feat: serve the underlying stock price on PriceFrame and Quote (v0.7.0, RAI-2197)

[hardyjosh]

What

Adds the underlying (stock) directional price to PriceFrame and Quote, alongside the existing vault-token rates and nav_ratio:

• underlying_rate_base_to_quote: WireFloat
• underlying_rate_quote_to_base: WireFloat

These are the directional rates for the vault's underlying ERC4626 asset (the offchain stock) — the same rates the model computes before scaling the mark by the vault NAV ratio. Same directionality and spread policy as rate_base_to_quote / rate_quote_to_base; the only difference is the NAV scaling.

Why (RAI-2197 / RAI-1479)

Root of the NAV-ratio "derive, don't gate" pivot. The exact-match NAV gate was found to be a DoS surface (audit H03). Serving the underlying lets on-chain consumers derive the vault price atomically (vault_price = underlying × convertToAssets(1 share)) instead of asserting a signed ratio. As Josh put it: serve both and let consumers derive if they like.

Compatibility

• Additive and wire-backward-compatible. Both fields carry #[serde(default)], so frames from producers that predate them decode to the all-zero WireFloat. A real stock rate is never all-zero, so that value reads as "not carried".
• Existing vault rates and nav_ratio are untouched.
• Non-vault base (nav_ratio zero): underlying_rate_* == rate_* (no separate underlying).

Version bump + re-pin

Wire-contract version bumped v0.6.0 → v0.7.0. Following the repo's post-merge tag convention, the merge commit gets tagged v0.7.0 and consumers re-pin their tag = "v0.6.0" to tag = "v0.7.0". The companion st0x.pricing PR pins this branch rev meanwhile and carries a Cargo.toml comment noting the re-pin step.

Tests

• Exact wire round-trip of both new fields (distinct byte patterns per field).
• Backward-compat decode: strip the keys from an encoded frame → both default to zero, rest of the frame intact.
• Wire-size ceiling updated for the two added byte-strings.

Local gate: cargo test, cargo clippy --all-targets -D warnings, cargo fmt --check, and the full pre-commit run --all-files in rainix#rust-shell (incl. denofmt markdown) all pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01TQ3QV1QrwmaS7ACSf7cds7

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[linear-code]

RAI-2197

[ueco-jb]

nit: unrelated to the wire change, and this ignore silently blocks committing a shared config here later. Possibly worth dropping.

[ueco-jb]

One optional nit comment posted, otherwise LGTM 👍