improvement(sandbox): exempt caller-consumed streams from the output retention budget

[icecrasher321]

Summary

A Pi agent turn emits one JSONL event per step and passes the 10 MB process output budget on an ordinary session, killing the run. The bytes were never a result: handleChunk parses every chunk as it arrives and keeps none of it, and the accumulated copy is only ever read back to build an error message.

The budget bounds what Sim RETAINS, so a stream the caller consumes itself is exempt and only a 64 KB diagnostic tail is kept. The limit is unchanged for everything else.

Gated per stream, not per command: a caller that streams stdout but not stderr still has stderr fully bounded. Both adapters gate on the handler's presence, so the calls that parse markers out of stdout (Pi's clone/prepare/push, which do not stream) keep full retention and full budgeting — the case daytona.ts already warns about.

E2B's SDK still accumulates internally, so this bounds what Sim retains rather than the provider's peak; Daytona accumulates locally and is bounded outright.

Type of Change

• Other: UX Improvement

Testing

Tested manually

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Aug 7, 2026 12:25am

[cursor]

PR Summary

Medium Risk
Changes sandbox output limit enforcement on a critical Pi execution path; behavior is scoped to caller-consumed streams but both E2B and Daytona command runners were updated and must stay aligned.

Overview
Fixes Pi agent turns dying on sandbox_output_limit_exceeded when JSONL step events exceed the 10 MB process retention cap even though the caller already consumed the stream via onStdout/onStderr.

Retention policy: If a stream handler is present, that stream skips SandboxProcessOutputBudget billing; Sim keeps only a 64 KB diagnostic tail (with a truncation note), via tailStreamedSandboxOutput and appendStreamedSandboxOutput. Exemption is per stream—streaming stdout alone still fully bounds stderr. Paths without handlers (e.g. marker parsing) keep full retention and budgeting.

Provider parity: E2B and Daytona adapters apply the same gating and final tail cut so failover does not change behavior when streams end between one and two tail lengths.

Conformance tests cover oversized streamed stdout, mid-band tail sizing, and non-exempt stderr.

^{Reviewed by Cursor Bugbot for commit 922b5fa. Configure here.}

[greptile-apps]

Greptile Summary

The PR exempts caller-consumed sandbox streams from retained-output budgeting while preserving a bounded diagnostic tail and continuing to enforce limits independently on unconsumed streams.

• Adds byte-aware helpers for retaining the final 64 KB of streamed output.
• Applies per-stream retention behavior consistently across the Daytona and E2B adapters.
• Adds cross-provider conformance coverage for oversized consumed streams, final-tail sizing, and unconsumed-stream limits.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
apps/sim/lib/execution/remote-sandbox/output-limits.ts	Adds UTF-8-aware streamed-output tailing and bounded incremental accumulation helpers.
apps/sim/lib/execution/remote-sandbox/daytona.ts	Exempts callback-consumed streams from budgeting, bounds their local diagnostic copies, and normalizes final tails on every result path.
apps/sim/lib/execution/remote-sandbox/e2b.ts	Applies per-stream retention decisions to normal, timeout, and non-zero-exit results while continuing to budget unconsumed output.
apps/sim/lib/execution/remote-sandbox/conformance.test.ts	Adds provider-conformance tests and fixes the previously reported mock typing issue through signature inference.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  Output[Sandbox output chunk] --> Handler{Caller supplied handler?}
  Handler -- No --> Budget[Charge retained-output budget]
  Budget --> Full[Retain full stream]
  Handler -- Yes --> Callback[Deliver chunk to caller]
  Callback --> Tail[Retain bounded diagnostic tail]
  Full --> Result[Command result]
  Tail --> Result

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[icecrasher321]

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[icecrasher321]

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[icecrasher321]

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[icecrasher321]

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