[GP4-S1] Retained Ref Crosswalk

[flyingrobots]

Roadmap slice: GP4-S1
Goalpost: Goalpost 4: Retained Evidence Durability
Parent: #519
Related: #512, #513, #517, #522

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

Scope

Parent issues:
#519,
#512,
#513.

Scope:

• Define the exact crosswalk among RetainedEvidenceRef,
  RetainedMaterialRecord, ReadingRefRecord, SemanticBlobCoordinate, and
  BlobHash.
• Keep query identity, reading identity, semantic coordinate, and byte digest
  separate.

Acceptance:

• Equal bytes under different semantic coordinates produce distinct retained
  refs.
• Query identity alone does not imply retained payload availability.
• Retained reading id does not stand in for payload digest.

Witness:

cargo test -p warp-core --test retained_evidence_ref_tests
cargo test -p warp-core --test optic_retention_tests

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

#323 - Witnessed suffix admission evaluator [merged]
#329 - Stack Witness 0001 fixture-backed jedit walking skeleton [merged]
#371 - feat(core): advance v0.1 contract evidence and retention [merged]
#380 - feat(core): expose retained evidence posture on readings [merged]
#551 - Finish braid historical membership and replay goalpost [merged]

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