feat(klaus-gateway-test): workspace selection per Slack thread #449

Problem

The gateway's workspace selection has to be shown working against a real platform before release: the Slack adapter with the workspace-manager and agent-manager behind muster, and a Session that really gets its session directory on the workspace's volume (workspaces design W4, W5). agentlab klaus-gateway-test drives the Slack adapter through a fake Slack Web API and signed events, but knows nothing of workspaces.

Proposed solution

One PR in this repository, extending klaus-gateway-test (behind --workspaces, on when the lab runs the workspace-manager on the NFS storage class of #450 and the switch of #451):

• Fixtures: a workspace on public repositories that the lab user may use, and one holding a repository the lab user cannot read (where the lab has its workspace App; otherwise skipped with a reason).
• Steps on the fake Slack API: a new thread is asked once; picking the workspace starts a Session whose first turn lists the workspace's repositories in its session directory; two more turns ask nothing and reuse the Session; a restart keeps the choice; "No workspace" starts a Session with an empty working directory; the refusal fixture is answered with the repository named and no Session.
• The slash command's agent picker modal carries an optional Workspace select preset to the workspace last used with the chosen agent, else "No workspace", and changing the agent changes the preset; a submission with a workspace starts a Session with it and posts no thread prompt.
• A collaborator granted into a workspace thread without access to a repository is refused privately and no turn reaches the agent.
• The gateway image under test is a flag (--gateway-image), so a pull request's dev image is proven before its release.

Acceptance criteria

• agentlab klaus-gateway-test --workspaces passes headless on a lab with the workspace-manager, and its report lists each step, the modal's preset included
• The run records that no Session exists for the refusal step (agent-manager and kagent state)
• Without the workspace-manager the flag fails fast with the reason, and the rest of the proof is unchanged