Add dry-run dataset existence checks with option to create missing datasets

During dry runs, query pool.dataset.query on the destination to verify that
every share path would have a backing ZFS dataset. Missing paths are collected
in Summary.missing_datasets and surfaced as a WARNING block in the report.

In interactive mode the user is prompted to create any auto-creatable
(/mnt/…) datasets before the live migration proceeds. Non-interactive
--dry-run mode prints the same warning in the summary report.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Single-file Python CLI tool (`truenas_migrate.py`) that reads SMB shares, NFS shares, and SMB global config from a TrueNAS debug archive (`.tar`/`.tgz`) and re-creates them on a destination TrueNAS system via its JSON-RPC 2.0 WebSocket API (TrueNAS 25.04+).
+
+## Running the Tool
+
+```bash
+# Install the only dependency
+pip install websockets
+
+# Inspect the archive
+python truenas_migrate.py --debug-tar debug.tgz --list-archive
+
+# Dry run (no changes made)
+python truenas_migrate.py --debug-tar debug.tgz --dest 192.168.1.50 --api-key "1-xxx" --dry-run
+
+# Live migration
+python truenas_migrate.py --debug-tar debug.tgz --dest 192.168.1.50 --api-key "1-xxx"
+
+# Migrate a subset (smb, nfs, smb-config)
+python truenas_migrate.py --debug-tar debug.tgz --dest 192.168.1.50 --api-key "1-xxx" --migrate smb
+```
+
+## Architecture
+
+The script is structured as a linear pipeline with no external config files or modules:
+
+1. **Archive parser** (`parse_archive`, `_find_data`) — Opens the `.tgz` using `tarfile`, tries a ranked list of known paths (`_CANDIDATES`) for each data type, then falls back to keyword heuristic scanning (`_KEYWORDS`). Handles both `ixdiagnose` (SCALE) and `freenas-debug` (CORE) archive layouts, as well as date-stamped top-level directories.
+
+2. **Payload builders** (`_smb_share_payload`, `_nfs_share_payload`, `_smb_config_payload`) — Strip read-only/server-generated fields (`id`, `locked`, `server_sid`) before sending to the destination API.
+
+3. **`TrueNASClient`** — Minimal async JSON-RPC 2.0 WebSocket client. Authenticates with `auth.login_with_api_key`, drains server-push notifications to match replies by `id`. Used as an async context manager.
+
+4. **Migration routines** (`migrate_smb_shares`, `migrate_nfs_shares`, `migrate_smb_config`) — Each queries existing shares on the destination first, then skips conflicts (SMB: by name case-insensitively; NFS: by path exactly), then creates or dry-runs each share.
+
+5. **`Summary` dataclass** — Accumulates counts and errors, renders a box-drawing table at the end. Exit code 2 if any errors occurred.
+
+## TrueNAS API Reference
+
+When working with TrueNAS API methods, payloads, or field names, consult the official documentation:
+
+- **API Docs**: https://api.truenas.com/v25.10/
+- Always verify method signatures, required fields, and valid enum values against the docs before modifying API calls or payload builders.
+- The API version in use is TrueNAS 25.10 (SCALE). Legacy CORE field names may differ.
+
+## Key Design Constraints
+
+- **Never overwrites or deletes** existing shares on the destination — conflict policy is skip-only.
+- SSL verification is off by default (self-signed certs are common on TrueNAS).
+- The WebSocket API endpoint is `wss://<host>:<port>/api/current` (TrueNAS 25.04+).
+- The `call()` method has a 60-second per-message timeout and skips server-initiated notifications (messages without an `id`).