gateway: OpenCode (Zen + Go) provider adapter

Wires opencode.ai as a /v1/chat provider. One sk-* key reaches 40
models across Anthropic, OpenAI, Google, Moonshot, DeepSeek, Zhipu,
Alibaba, Minimax — billed against either the user's Zen balance
(pay-per-token premium models) or Go subscription (flat-rate
Kimi/GLM/DeepSeek/etc.). The unified /zen/v1 endpoint routes both;
upstream picks the billing tier based on model id.

Notable adapter quirks:

- Strip "opencode/" prefix on outbound (mirrors openrouter/kimi
  pattern). Caller can use {provider:"opencode", model:"X"} or
  {model:"opencode/X"}.
- Drop temperature for claude-*, gpt-5*, o1/o3/o4 models. Anthropic
  and OpenAI's reasoning lineage rejects temperature with 400
  "deprecated for this model". OCChatBody now serializes temperature
  as Option<f64> with skip_serializing_if so omitting it produces
  clean JSON.
- max_tokens.filter(|&n| n > 0) catches Some(0) — defensive after
  the same trap bit kimi.rs (empty env -> Number("") -> 0 -> 503).
- 600s default upstream timeout; reasoning models on big audit
  prompts legitimately take 3-5 min. Override OPENCODE_TIMEOUT_SECS.

Key handling:
- /etc/lakehouse/opencode.env (0600 root) loaded via systemd
  EnvironmentFile. Same pattern as kimi.env.
- OPENCODE_API_KEY env first, file scrape as fallback.

Verified end-to-end:
  opencode/claude-opus-4-7   -> "I'm Claude, made by Anthropic."
  opencode/kimi-k2.6         -> PONG-K26-GO
  opencode/deepseek-v4-pro   -> PONG-DS-V4
  opencode/glm-5.1           -> PONG-GLM
  opencode/minimax-m2.5-free -> PONG-FREE

Pricing reference (per audit @ ~14k in / 6k out):
  claude-opus-4-7   ~$0.22  (Zen)
  claude-haiku-4-5  ~$0.04  (Zen)
  gpt-5.5-pro       ~$1.50  (Zen)
  gemini-3-flash    ~$0.03  (Zen)
  kimi-k2.6 / glm / deepseek / qwen / minimax / mimo: covered by Go
  subscription ($10/mo, $60/mo cap).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/gateway/src/v1/mod.rs

@@ -17,6 +17,7 @@ pub mod openrouter;
 pub mod gemini;
 pub mod claude;
 pub mod kimi;
+pub mod opencode;
 pub mod langfuse_trace;
 pub mod mode;
 pub mod respond;
@@ -60,6 +61,13 @@ pub struct V1State {
     /// from `KIMI_API_KEY` env or `/etc/lakehouse/kimi.env`. None =
     /// provider="kimi" calls 503.
     pub kimi_key: Option<String>,
+    /// OpenCode GO (opencode.ai) bearer token — multi-vendor curated
+    /// gateway. One sk-* key reaches Claude Opus 4.7, GPT-5.5-pro,
+    /// Gemini 3.1-pro, Kimi K2.6, DeepSeek, GLM, Qwen + free-tier.
+    /// Loaded at startup via `opencode::resolve_opencode_key()` from
+    /// `OPENCODE_API_KEY` env or `/etc/lakehouse/opencode.env`. None =
+    /// provider="opencode" calls 503.
+    pub opencode_key: Option<String>,
     /// Phase 40 early deliverable — Langfuse client. None = tracing
     /// disabled (keys missing or container unreachable). Traces are
     /// fire-and-forget: never block the response path.
@@ -234,6 +242,9 @@ fn resolve_provider(req: &ChatRequest) -> (String, String) {
     if let Some(rest) = req.model.strip_prefix("kimi/") {
         return ("kimi".to_string(), rest.to_string());
     }
+    if let Some(rest) = req.model.strip_prefix("opencode/") {
+        return ("opencode".to_string(), rest.to_string());
+    }
     // Bare `vendor/model` shape (e.g. `x-ai/grok-4.1-fast`,
     // `moonshotai/kimi-k2`, `openai/gpt-oss-120b:free`) → OpenRouter.
     // This makes the gateway a drop-in OpenAI-compatible middleware:
@@ -433,10 +444,23 @@ async fn chat(
                 .map_err(|e| (StatusCode::BAD_GATEWAY, format!("kimi: {e}")))?;
             (r, "kimi".to_string())
         }
+        "opencode" => {
+            // OpenCode GO multi-vendor gateway — Claude Opus 4.7,
+            // GPT-5.5-pro, Gemini 3.1-pro, Kimi K2.6, DeepSeek, GLM,
+            // Qwen, free-tier. OpenAI-compat at opencode.ai/zen/go/v1.
+            let key = state.opencode_key.as_deref().ok_or((
+                StatusCode::SERVICE_UNAVAILABLE,
+                "OPENCODE_API_KEY not configured".to_string(),
+            ))?;
+            let r = opencode::chat(key, &*req_for_adapter)
+                .await
+                .map_err(|e| (StatusCode::BAD_GATEWAY, format!("opencode: {e}")))?;
+            (r, "opencode".to_string())
+        }
         other => {
             return Err((
                 StatusCode::BAD_REQUEST,
-                format!("unknown provider '{other}' — supported: ollama, ollama_cloud, openrouter, gemini, claude, kimi"),
+                format!("unknown provider '{other}' — supported: ollama, ollama_cloud, openrouter, gemini, claude, kimi, opencode"),
             ));
         }
     };