Startup sweep for orphaned temp session directories

[Copilot]

Temp directories created by CreateSessionAsync when workingDirectory is null were never cleaned up if the app crashed or was force-killed, accumulating indefinitely under polypilot-sessions/ in the system temp folder.

Changes

• CreateSessionAsync: When workingDirectory is null, creates an isolated temp dir under TempSessionsBase ($TMPDIR/polypilot-sessions/<uuid>) instead of falling back to ProjectDir. Logs and falls back to ProjectDir if creation fails.
• CloseSessionAsync: Deletes the temp dir after session disposal if it's a direct child of TempSessionsBase.
• Startup sweep (RestorePreviousSessionsAsync): Calls new SweepOrphanedTempSessionDirs on startup, deleting any dirs under TempSessionsBase whose path doesn't appear in any WorkingDirectory in active-sessions.json.
• Test isolation: TempSessionsBase is a redirectable static property reset by SetBaseDirForTesting so tests never touch the real $TMPDIR/polypilot-sessions/.

// On startup, after loading persisted entries:
SweepOrphanedTempSessionDirs(TempSessionsBase, entries?.Select(e => e.WorkingDirectory) ?? []);

// Deletes dirs not referenced by any persisted session:
internal static void SweepOrphanedTempSessionDirs(string tempBase, IEnumerable<string?> persistedWorkingDirs)
{
    if (!Directory.Exists(tempBase)) return;
    var keepDirs = new HashSet<string>(
        persistedWorkingDirs.Where(d => !string.IsNullOrEmpty(d)).Select(d => d!),
        StringComparer.OrdinalIgnoreCase);
    foreach (var dir in Directory.GetDirectories(tempBase))
        if (!keepDirs.Contains(dir))
            try { Directory.Delete(dir, true); } catch { }
}

Warning

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• e7bvsblobprodcus348.vsblob.vsassets.io
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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Startup sweep for orphaned temp session directories</issue_title>
<issue_description>## Problem

When \CreateSessionAsync\ is called with \workingDirectory: null, it creates a temp directory under \polypilot-sessions/\ in the system temp folder. Cleanup only happens in \CloseSessionAsync. If the app crashes, is force-quit, or the process is killed (e.g. during
elaunch.ps1), these directories accumulate indefinitely.

Proposed Fix

On app startup (during \CopilotService.InitAsync\ or similar), scan for \polypilot-sessions/\ directories that don't correspond to any active or persisted session, and delete them.

Something like:
\\csharp
var tempBase = Path.Combine(Path.GetTempPath(), "polypilot-sessions");
if (Directory.Exists(tempBase))
{
foreach (var dir in Directory.GetDirectories(tempBase))
{
var dirName = Path.GetFileName(dir);
if (!_sessions.ContainsKey(dirName) && !persistedSessionIds.Contains(dirName))
try { Directory.Delete(dir, true); } catch { }
}
}
\\

Impact

Low risk — temp dirs are small (empty or near-empty). But over time with frequent relaunches during development, they accumulate.

Found during multi-model review of PR #205.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Startup sweep for orphaned temp session directories #217

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