Don't reclassify an emptied chat session as never-used

[Ahmed Mahdy (abmahdy)]

Fixes #333623

A local chat session whose requests are all removed — restoring the checkpoint on the first request, for example — keeps its title and full transcript on disk but disappears from the Chat Sessions list for good. Before it goes it also flickers in and out.

Why

Two paths decide session-list membership and they disagree about empty sessions.

getHistorySessionItems skips sessions that are currently loaded, and excludes empty ones:

.filter(entry => !this._sessionModels.has(LocalChatSessionUri.forSession(entry.sessionId))
    && entry.initialLocation === ChatAgentLocation.Chat
    && !entry.isEmpty)

shouldBeInHistory, which covers the loaded models, applies no emptiness filter at all:

return !entry.isImported && !entry.isDeleted
    && !!LocalChatSessionUri.parseLocalSessionId(entry.sessionResource)
    && entry.initialLocation === ChatAgentLocation.Chat;

So the same session is visible while its model is in memory and hidden once it is evicted — the flicker — and permanently gone after the last eviction.

isEmpty itself is written correctly from the live model (getSessionMetadataSync), so this is not a stale index. The problem is that "has no requests right now" is conflated with "was never used", and only the latter is what the filter is for.

The fix

Once a session has held requests, keep isEmpty: false. Sessions that never had any are still reported as empty and stay out of the list, so never-used "New Chat" entries remain hidden exactly as before.

The guard is applied at every site that writes an index entry — writeSession, writeSessionMetadataOnly, and the synchronous shutdown flush updateAndFlushIndexSync — so a shutdown flush can't undo it.

Tests

Two tests in chatSessionStore.test.ts:

• storeSessions marks a session with no requests as empty — pins the existing behaviour so the guard can't over-apply and start listing never-used sessions.
• storeSessions keeps a session non-empty after all of its requests are removed — the regression.

MockChatModel.getRequests() returned a hard-coded [] while the class already carried a requests field; it now returns that field, which is what makes request counts expressible in tests.

Negative control: with the guard disabled, the regression test fails with true !== false while the companion test still passes.

Validation

• npm run typecheck-client — no errors in contrib/chat. (21 pre-existing errors remain in platform/agentHost, all from a stale local @github/copilot-sdk; untouched by this change.)
• Full test-node suite: 15059 passing. The whole ChatSessionStore suite is green. The one failure is Request Service > Kerberos lookup, an environment artifact on a corporate network, unrelated to this change.

[Copilot]

Pull request overview

Preserves previously used chat sessions in history after all requests are removed.

Changes:

• Retains non-empty metadata across all index-write paths.
• Updates mocks and adds regression coverage for emptied sessions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
chatSessionStore.ts	Preserves prior non-empty state.
chatSessionStore.test.ts	Tests empty-session classification.
mockChatModel.ts	Exposes configurable mock requests.

Suppressed comments (1)

src/vs/workbench/contrib/chat/common/model/chatSessionStore.ts:906

• isEmpty is optional on legacy index entries, so this falsy check treats an unknown value as proof that the session was previously used. When such an entry is next written with zero requests, it is forced to false and can be surfaced as a used session. Preserve only an explicitly recorded false value.

	if (next.isEmpty && previous && !previous.isEmpty) {

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[karelyvalenzuela879-lang]

abmahdy:fix/empty-session-hidden-from-history