fix(sandbox): prevent state patch loss during block processing#15534
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Pull request overview
Fixes a sandbox-only race where sandbox_patch_state patches could be dropped when normal block processing is deferred due to an optimistic block already executing.
Changes:
- Stops draining
pending_state_patchat the start ofstart_process_block_impl. - Removes
state_patchthreading throughpreprocess_block→apply_chunks_preprocessing. - Drains
pending_state_patchinsideapply_chunks_preprocessing, after theshould_be_pending_executiondeferral check.
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #15534 +/- ##
==========================================
- Coverage 69.30% 69.30% -0.01%
==========================================
Files 940 940
Lines 212116 212130 +14
Branches 212116 212130 +14
==========================================
- Hits 147016 147014 -2
- Misses 59275 59279 +4
- Partials 5825 5837 +12
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stedfn
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Apr 9, 2026
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shreyan-gupta
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r-near
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Apr 16, 2026
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Background
sandbox_patch_statesometimes permanently loses patches — the patched account never appears, even on retry. This was reported in the Zulip thread and reproduced with near-sandbox-rs#51.Three interrelated bugs:
pending_state_patch.take()drains the queue at the start of block processing. If preprocessing fails (orphan, missing chunks, optimistic deferral), the patch is gone forever.patch_state_in_progress()checksis_empty(), which is true right aftertake()— before the patch is actually committed to state.apply()early-returns for old chunks and silently drops thestate_patch.What changed
Introduces
SandboxPatchTracker— a type that encapsulates the pending patch, a generation counter, and a committed-generation counter. LikeSandboxStatePatch, it uses the ZST pattern: real struct on sandbox builds, zero-sized no-op on non-sandbox builds. This replaces the three separate fields onChain(pending_state_patch,sandbox_patch_generation,sandbox_patch_committed_gen) with a singlesandbox_patches: SandboxPatchTracker.The key design change is taking the patch late — at point of use inside the per-shard loop of
apply_chunks_preprocessing, instead of at the top ofstart_process_block_impl. This eliminates the need for backup/clone/restore on error paths, since any error before the take leaves the patch in the tracker. The generation counter (in_progress()checksgeneration != committed_gen, notis_empty()) ensures the RPC doesn't return prematurely despite the late take.This removes the
state_patchparameter frompreprocess_blockandapply_chunks_preprocessing, and results in zero#[cfg(feature = "sandbox")]blocks inchain.rs.Related
clear()inpostprocess_ready_block)