Recover a persisted arena snapshot only when its layout matches
A warm-start experiment maps a snapshot written by an older layout and interprets its free-list metadata as current records.
- Focused work estimate
- 6h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Persistence formats · Validation · Recovery
Estimated field mix
- Systems programming65%
- Storage systems35%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional telemetry collector copies decoded packet fields into a small native arena. The prototype misaligns wide values and reuses memory while readers still hold views. Create a local Rust crate or C library with generated byte fixtures; no device traffic or production allocator replacement is supplied.
Setup prerequisites
- Pointers and slices
- Integer overflow
- Memory alignment
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- SMEM-101 · Specify aligned arena offsets without relying on host luck
- SMEM-102 · Return exhaustion without handing out a partial slice
- SMEM-104 · Free large spill blocks without double-releasing arena pages
- SMEM-105 · Coalesce adjacent free spans without corrupting the index
- SMEM-103 · Invalidate borrowed packet views when the arena resets
- SMEM-107 · Contain unsafe decoding behind a length-checked cursor
Acceptance criteria
- Snapshot header binds format version, byte order, size, and checksum
- Recovery validates every offset before exposing records
- Unknown versions fail closed without modifying the snapshot
Implementation constraints
- Use generated snapshots only; memory mapping does not make untrusted offsets safe.
Verification to include
- Write and restore a current snapshot with identical logical records.
- Corrupt each header field and one nested offset, then confirm rejection.
Deliverables
- Versioned snapshot reader and corruption matrix
Rollout and recovery
Keep cold reconstruction as the default until compatible recovery is repeatable.
Value of the work
For the engineer: Practice representation invariants, lifetimes, unsafe-boundary review and memory diagnostics.
For the team: Review a component whose allocation failures and corruption cases are explicit before reuse in latency-sensitive code.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.