v3.7.3

### 🐛 Bug Fixes

- **fix(claude):** strip existing billing headers from system array before injecting to prevent Anthropic prompt cache misses — stacked `x-anthropic-billing-header` blocks invalidated prefix matching, causing ~100% cache_create instead of cache_read (#1712)
- **fix(claude):** strip `output_config.format` for non-Anthropic Claude-compatible providers during passthrough — third-party Claude endpoints (MiniMax, DeepSeek via aggregators) reject structured output fields with 400 errors (#1719)
- **fix(combo):** set terminal error state on response quality validation failure — prevents misleading `ALL_ACCOUNTS_INACTIVE` 503 when the real issue is response quality validation (#1707, #1710)
- **fix(combo):** treat combo fallback as target-level orchestration — all non-ok responses (including generic 400s) now fall through to the next target instead of being terminal; removes complex bad-request allowlist regex (#1713)
- **fix(codex):** restore namespace MCP tools and hosted-tool whitelist — regression from #1581 that silently dropped all MCP tool groups and Responses-API hosted tools (#1715)
- **fix(codex):** add neutral instructions for bare chat requests — Codex Responses backend rejects requests without `instructions`, making Codex unusable for normal chat (#1709)
- **fix(proxy):** wrap proxy assignment queries in try-catch for missing `proxy_assignments` table — Electron installs where migration 004 hasn't run no longer crash with `no such table` error (#1706)
- **fix(migration):** improve Windows file URL path resolution in migration runner — adds direct URL path extraction and `process.cwd()` fallback for CI-built bundles with leaked build-time paths (#1704)
- **fix(ui):** fix light mode active request payload modal — add missing `--color-card` theme token, use opaque `bg-surface` instead of translucent `bg-card/70`, add backdrop blur (#1714)

### 🔄 Updates

- **chore(image-models):** refresh image generation model registry — replace stale FLUX aliases with FLUX Kontext / FLUX.2 mappings, remove deprecated FLUX Redux/Depth/Canny variants (#1722)