Keep locally provisioned sessions out of the list until they are real

[Osvaldo Ortega (osortega)]

Two list bugs with the same root: a session that exists remotely before the host knows about it.

1. The row appeared twice for ~8 seconds

A provider that creates a session remotely seeds it into its cache before connecting, so a later discovery pass reconciles against it instead of creating a second entry. But the caller is still showing an optimistic placeholder row for that same session until the first turn is dispatched — so publishing the seed straight away listed the session twice while the environment woke.

Measured on a real run: seed at 19.658, placeholder retired at 27.615.

Retiring the placeholder earlier is not an option — swapping when the session merely exists hands the UI a session it cannot open yet and the view falls back to the new-session screen. That was tried and reverted.

So the seed is withheld from getSessions instead, and revealed as the placeholder is retired:

• The reveal is silent. The list re-reads on any change, so a single event swaps both rows. Announcing separately would trade an 8-second overlap for a one-frame one.
• Withheld is not unreachable. getSessionByResource reads the cache directly, so opening still resolves — hidden from the list, not from the app.
• A failed first turn still reveals it, since the session outlives the failure and would otherwise be invisible.

2. The row vanished, the view went home, then it came back

Connecting triggers a reconciliation that prunes anything cached but not listed by the host. But the session id is minted before the host materializes the session, so that first listing can legitimately omit it. The prune landed ~400ms after the placeholder swap, deleting the row the user was looking at:

02.735  host: "not found: ahp-session:/355591eb…"
02.742  swap to the committed session
03.131  committed session removed → back to the new-session screen

Sessions seeded as provisional now resist that eviction until the host lists them. The base provider already made this exemption for a sibling case ("some hosts briefly omit the just-sent eager session"), so that is generalized into an overridable hook rather than adding a parallel mechanism.

The protection is bounded (2 min). Without a deadline, a session the host will never list becomes a permanent row that only a reload clears — trading a visible flash for an invisible one. Both directions are tested.

Risk

_isSessionEvictable defaults to true and _onHostListedSessions is empty, so every provider that does not opt in behaves exactly as before. Only sessions seeded with provisional take the new paths.

Validation

• npm run typecheck-client, npm run valid-layers-check
• ./scripts/test.sh --glob "**/vs/sessions/**/*.test.js" — 2469 passing
• The eviction guard was verified by deleting it and confirming the new test fails, then restoring it — a test that passes for the wrong reason is worse than no test.

[Copilot]

Pull request overview

Prevents locally provisioned sandbox sessions from duplicating or disappearing before the host recognizes them.

Changes:

• Withholds provisional sessions from listings while keeping them resolvable.
• Adds bounded eviction protection and host-list reconciliation hooks.
• Publishes sessions when placeholders retire, including failed-send handling.

Show a summary per file

File	Description
baseAgentHostSessionsProvider.ts	Adds overridable eviction hooks.
remoteAgentHostSessionsProvider.ts	Tracks withheld and provisional sessions.
cloudSandboxAgentHostContribution.ts	Seeds provisioned sessions provisionally.
copilotChatSessionsProvider.ts	Publishes sessions during placeholder retirement.
remoteAgentHostSessionsProvider.test.ts	Tests listing and eviction behavior.
cloudSandboxAgentHostContribution.test.ts	Updates provisioning test provider.
copilotChatSessionsProvider.test.ts	Tests successful and failed publication.

Review details

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• Files reviewed: 7/7 changed files
• Comments generated: 2
• Review effort level: Balanced