fix(gateway): filter anthropic-beta on the Vertex Anthropic path (#3358)

Vertex AI's Anthropic endpoint rejects unknown anthropic-beta tokens with
HTTP 400. buildUpstreamRequestAnthropicVertex forwarded the client header
verbatim via the allowedHeaders whitelist, so recent Claude Code CLIs that
send advisor-tool-2026-03-01, prompt-caching-scope-2026-01-05,
redact-thinking-2026-02-12 and thinking-token-count-2026-05-13 broke every
Vertex service_account request, even though plain account-test requests passed.

This is the only upstream builder that bypassed beta filtering: the
OAuth/API-key path uses computeFinalAnthropicBeta and the Bedrock path uses
filterBedrockBetaTokens. Close the gap with a Vertex-specific whitelist
(vertexSupportedBetaTokens) mirroring bedrockSupportedBetaTokens, plus the
existing BetaPolicy block check:

- evaluateBetaPolicy block check (symmetric to resolveBedrockBetaTokensForRequest)
- filterVertexBetaTokens strips policy-filtered + non-whitelisted tokens
- body context_management sanitize now keys on the final beta, not the raw client value
- overwrite the anthropic-beta header after the whitelist copy loop with the final value

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/internal/service/gateway_service.go

@@ -6830,6 +6830,48 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 	return req, body, nil
 }
 
+// vertexSupportedBetaTokens 是 Vertex AI 的 Anthropic 端点接受的 anthropic-beta
+// 白名单。Vertex 对任何未知 token 直接 HTTP 400，故采用白名单（与 Bedrock 的
+// bedrockSupportedBetaTokens 同思路）而非黑名单：未来 Claude Code 新增的、Vertex 尚未
+// 支持的 token 天然被剥离。当 Vertex 新增支持某 beta 时在此补充。
+//
+// 明确排除（issue #3358 中 Vertex 报 400 的 token）：advisor-tool-2026-03-01、
+// prompt-caching-scope-2026-01-05、redact-thinking-2026-02-12、
+// thinking-token-count-2026-05-13；以及 claude-code-20250219 / oauth-2025-04-20 等
+// 客户端身份 beta——Vertex service_account 走 Bearer 鉴权，不需要它们。
+var vertexSupportedBetaTokens = map[string]bool{
+	"context-1m-2025-08-07":                  true,
+	"context-management-2025-06-27":          true,
+	"fine-grained-tool-streaming-2025-05-14": true,
+	"interleaved-thinking-2025-05-14":        true,
+}
+
+// filterVertexBetaTokens 解析 client 的 anthropic-beta header，先剔除 drop 集合中的
+// token（BetaPolicy filter + 默认 drop），再只保留 Vertex 支持的 token，去重后逗号拼接。
+// 返回最终 header（可能为空字符串）。
+func filterVertexBetaTokens(header string, drop map[string]struct{}) string {
+	tokens := parseAnthropicBetaHeader(header)
+	if len(tokens) == 0 {
+		return ""
+	}
+	out := make([]string, 0, len(tokens))
+	seen := make(map[string]bool, len(tokens))
+	for _, t := range tokens {
+		if _, dropped := drop[t]; dropped {
+			continue
+		}
+		if !vertexSupportedBetaTokens[t] {
+			continue
+		}
+		if seen[t] {
+			continue
+		}
+		seen[t] = true
+		out = append(out, t)
+	}
+	return strings.Join(out, ",")
+}
+
 func (s *GatewayService) buildUpstreamRequestAnthropicVertex(
 	ctx context.Context,
 	c *gin.Context,
@@ -6844,14 +6886,27 @@ func (s *GatewayService) buildUpstreamRequestAnthropicVertex(
 		return nil, err
 	}
 
-	// 能力维度 sanitize：Vertex 路径上 anthropic-beta header 原样透传客户端值
-	// （下面白名单跳过 anthropic-version 但保留 anthropic-beta），依此决定是否
-	// 保留 body 中的 context_management，与 Anthropic 直连 / Bedrock 路径对称。
+	// 计算最终 outgoing anthropic-beta。Vertex AI 的 Anthropic 端点只接受一小撮
+	// beta token，未知 token 会直接 HTTP 400——近期 Claude Code CLI 透传的
+	// advisor-tool-2026-03-01 / prompt-caching-scope-2026-01-05 /
+	// redact-thinking-2026-02-12 / thinking-token-count-2026-05-13 都不被 Vertex 接受
+	// （issue #3358）。这里复用 BetaPolicy 的 block 检查（与 Bedrock 的
+	// resolveBedrockBetaTokensForRequest 对称），再按 vertexSupportedBetaTokens 白名单
+	// 剥离其余 token，使该路径与 Anthropic 直连 / Bedrock 路径行为一致。
+	clientBeta := ""
 	if c != nil && c.Request != nil {
-		clientBeta := getHeaderRaw(c.Request.Header, "anthropic-beta")
-		if sanitized, changed := sanitizeAnthropicBodyForBetaTokens(vertexBody, clientBeta); changed {
-			vertexBody = sanitized
-		}
+		clientBeta = getHeaderRaw(c.Request.Header, "anthropic-beta")
+	}
+	policy := s.evaluateBetaPolicy(ctx, clientBeta, account, modelID)
+	if policy.blockErr != nil {
+		return nil, policy.blockErr
+	}
+	finalBeta := filterVertexBetaTokens(clientBeta, mergeDropSets(policy.filterSet))
+
+	// 能力维度 sanitize：基于最终 beta（而非原始 client 值）决定是否保留 body 中的
+	// context_management，与 Anthropic 直连 / Bedrock 路径对称。
+	if sanitized, changed := sanitizeAnthropicBodyForBetaTokens(vertexBody, finalBeta); changed {
+		vertexBody = sanitized
 	}
 	fullURL, err := buildVertexAnthropicURL(account.VertexProjectID(), account.VertexLocation(modelID), modelID, reqStream)
 	if err != nil {
@@ -6883,6 +6938,13 @@ func (s *GatewayService) buildUpstreamRequestAnthropicVertex(
 	setHeaderRaw(req.Header, "authorization", "Bearer "+token)
 	setHeaderRaw(req.Header, "content-type", "application/json")
 
+	// 覆盖上面白名单 loop 写入的原始 client anthropic-beta，使用过滤后的最终值。
+	// finalBeta 为空（全部被剥离）时不下发该 header，与 Vertex 无 beta 请求一致。
+	deleteHeaderAllForms(req.Header, "anthropic-beta")
+	if finalBeta != "" {
+		setHeaderRaw(req.Header, "anthropic-beta", finalBeta)
+	}
+
 	s.debugLogGatewaySnapshot("UPSTREAM_FORWARD_VERTEX_ANTHROPIC", req.Header, vertexBody, map[string]string{
 		"url":        req.URL.String(),
 		"token_type": "service_account",