feat: partial fill support for large market orders against limited pool depth

[abayomicornelius]

Summary

When a large market order would exceed the pool's available OI capacity (due to max_open_interest cap), the entire order currently reverts. A partial fill model would allow the order to execute up to the OI cap and queue the remainder.

Proposed Design

Add allow_partial_fill: bool to CreateOrderParams.

When true:

• Execute up to min(requested_size, remaining_oi_capacity)
• Store the unfilled remainder as a new pending order with the same params
• Emit OrderPartiallyFilled { nonce, filled_size, remaining_size }

When false (default): current behaviour (revert if full size not fillable).

Acceptance Criteria

• allow_partial_fill = true executes partial fill when OI cap is hit
• Remainder is stored as a new order with a new nonce
• User is refunded collateral proportional to the unfilled portion immediately
• Integration test: order for 10 ETH, OI cap allows only 6 ETH — 6 filled, 4 refunded or queued
• Integration test: allow_partial_fill = false still reverts when OI cap reached

Affected Contracts

order_handler, exchange_router

[Hassanmovic98]

I'll add partial fills for large market orders. When allow_partial_fill is true and the order hits the OI cap, it executes what fits, queues the remainder as a pending order with a new nonce, and refunds collateral for the unfilled portion.

Emit OrderPartiallyFilled with filled_size and remaining_size. Default behavior (false) still reverts on full OI exhaustion, so existing callers don't break.

Integration tests hit both paths: order for 10 ETH with 6 ETH OI capacity fills 6 and queues 4, or reverts if partial fills are disabled.

[Hassanmovic98]

I'll add partial fills to market orders. When allow_partial_fill is true and the OI cap is hit, the order executes up to the cap and queues the remainder with a new nonce.

Collateral gets refunded for the unfilled portion immediately. Emit OrderPartiallyFilled with the breakdown. Default behavior (false) still reverts, so existing orders don't break.

Integration tests verify both paths: order for 10 ETH with 6 ETH capacity fills 6 and queues 4, or reverts if partials are off.

[firstJOASH]

@firstJOASH has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

i can solve this issue
kindly assign me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @firstJOASH to this issue.

[tobiadewola41-eng]

@tobiadewola41-eng has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue because

ℹ️ Repo Maintainers: To accept this application, review their application or assign @tobiadewola41-eng to this issue.