release: v0.20.0 — Rust implementation

[Fail-Safe]

Summary

• replace Noema's Go implementation with the qualified Rust 2024 CLI and MCP server
• preserve the established command, storage, federation, recovery, TUI, and plugin contracts
• move build, CI, release packaging, and Homebrew metadata generation to the Rust toolchain
• retain the completed Go-to-Rust evaluation and benchmark evidence in docs/why-rust.md

Release impact

This is the production cutover to the Rust implementation. Existing cortexes remain compatible, standard durability preserves the established write behavior, and strong durability is available as an explicit opt-in profile.

The release workflow is configured to build and smoke-test native archives for macOS, Linux, and Windows on x64 and arm64, publish checksums and plugin bundles, and update the stable Homebrew channel after the release tag is created.

Validation

• make test
  • formatting and strict Clippy checks
  • 132 Rust unit tests
  • 20 process-death, recovery, and restore integration tests
• make release-check (noema v0.20.0, Rust)
• Hermes plugin: 101 tests
• Obsidian plugin: regression test, production build, TypeScript check, and generated-bundle verification
• release metadata generator: 2 tests
• repository script tests
• git diff --check
• push and pull-request CI passed on the exact candidate commit

Live qualification

• existing cortex opened and served without migration or data loss
• Obsidian connection, authentication, trace creation, external editing, hybrid search, append, and bidirectional lineage passed
• MCP session recovery passed after a supervised daemon restart
• sustained Obsidian use returned the watcher to near-idle CPU without renewed write amplification

After this PR merges, a v0.20.0 tag on the resulting main commit will trigger the release workflow.