Function updateUsage

src/services/api/claude.ts:2951–3014

(
  usage: Readonly<NonNullableUsage>,
  partUsage: BetaMessageDeltaUsage | undefined,
)

 * We only update these fields if they have a non-null, non-zero value.
 */
export function updateUsage(
  usage: Readonly<NonNullableUsage>,
  partUsage: BetaMessageDeltaUsage | undefined,
): NonNullableUsage {
  if (!partUsage) {
    return { ...usage }
  }
  return {
    input_tokens:
      partUsage.input_tokens !== null && partUsage.input_tokens > 0
        ? partUsage.input_tokens
        : usage.input_tokens,
    cache_creation_input_tokens:
      partUsage.cache_creation_input_tokens !== null &&
      partUsage.cache_creation_input_tokens > 0
        ? partUsage.cache_creation_input_tokens
        : usage.cache_creation_input_tokens,
    cache_read_input_tokens:
      partUsage.cache_read_input_tokens !== null &&
      partUsage.cache_read_input_tokens > 0
        ? partUsage.cache_read_input_tokens
        : usage.cache_read_input_tokens,
    output_tokens: partUsage.output_tokens ?? usage.output_tokens,
    server_tool_use: {
      web_search_requests:
        partUsage.server_tool_use?.web_search_requests ??
        usage.server_tool_use.web_search_requests,
      web_fetch_requests:
        partUsage.server_tool_use?.web_fetch_requests ??
        usage.server_tool_use.web_fetch_requests,
    },
    service_tier: usage.service_tier,
    cache_creation: {
      // SDK type BetaMessageDeltaUsage is missing cache_creation, but it's real!
      ephemeral_1h_input_tokens:
        (partUsage as BetaUsage).cache_creation?.ephemeral_1h_input_tokens ??
        usage.cache_creation.ephemeral_1h_input_tokens,
      ephemeral_5m_input_tokens:
        (partUsage as BetaUsage).cache_creation?.ephemeral_5m_input_tokens ??
        usage.cache_creation.ephemeral_5m_input_tokens,
    },
    // cache_deleted_input_tokens: returned by the API when cache editing
    // deletes KV cache content, but not in SDK types. Kept off NonNullableUsage
    // so the string is eliminated from external builds by dead code elimination.
    // Uses the same > 0 guard as other token fields to prevent message_delta
    // from overwriting the real value with 0.
    ...(feature('CACHED_MICROCOMPACT')
      ? {
          cache_deleted_input_tokens:
            (partUsage as unknown as { cache_deleted_input_tokens?: number })
              .cache_deleted_input_tokens != null &&
            (partUsage as unknown as { cache_deleted_input_tokens: number })
              .cache_deleted_input_tokens > 0
              ? (partUsage as unknown as { cache_deleted_input_tokens: number })
                  .cache_deleted_input_tokens
              : ((usage as unknown as { cache_deleted_input_tokens?: number })
                  .cache_deleted_input_tokens ?? 0),
        }