[EPIC] ArchiveService

[kirich1409]

Context

zstd archival with streaming sha256 verify (P4). Atomic index update. archive-verify-fsync-then-trash invariant (S7a).

Goals

• ArchiveService in DevsweepCorePrivate.
• zstd compression via Swift-compatible library (dep choice via spike T-12-1).
• Streaming sha256 via CryptoKit.SHA256.Hasher during compress.
• Atomic JSON index update via temp + rename + fsync.
• Verify = size>0 + hash match; only then trash original.

Child tasks

Will be added as sub-issues after task batch.

Exit criteria

• AC-7a, AC-32 pass.

Related documents

n/a