fix(dash-spv): preserve buffered block headers across disconnect

[xdustinface]

BlockHeadersManager::clear_in_flight_state rebuilt the entire HeadersPipeline on every disconnect, throwing away each segment's current_tip_hash, current_height, buffered_headers, and complete flags.

This PR splits it so that SegmentState::clear_in_flight and HeadersPipeline::clear_in_flight now reset only the DownloadCoordinator per segment. BlockHeadersManager::clear_in_flight_state calls the pipeline-level helper instead of constructing a new pipeline. start_sync skips pipeline.init when the pipeline is already initialized and calls reset_tip_segment so a previously synced tip is prepared to let send_pending re-fire GetHeaders.

Adds unit coverage for the new clear path at the segment, pipeline, and manager levels (mid-sync and post-sync disconnect/reconnect cycles), plus a header-progress monotonicity assertion in run_disconnect_loop so the dashd integration tests catch a future regression that drops validated chain state on disconnect.

Summary by CodeRabbit

• Tests

  • Added peer disconnect/reconnect tests verifying chain state preservation and sync resumption.

• Refactor

  • Improved disconnect/reconnect flow to preserve validated segment state across network interruptions, enabling faster resumption.
  • Enhanced test helpers with header height monotonicity assertions to detect chain state regressions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 25382f3f-3309-465b-a23a-90b5051615af

📥 Commits

Reviewing files that changed from the base of the PR and between 55cf3c7 and 6ae8662.

📒 Files selected for processing (5)

• dash-spv/src/sync/block_headers/manager.rs
• dash-spv/src/sync/block_headers/pipeline.rs
• dash-spv/src/sync/block_headers/segment_state.rs
• dash-spv/src/sync/block_headers/sync_manager.rs
• dash-spv/tests/dashd_sync/helpers.rs

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📝 Walkthrough

Walkthrough

This PR refactors the block header synchronization pipeline to preserve segment state and per-segment progress during peer disconnection/reconnection. It introduces a clear_in_flight method to reset only per-peer download tracking while maintaining chain validation progress, adds async tests for reconnection scenarios, and enhances integration tests with monotonicity assertions.

Changes

Cohort / File(s)	Summary
Pipeline state preservation dash-spv/src/sync/block_headers/pipeline.rs, dash-spv/src/sync/block_headers/segment_state.rs, dash-spv/src/sync/block_headers/sync_manager.rs	Removes checkpoint manager getter from HeadersPipeline; introduces clear_in_flight() method to reset per-peer download tracking (coordinator state) while preserving segment buffers and validated tip state; refactors start_sync to conditionally initialize pipeline and reset tip segment on resume instead of recreating pipeline from scratch.
Header sync tests dash-spv/src/sync/block_headers/manager.rs	Adds two async tests: one simulating initial sync with pipeline disconnect/reconnect and header advancement, verifying locator hash preservation; another verifying resumed GetHeaders after reconnect with higher peer height targets the previously-synced tip.
Integration test enhancements dash-spv/tests/dashd_sync/helpers.rs	Introduces helper to compute SPV headers manager effective height from progress watch channel; enhances run_disconnect_loop to snapshot and re-check header height across disconnect cycles, asserting monotonicity to detect regressions.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰 Through disconnects and reconnects we hop,
State preserved, our progress won't drop,
In-flight cleared but chains stay true,
Headers synced, made fresh and new! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix(dash-spv): preserve buffered block headers across disconnect' directly and precisely describes the main change—that buffered block headers are now preserved when peers disconnect, rather than being lost by pipeline reconstruction.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/preserve-buffered-headers-on-disconnect

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[codecov]

Codecov Report

❌ Patch coverage is 97.31544% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.64%. Comparing base (55cf3c7) to head (6ae8662).

Files with missing lines	Patch %	Lines
dash-spv/src/sync/block_headers/manager.rs	94.36%	4 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           v0.42-dev     #702      +/-   ##
=============================================
+ Coverage      70.58%   70.64%   +0.06%     
=============================================
  Files            320      320              
  Lines          68028    68172     +144     
=============================================
+ Hits           48018    48162     +144     
  Misses         20010    20010              

Flag	Coverage Δ
core	75.81% <ø> (ø)
ffi	43.53% <ø> (ø)
rpc	20.00% <ø> (ø)
spv	87.38% <97.31%> (+0.12%)	⬆️
wallet	69.49% <ø> (ø)

Files with missing lines	Coverage Δ
dash-spv/src/sync/block_headers/pipeline.rs	94.21% <100.00%> (+0.88%)	⬆️
dash-spv/src/sync/block_headers/segment_state.rs	97.36% <100.00%> (+0.36%)	⬆️
dash-spv/src/sync/block_headers/sync_manager.rs	84.61% <100.00%> (-0.39%)	⬇️
dash-spv/src/sync/block_headers/manager.rs	90.03% <94.36%> (+0.41%)	⬆️

... and 4 files with indirect coverage changes