refactor(agent): reuse NOW execution for PSU gRPC

[Marc-André Moreau (mamoreau-devolutions)]

Reuses the existing Devolutions Session NOW_EXEC process backend for PSU gRPC remote execution on Windows while keeping the gRPC protocol unchanged. This aligns process launch, stdin/stdout handling, cancellation, and cleanup with the Agent's existing NOW behavior instead of maintaining a separate Windows execution path.

Keeps the non-Windows fallback on tokio process execution and hardens duplicate process/stream validation and failure cleanup around the gRPC adapter.

Issue: N/A

[Marc-André Moreau (mamoreau-devolutions)]

Implementation notes:

• Windows PSU gRPC StartProcess now adapts into the existing NOW/DVC WinApiProcessBuilder path from devolutions-session, using raw data encoding because the current gRPC protocol has no NOW encoding flags.
• StopProcess maps kill_process=true to NOW abort and kill_process=false to NOW cancel; stdin StreamData is forwarded through the DVC process input channel.
• The gRPC protocol still has no stdout/stderr stream kind, so stdout remains StreamData and stderr is surfaced as diagnostics instead of being silently dropped.
• Added duplicate process and stream ID handling before spawning process work, plus explicit working-directory validation and registry cleanup on spawn failure.
• Added opt-in kill-on-drop support to the shared WinApiProcess wrapper and enabled it only for the gRPC adapter so dropped gRPC process tasks do not orphan child processes; existing NOW/DVC sessions keep the previous default.
• Validation: cargo +nightly fmt --all; cargo check -p devolutions-agent -p devolutions-session --features devolutions-session/dvc; cargo test -p devolutions-agent psu_grpc_agent -- --nocapture; cargo clippy --workspace --tests -- -D warnings; cargo test --workspace --exclude devolutions-agent-updater -- --test-threads=1. Full cargo test --workspace requires elevation for the updater test binary in this environment.

[Copilot]

Pull request overview

This PR refactors the Devolutions Agent's PSU gRPC remote-execution feature so that, on Windows, process launch, stdin/stdout handling, cancellation, and cleanup are delegated to the Agent's existing NOW_EXEC (WinApiProcessBuilder) backend instead of a separate tokio::process path. The gRPC protocol is unchanged. The non-Windows fallback keeps using tokio::process::Command, and duplicate process/stream validation plus failure cleanup around the gRPC adapter are hardened. This aligns the two agent execution surfaces (DVC NOW sessions and PSU gRPC) on a single Windows implementation.

Changes:

• Added a Windows-only run_process_inner_windows that drives the NOW backend (IO redirection, raw encoding, kill-on-drop) and maps NOW ServerChannelEvents to PSU protocol messages.
• Extended WinApiProcessBuilder/WinApiProcess with opt-in with_kill_on_drop/disable_kill_on_drop, and added process_id to ServerChannelEvent::SessionStarted.
• Hardened PSU gRPC handling: reject empty/duplicate correlation & stream IDs, stricter working-directory validation, raw stdout chunking, and pass-through stdin (no injected newlines).

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
devolutions-agent/src/psu_grpc_agent/process.rs	Adds the Windows NOW-backed execution path, duplicate-registry rejection, and raw stdout/stdin handling; adds tests.
devolutions-agent/src/psu_grpc_agent/mod.rs	Validates StartProcess IDs and handles duplicate process/stream registration with failure responses.
devolutions-session/src/dvc/process.rs	Adds process_id to SessionStarted and opt-in kill-on-drop for WinApiProcess.
devolutions-session/src/dvc/task.rs	Updates the SessionStarted consumer to ignore the new field.
devolutions-agent/Cargo.toml, Cargo.lock, src/main.rs	Wire in devolutions-session (dvc) and now-proto-pdu as Windows-only dependencies.

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