Summary

• add an opt-in warn_on_cache_miss user setting
• expose the setting in the Notifications tab of /settings
• emit warning notifications when model turns after the first session response report no cached input tokens
• support both regular model calls and coding harness responses

Validation

• task build ✅
• go test ./pkg/runtime ./pkg/tui/page/chat ✅
• go test ./pkg/tui/dialog ./pkg/tui/page/chat ./pkg/tui ./pkg/userconfig ✅
• task test ⚠️ unrelated existing failures in the scheduler docs schema snippet and live Moonshot provider test
• task lint ⚠️ unrelated existing Lint/DeferMutexUnlock offense in pkg/tools/builtin/scheduler/scheduler.go