fix(backup): support older rclone on restore and add a backup --list preflight

[mrrobot47]

Summary

Two robustness follow-ups to the rclone memory-budgeting work merged in #477, both addressing issues reported from the field:

1. Restore is broken on older rclone (regression from fix: cap rclone backup/restore memory to prevent OOM kills #477).
2. ee site backup --list shows a raw sh: 1: rclone: not found when rclone is missing, instead of the friendly install message that already exists for other paths.

1 — Gate multi-thread download flags by rclone version

#477's rclone_download() unconditionally passes --multi-thread-write-buffer-size and --multi-thread-chunk-size. These flags are recent, and rclone hard-fails on unknown flags (Fatal error: unknown flag, exit code 2) — it does not ignore them — so any older rclone aborts the copy and restore/rollback fails entirely. Distro-packaged rclone is frequently older than these versions.

Confirmed introduction versions (rclone changelog):

Flag	Introduced	Released
--multi-thread-streams, --multi-thread-cutoff	v1.48.0	Jun 2019
--multi-thread-write-buffer-size	v1.63.0	Jun 2023
--multi-thread-chunk-size	v1.64.0	Sep 2023

The two newer flags are now gated behind the detected rclone version (get_rclone_version()), with thresholds in RCLONE_MIN_VERSION_MT_* constants:

• < 1.63 → only --multi-thread-streams (+ --transfers/--buffer-size), all available since v1.48.
• >= 1.63 → adds --multi-thread-write-buffer-size.
• >= 1.64 → adds --multi-thread-chunk-size.
• version undeterminable → newer flags skipped (safe default).

The memory budget already assumes these flags' defaults, so gating them out changes only which knobs reach rclone, not the computed footprint — the OOM protection from #477 is unaffected on every rclone version.

2 — Friendly preflight for ee site backup --list

The rclone-presence and backend-config checks (with their friendly "rclone is not installed… install via https://rclone.org/downloads/" messages) lived inside pre_backup_restore_checks(). The --list branch returns before that runs, so a missing rclone surfaced as a raw sh: 1: rclone: not found.

Extracted those checks into check_rclone_available() and call it on the --list path (and from pre_backup_restore_checks() for the backup/restore paths), so --list now gets the same clear guidance.

Testing

• php -l src/helper/Site_Backup_Restore.php passes.
• Verified the gated command across rclone versions (1.53/1.60.1/1.62.2 → streams only; 1.63 → + write-buffer; 1.64/1.70 → + both; unknown → streams only) — well-formed, no stray flags or double spaces.
• Verified ee site backup --list now routes through check_rclone_available() before any rclone invocation.

Notes

• No public command/flag/config changes; behavior changes only toward broader compatibility and a clearer error.
• Follow-up to fix: cap rclone backup/restore memory to prevent OOM kills #477.

[Copilot]

Pull request overview

This PR improves robustness of EasyEngine’s rclone-backed site backup/restore flow by (1) avoiding restore failures on older rclone versions that hard-fail on unknown flags, and (2) ensuring ee site backup --list runs the same friendly rclone/config preflight as backup/restore paths.

Changes:

• Gate newer rclone multi-thread download flags (--multi-thread-write-buffer-size, --multi-thread-chunk-size) behind detected rclone version.
• Add get_rclone_version() and minimum-version constants to drive the gating behavior (safe default when version cannot be determined).
• Extract rclone presence/backend checks into check_rclone_available() and invoke it on the --list path and from pre_backup_restore_checks().

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/helper/Site_Backup_Restore.php:893

• The rclone presence check runs rclone --version, which can still emit a raw shell error like sh: 1: rclone: not found (and can also print the version on success). Since the goal here is a clean, friendly preflight, prefer checking availability via command -v rclone (silenced) before any rclone invocation.

		$command     = 'rclone --version';
		$return_code = EE::exec( $command );

		if ( ! $return_code ) {