grok修复: x-statsig-id 改用 goja 跑原版签名器, 自愈跨 reship

手抄的字节算法每次 grok 换 web build 就失效(403 anti-bot), 天天死。
改为内嵌 goja 执行 grok 自己的签名器 chunk + 合成 DOM/WAAPI 垫片, 由 grok
自己的代码做所有随 build 轮换的字节索引/曲线选择, 我们只提供稳定的浏览器原语。

- statsig_engine.go: goja 引擎池 + 构建无关地自动定位当前签名器 chunk
- statsig_shim.js(//go:embed): document/getComputedStyle(WAAPI 采样)/
  crypto.subtle/TextEncoder/base64 垫片 + Turbopack bootstrap
- client.go: statsigID 优先走引擎, 任何失败回退旧静态算法; ensureChallenge
  捕获 seed+curves 并按 reship(chunk 列表变化)重建引擎池
- 旧静态 computeStatsigTail 降级为兜底; 其离线回归测试改 Skip(ground truth
  无法离线重生), 新增 40 并发签名测试

已验证: 动态定位当前 build → conversations/new 返回 200 + conversationId。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/provider/grok/statsig_selfheal_test.go

@@ -4,8 +4,10 @@ import (
 	"context"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"os"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -34,8 +36,15 @@ var statsigTriples = []struct {
 
 const statsigTestCurves = `[[{"color":[48,44,6,37,198,15],"deg":192,"bezier":[118,76,158,16]},{"color":[224,216,196,111,43,97],"deg":119,"bezier":[67,167,95,219]},{"color":[90,235,250,5,223,64],"deg":104,"bezier":[100,57,106,204]},{"color":[6,109,253,44,29,224],"deg":151,"bezier":[204,60,142,122]},{"color":[81,0,121,208,228,133],"deg":181,"bezier":[182,89,105,123]},{"color":[31,3,160,181,226,184],"deg":98,"bezier":[207,150,215,136]},{"color":[231,243,81,28,109,131],"deg":175,"bezier":[17,103,7,81]},{"color":[222,250,130,169,55,247],"deg":141,"bezier":[21,238,12,84]},{"color":[74,62,116,145,209,185],"deg":109,"bezier":[0,74,58,233]},{"color":[204,168,203,138,107,125],"deg":214,"bezier":[41,13,239,45]},{"color":[246,116,162,162,84,234],"deg":127,"bezier":[160,202,52,76]},{"color":[138,202,210,36,61,195],"deg":234,"bezier":[31,50,177,229]},{"color":[47,46,196,176,79,255],"deg":221,"bezier":[39,14,9,76]},{"color":[245,164,227,71,201,110],"deg":190,"bezier":[193,208,125,9]},{"color":[199,253,44,33,130,240],"deg":191,"bezier":[168,247,61,37]},{"color":[19,91,5,180,202,243],"deg":216,"bezier":[96,152,42,123]}],[{"color":[42,154,230,170,197,128],"deg":108,"bezier":[160,52,34,184]},{"color":[224,132,83,0,231,162],"deg":238,"bezier":[227,37,122,102]},{"color":[24,82,237,199,100,74],"deg":130,"bezier":[186,106,188,209]},{"color":[47,50,169,65,124,44],"deg":228,"bezier":[198,22,146,225]},{"color":[111,131,95,195,131,73],"deg":207,"bezier":[134,146,202,172]},{"color":[192,10,166,28,236,3],"deg":219,"bezier":[85,77,157,235]},{"color":[236,139,199,72,233,250],"deg":197,"bezier":[180,9,79,147]},{"color":[146,195,78,16,231,211],"deg":93,"bezier":[123,18,87,27]},{"color":[168,211,49,42,124,18],"deg":172,"bezier":[232,171,120,118]},{"color":[43,146,96,11,203,53],"deg":146,"bezier":[11,4,83,198]},{"color":[183,97,101,38,115,41],"deg":159,"bezier":[69,223,197,236]},{"color":[78,73,207,132,109,134],"deg":49,"bezier":[59,18,133,168]},{"color":[239,153,225,207,127,157],"deg":194,"bezier":[13,206,154,182]},{"color":[19,146,127,191,68,199],"deg":165,"bezier":[148,212,7,16]},{"color":[93,225,249,144,88,255],"deg":215,"bezier":[62,30,77,69]},{"color":[203,79,164,145,3,20],"deg":81,"bezier":[228,28,93,130]}],[{"color":[171,53,4,125,232,43],"deg":122,"bezier":[136,9,128,97]},{"color":[143,97,205,57,63,69],"deg":192,"bezier":[232,20,219,189]},{"color":[28,173,18,107,158,44],"deg":255,"bezier":[93,187,184,198]},{"color":[170,17,62,142,200,32],"deg":29,"bezier":[14,31,12,97]},{"color":[19,117,122,173,239,66],"deg":74,"bezier":[117,176,139,212]},{"color":[213,151,230,112,224,255],"deg":25,"bezier":[1,223,72,233]},{"color":[153,131,51,105,69,47],"deg":108,"bezier":[123,177,126,140]},{"color":[120,114,44,151,88,83],"deg":165,"bezier":[16,104,134,75]},{"color":[245,145,194,75,120,26],"deg":142,"bezier":[79,235,38,43]},{"color":[147,63,50,255,239,106],"deg":190,"bezier":[122,143,160,150]},{"color":[233,78,184,130,25,123],"deg":54,"bezier":[87,18,184,226]},{"color":[162,180,233,70,57,249],"deg":87,"bezier":[123,238,61,124]},{"color":[146,95,56,171,38,240],"deg":239,"bezier":[241,134,228,44]},{"color":[111,11,149,62,208,177],"deg":70,"bezier":[103,149,4,37]},{"color":[159,128,118,21,197,153],"deg":175,"bezier":[246,215,172,236]},{"color":[194,131,68,247,215,108],"deg":30,"bezier":[23,91,151,231]}],[{"color":[239,129,141,243,85,208],"deg":38,"bezier":[252,248,245,195]},{"color":[205,56,138,49,126,99],"deg":107,"bezier":[72,85,228,91]},{"color":[185,54,148,122,170,158],"deg":192,"bezier":[33,88,51,136]},{"color":[7,14,75,26,23,41],"deg":93,"bezier":[153,21,55,147]},{"color":[245,211,213,64,5,253],"deg":49,"bezier":[253,19,106,155]},{"color":[144,232,165,21,114,130],"deg":200,"bezier":[193,179,133,226]},{"color":[34,196,100,42,114,0],"deg":52,"bezier":[4,4,71,65]},{"color":[195,8,130,102,201,141],"deg":210,"bezier":[8,173,23,33]},{"color":[86,136,44,95,223,62],"deg":249,"bezier":[220,98,68,113]},{"color":[205,48,9,247,236,71],"deg":75,"bezier":[163,240,28,25]},{"color":[43,190,29,239,55,135],"deg":146,"bezier":[109,245,34,188]},{"color":[146,91,92,2,3,251],"deg":97,"bezier":[183,188,95,157]},{"color":[40,213,196,70,81,174],"deg":120,"bezier":[153,197,61,201]},{"color":[131,92,180,68,131,214],"deg":251,"bezier":[94,191,198,89]},{"color":[47,113,219,96,115,228],"deg":238,"bezier":[22,35,60,63]},{"color":[246,244,203,196,78,136],"deg":44,"bezier":[88,23,205,184]}]]`
 
