[Emmazlee]

Overview

This PR makes market-core decimals-aware: collateral decimals() is read once at construction, the economic bounds (min_seed, max_sets) are derived from those decimals, and the fixed-point multiply-divide helpers move to 256-bit intermediates so correctness no longer depends on the 1e30 headroom argument. The Python and TypeScript mirrors are kept in lockstep so off-chain quoting matches on-chain behavior.

Related Issue

Changes

🔢 Decimals-aware bounds

• [MODIFY] contracts/market-core/src/math.rs
  • Added Bounds { min_seed, max_sets } and bounds_for_decimals(d) deriving min_seed = 100 * 10^d and max_sets = 1e8 * 10^d via checked_pow, with d in 0..=18.
  • Kept math::MAX_SETS as a #[deprecated] 7-decimal alias for tests only.
  • Updated the module header conventions to describe decimals handling instead of the 1e30 headroom argument.

🧮 256-bit widening arithmetic (Env-free)

• [MODIFY] contracts/market-core/src/math.rs
  • Added an Env-free wide module with U256 { hi, lo }, mul_u128, and divrem_u256_by_u128 (returns Overflow when the quotient exceeds u128::MAX).
  • Rewrote mul_div_floor / mul_div_ceil to use 256-bit intermediates, preserving existing rounding directions; signatures unchanged so no caller changes.
  • math.rs still has no soroban_sdk imports and its tests run natively.

🐍 Python mirror

• [MODIFY] model/fpmm_model.py
  • Added bounds_for_decimals and an explicit _fits_i128 assertion in mul_div_* so the model fails where the contract would.
  • Added 18-decimal fixtures matching the Rust outputs.

🟦 TypeScript mirror

• [MODIFY] agents/core/fpmm.ts
  • Added boundsForDecimals(d) and I128_MAX checks in mulDivFloor / mulDivCeil.
  • Added 18-decimal fixtures matching the Rust outputs.

📚 Docs

• [MODIFY] docs/architecture.md — updated the market size bound description to reflect decimals-derived max_sets.
• [MODIFY] docs/STATUS.md — updated references that assumed 7 decimals.

Verification Results

cargo test -p market-core && cargo test --workspace
make lint
python3 model/fpmm_model.py
cd agents && npm test && npm run build

Acceptance Criteria	Status
DataKey::Decimals set in __constructor, Error::UnsupportedDecimals added, Config.decimals returned by get_config	✅
MIN_SEED / MAX_SETS no longer used by contract logic; bounds come from bounds_for_decimals	✅
mul_div_floor / mul_div_ceil use 256-bit intermediates with bit-identical results on the legacy domain	✅
math.rs has no soroban_sdk imports and its tests run natively	✅
settle_value uses checked addition; redeem / claim_pool_remainder propagate errors	✅
Python and TS mirrors include 18-decimal fixtures matching Rust outputs	✅
CPU instruction delta for buy reported	✅ (see cost_buy_7dp_vs_18dp)
Vendored wasm copies and bindings packages regenerated and committed	✅
cargo test --workspace, make lint, python3 model/fpmm_model.py, agents npm test / npm run build pass	✅
math.rs header, docs/architecture.md and docs/STATUS.md updated to describe decimals handling	✅

Closes #3