## Thinking Path
> - Paperclip is the open source app people use to manage AI agents for
work
> - Adapter utilities run agent turns and report their results to the
control plane
> - A lost sandbox control channel can leave an agent turn without a
result
> - The host then waits for the full adapter timeout instead of
reporting the loss
> - This pull request adds a push loss signal and a bounded host wait
> - The benefit is a prompt failure terminal when the agent stops
answering
## Linked Issues or Issue Description
**What happened?**
A sandbox control channel loss during an Agent Client Protocol turn left
the host waiting for the four-hour adapter execution timeout.
**Expected behavior**
The host should detect the terminal channel loss, stop the turn, and
report a safe failure without waiting for the agent.
**Steps to reproduce**
1. Start an Agent Client Protocol turn through a sandbox adapter.
2. Close the duplex control channel while the turn remains active.
3. Observe the host response before the adapter timeout expires.
**Paperclip version or commit**
Test the pull request commit set at
`10b6bbc5525a79fd575298607dd5a25ae448fc8a`.
**Deployment mode**
The change applies to sandbox-backed adapter execution.
## What Changed
- Add `onLoss(listener)` to the duplex bridge handle.
- Register the loss listener at turn start and read losses latched
before turn start.
- Cancel the turn on loss and arm a 30-second host deadline.
- Close the stream locally when the deadline wins and create a host
terminal.
- Derive the public error from the closed `DuplexLossReason` enum.
- Add tests for loss order, cancellation, timeout, and safe error
output.
## Verification
- Run `pnpm --filter @paperclipai/adapter-utils exec tsc --noEmit`.
- Run `pnpm --filter @paperclipai/adapter-utils exec vitest run
src/acpx-engine/execute.test.ts -t "run-disposition seam"`.
- Confirm that the full pull request workflow passes.
## Risks
The new deadline changes a lost-channel path from a long wait to a
host-built failure after 30 seconds. Orderly completion keeps its
existing behavior. The deadline race against a pending `turn.result` has
no direct test.
## Model Used
OpenAI Codex, GPT-5, with tool use and code execution. The runtime does
not expose a more specific deployment version or context-window size.
## Checklist
- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` /
`Closes: #` / `Refs: #` OR (b) described the issue in-PR following the
relevant issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge
---------
Co-authored-by: Paperclip <noreply@paperclip.ing>
d1ba17eeca