chore: import upstream snapshot with attribution

internal/llm/provider/opencode/opencode.go

@@ -0,0 +1,33 @@
+// Package opencode is the opencode CLI llm.Provider.
+//
+// It shells out to the user's locally installed `opencode` binary in
+// non-interactive mode (`opencode run`), reusing the existing opencode
+// credentials — no API key in gortex's environment. The prompt is the
+// trailing positional argument and the model uses opencode's
+// `provider/model` form (e.g. "anthropic/claude-sonnet-4-6"). The
+// shared agentcli engine handles spawning, timeout, capture, and
+// structured extraction.
+package opencode
+
+import (
+	"strings"
+	"time"
+
+	"github.com/zzet/gortex/internal/llm"
+	"github.com/zzet/gortex/internal/llm/provider/agentcli"
+)
+
+// New constructs the opencode CLI provider, verifying the binary is on
+// $PATH. The prompt is the trailing positional after `run`; the model
+// is passed via `--model`.
+func New(cfg llm.CLIConfig) (llm.Provider, error) {
+	return agentcli.New(agentcli.Spec{
+		ProviderID: "opencode",
+		Model:      strings.TrimSpace(cfg.Model),
+		ModelFlag:  "--model",
+		BaseArgs:   []string{"run"},
+		Delivery:   agentcli.DeliveryArg,
+		ExtraArgs:  append([]string(nil), cfg.Args...),
+		Timeout:    time.Duration(cfg.TimeoutSeconds) * time.Second,
+	}, cfg.Binary, "opencode")
+}