actus: thread management parity -- fork, delete/archive, auto-title

[metasmile]

Summary

Zed UI auto-generates thread titles from conversation content, supports forking threads, and lets users delete or archive stale threads. The headless Rust server (actus) needs equivalent functionality.

Requirements

Auto-generate thread titles

• Listen for thread_title_changed events from the Zed WebSocket protocol
• Fallback: derive a title from the first user message (truncate to ~60 chars)
• Store and persist titles in ~/.actus/threads/threads.json
• Update terminal.py CLI to display thread titles in /history output

Fork threads

• POST /v1/threads/:id/fork -- creates a new thread copying the full message history from an existing thread
• The forked thread gets a new ID; the original thread remains unchanged
• The forked thread starts with completed: true (user sends the first message)
• CLI: /fork <thread_id> command in terminal.py

Delete / Archive threads

• DELETE /v1/threads/:id -- mark thread as archived
• GET /v1/threads with ?include_archived=true -- filter archived threads
• Archival is soft-delete: thread data stays on disk but hidden from default listing
• CLI: /delete <thread_id> (or equivalent) command in terminal.py
• Reaper: optionally auto-archive threads older than N days (configurable)

API Design

GET    /v1/threads                    # list active threads (with ?include_archived)
GET    /v1/threads/:id                # get thread detail
POST   /v1/threads/:id/fork           # fork a thread
DELETE /v1/threads/:id                # archive (soft-delete)

Current state

• Thread CRUD: GET /v1/threads, GET /v1/threads/:id exists
• Thread persistence: auto-saved to JSON file in ~/.actus/threads/
• Thread completed flag already tracked per session
• CLI: /history lists recent threads

Related

• Part of actus: achieve Zed UI-level agent capability from native Rust server #1 (actus master epic)
• nexus #128 Section 2 (Thread Management)

[metasmile]

Migrated from ssccsorg/nexus#128 (Thread Management section).