[WAL-1345] feat(mdoc): add mobile BLE proximity transport

[szijpeter]

Summary

This adds the Kotlin Multiplatform BLE transport for ISO mdoc proximity presentation defined by WAL-1345.

The work is stacked directly on walt-id/waltid-identity#2155, which provides the radio-independent transport and holder-protocol contracts. Until #2155 merges, this PR targets its feature branch so the review delta contains only WAL-1345. After #2155 merges, replay the WAL-1345-only commits onto current main and retarget this PR.

Architecture contract: walt-id/waltid-architecture#60.

What Changed

Shared BLE transport

• Adds validated transaction UUID, central-client/peripheral-server/dual-role, and GATT-only/L2CAP-preferred models that prevent illegal role and bearer combinations.
• Implements BLEIdent HKDF-SHA-256 verification from the complete tagged EDeviceKeyBytes, normalizes supported public-key export encodings before COSE conversion, and provides ISO GATT chunking/reassembly, L2CAP length framing, message limits, truncation detection, and dynamic LE PSM validation.
• Provides deterministic role and bearer races, serialized sends, one receive consumer, bounded preparation setup and post-connection inactivity, normalized errors, structured cancellation, and idempotent cleanup; a prepared listener remains available for the session-owned engagement lifetime, and the selected connection is completed and closed exactly once.
• Moves opaque session messages only; engagement construction, session cryptography, requests, consent, trust, and wallet policy remain in the shared proximity engine and wallet layers.

Android and Apple adapters

• Implements Android scanning/advertising, both GATT roles, negotiated MTU handling, notification backpressure, and insecure LE L2CAP client/listener channels from API 30.
• Implements the equivalent CoreBluetooth central/peripheral GATT roles and L2CAP open/publish paths on iOS, including legacy and current disconnect callbacks and draining the final State characteristic write before teardown.
• Binds GATT-discovered L2CAP channels to the same peer while preserving the standard's direct-L2CAP path when the PSM is carried in Device Engagement.
• Reports permissions, Bluetooth state, and missing runtime capabilities through the shared capability contract without launching permission UI.
• Adds a role-aware, side-effect-free prerequisite probe that reuses the configured provider's native capability checks, allowing the Wallet SDK to report readiness before generating session material.

Building-block decision

• Adds an ADR with the authorized ISO DIS baseline, exact BlueFalcon, kmp-ble, Multipaz, and GOV.UK inputs, responsibility split, and qualification boundary.
• Selects walt-owned common protocol/lifecycle code over thin native Android and Apple adapters. No third-party BLE runtime, copied upstream source, or new native package dependency is added.

Architecture Notes

• ISO roles, UUID/Ident, framing, limits, races, timeouts, errors, and cleanup are shared; platform code is limited to Bluetooth APIs, callbacks, sockets, and streams.
• The shared proximity engine owns the advertised engagement lifetime; BLE bounds adapter setup and post-connection inactivity without imposing a shorter local listener expiry.
• Platform objects and dependency types never cross the public common contract. Consumers enter through the public provider factory; concrete platform providers remain internal.
• GATT remains mandatory. L2CAP is advertised and attempted only when the selected policy and platform permit it; malformed PSM data fails closed.
• A fresh retry belongs to the wallet/session layer and requires fresh engagement and ephemeral material.

Caveats and Follow-Ups

• Wallet SDK integration is in walt-id/waltid-identity#2159, with Compose Android, Compose iOS, and native SwiftUI journeys in walt-id/waltid-identity#2160.
• The DIS specifies a fixed four-byte L2CAP length but not its byte order. This implementation uses unsigned big-endian encoding, matching the inspected Multipaz behavior, and records external interoperability as the reconciliation gate.
• Cross-device GATT/L2CAP reliability, external-reader interoperability, and release qualification remain in WAL-1349.

Breaking

• None for existing consumers. This introduces a new mobile transport module and public provider factory for the unreleased Wallet SDK.

[linear-code]

WAL-1345

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: ac00caed-cbc5-455f-b894-ef74a8eae0c9

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

❌ The last analysis has failed.

See analysis details on SonarQube Cloud