v0.15.4: ARCH-1 step 4 — extract MountManager (final ARCH-1 step)

[NathanNeurotic]

Summary

Fourth and final ARCH-1 collaborator. No user-visible changes. Rebased onto main after v0.15.3 (#46) merged (supersedes #45, which was stacked on the pre-squash branch). Closes the audit's incremental ARCH-1 work.

• New `src/MountManager.cs` owns:
  • `BuildMountArgs(profile, fullCache, rcCommonFlags, effectiveBandwidth)` — pure helper assembling the full `rclone mount` argv (cache-mode / VFS / network-mode / RC / log / bandwidth). Unit-testable without disk.
  • `StartMountProcess(rclonePath, args, logJobWarn)` — `Process.Start` + v0.11.4 Job Object binding.
• `TrayContext.Mount.cs` delegates argv assembly + spawn; the UI-coupled dialog flow stays put.

ARCH-1 close-out

Step	Class	Owns
v0.15.1	`RcloneClient`	rclone invocation + `ProcessResult`
v0.15.2	`SettingsStore`	settings.json read/write/cache/backup
v0.15.3	`DependencyProbe`	rclone/WinFsp availability cache + probes
v0.15.4	`MountManager`	mount argv + Process.Start + Job Object

Test plan

• `scripts/run-tests.ps1` — 53/53 green (rebased on current main)
• Real-world: mount a profile; Job Object binding still kills rclone when Pixelpipe dies

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request refactors the rclone mount process lifecycle by extracting the argument assembly and process spawning logic from Pixelpipe.Mount.cs into a new MountManager class. Feedback is provided to handle potential issues in MountManager.cs, specifically by conditionally appending the --log-file argument to prevent startup failures when the log file path is empty, and adding a null check on the spawned process to avoid a potential NullReferenceException.

[gemini-code-assist]

If p.LogFile is null or empty, passing --log-file "" to rclone can cause it to fail to start on Windows due to an invalid path. It is safer to conditionally append the --log-file argument only when a valid log file path is provided.

                + (!String.IsNullOrEmpty(p.LogFile) ? " --log-file " + TrayContext.QuoteArg(p.LogFile) : "");

[gemini-code-assist]

Defensive programming: Process.Start can theoretically return null (e.g., if an existing process is reused, though less likely with UseShellExecute = false). To prevent a potential NullReferenceException in RcloneJob.TryAssign, we should add a null check for child before assigning it.

            Process child = Process.Start(psi);
            if (child != null)
            {
                RcloneJob.TryAssign(child, logJobWarn);
            }