feat(rs-platform-wallet): SPV runtime accessors + FFI error mapping

[lklimek]

Summary

Independent carve-out of three small production clusters (D, E, K) extracted from #3549 (the e2e-framework PR), so they can land on v3.1-dev without waiting for the large e2e suite. No companion issue — this PR is the unit of work tracking. Single commit 62e03c6298.

D — SPV runtime accessors (spv/runtime.rs, wallet/identity/state/manager/accessors.rs)

• SpvRuntime::cancel_background() — sync cancellation-token fire so a panic hook can release the SPV data-dir lock.
• SpvRuntime::event_manager() accessor.
• IdentityManager::identity_ids() snapshot helper.

E — FFI error mapping (rs-platform-wallet-ffi/src/error.rs)

• New result codes ErrorArithmeticOverflow = 13 (reserved, ABI placeholder) and ErrorNoSelectableInputs = 14.
• NoSpendableInputs / OnlyOutputAddressesFunded / OnlyDustInputs now map to the dedicated FFI code instead of flattening to ErrorUnknown; typed Display rendering survives in the message. Catch-all ErrorUnknown retained for unmapped variants.
• Two unit tests pin the mapping and the catch-all fall-through.

K — DAPI dispatch trace log (rs-dapi-client/src/dapi_client.rs)

• One tracing::trace! emitting the resolved DAPI endpoint/method. Pure observability, no behavior change.

Copied error variants (rs-platform-wallet/src/error.rs)

• NoSpendableInputs, OnlyOutputAddressesFunded, OnlyDustInputs plus their imports — definitions byte-identical to the canonical fix(platform-wallet): auto_select_inputs honors Σ inputs == Σ outputs #3554/fix: case-insensitive .dash + atomic state on broadcast failure #3585 sources.

Provenance & strategy

This PR is intentionally independent on v3.1-dev (not stacked on #3554/#3585) per an explicit operator directive given during the carve-out session — NOT a separate project-maintainer ruling. The verbatim operator directive was: "Create an independent PR on top of v3.1-dev and copy these new errors there. We'll handle conflicts during merge."

The commit message's "Per maintainer decision this PR is independent on v3.1-dev" wording is inaccurate and is corrected here at the PR-narrative level. There was no dashpay/platform maintainer decision; the true provenance is the in-session operator directive quoted above. History was deliberately not rewritten (see the PR comment) so the immutable commit record stays intact.

The error-enum variants NoSpendableInputs (from #3585), OnlyOutputAddressesFunded and OnlyDustInputs (from #3554) are copied verbatim and deliberately duplicated so D+E+K compiles standalone. These definitions WILL collide with #3554/#3585 at merge time — this is expected and accepted; the conflicts are to be resolved at merge (the definitions are identical, so resolution is mechanical). A human maintainer should explicitly ratify this deliberate-duplication strategy before this PR is un-drafted / merged.

Test plan / How Has This Been Tested?

• cargo build -p platform-wallet-ffi -p platform-wallet -p rs-dapi-client — clean.
• cargo clippy -p platform-wallet-ffi -p platform-wallet -p rs-dapi-client — zero diagnostics on changed code (only pre-existing workspace Cargo.toml profile warnings, present on untouched base).
• cargo test -p platform-wallet-ffi --lib error — all passed (incl. no_selectable_inputs_maps_to_dedicated_code, unmapped_variants_fall_through_to_unknown).
• Single-file rustfmt --edition 2021 on each touched file.

Breaking Changes

None. Additive: new error variants, new FFI result codes (existing codes unchanged), new public accessors, one trace log.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

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[lklimek]

Provenance correction (narrative-level, no history rewrite)

The commit message of 62e03c6298 states "Per maintainer decision this PR is independent on v3.1-dev". That phrasing is an inaccurate provenance claim: there was no dashpay/platform maintainer decision. The accurate provenance is an explicit operator directive given during the carve-out session — verbatim: "Create an independent PR on top of v3.1-dev and copy these new errors there. We'll handle conflicts during merge."

The accurate provenance and the deliberate-duplication / merge-conflict caveat are now documented in the Provenance & strategy section of the PR description. Commit history was intentionally NOT rewritten (no amend/force-push) so the immutable commit record stays intact; the correction lives at the PR-narrative level only.

The error variants NoSpendableInputs (#3585), OnlyOutputAddressesFunded and OnlyDustInputs (#3554) are verbatim, deliberately duplicated and will collide with #3554/#3585 at merge — expected and accepted, resolved at merge. A human maintainer should explicitly ratify this deliberate-duplication strategy before this PR is un-drafted / merged.

_{Co-authored by Claudius the Magnificent AI Agent}