repro: a hash discontinuity inside a non-verify load aborts the sync session

[dorianvp]

Claim (mid-load-reorg-aborts-sync)

process_scan_results in pepper-sync/src/sync.rs:1536-1585 treats a ScanError::ContinuityError(HashDiscontinuity { height, .. }) as a re-org only when height equals the start of the load's range and the load's priority is Verify. Every other hash discontinuity falls through to scan_results? at pepper-sync/src/sync.rs:1584, which returns the error from process_scan_results and therefore from the sync loop at pepper-sync/src/sync.rs:520-531, so the sync session aborts instead of marking the affected blocks Verify and re-scanning.

Secondary: on the re-org path, state::set_scan_priority is called with the load's block range (pepper-sync/src/sync.rs:1550-1554). That function panics when no wallet scan range has exactly that block range (pepper-sync/src/sync/state.rs:436-447). The loader splits a load by output budget (pepper-sync/src/scan/task.rs:504-531), and ScanTask::split truncates the load's scan_range (pepper-sync/src/scan/task.rs:822-838), so a Verify load can arrive as a sub-range of the wallet's scan range and the panic is reachable.

What the tests do

Both tests live in pepper-sync/src/sync.rs under mod test::load_continuity_failure and call process_scan_results directly on a MockWallet.

• discontinuity_inside_chain_tip_load_is_treated_as_reorg: the wallet holds 90..100 Scanned and 100..200 Scanning. The load 100..200 ChainTip reports HashDiscontinuity { height: 150 }. The test asserts Ok(()) and a Verify range covering the discontinuity.
• reorg_in_split_verify_load_does_not_panic: the wallet holds 100..110 Scanning (the verify range selected by the loader). The load 100..105 Verify reports HashDiscontinuity { height: 100 }. The test asserts the call does not panic and leaves a Verify range.

The commit also adds Send to the two closure type aliases in the test-only pepper-sync/src/mocks.rs so that MockWallet satisfies the W: Send bound of process_scan_results.

Observed output on dev

test sync::test::load_continuity_failure::discontinuity_inside_chain_tip_load_is_treated_as_reorg ... FAILED
  a discontinuity inside a chain tip load aborted the sync session: Err(ScanError(ContinuityError(HashDiscontinuity { height: BlockHeight(150), .. })))
test sync::test::load_continuity_failure::reorg_in_split_verify_load_does_not_panic ... FAILED
  panicked at pepper-sync/src/sync/state.rs:446:9: scan range with block range BlockHeight(100)..BlockHeight(105) not found!

Notes

This PR is a reproduction and not a fix. Both tests are expected to fail on dev.

The abort in the first case is recoverable on the next sync session, because update_scan_ranges places a fresh Verify range above the highest scanned height. The session itself still ends with an error.

The sync-bench A/B rule was not run because the commit adds tests only.

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