+                    f"hermes setup model or {_dhh()}/.env to use xAI TTS. "
+                    "Falling back to Edge TTS."
+                )
+                selected = "edge"
+
     elif selected == "minimax":
         existing = get_env_value("MINIMAX_API_KEY")
         if not existing: