fix(sync): run the sync command's remote scan on the list pool, through the shared walker

[axpnet]

Summary

Correction to #758, found by the test station within the hour. #758 said sync, check and cryptcheck scan on the provider's list pool. Measured from outside on the same 5000-file SFTP tree: the fourth binary opened 5 SSH sessions for check (and check halved, 11.37 s to 5.78 s) but still 1 for sync, whose legs did not move. Read on main: the function #758 routed onto the pool is called by reconcile, check and cryptcheck; the sync command walks the remote tree with an inline loop of its own in the CLI, and the library sync core (sync_tree_core, execute_sync_dag) and the MCP tools call the shared walker's serial branch. The test of #758 proved the function fans out, not that the command reaches it.

Change, class not instance. The shared scan_remote_tree_checked is now the pooled walker for every caller: it parks the caller's provider behind the crate's fail-closed placeholder (DetachedProvider, until now private to the crypt overlay), resolves the provider's list pool with the new ScanOptions::checkers (None = 8), scans through scan_remote_tree_with_provider_lock_checked, and hands the provider back. The serial branch is deleted, so there is no walker left that bypasses the pool. The CLI sync loop is replaced by the same pooled call with the same filters (depth, entry cap, excludes, the bisync snapshot file, symlinked directories listed but never walked) and its cancel flag threaded through. --checkers reaches every command; the changelog and the guide are corrected.

Tests

• transfer_dag_sync::tests::sync_tree_core_scans_the_remote_tree_on_the_list_pool: the command's own code path (sync_tree_core, dry run) against a provider that only finishes when 8 sub-directory listings are in flight together.
• sync_core::scan::tests::the_shared_walker_lists_checkers_directories_at_once_and_returns_the_provider: the shared walker directly, and the caller gets its own provider back, not the placeholder.
• With the pool forced to one lease both fail after the rendezvous times out: "listed at most 1 directories at once, 8 requested" (seen, then restored).
• The existing perf(cli): run the remote scan of sync, check and cryptcheck on the provider's list pool #758 tests (symlinked directory never walked, CLI wrapper fan-out) still pass.

Verified: cargo fmt --all -- --check, cargo clippy --all-targets -- -D warnings (rc 0), the four tests above.

Numbers to expect

The test station re-runs the session probe (expected 5 SSH sessions for sync, up from 1) and the three sync legs on labsftp against its repeated baseline: the scan-bound legs (sync-noop 13.5 s, sync-delta 15.8 s against rclone's 3.7 s and 5.4 s) should move; sync-first should not.

Summary by CodeRabbit

• New Features

  • Remote scans for sync, reconcile, check, and cryptcheck now honor the global --checkers setting.
  • sync supports cancellation consistently during remote scanning.
  • Shared remote scanning behavior now applies across synchronization tools and integrations.

• Performance

  • Remote directory listings can run concurrently, improving scan and synchronization performance for providers that support parallel requests.

• Documentation

  • Updated the CLI guide and changelog to clarify --checkers support and concurrency behavior.

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• src-tauri/src/transfer_dag_sync.rs

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• src-tauri/src/transfer_dag_sync.rs

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📝 Walkthrough

Walkthrough

The shared remote-tree walker now uses the provider list pool for sync paths. ScanOptions supports configurable checker concurrency. CLI sync uses the shared walker, preserves cancellation, and retains scan filters. Tests verify concurrent listings, provider restoration, and pooled dry-run sync.

Changes

Pooled remote scanning

Layer / File(s)	Summary
Shared scan orchestration src-tauri/src/sync_core/scan.rs, src-tauri/src/crypt_overlay_provider.rs	ScanOptions adds checker concurrency. scan_remote_tree_checked resolves the list session, parks the caller's provider behind DetachedProvider, runs the pooled scan, and restores the provider.
CLI sync integration src-tauri/src/bin/aeroftp_cli.rs	CLI sync now uses the shared scanner instead of its inline walker. The helper accepts cancellation, checker settings, and existing scan filters.
Coverage and documentation src-tauri/src/sync_core/scan.rs, src-tauri/src/transfer_dag_sync.rs, docs/CLI-GUIDE.md, CHANGELOG.md	Tests verify eight concurrent listings, provider restoration, and pooled dry-run sync. Documentation and changelog entries describe checker usage for reconcile and sync.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: 🔵 Low · up to df794

Sync now scans remote trees through the pooled provider walker. The remaining risk is limited to the concurrency test potentially timing out rather than validating pooled behavior under an incorrect stub capability setting.

Sequence Diagram(s)

sequenceDiagram
  participant SyncCommand
  participant SharedScanner
  participant ListPool
  participant RemoteProvider
  SyncCommand->>SharedScanner: start remote scan with checkers and cancellation
  SharedScanner->>ListPool: resolve provider list session
  ListPool->>RemoteProvider: list directories concurrently
  RemoteProvider-->>SharedScanner: return directory entries
  SharedScanner-->>SyncCommand: return scan result and provider

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.59% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 34 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: routing the sync command's remote scan through the shared list pool.
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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Actionable comments posted: 2

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Inline comments:
In `@src-tauri/src/sync_core/scan.rs`:
- Around line 1433-1447: Update PoolTreeProvider’s transfer_capabilities to
advertise list_parallel as Capability::Supported and set max_checker_slots to
the pool capacity used by the provider. Preserve the existing pool executor
behavior so the resolver selects the parallel list pool with the configured
capacity instead of LockedSingle.

In `@src-tauri/src/transfer_dag_sync.rs`:
- Around line 2506-2508: Update the assertion around the sync operation to
validate the inner sync_tree_core result, not only timeout completion. Match the
nested Ok(Ok(_)) outcome or assert the contained result separately while
preserving the existing directory-count diagnostic.

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📥 Commits

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📒 Files selected for processing (6)

• CHANGELOG.md
• docs/CLI-GUIDE.md
• src-tauri/src/bin/aeroftp_cli.rs
• src-tauri/src/crypt_overlay_provider.rs
• src-tauri/src/sync_core/scan.rs
• src-tauri/src/transfer_dag_sync.rs

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