-// TestComputeStatsigTail is the offline regression test for the F derivation.
+// TestComputeStatsigTail was the offline regression for the hand-ported F
+// derivation (computeStatsigTail). That algorithm is now only a last-resort
+// fallback: the durable path runs grok's own signer in goja (statsig_engine.go),
+// which self-heals across web reships. grok rotates the F algorithm on every
+// reship, so these browser-captured (seed,F) triples go stale and CANNOT be
+// regenerated offline. TestSelfHealStatsigE2E (live, via goja) is the real
+// regression now. Kept skipped so the reference vectors aren't lost.
 func TestComputeStatsigTail(t *testing.T) {
+	t.Skip("static F derivation is a deprecated fallback; see TestSelfHealStatsigE2E (goja)")
 	var curves [][]statsigCurve
 	if err := json.Unmarshal([]byte(statsigTestCurves), &curves); err != nil {
 		t.Fatalf("curves: %v", err)
@@ -92,6 +101,55 @@ func TestSelfHealStatsigE2E(t *testing.T) {
 	t.Logf("OK bytes=%d head=%.80s", len(body), strings.ReplaceAll(body, "\n", " "))
 }
 
+// TestStatsigEngineConcurrent fires many concurrent goja signs through the pool to
+// catch data races / engine cross-talk (run with -race). Requires a live GROK_TOK
+// so the engine is built and the challenge cached.
+func TestStatsigEngineConcurrent(t *testing.T) {
+	token := strings.TrimSpace(os.Getenv("GROK_TOK"))
+	if token == "" {
+		t.Skip("no GROK_TOK")
+	}
+	c := NewClient("")
+	client, err := c.newTLSClient()
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 45*time.Second)
+	defer cancel()
+	c.ensureChallenge(ctx, client, token)
+	statsigMu.Lock()
+	ch, ok := statsigCache[token]
+	statsigMu.Unlock()
+	if !ok || ch.seedB64 == "" || ch.curvesJSON == "" {
+		t.Fatal("engine inputs not cached")
+	}
+
+	const n = 40
+	var wg sync.WaitGroup
+	errs := make(chan error, n)
+	for i := 0; i < n; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			id, err := signWithEngine(ch.seedB64, ch.curvesJSON, "/rest/app-chat/conversations/new", "POST")
+			if err != nil {
+				errs <- err
+				return
+			}
+			if len(id) < 40 {
+				errs <- errTooShort
+			}
+		}(i)
+	}
+	wg.Wait()
+	close(errs)
+	for e := range errs {
+		t.Fatalf("concurrent sign: %v", e)
+	}
+}
+
+var errTooShort = errors.New("statsig id too short")
+
 // TestGenerateVideoE2E generates a real grok video using only the dynamic
 // self-healed statsig (no env overrides). Requires a live GROK_TOK.
 func TestGenerateVideoE2E(t *testing.T) {