Fixed: #140 #133 #80

feat(translator): add token counting functionality for Gemini, Claude, and CLI

- Introduced `TokenCount` handling across various Codex translators (Gemini, Claude, CLI) with respective implementations.
- Added utility methods for token counting and formatting responses.
- Integrated `tiktoken-go/tokenizer` library for tokenization.
- Updated CodexExecutor with token counting logic to support multiple models including GPT-5 variants.
- Refined go.mod and go.sum to include new dependencies.

feat(runtime): add token counting functionality across executors

- Implemented token counting in OpenAICompatExecutor, QwenExecutor, and IFlowExecutor.
- Added utilities for token counting and response formatting using `tiktoken-go/tokenizer`.
- Integrated token counting into translators for Gemini, Claude, and Gemini CLI.
- Enhanced multiple model support, including GPT-5 variants, for token counting.

docs: update environment variable instructions for multi-model support

- Added details for setting `ANTHROPIC_DEFAULT_OPUS_MODEL`, `ANTHROPIC_DEFAULT_SONNET_MODEL`, and `ANTHROPIC_DEFAULT_HAIKU_MODEL` for version 2.x.x.
- Clarified usage of `ANTHROPIC_MODEL` and `ANTHROPIC_SMALL_FAST_MODEL` for version 1.x.x.
- Expanded examples for setting environment variables across different models including Gemini, GPT-5, Claude, and Qwen3.

internal/runtime/executor/openai_compat_executor.go

@@ -219,7 +219,29 @@ func (e *OpenAICompatExecutor) ExecuteStream(ctx context.Context, auth *cliproxy
 }
 
 func (e *OpenAICompatExecutor) CountTokens(ctx context.Context, auth *cliproxyauth.Auth, req cliproxyexecutor.Request, opts cliproxyexecutor.Options) (cliproxyexecutor.Response, error) {
-	return cliproxyexecutor.Response{Payload: []byte{}}, fmt.Errorf("not implemented")
+	from := opts.SourceFormat
+	to := sdktranslator.FromString("openai")
+	translated := sdktranslator.TranslateRequest(from, to, req.Model, bytes.Clone(req.Payload), false)
+
+	modelForCounting := req.Model
+	if modelOverride := e.resolveUpstreamModel(req.Model, auth); modelOverride != "" {
+		translated = e.overrideModel(translated, modelOverride)
+		modelForCounting = modelOverride
+	}
+
+	enc, err := tokenizerForModel(modelForCounting)
+	if err != nil {
+		return cliproxyexecutor.Response{}, fmt.Errorf("openai compat executor: tokenizer init failed: %w", err)
+	}
+
+	count, err := countOpenAIChatTokens(enc, translated)
+	if err != nil {
+		return cliproxyexecutor.Response{}, fmt.Errorf("openai compat executor: token counting failed: %w", err)
+	}
+
+	usageJSON := buildOpenAIUsageJSON(count)
+	translatedUsage := sdktranslator.TranslateTokenCount(ctx, to, from, count, usageJSON)
+	return cliproxyexecutor.Response{Payload: []byte(translatedUsage)}, nil
 }
 
 // Refresh is a no-op for API-key based compatibility providers.