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Lower the checkpoint shadow budget default from 5 s to 1 s - #55
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Evidence (release-1 soak, 0.5 calls/s, fresh history): the scheduled shadow check recomputes the full checkpoint body under the project write lock inside the budget. From about 5 h of history it stopped fitting 5 s reliably. Near that boundary a success (which resets the backoff) alternates with failures, so attempts stay about hourly and EACH is a 3.5 to 5 s write stall (metered calls of 3.3 to 5.1 s at six consecutive attempts). At lighter load this zone lasts days. With a 1 s default one shadow attempt holds the write lock for about 1 s. The trade: the cross-check covers less history. Estimated (scaled from the measurement, about 5 s at about 5 h on the soak host) it stops fitting after roughly an hour of history at 0.5 calls/s, later at lighter load. It was already ineffective beyond a few hours. The differential tests remain the primary assurance. Backoff, min interval and refusal semantics are unchanged: a mismatch still refuses. Adds a test pinning the default at 1 s, updates LIMITATIONS, CONFIGURATION, the claims text and the rendered FORMAL.md. Co-Authored-By: Claude Opus 5.5 <[email protected]>
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Why
Release-1 soak (0.5 calls/s, fresh history): the scheduled shadow check recomputes the full checkpoint body under the project write lock inside the budget. From about 5 h of history it stopped fitting 5 s reliably. Near the boundary a success (which resets the backoff) alternates with failures, so attempts stay about hourly and each is a 3.5 to 5 s write stall (metered calls of 3.3 to 5.1 s at 07:25, 08:26, 09:27, 10:28, 11:50, 12:51Z). At lighter load this zone lasts days.
Change
DefaultCheckpointShadowBudget5 s -> 1 s, so one attempt holds the write lock for about 1 s. Backoff, min interval (#52) and refusal semantics are unchanged; a mismatch still refuses.Trade (stated in LIMITATIONS, CONFIGURATION, claims)
The cross-check covers less history: an estimate scaled from the measurement (about 5 s at about 5 h on the soak host) is that it stops fitting after roughly an hour of history at 0.5 calls/s, later at lighter load. It was already ineffective beyond a few hours. The differential tests remain the primary assurance.
Verification
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