Feat 28 clawback

[JoeX17]

feat(core): add clawback and clawback_claimable_balance operation explainers

Closes #87

---

Summary

Implements first-class explainers for both clawback and clawback_claimable_balance operations. These are regulated-asset operations that users often encounter without context. Both explainers include a fixed contextual note explaining what clawback means so users understand why funds were recovered.

All 303 tests pass (142 lib + 146 bin + 15 doc-tests).

---

Changes

src/explain/operation/clawback.rs (new file)

Core deliverable for Issue #28:

• ClawbackExplanation struct with summary, issuer, from, asset_code, asset_issuer, amount
• ClawbackClaimableBalanceExplanation struct with summary, issuer, balance_id
• explain_clawback() — produces: "The asset issuer reclaimed 100 USDC from GHOLDER. Clawback is a feature of regulated assets that allows issuers to recover funds under specific conditions."
• explain_clawback_claimable_balance() — produces: "The asset issuer clawed back claimable balance 00000000...ef12. Clawback is a feature..."
• Balance IDs are shortened to XXXXXXXX...XXXX in summaries for readability; full ID preserved in the balance_id field
• Graceful "Unknown issuer" fallback when source_account is absent
• 15 unit tests covering both variants, context note presence, field preservation, fractional amounts, non-USDC assets, unknown issuer fallback, and ID truncation behaviour

src/models/operation.rs

• Added ClawbackOperation struct: id, source_account, from, asset_code, asset_issuer, amount
• Added ClawbackClaimableBalanceOperation struct: id, source_account, balance_id
• Added Clawback(ClawbackOperation) and ClawbackClaimableBalance(ClawbackClaimableBalanceOperation) variants to Operation enum
• Added id() match arms for both new variants
• Added "clawback" and "clawback_claimable_balance" arms to From<HorizonOperation>

src/services/horizon.rs

• Added balance_id: Option<String> to HorizonOperation so the clawback_claimable_balance mapping can read the balance ID off the Horizon response

src/explain/operation/mod.rs

• Added pub mod clawback;

---

Test Results

test result: ok. 142 passed; 0 failed; 0 ignored   (lib)
test result: ok. 146 passed; 0 failed; 0 ignored   (bin)
test result: ok.  15 passed; 0 failed; 0 ignored   (doc-tests)
─────────────────────────────────────────────────
Total: 303 passed, 0 failed

Clawback tests (15 new tests all passing)

explain::operation::clawback::tests::test_clawback_summary_contains_amount_and_asset           ok
explain::operation::clawback::tests::test_clawback_summary_contains_recipient                  ok
explain::operation::clawback::tests::test_clawback_summary_contains_context_note               ok
explain::operation::clawback::tests::test_clawback_summary_format                              ok
explain::operation::clawback::tests::test_clawback_fields_preserved                            ok
explain::operation::clawback::tests::test_clawback_unknown_issuer_fallback                     ok
explain::operation::clawback::tests::test_clawback_fractional_amount                           ok
explain::operation::clawback::tests::test_clawback_non_usdc_asset                              ok
explain::operation::clawback::tests::test_clawback_claimable_balance_summary_contains_context  ok
explain::operation::clawback::tests::test_clawback_claimable_balance_summary_starts_correctly  ok
explain::operation::clawback::tests::test_clawback_claimable_balance_id_shortened              ok
explain::operation::clawback::tests::test_clawback_claimable_balance_full_id_in_field          ok
explain::operation::clawback::tests::test_clawback_claimable_balance_issuer_field              ok
explain::operation::clawback::tests::test_clawback_claimable_balance_unknown_issuer_fallback   ok
explain::operation::clawback::tests::test_short_balance_id_not_truncated                       ok

---

Acceptance Criteria

Criterion	Status
Clawback operations include contextual note about regulated assets	✅
clawback_claimable_balance variant is handled	✅
Tests pass	✅