feat(engine): add reylo-engine, the engine crate a rust host links - #100

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ℹ️ No critical issues. One small cleanup is suggested inline.

Reviewed changes

This review covers the new reylo-engine facade crate and the move of the oracle's three answerers into it.

• reylo-engine crate: there is one feature per database engine, and each client feature (tokio-postgres, rusqlite, mysql_async) turns on its engine. The crate re-exports core's replay loop and analysis types, and adds HostError.
• Clients: each client module has an Answers and an analyze(client, sql, cache). The bodies match the oracle code they replace; the error type changed from String to HostError. The one behavior change: the rusqlite client now binds catalog-query parameters, where the oracle bound []. That's harmless. The SQLite engine only sends empty parameter lists (engine/sqlite/src/sqlite.rs:147-148), and binding them matches src/sqlite-describe.ts.
• Oracle: it now answers through the facade's clients, so the oracle run tests them. The MySQL interpolation test moves with the code.
• CI and docs: -p reylo-engine is added to the engine job's cargo test and to AGENTS.md, and engine/README.md describes the crate. The facade's own test only compiles with its client features on. It gets them through feature unification with -p reylo-oracle in the same command, which the README explains.

  ^{｜ Fix all ➔ ｜ Fix 👍s ➔ ｜ View workflow run ｜ Using claude-opus-5-5 ｜ 𝕏}

✅ No new issues found.

Reviewed changes

This review covers the one commit since the last Pullfrog review, which handles that review's only finding.

• Removed the oracle's direct engine dependencies: oracle/Cargo.toml no longer lists reylo-engine-postgres, reylo-engine-sqlite or reylo-engine-mysql. They now come in only through reylo-engine's client features. reylo-engine-core stays because the oracle uses analysis::CONSTANT_KEY and schema_type::admits. Nothing in oracle/src names the removed crates any more, and Cargo.lock was updated to match.

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ℹ️ No critical issues. The rebase dropped one small docs edit, described below.

Reviewed changes

This push rebased the branch onto main (f1394c1), whose test.yml now picks checks by path. A range-diff shows bf38e2a is identical to the previously reviewed 247952f. 20a95bd differs from d243607 only where it adapts to the new workflow:

• Added reylo-engine to the run-everything test list: everything() now passes -p reylo-engine to cargo test.
• Made engine/facade/ run every check: the path filter's grep now includes facade, and its comment names the crate the oracle answers through. A pull request that changes only one database still builds the facade through cargo build --workspace --all-targets.
• Updated the guide's CI description: the engine bullet in AGENTS.md lists -p reylo-engine and engine/facade/.

ℹ️ The rebase dropped the guide's Setup → Rust edits

Before the rebase, the PR also changed the Setup → Rust section of AGENTS.md. Those edits are gone now. The workspace paragraph no longer lists engine/facade, and the local cargo test command no longer has -p reylo-engine. Someone following the guide's setup therefore never runs the facade's tests. The guide also disagrees with engine/README.md, CI's everything() list, and the guide's own engine bullet.

# Restore the AGENTS.md Setup → Rust edits lost in the rebase

## Affected sites
- AGENTS.md:76 — the workspace paragraph no longer lists `engine/facade` (`reylo-engine`, the crate a Rust host links: each database's engine behind a feature, and the answers to its needs over `tokio-postgres`, `rusqlite` or `mysql_async`)
- AGENTS.md:80 — `cargo test -p reylo-engine-core -p reylo-engine-postgres -p reylo-engine-sqlite -p reylo-engine-mysql -p reylo-oracle` lacks `-p reylo-engine`

## Required outcome
- Both lines match what d243607 had: line 76 names `engine/facade`, and line 80's command includes `-p reylo-engine` before `-p reylo-oracle`, the same as `engine/README.md:20` and the `everything()` list in `.github/workflows/test.yml:53`

  ^{｜ Fix it ➔ ｜ View workflow run ｜ Using claude-opus-5-5 ｜ 𝕏}

✅ No new issues found.

Reviewed changes

This review covers the one commit since the last Pullfrog review. It addresses that review's only finding.

• Restored the guide's Setup → Rust edits: the workspace paragraph in AGENTS.md names engine/facade (reylo-engine) again, and the local cargo test command has -p reylo-engine again, just before -p reylo-oracle. The guide now agrees with engine/README.md, the everything() list in test.yml, and its own engine bullet.

  ^{｜ View workflow run ｜ Using claude-opus-5-5 ｜ 𝕏}