Support deferred workspace binding for folderless agent sessions

[meganrogge]

Feature request

Allow an agent chat/session to start without a folder or workspace, then bind it to the appropriate workspace later after the request and conversation context provide enough information.

Related workspace discovery work: #330948 and #331525.

Motivation

The correct workspace is not always known when a chat starts. A user may begin with a general request, refer to a project naturally later, or ask the agent to investigate before deciding where work belongs. Requiring an up-front folder either interrupts the flow or risks selecting an unrelated current/recent workspace.

Workspace discovery provides candidate workspaces, but there is currently no end-to-end flow for starting folderless and applying the selected workspace to the existing conversation.

Proposed behavior

• Permit creating an agent chat/session without an initial folder or workspace.
• Keep the session folderless while handling requests that do not require workspace access.
• Resolve a workspace later from the user's request, attached context, or an explicit workspace-discovery result.
• Ask the user when resolution is ambiguous or would expand filesystem access.
• Bind the selected workspace to the existing session without losing its conversation.
• Initialize workspace-dependent configuration, customizations, source control, tools, and provider state after binding.
• Support local and remote workspace URIs.
• Avoid silently selecting an arbitrary recent workspace when there is no confident match.

The first successful binding should establish the session's workspace. Changing an already-bound session to an unrelated workspace can remain a separate capability.

Example

1. A user opens a new folderless chat and asks, “Investigate the flaky authentication tests.”
2. The agent uses the request and known-workspace context to identify likely repositories.
3. If one match is clear, the agent proposes or selects it according to existing permission policy; if several match, it asks the user.
4. The existing chat becomes bound to that workspace and continues the task with its conversation intact.

Acceptance criteria

• A new agent session can remain folderless until workspace access is needed.
• A workspace can be selected and attached after session creation.
• Existing conversation history survives the transition.
• Ambiguous or permission-expanding choices require user confirmation.
• Workspace-dependent state is initialized consistently after binding.
• No unrelated workspace is selected as an implicit fallback.