Add evolution plan and roadmap for resident-tier integrity, API parity, and performance work

[arty-kk]

Motivation

• Capture a prioritized, incremental plan to close integrity, API contract, and performance gaps discovered in the resident tier audit.
• Define non-breaking constraints and a phased roadmap to stabilize core invariants (manifest hash enforcement), align API semantics, and reduce verification overhead.
• Create clear task specs (EVO-001..EVO-006) with acceptance criteria and rollout/rollback notes to reduce risk and speed follow-up work.

Description

• Add evolution_plan.md that documents the baseline architecture, pain points, north-star outcomes, a three-phase roadmap, and six atomic task specs (EVO-001..EVO-006) addressing integrity, API parity, verification efficiency, refactor boundaries, and CI harmonization.
• Specify concrete fixes including requiring payload_sha256 for materialized pages, aligning vector decompress policy with envelope/server preferences, exposing protected_vector_indices in the resident plan API, and eliminating duplicate reads during verification.
• Provide acceptance criteria and validation commands for each task and recommend phased refactors to replace private ContextCodec calls with public helpers.
• Recommend adding an aggregate CI target (e.g., make ci-check) and point to pytest -q/make test as the repository validation commands.

Testing

• No automated tests were executed as part of this change; this PR only adds the planning/documentation artifact.
• The plan recommends running pytest -q and make test when implementing the task specs and adding the related unit and API tests.

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Codex Task