feat(broker): stream live output and status from remote agent operations

[Vladyslav Nikonov (vnikonov-devolutions)]

Brokered (remote agent) package operations now show live process output while they run. When an operation is routed through the Devolutions Agent broker, UniGetUI opens the broker's new per-operation event channel and streams the remote process's stdout/stderr straight into the operation output pane, line by line, exactly like a locally executed operation — including progress lines.

What this changes for users:

• Live output: brokered installs/updates/uninstalls display the package manager's output as it happens, instead of showing no output at all.
• Instant status updates: status changes (Starting → Running → Completed/Failed/Canceled) are picked up as soon as the broker signals them, rather than waiting for the next poll.
• Restored result parsing: since output is captured again, package managers can parse it to produce accurate operation results (e.g. detecting specific failure conditions in the output text).
• Graceful fallback: if the broker does not advertise an event channel, or the channel cannot be opened or breaks mid-stream, the operation transparently falls back to the previous status-polling behavior — the operation itself is never failed because live streaming was unavailable.
• Cancellation: canceling a streamed operation still requests a broker-side cancel; the tail of the process output is preserved while the cancellation is confirmed.

Stacked on #5253 (Devolutions.Now.Policy 2026.8.5 bump + remote cancellation); only the last commit belongs to this PR.

Issue: DGW-438

[Vladyslav Nikonov (vnikonov-devolutions)]

Implementation notes

Event-channel consumption (src/UniGetUI.PackageEngine.Operations/PackageOperations.cs):

• After Execute, if ExecutionResponse.Operation.EventChannel is present, the channel is opened with BrokerClient.OpenEventChannel and consumed via OperationEventChannel.ReadEvents (Devolutions.Now.Policy 2026.8.5 — already referenced by feat(broker): support cancelling remote agent operations #5253, so no package bump was needed).
• Frame handling: Stdout/Stderr → incremental Line(...) calls (stderr as LineType.Error); StatusUpdated → QueryStatus (status transitions logged once); StdoutOverflow/StderrOverflow → warning line with the number of skipped bytes; Finish → immediate final QueryStatus (no poll delay) feeding the existing terminal-status interpretation.
• Line buffering mirrors the local process reader (AbstractProcessOperation): frame payloads may split lines arbitrarily, so a per-stream buffer reassembles them; LF-terminated text is emitted as a regular line, CR-terminated text (progress bars) as LineType.ProgressIndicator, promoted to a regular line on a following bare LF.

Fallback matrix — streaming problems never fail the operation:

Condition	Behavior
EventChannel is null (broker without support)	status polling, info log
OpenEventChannel throws (connect failure/timeout)	warning + status polling
Fatal mid-stream error (EventFrameException, IOException — corrupt frames, unsupported Hello major, truncated stream)	flush buffered output, warning + status polling

Cancel while streaming: the cancel request path from #5253 is reused (RequestBrokerCancel, bounded by the request timeout); afterwards the channel is drained under the confirm timeout so the output tail and the Finish frame are honored, then the terminal status is confirmed over the status endpoint (poll-based confirm as fallback if the drain fails). The remote-process-wins race (Completed/Failed before cancel takes effect) is honored as before.

Output-based veredicts restored: InterpretBrokerTerminalStatus now feeds accumulated Error/Information lines to GetProcessVeredict — the same filter the local process path applies — so manager result parsers see the streamed output text again.

Tests (src/UniGetUI.PackageEngine.Tests/PackageOperationsTests.cs):

• EventChannelPipeServer: a real NamedPipeServerStream writing hand-encoded NOW_BROKER frames (u32 body_size LE | u16 kind LE | body), mirroring the approach of the library's own OperationEventChannelTests.
• ScriptedBrokerTransport extended with EventChannelPipeName (advertises a LocalPipe channel in the execution response) and OnCancelRequested (test synchronization).
• 5 new tests: streamed stdout/stderr reaches both the operation output and the manager result parser (incl. cross-frame partial-line reassembly, overflow warning, and exactly one status query after FINISH); STATUS_UPDATED triggers a status query; missing event channel falls back to polling; unsupported Hello major version (fatal decode error) falls back to polling and the operation still succeeds; cancel during streaming sends the broker cancel, preserves the post-cancel output tail, and yields Canceled.

Validation: full dotnet test UniGetUI.Windows.slnx /p:Platform=x64 suite green (all projects; PackageOperationsTests 29/29 on both net10.0 and net10.0-windows). NativeAOT/trim-safe: no reflection or reflection-based JSON on production paths (tests use the library's source-generated BrokerJson).

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds support for consuming the broker’s per-operation event channel to stream live stdout/stderr and status hints during brokered operations, with robust fallback to status polling.

Changes:

• Implement event-channel streaming in brokered operations (stdout/stderr + status hints), with fallback to polling on failure.
• Refactor broker cancel flow to separate “request cancel” vs “confirm terminal status”, and drain the event stream during cancellation when possible.
• Add end-to-end tests using a named-pipe event-channel server and scripted broker transport.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/UniGetUI.PackageEngine.Operations/PackageOperations.cs	Adds event-channel streaming, streaming output buffering, and updated cancel/status logic.
src/UniGetUI.PackageEngine.Tests/PackageOperationsTests.cs	Adds tests + test pipe server to validate streaming, fallback, and cancellation behaviors.

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