fix: address review feedback — remove Opus-only flag from static base, add redact-thinking to CC bridge

- Remove mid-conversation-system-2026-04-07 from ANTHROPIC_BETA_BASE
  (Opus-only — already handled correctly in the dynamic selectBetaFlags())
- Add redact-thinking-2026-02-12 to CLAUDE_CODE_COMPATIBLE_ANTHROPIC_BETA
- Update STEALTH_GUIDE.md documented beta string to include redact-thinking

docs/security/STEALTH_GUIDE.md

@@ -91,7 +91,7 @@ For third-party Anthropic relays that only accept "real Claude Code" traffic:
 - `CLAUDE_CODE_COMPATIBLE_USER_AGENT = "claude-cli/2.1.158 (external, sdk-cli)"`
 - `CLAUDE_CODE_COMPATIBLE_STAINLESS_PACKAGE_VERSION = "0.94.0"`
 - `CLAUDE_CODE_COMPATIBLE_STAINLESS_RUNTIME_VERSION = "v24.3.0"`
-- `anthropic-beta = "claude-code-20250219,interleaved-thinking-2025-05-14,effort-2025-11-24"`
+- `anthropic-beta = "claude-code-20250219,interleaved-thinking-2025-05-14,effort-2025-11-24,redact-thinking-2026-02-12"`
 - `CONTEXT_1M_BETA_HEADER = "context-1m-2025-08-07"` (Opus/Sonnet 4.x family)
 - Default path: `/v1/messages?beta=true`
 

open-sse/config/anthropicHeaders.ts

@@ -11,7 +11,6 @@ const ANTHROPIC_BETA_BASE = Object.freeze([
   "structured-outputs-2025-12-15",
   "fast-mode-2026-02-01",
   "redact-thinking-2026-02-12",
-  "mid-conversation-system-2026-04-07",
   "token-efficient-tools-2026-03-28",
   "advisor-tool-2026-03-01",
   "extended-cache-ttl-2025-04-11",

open-sse/services/claudeCodeCompatible.ts

@@ -38,6 +38,7 @@ export const CLAUDE_CODE_COMPATIBLE_ANTHROPIC_BETA = [
   "claude-code-20250219",
   "interleaved-thinking-2025-05-14",
   "effort-2025-11-24",
+  "redact-thinking-2026-02-12",
 ].join(",");
 export const CLAUDE_CODE_COMPATIBLE_VERSION = "2.1.158";
 export const CLAUDE_CODE_COMPATIBLE_USER_AGENT = "claude-cli/2.1.158 (external, sdk-cli)";