{"record":{"id":"3e89396c8083e57c","repo":"deepseek-ai/deepseek-harness","slug":"location-uses-unsupported-legacy-request-header-3e8939","errorCode":null,"errorMessage":"${location} uses unsupported legacy request/header reason \"fallback\"","messagePattern":"(.+?) uses unsupported legacy request/header reason \"fallback\"","errorType":"validation","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"packages/core/session/src/index.ts","lineNumber":370,"sourceCode":"}\n\n/** Whether an unknown value carries the current provider/model pair. */\nfunction hasProviderModel(value: unknown): boolean {\n  if (typeof value !== 'object' || value === null) return false\n  const pair = value as Record<string, unknown>\n  return typeof pair['provider'] === 'string' && pair['provider'].length > 0\n    && typeof pair['model'] === 'string' && pair['model'].length > 0\n}\n\n/** Reject request-header vocabulary removed with the legacy delta codec. */\nfunction assertSupportedRequestHeader(type: string, data: unknown, location: string): void {\n  if (type === 'request/header-delta') {\n    throw new Error(`${location} uses unsupported legacy request/header-delta format`)\n  }\n  if (type === 'request/header'\n    && data !== null && typeof data === 'object' && !Array.isArray(data)\n    && (data as Record<string, unknown>)['reason'] === 'fallback') {\n    throw new Error(`${location} uses unsupported legacy request/header reason \"fallback\"`)\n  }\n}\n\ntype SessionCallback = (...args: unknown[]) => unknown\n\n/** Resolve one listener snapshot, including Cordis's internal dispatch checks. */\nfunction collectSessionCallbacks(ctx: Context, args: unknown[]): SessionCallback[] {\n  return [...ctx.events.dispatch('emit', args)] as SessionCallback[]\n}\n\n/** Invoke one resolved observe-only listener snapshot with per-listener containment. */\nfunction invokeContainedSessionObservers(\n  ctx: Context,\n  name: 'session/event' | 'session/disposed',\n  id: SessionId,\n  args: unknown[],\n  callbacks: SessionCallback[],\n): void {","sourceCodeStart":352,"sourceCodeEnd":388,"githubUrl":"https://github.com/deepseek-ai/deepseek-harness/blob/b150a551b8d465e31e418e1b2eaf5e79bbb7d28e/packages/core/session/src/index.ts#L352-L388","documentation":"Error \"${location} uses unsupported legacy request/header reason \"fallback\"\" thrown in deepseek-ai/deepseek-harness.","triggerScenarios":"Thrown at packages/core/session/src/index.ts:370 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":["Remove the legacy request/header fallback reason usage."],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"b150a551b8d465e31e418e1b2eaf5e79bbb7d28e","analyzedAt":"2026-08-24T18:12:29.105Z","schemaVersion":2},"datasetVersion":"2026-08-24T22:17:12.610Z"}