[FEATURE] Programmatic way to file a session into a Claude Desktop Project

Feature Description

When fanning out work across multiple sessions — e.g. spawning one Claude session per child issue under a parent GitHub issue — there's currently no way for a session (or the agent itself) to file itself into a Claude Desktop Project. Filing a conversation into a Project is a UI-only action a human has to do by hand, one conversation at a time, after the fact.

Requested capability: expose a way (API, MCP tool, or CLI flag) for a session to be created directly inside a given Project, or for an active/completed session to attach itself to a Project programmatically — without a human manually dragging/filing each conversation through the UI.

Use case

A parent GitHub issue has N child issues. I spawn N sessions (one per child issue) to work them in parallel. I'd like all N sessions to land in a single Project named after the parent issue automatically, so they're visually grouped and shareable as a unit — instead of hand-filing each one after the fact.

Current workaround

Manually create the Project once, then manually move each new conversation into it via the UI as it's created. This doesn't scale past a handful of sessions and breaks the point of parallel fan-out.

Related issues

• #67946 — general Projects/CLI parity for Desktop, doesn't cover programmatic project assignment
• #74129 — nested folder hierarchy in the session sidebar (UI-only, human-driven)
• #75126 — folder/group organization for sessions (UI-only, human-driven)

This request is specifically about a programmatic hook (agent- or script-driven), distinct from those UI-organization requests.

Environment

• Platform: darwin (macOS)
• Product: Claude Desktop app