fix(kotlin-sdk): unmanaged-identity reads return absence + typed SigningKeyUnavailable (split from #4183)

[bfoss765]

Splits the two conflict-free, review-approved slices out of #4183 so they aren't blocked on the
Keystore rework, as suggested by @shumkov in review.

What's included

Unmanaged-identity local reads return absence, not an exception. The FFI's blanket
Option → result conversion reports an identity the wallet does not manage as
PlatformWalletFFIResultCode::NotFound (98), so the Kotlin callers' zero-handle checks were dead and
any local read over an unmanaged identity (e.g. Dashpay.syncState on a contact's identity) threw
instead of returning null/empty.

• Dashpay routes getManagedIdentity through a translateManagedIdentityNotFoundToZero helper:
  contacts() / syncState() / payments() / sendContactRequest() treat "not managed" as
  null / empty / false. ErrorInvalidHandle still propagates — a stale wallet handle never
  masquerades as an unmanaged identity.
• Sweep of the remaining dead == 0L sites flagged in review:
  ManagedPlatformWallet.inMemoryIdentityStates() (one unmanaged id no longer throws through the
  whole listing) and IdentityRegistration.contestedDpnsNames() (the intended "identity is not
  managed by this wallet" error now actually surfaces).
• platform-wallet-ffi: platform_wallet_get_managed_identity keeps the three lookup outcomes
  distinct (handle absent / wallet removed from the manager map → ErrorInvalidHandle; valid wallet
  not managing the id → NotFound), with unit tests pinning both error arms.

Typed SigningKeyUnavailable. The KeystoreSigner "missing key" completion error travels as
free text through Rust and came back as an opaque Generic/WalletOperation failure. It is now
built from a shared MESSAGE_MARKER constant and recognized at the Kotlin boundary as
DashSdkError.PlatformWallet.SigningKeyUnavailable, so hosts can route users to key repair. The
marker is only consulted on the catch-all codes, so dedicated retry-semantics types are never
overridden.

Known limitation, kept deliberately: the discriminator is still message-text-based
(message.contains); moving to a structured code across the FFI boundary is follow-up work in the
parent PR line.

What's NOT included (stays in #4183)

• The Keystore rework: KeySecurityPolicy (AUTH_GATED/DEVICE_BOUND), the keys-alias split and
  legacy-blob migration matrix, decrypt-probing, pending-identity-key state, and their tests.
• The host-visible retarget of native code 98 to a typed PlatformWallet.NotFound (this PR keeps the
  existing 98 → DashSdkError.NotFound mapping, only naming the code via
  PLATFORM_WALLET_NOT_FOUND_CODE).

Testing

• :sdk:compileDebugKotlin and :sdk:testDebugUnitTest (new: ManagedIdentityNotFoundTranslationTest,
  two SigningKeyUnavailable mapping tests; existing 98-mapping tests unchanged and passing).
• cargo test -p platform-wallet-ffi dashpay unit tests, including the two new outcome-classification
  tests.

🤖 Generated with Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 2b3e3fc and ce3a17d.

📒 Files selected for processing (8)

• packages/kotlin-sdk/sdk/src/main/kotlin/org/dashfoundation/dashsdk/errors/DashSdkError.kt
• packages/kotlin-sdk/sdk/src/main/kotlin/org/dashfoundation/dashsdk/identity/IdentityRegistration.kt
• packages/kotlin-sdk/sdk/src/main/kotlin/org/dashfoundation/dashsdk/security/KeystoreSigner.kt
• packages/kotlin-sdk/sdk/src/main/kotlin/org/dashfoundation/dashsdk/tokens/Dashpay.kt
• packages/kotlin-sdk/sdk/src/main/kotlin/org/dashfoundation/dashsdk/wallet/ManagedPlatformWallet.kt
• packages/kotlin-sdk/sdk/src/test/kotlin/org/dashfoundation/dashsdk/errors/DashSdkErrorTest.kt
• packages/kotlin-sdk/sdk/src/test/kotlin/org/dashfoundation/dashsdk/tokens/ManagedIdentityNotFoundTranslationTest.kt
• packages/rs-platform-wallet-ffi/src/dashpay.rs

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• Create PR with unit tests

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[thepastaclaw]

🔍 Review in progress — actively reviewing now (commit ce3a17d)
Stage: Sonnet review + final verification
ETA: complete ~05:05 UTC (median 21m across 30 recent reviews)
Running 25m · Last checked: 2026-07-23 05:00 UTC

[shumkov]

Reviewed the split (two independent passes): exactly the two conflict-free slices, semantically unchanged from the earlier review, with all five getManagedIdentity call paths routed through the translation helper — including the two previously-missed sites (ManagedPlatformWallet.kt:556, IdentityRegistration.kt:100) — and the host-breaking 98-remap correctly left in #4183 with an explicit "not included" note. Stale handles now surface as InvalidHandle instead of masquerading as not-managed, unit-tested at both the FFI path and the classification seam. One note: the changed-packages CI gate skipped the new platform-wallet-ffi unit tests — they've only run locally until a Rust job picks them up. Ready from our side.