a successful full-replace sample stashes its CompactOutput

Error message

a successful full-replace sample stashes its CompactOutput

What it means

During two-pass compaction, when a compact summary was produced the code needs the sampler's stashed `CompactOutput` from the last successful full-replace sample and unwraps with expect. The invariant: if `compact_summary` is Some, a successful full-replace sample must have been recorded; the panic signals that bookkeeping broke.

Source

Thrown at crates/codegen/xai-grok-shell/src/session/compaction.rs:1315

                user_context.as_deref(),
                use_short_prompt,
                &sampling_config.model,
                trigger,
                compact_summary
                    .as_deref()
                    .or(telemetry.last_rejected_summary.as_deref()),
                last_error.as_ref(),
                telemetry.attempts,
                telemetry.attempt_details,
                started_at,
            );
        }
        let compact_output = match compact_summary {
            Some(_) => match two_pass_output {
                Some(tp) => tp,
                None => sampler
                    .take_last_success()
                    .expect("a successful full-replace sample stashes its CompactOutput"),
            },
            None => {
                let span = tracing::Span::current();
                span.record("compaction_attempts", telemetry.attempts as i64);
                span.record(
                    "compaction_degenerate_rejections",
                    telemetry.degenerate_rejections as i64,
                );
                span.record(
                    "compaction_input_overflow_rejections",
                    input_overflow_rejections as i64,
                );
                span.record(
                    "compaction_deterministic_rejections",
                    telemetry.deterministic_rejections as i64,
                );
                span.record(
                    "compaction_transient_rejections",

View on GitHub (pinned to bc7f02eddd)

Solutions

Trace why the sampler recorded no success: log each full-replace sample attempt and its accept/reject outcome.
Ensure compact_summary is only set when a successful full-replace sample was stashed (make the coupling explicit in code).
Check degenerate-rejection logic — a rejected sample shouldn't coexist with a set compact_summary.
Propagate a CompactionError instead of panicking so the session can fall back to no-compaction.

Example fix

// before
.expect("a successful full-replace sample stashes its CompactOutput")
// after
.ok_or_else(|| CompactionError::SamplerStateInconsistent)?

Defensive patterns

Strategy: type-guard

Validate before calling

// only consume the sampler when a success was actually recorded
if compact_summary.is_some() && two_pass_output.is_none() && !sampler.has_last_success() {
    return Err(CompactionError::SamplerStateInconsistent);
}

Type guard

fn sampler_ready(sampler: &Sampler) -> bool {
    sampler.has_last_success()
}

Try / catch

let out = sampler.take_last_success().ok_or_else(|| {
    tracing::error!("summary present without a successful full-replace sample");
    CompactionError::SamplerStateInconsistent
})?;

Prevention

Set compact_summary only in the same code path that stashes the sample success
Log every sample accept/reject to keep sampler state observable
Add a test where all full-replace samples degenerate and assert no summary is produced

When it happens

Trigger: `compact_summary` is Some but `two_pass_output` is None and `sampler.take_last_success()` returns None — i.e. the summary was derived without a corresponding successful full-replace sample being stashed in the sampler.

Common situations: Sampler rejection bookkeeping drift after a refactor of the sample/summary flow; compaction runs where all full-replace samples degenerated yet a summary was still produced; interplay between retry attempts and sampler state on repeated compaction calls.

Related errors

AI-assisted analysis of xai-org/grok-build@bc7f02eddd (2026-08-31). Data as JSON: /api/errors/dfd97c0302e06c18. Report an issue: GitHub.