Agent Window issue pill discards the recorded issue title

[chryw]

Type of Issue

Bug

Description

When an Agent Host session records a GitHub issue through add_artifact_or_reference, the Agent Window's Issues pill displays only the issue number and raw URL. The recorded artifact already includes a required user-facing label, but that label is discarded when the artifact is promoted into the dedicated Issues pill.

This makes multiple-issue dropdowns difficult to scan and leaves the single-issue hover with no useful context beyond the URL.

Reproduction

1. Open a fresh Agent Window session in the microsoft/vscode workspace.

2. Send this prompt:

   Record microsoft/vscode#335354 as the GitHub issue this session will work on.
   
   Call add_artifact_or_reference exactly once with:
   - type: issue
   - label: Predictable UI composition: spacing ownership and icon sizing
   - isArtifact: true
   - link: https://github.com/microsoft/vscode/issues/335354
   
   Do not modify any files or perform additional investigation. After recording it, reply only with: Issue recorded.
   

3. Open or hover the resulting Issues pill.

Actual Behavior

The pill displays #335354, and its hover/dropdown exposes only https://github.com/microsoft/vscode/issues/335354 or Issue #335354.

Expected Behavior

The recorded title should be displayed immediately, for example:

Issue #335354: Predictable UI composition: spacing ownership and icon sizing

If live GitHub issue data is available, its canonical title can supersede the recorded label. The desired fallback order is:

1. Live GitHub title
2. Recorded artifact label
3. Issue #<number>

Technical Notes

• add_artifact_or_reference requires label and describes it as the short label shown to the user.
• Persisted ISessionArtifact retains that label.
• partitionSessionArtifacts retains labels for promoted pull requests in pullRequestTitles, but promoted issues are reduced to issueUrls.
• IGitHubPullRequestRef has an optional title; IGitHubIssueRef does not.
• The Agents Window attempts a best-effort live GitHub lookup, but its unresolved/failure fallback has no access to the recorded title.
• The editor/panel Agent Host pill path also reduces promoted issue artifacts to URLs and regenerates Issue #<number> labels.

Related implementation history: #331724, #332495, #332982.