feat(mwa-v2): rewrite adapter with full v2 session lifecycle

[Zurcusa]

⚠️ NOTE: This is PR 3 of 3 in the MWA v2 stack. Targets pr/4-wire-client-cache. Completes the MWA v2 migration and removes the v1 backward-compat shims from PR #4.

Status	Type	⚠️ Core Change	Issue
Ready	Feature	Yes	Closes #273, closes #189, partial for #250

Problem

The existing SolanaMobileWalletAdapter has multiple gaps reported in #273:

1. No built-in auth token cache — developers must build their own (MWA integration issues found on Solana Seeker with Seed Vault — Unity MWA Example App magicblock-labs/Solana.Unity-SDK#273 item 3)
2. Logout() only clears local state — no way to revoke MWA authorization (MWA integration issues found on Solana Seeker with Seed Vault — Unity MWA Example App magicblock-labs/Solana.Unity-SDK#273 item 2)
3. GetCapabilities not exposed (MWA integration issues found on Solana Seeker with Seed Vault — Unity MWA Example App magicblock-labs/Solana.Unity-SDK#273 item 4)
4. No Sign-In With Solana — users must authorize + sign separately (#189)
5. No silent reconnect — every app launch prompts the wallet picker
6. No concurrency protection — overlapping wallet calls cause race conditions

Solution

Complete rewrite of SolanaMobileWalletAdapter with:

Auth cache integration (magicblock-labs#272, magicblock-labs#273 item 3): Constructor-injected IAuthorizationCache with PlayerPrefsAuthorizationCache default. Schema-versioned records with chain-aware validation. Legacy key migration from both pre-v2 "pk"/"authToken" and PR#269 "solana_sdk.mwa.*" keys.

Session lifecycle (magicblock-labs#273 items 2, 4): Disconnect(), Reconnect() (4-state result), Deauthorize() (tri-state), GetCapabilities(), [Obsolete] Logout() with migration path.

Sign-In With Solana (#189): LoginWithSignIn(SignInPayload) — single wallet round-trip that authorizes + signs a SIWS message. Falls back to authorize-then-sign for wallets without native SIWS support.

Concurrency & reliability: SemaphoreSlim(1,1) gate prevents overlapping wallet calls. SignAndSendTransactions auto-populates MinContextSlot from latest blockhash. Error code mapping updated for v2 spec.

Silent-first login: _Login() checks cached auth token first, attempts silent authorize, falls back to fresh authorize only on cache miss or auth_token_rejected.

Shim removal: Removes [Obsolete] Authorize/Reauthorize from IAdapterOperations and MobileWalletAdapterClient. Removes [Obsolete] PublicKey/AccountLabel from AuthorizationResult.

Tests: 5 new EditMode test suites in Tests/EditMode/MwaAdapter/ covering deauthorize, sign-and-send, concurrency, disconnect, and reconnect flows.

Known Issue: Backpack sign_and_send_transactions

⚠️ sign_and_send_transactions fails with Backpack wallet. The transaction is successfully created, signed, and submitted on-chain — the issue is only in receiving the response back in the dApp. Backpack's WebSocket server crashes during the on-chain RPC submission phase (~23s into processing), corrupting the local association before the response can be delivered. The dApp's pending request hangs indefinitely. This is a Backpack-specific issue — Phantom and Solflare handle the same flow correctly, surviving 8–12 seconds of Android activity STOP without any WebSocket errors.

sign_transactions works with all wallets including Backpack (no RPC submission required). See docs/sign-and-send-investigation.md for full analysis.

Pre-existing LocalAssociationScenario Issues

These issues exist in the upstream LocalAssociationScenario.cs and are outside the scope of this PR's adapter rewrite:

1. Missing return in ExecuteNextAction (line 134-135): After CloseAssociation(response), execution falls through to _actions.Dequeue() on an empty queue, throwing InvalidOperationException.
2. Unbounded OnClose reconnect loop (line 46-50): Reconnects immediately with no delay, no retry limit, and no close-awareness. Creates a thread pool storm when the wallet server is gone.
3. Wrong timeout unit (line 33): TimeSpan.FromSeconds(clientTimeoutMs) where clientTimeoutMs=9000 creates a 2.5-hour timeout instead of 9 seconds. Should be FromMilliseconds.
4. Null-unsafe scenarioResult access (line 449 in adapter): scenarioResult.WasSuccessful throws NullReferenceException if the scenario returns null.

Pre-existing test limitations

5 tests that instantiate SolanaMobileWalletAdapter via reflection fail on non-Android platforms because the constructor throws "SolanaMobileWalletAdapter can only be used on Android". This is the same pre-existing limitation documented in upstream PR #276. These tests pass on Android devices.

Deploy Notes

Breaking changes (relative to PR #4):

• IAdapterOperations.Authorize() and Reauthorize() removed — use AuthorizeAsync()
• AuthorizationResult.PublicKey and AccountLabel removed — use AuthorizationHelpers.PrimaryAccountPublicKeyBytes() and PrimaryAccount().Label

New public API:

• SolanaMobileWalletAdapter.Disconnect()
• SolanaMobileWalletAdapter.Reconnect()
• SolanaMobileWalletAdapter.Deauthorize()
• SolanaMobileWalletAdapter.LoginWithSignIn(SignInPayload)
• SolanaMobileWalletAdapter.GetCapabilities()
• SolanaMobileWalletAdapter.SignAndSendTransactions(Transaction[], SendOptions)

Testing Matrix

Tested on Pixel 7 emulator and Solana Seeker (real device).

Wallets Tested

Wallet	Networks
Seed Vault (Solana Phone)	DevNet, MainNet
Phantom	DevNet, MainNet
Solflare	DevNet, MainNet
Backpack	MainNet
Jupiter	MainNet

Functionality Coverage

Feature	Emulator (Pixel 7)	Solana Seeker
Login	Passed	Passed
Disconnect	Passed	Passed
Reconnect	Passed	Passed
Deauthorize	Passed	Passed
Sign Transaction	Passed	Passed
Sign All Transactions	Passed	Passed
Sign Message	Passed	Passed
Sign and Send	⚠️ Backpack fails (see Known Issue)	⚠️ Backpack fails (see Known Issue)
Get Capabilities	Passed	Passed
Sign-In With Solana (SIWS)	Passed	Passed