server negotiated unsupported position encoding "${encoding}

Error message

server negotiated unsupported position encoding "${encoding}"; this host requires utf-16

What it means

Error "server negotiated unsupported position encoding "${encoding}"; this host requires utf-16" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/lsp/lsp-stdio/src/translate.ts:99

  if (typeof sync === 'number') return isOpenCloseKind(sync)
  return sync.openClose === true
}

/** Legacy enum: `Full` (1) or `Incremental` (2) imply open/close support; `None` (0) does not. */
function isOpenCloseKind(kind: WireTextDocumentSyncKind): boolean {
  return kind === 1 || kind === 2
}

/**
 * Normalize the negotiated position encoding. An omitted encoding defaults to `utf-16`; any value
 * other than `utf-16` is a protocol error this host does not support.
 * @param encoding - the server's advertised `positionEncoding`, if any.
 * @returns the string `'utf-16'`.
 * @throws Error for any non-`utf-16` encoding.
 */
export function negotiatePositionEncoding(encoding: string | undefined): 'utf-16' {
  if (encoding === undefined || encoding === 'utf-16') return 'utf-16'
  throw new Error(`server negotiated unsupported position encoding "${encoding}"; this host requires utf-16`)
}

/** Convert a wire range to the seam's range (structurally identical, but re-shaped as `readonly`). */
function toRange(range: WireRange): LspRange {
  return {
    start: { line: range.start.line, character: range.start.character },
    end: { line: range.end.line, character: range.end.character },
  }
}

/** Whether a record is a `LocationLink` (has `targetUri` + `targetSelectionRange`). */
function isLocationLink(value: Record<string, unknown>): boolean {
  return typeof value.targetUri === 'string' && isRange(value.targetSelectionRange)
}

/** Whether a record is a `Location` (has string `uri` + a range). */
function isLocation(value: Record<string, unknown>): boolean {
  return typeof value.uri === 'string' && isRange(value.range)

View on GitHub (pinned to b150a551b8)

Solutions

Use a language server that supports utf-16 position encoding.

When it happens

Trigger: Thrown at packages/lsp/lsp-stdio/src/translate.ts:99 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/5de548b7cfa5d338. Report an issue: GitHub.