Move a conversation to a new project root folder

Start by tracing the existing Provider boundary, session scanning, cache handling, and running-session detection, then inspect src/providers/claude/ for encoding and transcript handling. Define the relocation plan and apply flow around the TUI and --move --dry-run entry point. Done means safe, provider-scoped relocation with correct cwd rewrites, backups, conflict and running-session checks, and resumability.

Summary

Let the user change a session's project root folder from ccpick, so a conversation whose project was moved or renamed on disk can be resumed from the new location.

Today such a session is dimmed and Enter is blocked with project dir no longer exists. Claude Code ties a session to its original directory: the transcript lives under projects/<encoded-cwd>/<session-id>.jsonl and every message line records cwd. Resuming from a different folder doesn't find the session.

Proposed behaviour

• A key on the selected session (e.g. Ctrl-M / "move") opens a dialog to enter the new root folder. Pre-filled with the current cwd and completed against real directories.
• It works for sessions whose project dir is missing and for ones that still exist (e.g. a repo cloned to a new path).
• Before applying, a confirmation shows what will change: files moved and number of lines rewritten.
• After a move the session is re-scanned and resumable from the new folder.

What a move does (Claude provider)

To verify against current Claude Code behaviour before implementing:

1. Compute the new project directory name with Claude's encoding (every non-alphanumeric character in the absolute path becomes -, e.g. /home/me/code/app → -home-me-code-app).
2. Move <store>/<old-encoded>/<session-id>.jsonl to <store>/<new-encoded>/<session-id>.jsonl. Also move the session's sibling data directory (<session-id>/, e.g. subagent transcripts) if present.
3. Rewrite cwd on every line that has it, only where it equals the old root or is under it (/old/root/sub → /new/root/sub). Leave all other content untouched, including message text and tool payloads.
4. Check other per-session state that references the path (e.g. file-history, todos, sessions/<pid>.json) and decide per item whether to update it or leave it.

Safety

• Refuse while the session is running (running-session detection already exists).
• Write atomically: the new file goes to a temp path and is renamed; the old file is removed only after the new one is fully written.
• Keep a backup of the original transcript (e.g. <session-id>.jsonl.ccpick-bak), or offer an undo of the last move.
• If the destination already has a file for that session id, abort.
• Dry-run output (ccpick --move <session-id> <new-root> --dry-run) so the change can be inspected, and so it can be scripted and tested.

Architecture

• This is ccpick's first write operation. It needs an explicit new Provider method, e.g. relocate_session(&self, source, session, new_root) -> Result<RelocationPlan> and apply(plan). Claude-specific encoding and line rewriting stay in src/providers/claude/.
• Shared UI shows the plan and asks for confirmation.
• The cache entry for the old path is dropped and the new file scanned.
• Sessions from the other environment (WSL ↔ Windows, see #1): support moving within that environment's path form, or disable the action for foreign sessions in the first version.

Acceptance criteria

• A session whose project dir was renamed can be moved to the new dir from the TUI and then resumed with its history intact.
• --move … --dry-run prints the planned file moves and cwd rewrites without changing anything; without --dry-run it applies them.
• Only cwd values equal to or under the old root are rewritten; tests prove message content containing the old path is untouched.
• Running sessions can't be moved; destination conflicts abort without changes; the original is backed up.
• Encoding matches Claude Code's for paths with spaces, dots, underscores and non-ASCII characters (fixtures).
• Provider boundary kept: no Claude-specific logic outside src/providers/claude/.