deepseek-ai/deepseek-harness · error · Error

compactRegion: end seq ${end} not found in surface

Error message

compactRegion: end seq ${end} not found in surface

What it means

compactRegion's `end` must be a seq currently present in session.surface.nodes. This error means the end seq is not on the surface: an earlier compaction replacement shadowed it, pruning rewrote it, or the value was never a surface node (log-only events such as compaction/* never appear on the surface).

Source

Thrown at packages/compaction/compaction-basic/src/region.ts:320

 * @param session - session whose latest marker state is inspected.
 * @param stage - operation label included in the busy diagnostic.
 */
export function assertNoActiveCompaction(session: Session, stage: string): void {
  const entryState = inspectCompactionEntryState(session.events)
  assertCompactionInactive(
    entryState.unmatchedCompactionStart,
    entryState.latestEndSeedSeq,
    stage,
  )
}

/** Validate one requested surface-position span before asynchronous work begins. */
function validateSurfaceRegion(session: Session, start: number, end: number): SurfaceSelection {
  const nodes = session.surface.nodes
  const startIdx = nodes.indexOf(start)
  const endIdx = nodes.indexOf(end)
  if (startIdx === -1) throw new Error(`compactRegion: start seq ${start} not found in surface`)
  if (endIdx === -1) throw new Error(`compactRegion: end seq ${end} not found in surface`)
  if (startIdx > endIdx) {
    throw new Error(
      `compactRegion: start seq ${start} (position ${startIdx}) is after end seq ${end} (position ${endIdx}) on the surface`,
    )
  }
  // oxlint-disable-next-line typescript/no-non-null-assertion
  if (!toolPairingBalancedBefore(session, nodes[startIdx]!)) {
    throw new Error(`compactRegion: start seq ${start} is not a balanced boundary (would split a step's tool-call/result pair)`)
  }
  // oxlint-disable-next-line typescript/no-non-null-assertion
  if (!toolPairingBalancedAfter(session, nodes[endIdx]!)) {
    throw new Error(`compactRegion: end seq ${end} is not a balanced boundary (would split a step, or the step is still open)`)
  }

  return { start, end, startIdx, endIdx, shadowedSeqs: nodes.slice(startIdx, endIdx + 1) }
}

/** Snapshot pricing and replay input for a validated surface range. */

View on GitHub (pinned to b150a551b8)

Solutions

1. Read agent.session.surface.nodes immediately before the call and take `end` from that array
2. Prefer the last node of the span validated in the same synchronous block that issues the call
3. Log surface.nodes to confirm which seqs are visible when the error fires

Example fix

// before: end derived by arithmetic on old seqs
await ctx.compaction.compactRegion(start, start + 10, agent)

// after: end picked from the current surface
const nodes = agent.session.surface.nodes
await ctx.compaction.compactRegion(nodes[0]!, nodes[nodes.length - 1]!, agent)

const nodes = agent.session.surface.nodes
if (!nodes.includes(end)) {
  throw new RangeError(`end seq ${end} is not on the current surface`)
}

When it happens

Trigger: Passing an end seq from a superseded surface generation; passing a compaction/summary or turn/* event seq as `end`; using seqs read before a prior compactionRegion or auto-compaction committed a replacement.

Common situations: Boundary seqs cached across awaits; recomputing `end` by arithmetic (start + n) after replacements made seqs non-contiguous; replaying recorded command arguments on a mutated session.

Related errors

• compactRegion: start seq ${start} not found in surface
• compactRegion: start seq ${start} (position ${startIdx}) is
• compactRegion: start seq ${start} is not a balanced boundary
• compactRegion: end seq ${end} is not a balanced boundary (wo
• BasicCompactionConfig: auto must be a boolean

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/e962e665eb998aec. Report an issue: GitHub.