bindings/node: add Client.joinGroupByExternalInvite NAPI binding

[tylerhawkes]

Summary

NAPI binding for Client::join_group_by_external_invite (PR-L11).

• New file bindings/node/src/client/external_invite.rs.
• Buffer in (invite payload bytes + encrypted blob bytes), returns the new conversation handle plus the refreshed encrypted blob bytes the application should upload to its service slot.

Stack

• Base: tyler/qr-invite-l11-join-by-invite (xmtp_mls: Client::join_group_by_external_invite (atomic external-commit join) #3674).
• Pair: PR-B1 (createExternalInvite binding, bindings/node: add Conversation.createExternalInvite NAPI binding #3675).

Test plan

• cargo check -p bindings_node passes.
• End-to-end smoke test wired up via PR-T1's NAPI smoke (follow-on).

Note

Add Client.joinGroupByExternalInvite NAPI binding to Node bindings

Adds an async join_group_by_external_invite method to the Node.js Client binding in external_invite.rs. The method accepts invite_payload and encrypted_group_info as Uint8Array, delegates to the inner client, and returns a new JoinGroupByExternalInviteOutput object exposing the joined Conversation and a refreshed_encrypted_group_info Uint8Array.

^{Macroscope summarized b5b3b51.}

[claude]

Claude finished @tylerhawkes's task —— View job

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PR Review

Todo List

• Read changed files
• Review code for quality, bugs, performance, security, and test coverage
• Post review feedback

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Code Review — 2026-05-27 18:34 UTC

The binding implementation is clean and follows established patterns in the codebase. I have one minor observation:

Observation

Getter method clones unnecessarily (bindings/node/src/client/external_invite.rs:25-27)

The conversation() getter clones the Conversation struct. While this works correctly, it's worth noting that:

• Conversation wraps a RustMlsGroup (which is MlsGroup<MlsContext>), and contains Arc-wrapped internals
• The clone is relatively cheap due to Arc reference counting, but creates a new wrapper struct
• This pattern is consistent with other NAPI bindings in this codebase (e.g., other methods return cloned Conversation objects)

No change needed — this follows the existing NAPI patterns and performs acceptably.

Summary

✅ Code quality: Clean, idiomatic NAPI binding
✅ Error handling: Properly uses ErrorWrapper::from
✅ Type conversions: Correct use of Uint8Array ↔ Vec<u8> via .as_ref() and .into()
✅ Documentation: Well-documented with clear explanation of the refresh workflow
✅ Security: No concerns; delegates to underlying Rust implementation
✅ Performance: Appropriate for binding layer
⚠️ Test coverage: As noted in PR description, end-to-end testing is follow-on work (tracked separately)

The implementation correctly wraps the Rust functionality and maintains the expected contract for external invite joining.

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[macroscopeapp]

Approvability

Verdict: Approved

This PR adds a Node.js NAPI binding that wraps an existing Rust method without introducing new business logic. The changes are a standard binding layer with type marshaling, and the author owns all modified files.

No code changes detected at b5b3b51. Prior analysis still applies.

^{You can customize Macroscope's approvability policy. Learn more.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (tyler/qr-invite-l11-join-by-invite@a6ec61d). Learn more about missing BASE report.

Additional details and impacted files

@@                          Coverage Diff                          @@
##             tyler/qr-invite-l11-join-by-invite    #3676   +/-   ##
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