feat(vault): adds atomic swap feature flag

[jonybur]

#1240

Greptile Summary

This PR adds a new opt-in feature flag isAtomicSwapPeginEnabled to the vault's feature flag registry, gating the atomic swap pegin deposit flow behind NEXT_PUBLIC_FF_ATOMIC_SWAP_PEGIN=true. The change is minimal, well-documented inline, and consistent with the existing opt-in flag pattern established by isSimplifiedTermsEnabled.

Key observations:

• The implementation is correct — the flag safely defaults to false, so the existing deposit flow is unaffected until the env var is explicitly enabled.
• README.md is not updated: all other feature flags are documented in the ### Feature Flags section of services/vault/README.md, but NEXT_PUBLIC_FF_ATOMIC_SWAP_PEGIN is missing from it. Consider adding an entry describing its purpose and how to enable it.
• The module-level comment ("Default value for all feature flags is true") is outdated — both this flag and isSimplifiedTermsEnabled are opt-in (default false). Updating the comment to reflect both patterns would improve maintainability.

Confidence Score: 5/5

• This PR is safe to merge — the change is isolated to a single getter that defaults to false, so no existing functionality is affected.
• The change is a one-line getter addition following a well-established pattern in the codebase, with no side-effects and a safe default value. The only gaps are a missing README entry and a stale module comment, neither of which are blocking.
• No files require special attention beyond the minor documentation gaps noted above.

Important Files Changed

Filename	Overview
services/vault/src/config/featureFlags.ts	Adds a new opt-in feature flag isAtomicSwapPeginEnabled (env var NEXT_PUBLIC_FF_ATOMIC_SWAP_PEGIN) defaulting to false; follows the same pattern as isSimplifiedTermsEnabled. Minor inconsistency with the module-level comment claiming all flags default to true.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Page renders deposit flow] --> B{isAtomicSwapPeginEnabled?}
    B -->|NEXT_PUBLIC_FF_ATOMIC_SWAP_PEGIN === 'true'| C[Render Atomic Swap Pegin deposit flow]
    B -->|env var unset or !== 'true'| D[Render existing deposit flow]

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_{Last reviewed commit: 05dcf2d}

Greptile also left 1 inline comment on this PR.

[github-actions]

🔐 Commit Signature Verification

✅ All 1 commit(s) passed verification

Commit	Author	Signature	Key Type	Key Check
05dcf2dfc16e	Jonathan Bursztyn	✅	sk-ssh-ed25519	✅

Summary

• Commits verified: 1
• Signature check: ✅ All passed
• Key type enforcement: ✅ All sk-ssh-ed25519

---

Required key type: sk-ssh-ed25519 (FIDO2 hardware key)

Last verified: 2026-03-16 17:10 UTC

[greptile-apps]

Module-level documentation inconsistency

The file header comment on line 11 states: "Default value for all feature flags is true (feature is enabled)", but this flag (like isSimplifiedTermsEnabled before it) defaults to false. The module-level comment is no longer accurate for opt-in flags. Consider updating the header to reflect that there are two patterns — opt-out flags (default true, disable by setting to "false") and opt-in flags (default false, enable by setting to "true").

[jrwbabylonlab]

@jonybur u need to put this flag in the right place as part of this PR tho.