[GP3-S3] Self-Contained WSC Export Fixture

[flyingrobots]

Roadmap slice: GP3-S3
Goalpost: Goalpost 3: WSC Causal-History Export And Import
Parent: #522
Related: #521

Source: docs/design/wal-wsc-durability-roadmap.md on branch cycle/521-wal-wsc-storage-relationship at bde7957c.

Scope

Parent issues: #522.

Scope:

• Export WAL segment bytes or bundled retained material inside WSC.
• Validate segment bytes against segment digest and commit chain on import.

Acceptance:

• Tampering with embedded segment bytes produces a typed digest/commit-chain
  obstruction.
• Self-contained import can rebuild accepted submission and receipt indexes
  without access to the original filesystem WAL root.

Witness:

cargo test -p warp-core wsc_self_contained_export_replays_segment_bytes

Dedupe note

This is the PR-sized implementation slice for the roadmap item above. Existing umbrella or adjacent issues remain linked as Parent/Related rather than duplicated here.

[coderabbitai]

🔗 Related PRs

#298 - feat(warp-core): TTD domain logic — provenance storage + causal cone walk [merged]
#329 - Stack Witness 0001 fixture-backed jedit walking skeleton [merged]
#379 - feat(core): commit runtime WAL ACK evidence [merged]
#550 - Expose braid membership history [merged]
#551 - Finish braid historical membership and replay goalpost [merged]

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