Deduplicate transfer managers into transfer_common and cap finished history

[iamnoksio]

Greptile Summary

This PR extracts duplicated transfer logic (progress tracking, speed/ETA computation, history capping) from the SFTP, SCP, and S3 managers into a new transfer_common module, and caps the finished-transfer history at 200 entries on both the Rust and TypeScript sides. It also upgrades S3 uploads to multipart and downloads to range-based fetching, makes SFTP directory-download stat walks asynchronous for faster UI appearance, and fixes the previously flagged DashMap re-entrancy deadlock and double record_finished call via an is_terminal() guard in set_job_status.

• transfer_common: new shared record_progress (with EMA speed smoothing, SPEED_WINDOW shortened to 500 ms), record_finished with cap + eviction, apply_concurrency, eta_secs, and accompanying unit tests including a deadlock watchdog.
• Rust managers: set_job_status now drops the DashMap shard guard before calling record_finished, and early-returns if the job is already terminal — resolving both the shard-lock reëntry deadlock and the duplicate history entry from queued-cancel racing the worker.
• TypeScript store: finished_order tracks terminal transfer IDs in insertion order; trimFinished evicts the oldest terminal entry when the 200-entry cap is exceeded; a deduplication guard prevents the same ID from occupying two slots.

Confidence Score: 4/5

Safe to merge; all previously flagged deadlock and double-push paths are correctly guarded. One untreated gap: retry() does not remove the transfer ID from finished_order, leaking phantom history slots on repeated retries.

The three transfer managers each have a retry() function that resets a failed/cancelled job to Queued without removing its ID from finished_order. Each subsequent failure re-appends the ID, so N retries produce N−1 stale phantom entries that consume history slots without ever being cleaned up. With enough retries per job the effective history cap silently shrinks. All other logic—deadlock avoidance, terminal-state idempotency, TypeScript deduplication, and the Rust eviction tests—looks correct.

Files Needing Attention: retry() in src-tauri/src/sftp/transfer_manager.rs, src-tauri/src/s3/transfer_manager.rs, and src-tauri/src/scp/transfer_manager.rs each need a finished_order cleanup step.

Important Files Changed

Filename	Overview
src-tauri/src/transfer_common.rs	New shared module extracting progress tracking, ETA, speed (now with EMA smoothing), and history-capping logic. All previously-flagged deadlock and double-push paths are guarded correctly. Tests cover eviction, stale IDs, non-terminal guard, and a deadlock watchdog.
src-tauri/src/sftp/transfer_manager.rs	Delegates progress and history to transfer_common; adds async stat-walk for dir downloads (starts at 0/0); upload now uses an aggregator channel for progress. retry() does not remove the ID from finished_order, leaving stale phantom entries per retry cycle.
src-tauri/src/s3/transfer_manager.rs	Upgrades upload to multipart (8 MB chunks) and download to range-based fetching; integrates transfer_common. retry() has the same stale finished_order entry gap as SFTP.
src-tauri/src/scp/transfer_manager.rs	Delegates to transfer_common; set_job_status now guards against duplicate terminal transitions with is_terminal(). retry() has the same stale finished_order entry gap.
src/stores/transfer-store.ts	Adds finished_order array and 200-entry history cap; deduplication guard prevents the same transfer from occupying two slots on repeated terminal events; removeTransfer and clearFinished correctly maintain the order array.
src/stores/transfer-store.test.ts	New test file covering duplicate terminal events, cap eviction, active-transfer protection, removeTransfer slot release, and clearFinished. Good coverage of the new finished_order invariants.
src-tauri/src/sftp/commands.rs	Refactors sftp_chmod_recursive target-push to separate if/else branches for dirs and files; semantically equivalent to the original but clarifies intent.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A([Job enqueued\nQueued]) --> B{cancel_token\ncancelled?}
    B -- yes, Queued --> C[set status = Cancelled\ndrop shard guard\nemit event]
    C --> RF1[record_finished\nfinished_order mutex\n→ push + evict]
    B -- no --> D[set status = InProgress\nworker runs]
    D --> E{Result}
    E -- Ok --> F[bytes_transferred = total\nset Completed]
    E -- TransferCancelled --> G[set Cancelled]
    E -- Err --> H[set Failed]
    F & G & H --> SJS[set_job_status\nacquire shard guard]
    SJS --> IT{is_terminal\nalready?}
    IT -- yes --> NOOP([return — no duplicate\nrecord_finished])
    IT -- no --> UPD[update status/error\ndrop shard guard\nemit event]
    UPD --> RF2[record_finished\nfinished_order mutex\n→ push + evict]
    RF2 --> DONE([Done])
    RF1 --> RETRY{retry\ncalled?}
    RETRY -- yes --> RST[reset to Queued\nNOT removed from\nfinished_order ⚠️]
    RST --> D
    RETRY -- no --> DONE

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_{Reviews (3): Last reviewed commit: "test(transfers): pin finished-history in..." | Re-trigger Greptile}

[iamnoksio]

Fixed #111