PDChat: let a conversation be un-archived (fixes #121)

[davidnmbond]

Closes #121. Jira: MS-25789 (un-archive slice).

UnarchiveAsync has existed since #108 and nothing called it. Archive was effectively one-way in the UI — and an archive with no way back is a delete wearing a different name, which is the one thing this feature promises never to do.

A contradiction I had to resolve

• ChatConversation.IsArchived (from PDChat: model a conversation as a first-class object #102): "Interacting with an archived conversation is expected to un-archive it."
• MS-25789: un-archive control "shown only when the current conversation is archived".

Mutually exclusive — if opening auto-un-archives, an open conversation is never archived and the control never appears.

MS-25789 wins, and not just for being newer: auto-un-archiving on open makes the archived filter self-defeating, since merely looking at an archived conversation drags it back into the default list. You could never browse your archive without destroying it. The IsArchived remark is corrected here, recording what it used to say and why, so nobody reintroduces it.

Decisions

• Hidden, not disabled, when not archived — MS-25789's own stated exception to its "disable with a reason" rule.
• Archiving closes the tab; un-archiving does not. The user has just said they want the conversation back; removing it from their screen would be perverse.

Verified in a browser — the whole journey

Step	Result
Default list (archived hidden)	3 conversations
Un-archive control shown initially	no
Tick Include archived	4 conversations
Open the archived one	opens as its own tab
Still archived after opening	yes
Un-archive control now shown	yes
Use it → control disappears	yes
Tab stays open	yes
Untick Include archived → conversation in the DEFAULT list	yes
Console errors	none

That last row is the one that matters: it proves the store changed, not just the component.

5 bUnit tests, red-checked by stubbing out the UnarchiveAsync call. 473 tests pass; Release build clean.

Not in scope

The import/export controls MS-25789 also describes depend on MS-25790 (the JSON format).

🤖 Generated with Claude Code

[codacy-production]

Not up to standards ⛔

🔴 Issues 6 medium

Alerts:
⚠ 6 issues (≤ 0 issues of at least minor severity)

Results:
6 new issues

Category	Results
BestPractice	6 medium

View in Codacy

🟢 Metrics 1 duplication

Metric	Results
Duplication	1

View in Codacy

AI Reviewer: run a review on demand. To trigger the first review automatically, go to your organization or repository integration settings. AI can make mistakes. Always validate suggestions.

_{TIP This summary will be updated as you push new changes.}