Replace gRPC download call in proxy with local download_task using task manager

[Copilot]

The proxy downloaded tasks through the dfdaemon download gRPC client over a unix socket (dfdaemon_download_client.download_task in proxy/mod.rs), adding unnecessary gRPC transport overhead to every proxied download. This implements the same download_task logic locally in the proxy using resource::task::Task functions directly, removing the gRPC hop.

Local download_task in proxy/mod.rs

Mirrors the gRPC download_task handler in grpc/dfdaemon_download.rs, but calls the task manager directly:

• Generates task/host/peer IDs via task.id_generator (content, blob-digest-based, and URL-based TaskIDParameter).
• Calls task.download_started, resolves the range from the request header via get_range, then spawns task.download writing into a local mpsc channel (DOWNLOAD_STREAM_BUFFER_SIZE), returning the receiver as the response stream.
• Preserves the success path (download_finished, output-path hard-link/copy checks, digest verification), failure path (download_failed, backend error details), and all download task metrics.
• Drops gRPC-only concerns: tonic Request/Response wrappers, OpenTelemetry context extraction, and blocklist checks.

Local prefetch_task

Mirrors grpc::prefetch_task but invokes the local download_task instead of creating a gRPC client. download_task returns a boxed future to break the recursive future type between download_task and prefetch_task.

proxy_via_dfdaemon rework

// Before: gRPC stream over unix socket
let response = dfdaemon_download_client.download_task(request).await?;
let mut out_stream = response.into_inner();

// After: local mpsc stream from the task manager
let mut out_stream = download_task(config.clone(), task.clone(), request).await?;

• Consumes mpsc::Receiver<Result<DownloadTaskResponse, Status>> instead of a tonic stream.
• Handles ClientError::BackendError directly (status code + headers) instead of decoding tonic Status details JSON.
• Removes ResourceExhausted/PermissionDenied mappings that only originated from gRPC server middleware.

Cleanup

Removed DfdaemonDownloadClient construction from Proxy::run and its parameter from all proxy handlers (handler, http_handler, https_handler, upgraded_tunnel, upgraded_handler, registry mirror handlers).

[codecov]

Codecov Report

❌ Patch coverage is 0% with 155 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.85%. Comparing base (72f989f) to head (0ea9c8b).

Files with missing lines	Patch %	Lines
dragonfly-client/src/proxy/task.rs	0.00%	136 Missing ⚠️
dragonfly-client/src/proxy/mod.rs	0.00%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1915      +/-   ##
==========================================
- Coverage   46.11%   45.85%   -0.27%     
==========================================
  Files          93       94       +1     
  Lines       23526    23662     +136     
==========================================
  Hits        10850    10850              
- Misses      12676    12812     +136     

Files with missing lines	Coverage Δ
dragonfly-client/src/proxy/mod.rs	0.00% <0.00%> (ø)
dragonfly-client/src/proxy/task.rs	0.00% <0.00%> (ø)

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