fix(serde): accept JSON numbers as Decimal in CLOB/data/gamma responses

[moeuu]

Accept JSON numbers as Decimal across CLOB, data, and Gamma response types

Summary

Several Polymarket CLOB / data-api / Gamma responses return numeric fields as JSON
numbers (e.g. {"minimum_tick_size": 0.01}, {"avgPrice": 0.36},
{"lastTradePrice": 0.54}) rather than strings. The default
rust_decimal::Decimal deserializer in serde rejects these with errors like:

invalid type: floating point `0.01`, expected a Decimal type representing a fixed-point number

This blocks every consumer of these structs at deserialization time. In particular,
Client::tick_size is called transitively by the order-builder
(limit_order().build() / market_order().build()), so any attempt to place a
live order currently fails before the order is signed, and sync_markets-style
workflows that iterate the Gamma catalog fail on the first sports / prediction
market with numeric bestBid / bestAsk / etc.

Reproduction

Against production endpoints (as of the date of this PR):

let client = ClobClient::new("https://clob.polymarket.com", ClobConfig::default())?;
client.tick_size(U256::from_str_radix("49104850...145930", 10)?).await?;
// Err: invalid type: floating point `0.01`, expected a Decimal type representing a fixed-point number

let data = data::Client::new("https://data-api.polymarket.com")?;
data.positions(&PositionsRequest::builder().user(addr).build()).await?;
// Err: invalid type: floating point `0.36`, expected a Decimal type representing a fixed-point number

let gamma = gamma::Client::new("https://gamma-api.polymarket.com")?;
gamma.markets(&MarketsRequest::builder().limit(500).build()).await?;
// Err: invalid type: floating point `0.54`, expected a Decimal type representing a fixed-point number

Live JSON samples observed:

GET /tick-size            → {"minimum_tick_size":0.01}
GET /positions            → [{"proxyWallet":"0x...","avgPrice":0.36,"size":19.79,...}]
GET /markets              → [{"lastTradePrice":0.54,"bestBid":0.037,"bestAsk":0.04,...}]

Change

Introduce a reusable serde_with::DeserializeAs / SerializeAs adapter
serde_helpers::DecimalFromAny that accepts strings, integers, or floats, and
apply it to every affected field across CLOB, data, and Gamma response types.

src/serde_helpers.rs

New DecimalFromAny adapter. Visits:

• visit_str / visit_string → Decimal::from_str
• visit_i64 / visit_u64 → Decimal::from
• visit_f64 → Decimal::from_str(&v.to_string()) (round-trips
  through the shortest-round-trip f64 → string conversion to avoid the binary
  float precision trap, e.g. 0.1 → 0.1000000000000000055...)

On the serialize side it delegates to the existing Decimal: Serialize impl so
output format is unchanged when these types are re-serialized in tests or mock
helpers.

Gated on the same feature set as the existing StringFromAny helper
(bridge | clob | data | gamma).

src/clob/types/mod.rs

TickSize::Deserialize now delegates to DecimalFromAny and then passes the
Decimal through the existing TryFrom<Decimal> for TickSize conversion. The
validation that the value must be one of {0.1, 0.01, 0.001, 0.0001} is
preserved.

src/data/types/response.rs

• Position — #[serde_as(as = "DecimalFromAny")] on all ten Decimal
  fields (size, avg_price, initial_value, current_value, cash_pnl,
  percent_pnl, total_bought, realized_pnl, percent_realized_pnl,
  cur_price).
• ClosedPosition — adds #[serde_as] on the struct (was missing) and
  DecimalFromAny on its four Decimal fields.
• Trade — DecimalFromAny on size and price.

src/gamma/types/response.rs

Market, Event, and related structs: #[serde_as(as = "Option<DecimalFromAny>")]
applied to every Option<Decimal> field (56 fields across the module). Structs
that didn't previously carry the #[serde_as] proc-macro marker get it added.

Covered fields include price / book fields (best_bid, best_ask,
last_trade_price, spread), volume fields (volume, volume_num,
volume_24hr, volume_1wk, volume_1mo, volume_1yr, and their _amm/_clob
variants), liquidity fields (liquidity, liquidity_num, liquidity_amm,
liquidity_clob), price-change fields (one_day_price_change,
one_hour_price_change, one_week_price_change, one_month_price_change,
one_year_price_change), and misc numeric fields (fee, rewards_min_size,
rewards_max_spread, competitive, line, uma_reward,
order_price_min_tick_size, order_min_size, spreads_main_line,
totals_main_line).

The outcome_prices: Option<Vec<Decimal>> field is left unchanged because it
uses #[serde_as(as = "Option<JsonString>")] and is wrapped in a stringified
JSON array whose inner Decimals are already strings in live responses.

Scope / non-goals

• Request types and order serialization (SignedOrder, Order) are untouched;
  these are still serialized as strings when sent to the API as required.
• The change is backwards compatible with responses that return Decimals as
  strings; DecimalFromAny handles both.
• No behavior change for any consumer that previously deserialized successfully.
• No dependency additions: the patch reuses the crate's existing
  rust_decimal, serde, and serde_with dependencies.

Tests

The existing httpmock-based tests continue to pass. I can add regression
coverage in a follow-up that feeds raw JSON-number responses through an
httpmock server, modeled on tests/clob.rs::tick_size_* and
tests/data.rs::positions_*.

Context

Surfaced from a downstream consumer wiring Polymarket into a live trading
runtime. The bug currently blocks end-to-end order placement and any
sync_markets-style metadata pull. A minimal local reproduction walks through
ClobClient::tick_size → /tick-size → 200 {"minimum_tick_size":0.01} and fails
in TickSize::deserialize inside Decimal::deserialize.

---

Note

Medium Risk
Touches many response structs and changes how numerous Decimal fields deserialize, so regressions could surface if any endpoints relied on strict string-only parsing or if float-to-string round-tripping behaves unexpectedly.

Overview
Fixes deserialization failures when Polymarket APIs return Decimal-typed fields as JSON numbers instead of strings.

Introduces a reusable serde_helpers::DecimalFromAny adapter (with tests) that accepts string/int/float JSON values, and applies it to CLOB TickSize plus affected Decimal fields across Data API (Position/ClosedPosition/Trade) and Gamma response types (many Option<Decimal> market/event metrics like liquidity, volume, prices, and spreads).

^{Reviewed by Cursor Bugbot for commit 350a69a. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

❌ Patch coverage is 89.41176% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.60%. Comparing base (77264a4) to head (350a69a).

Files with missing lines	Patch %	Lines
src/serde_helpers.rs	90.24%	8 Missing ⚠️
src/clob/types/mod.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #328      +/-   ##
==========================================
+ Coverage   85.54%   85.60%   +0.05%     
==========================================
  Files          32       32              
  Lines        5167     5251      +84     
==========================================
+ Hits         4420     4495      +75     
- Misses        747      756       +9     

Flag	Coverage Δ
rust	85.60% <89.41%> (+0.05%)	⬆️

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