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fix(agents): checkpoint Sandboxes whose repositories have credentials upstream - #78
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… upstream No Sandbox checkpoint was ever written. Two causes: - The secret scan covered each repository's full history and every file, so a repository with a credential already on the remote (voltagecloud/cd) refused every checkpoint. The scan now covers only what the agent added: commits on no remote, and files that differ from HEAD or are untracked. - A turn's background save checks for idle prompt tasks when the turn's result arrives, before that turn's own prompt task is joined, so it could find the pool busy and never retry. A save that cannot start stays pending and starts at the next idle maintenance tick. The helper also exits with one code per step, and buzz-acp logs and reports that step, because it discards the helper's output.
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Merge Risk: 🟡 Moderate · up to
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| Check name | Status | Explanation | Resolution |
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| Docstring Coverage |  |
Docstring coverage is 55.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 3 files. (1 skipped: … | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly identifies the primary change: allowing Sandbox checkpoints when repositories contain credentials upstream. It is concise and directly related to the pull request objectives. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
Full details: Docstring Coverage
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Explanation
Docstring coverage is 55.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 3 files. (1 skipped: 1 too large.)
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
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Actionable comments posted: 3
- 🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @crates/buzz-acp/src/lib.rs:
- Line 3394: Update the maintenance flow around turn_checkpoints.is_pending() so
a pending save is scheduled even when pool_ready is false, or prevent the
idle-pool reaper from sleeping the pool until that save starts; ensure an
otherwise idle Sandbox eventually receives its turn checkpoint without requiring
another wake event.
Review comments at @voltage/images/buzz-agent/checkpoint.py:
- Around line 167-170: Update the checkpoint credential scan so findings in the
edited review are compared with findings from the upstream version of each
tracked file. Reject packing only when the review introduces a credential
finding absent upstream; preserve acceptance when an existing credential remains
unchanged while non-secret content is edited. Use the scan and edited-file flow
shown in the diff.
- Around line 181-182: Update restore() validation around scan(stage) to honor
pack()’s upstream-credential policy: allow credentials already present in the
archived checkpoint, while still rejecting credentials newly added during
restore. Preserve validation for all other disallowed content.
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- Repository: voltagecloud/buzz
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📒 Files selected for processing: 4
crates/buzz-acp/src/checkpoint.rscrates/buzz-acp/src/lib.rsvoltage/images/buzz-agent/checkpoint.pyvoltage/images/buzz-agent/test-checkpoint.py
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…e the pool sleeps - An edited tracked file contributes only its added lines to the secret scan, so a credential already upstream in that file is not a finding. - restore() scans what each restored repository adds to its HEAD, the same scope as pack(), so a checkpoint of such a repository restores. A refused restore removes its new destination. - A pending turn save keeps its maintenance tick while a lazy pool sleeps, so it starts without waiting for the next event.
What
No staging Sandbox has ever written a checkpoint. The checkpoint bucket has no objects or versions. A Sandbox that is stopped, or whose Spot node is lost, therefore loses all work that the agent did not push.
There are two causes, and a third problem that hid them.
1. The secret scan refused credentials already upstream
buzz-agent-checkpointran gitleaks on each repository's full history (--all HEAD), and on every file in the snapshot.voltagecloud/cdhas credentials committed invalues/monitoring/*.yaml, so a Sandbox that clonedcdcould never checkpoint. I reproduced this in a live Sandbox:packfailed in the history scan, and the file scan found 8 results incd.Fix: scan only what the agent added. That content is not yet on the forge:
--log-opts=--all HEAD --not --remotes).HEAD(git diff --name-only HEAD), plus untracked paths. The helper links these from the stage into a separate directory and scans that directory and the manifest.A repository without remote-tracking refs still gets its whole history scanned. The checkpoint contents do not change: the history bundle and all files are still packed, so restore is unchanged. This means that credentials which are already upstream go into the developer's private checkpoint prefix. The agent's GitHub token can read them anyway.
2. Turn checkpoints could fail to start
A turn's background save starts only when the pool is idle, and the idle check counts unjoined prompt tasks. The check runs when the turn's result arrives, before that turn's own prompt task finishes and is joined. The main loop observes joins only for panics, so nothing checked again. In the live Sandbox, the turn completed at 13:58:16 and then the Sandbox was idle, but no save started: there was no
checkpoint_startedrecord and no failure log.Fix: a turn checkpoint that cannot start stays pending. This happens when the pool is busy, a save is already running, or the save falls inside the interval. The 30-second maintenance tick joins finished prompt tasks and starts the pending save at the first idle point. The rules are the same as before: idle only, one save at a time, and at most one per
BUZZ_ACP_CHECKPOINT_AFTER_TURN_SECS.3. The failure did not say why
buzz-acpdiscards the helper's stderr because it can carry storage credentials. So a failure logged onlycheckpoint helper failed (exit status: 1).Fix: the helper now exits with one code per step.
buzz-acpmaps the code to the step, puts the step in theworkspace checkpoint failedlog and in thecheckpoint_failedactivity record, and still never reads the helper output.When you run the helper by hand, it prints
Checkpoint failed while <step>; ….Tested
test-checkpoint.py: a new case passes, and fails with the current helper. It checks that:pack;while scanning for secrets;reset --hard origin/main,packsucceeds again.The existing cases still pass: an untracked GitHub or Claude token is refused, and unsafe symlinks and archive paths are refused.
Other image tests:
test-restore.pyandtest-checkpoint-storage.py(S3 round trip and SIGTERM drain) pass on an image with the new helper.buzz-acp:a_deferred_turn_checkpoint_saves_at_the_next_idle_pointchecks that a turn completed while its prompt task was unjoined saves at the next idle point. It also checks that a turn inside the interval saves when the interval ends.helper_failures_record_their_reason_and_never_a_saved_checkpointnow also checks that exit 11 reports"step":"scanning for secrets".cargo test -p buzz-acppasses (1,120 tests), andcargo clippy -p buzz-acp --all-targets -- -D warningsis clean.Deploy
buzz-agent-gate,sandboxProviderConfig.image, and voltage-terraformagent_image.staging-agent.tee8z/<session>/…tar.gzobjects within 30 seconds of a completed turn.Summary by CodeRabbit