fix(swapper): buffer BobGateway EVM gas limit and raise default slippage

[kaladinlight]

Description

Two small, focused fixes for the BOB Gateway swapper:

1. Buffer the EVM broadcast gas limit by 20% — getUnsignedEvmTransaction now pads the gas limit of the tx we actually sign/broadcast by 1.2×. This reduces the risk of out-of-gas reverts on the final tx, since the quote-time gas estimate can under-estimate actual execution.

   • The buffer is applied only to the broadcast gas limit (a ceiling). The displayed network fee (getEvmTransactionFees) is intentionally left unbuffered so quote fee comparisons stay honest, and unused gas is refunded — so the fee actually paid by the user is unaffected.
   • Consistent with the existing ~20% gas-limit buffer pattern used elsewhere (e.g. 0x/ZRX swapper).

2. Raise BOB Gateway default slippage to 3% (0.005 → 0.03) — aligns with the higher default already used for other bridge-style swappers where off-chain quote estimates can drift.

Issue (if applicable)

closes #

Risk

Low-to-moderate. Touches the on-chain EVM transaction for BOB Gateway sells (gas limit only — no change to to/value/data), plus a default slippage tolerance bump.

What protocols, transaction types, wallets or contract interactions might be affected by this PR?

BOB Gateway swapper only (EVM → BOB / EVM sells, and EVM→BTC offramp). Gas-limit padding affects every BOB Gateway EVM broadcast tx; slippage change affects BOB Gateway quotes.

Testing

Engineering

• Initiate a BOB Gateway EVM sell and inspect the unsigned tx — confirm gasLimit is ~1.2× the raw estimate, while the network fee shown in the trade input is unchanged (uses the unbuffered estimate).
• Confirm a BOB Gateway quote now defaults to 3% slippage tolerance.

Operations

• 🏁 My feature is behind a flag and doesn't require operations testing (yet)

Screenshots (if applicable)

N/A

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Increased default slippage tolerance for BobGateway swapper to improve transaction stability.
  • Enhanced gas limit calculation for BobGateway EVM transactions with additional padding for improved reliability.

[coderabbitai]

📝 Walkthrough

Walkthrough

Two numeric parameter adjustments for the BobGateway swapper: the default slippage decimal percentage is raised from '0.005' to '0.03', and getUnsignedEvmTransaction now computes a padded gas limit (feeData.gasLimit × 1.2) via bnOrZero and passes it explicitly to adapter.buildCustomApiTx.

Changes

BobGateway Parameter Adjustments

Layer / File(s)	Summary
Default slippage constant packages/swapper/src/constants.ts	BobGateway's entry in getDefaultSlippageDecimalPercentageForSwapper is updated from '0.005' to '0.03'.
Gas limit 1.2× padding packages/swapper/src/swappers/BobGatewaySwapper/endpoints.ts	bnOrZero is imported and getUnsignedEvmTransaction multiplies feeData.gasLimit by 1.2, forwarding the result as an explicit gasLimit to adapter.buildCustomApiTx.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

Poem

🐇 A slippage so small made the bunny fret,
So we bumped it up — no regrets yet!
The gas was too tight, transactions would fail,
We padded by 1.2 — now swaps shall prevail!
Hop on, BobGateway, smooth is the trail! 🌿

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes both main changes: buffering the BobGateway EVM gas limit by 20% and raising the default slippage tolerance, which are the primary modifications in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/bob-gateway-evm-gas-buffer-slippage

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/swapper/src/swappers/BobGatewaySwapper/endpoints.ts`:
- Around line 100-102: The gasLimit calculation in the file uses toFixed(0)
which performs standard rounding and can round down, potentially undermining the
intended 20% padding buffer. Replace the toFixed(0) rounding with an explicit
ceiling operation (using a method like Math.ceil or equivalent BigNumber ceiling
method) to ensure the padded gas limit is always rounded up and never falls
below the computed 1.2x multiplier result.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 98331311-0229-4a19-9cf3-34de14837464

📥 Commits

Reviewing files that changed from the base of the PR and between 3ff114f and 7628c01.

📒 Files selected for processing (2)

• packages/swapper/src/constants.ts
• packages/swapper/src/swappers/BobGatewaySwapper/endpoints.ts