Slice: Publish causal rope architecture regression suite and docs

[flyingrobots]

Goal

Lock the architecture into tests and documentation so it cannot decay back into snapshot authority.

Acceptance criteria

• Docs cover Text Authority Doctrine, Materialization Is A Reading, Save/Export/Checkpoint Semantics, Causal Gutter Semantics, and :why Evidence Contract.
• Regression suite covers fixture import bans, basis-required reads, save not mutating authority, and retained-byte budgets.
• Roadmap issue links final status for all CR milestones.

[coderabbitai]

🔗 Related PRs

#23 - feat(echo): add Echo release gate witness [closed]
#27 - feat(echo): wire trusted runtime lifecycle into jedit [closed]
#135 - Docs: lock Jim causal roadmap [closed]
#193 - docs: lock Jim roadmap evidence slices [merged]
#205 - Document graph-backed rope runtime gate [merged]

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