feat: multi-provider support — Ollama Cloud + OpenCode Go

- Account.Provider field (ollama-cloud | opencode-go), backward compatible
- Model-based routing: common models served by combined pool, unique models
  routed to their provider only
- /go/v1/* path forces OpenCode Go provider (prefix stripped upstream)
- Merged /v1/models endpoint returns union of both catalogs (44 models)
- Failover: 429/402 → cooldown + failover; 5xx → retry without cooldown
- CLI: accounts add --provider flag, list shows provider column
- Body buffering: request body buffered (8 MiB cap) for failover replay
- opencode integration: unified provider 'oc' with all merged models
- 64 tests pass (unit + integration)
- Verified: glm-5 → ollama, mimo-v2.5 → go, gpt-oss:20b → ollama

internal/config/accounts.go

@@ -14,13 +14,44 @@ import (
 	"time"
 )
 
-// Account is a single Ollama Cloud API key with an optional alias.
+// ProviderType identifies which upstream service an account belongs to.
+type ProviderType string
+
+const (
+	// ProviderOllamaCloud is the Ollama Cloud API at https://ollama.com.
+	ProviderOllamaCloud ProviderType = "ollama-cloud"
+	// ProviderOpenCodeGo is the OpenCode Go API at https://opencode.ai/zen/go/v1.
+	ProviderOpenCodeGo ProviderType = "opencode-go"
+)
+
+// DefaultProviderBaseURL returns the canonical upstream root for a provider.
+func DefaultProviderBaseURL(p ProviderType) string {
+	switch p {
+	case ProviderOpenCodeGo:
+		return "https://opencode.ai/zen/go"
+	default:
+		return "https://ollama.com"
+	}
+}
+
+// ValidProvider reports whether p is a recognised provider type.
+func ValidProvider(p ProviderType) bool {
+	switch p {
+	case ProviderOllamaCloud, ProviderOpenCodeGo:
+		return true
+	default:
+		return false
+	}
+}
+
+// Account is a single upstream API key with an optional alias.
 type Account struct {
-	ID      string    `json:"id"`
-	Name    string    `json:"name"`
-	APIKey  string    `json:"api_key"`
-	BaseURL string    `json:"base_url,omitempty"` // overrides ServerConfig.BaseURL; empty = use default
-	Created time.Time `json:"created"`
+	ID       string       `json:"id"`
+	Name     string       `json:"name"`
+	Provider ProviderType `json:"provider,omitempty"` // empty = ollama-cloud (backward compat)
+	APIKey   string       `json:"api_key"`
+	BaseURL  string       `json:"base_url,omitempty"` // overrides the provider default; empty = use default
+	Created  time.Time    `json:"created"`
 }
 
 // AccountsFile is the on-disk JSON structure.
@@ -73,6 +104,13 @@ func LoadAccounts() (*AccountsFile, error) {
 	if err := json.Unmarshal(data, &af); err != nil {
 		return nil, fmt.Errorf("parse accounts: %w", err)
 	}
+	// Backward compat: accounts without an explicit provider default to
+	// ollama-cloud (the original behaviour before multi-provider support).
+	for i := range af.Accounts {
+		if af.Accounts[i].Provider == "" {
+			af.Accounts[i].Provider = ProviderOllamaCloud
+		}
+	}
 	return &af, nil
 }