Version 2.2.0

Parallel large-file transfers (all engines)

• Multipart uploads now upload parts concurrently in the Python, Go, Rust, and Java engines with a bounded worker pool (up to 8 concurrent parts, capped by the profile's max concurrent requests).
• Ranged downloads fetch byte ranges concurrently and write them at the correct offsets into a pre-sized file.
• Go and Java no longer read the entire file into memory for multipart uploads; parts are read on demand with positional reads. Rust no longer buffers whole objects in memory on either path — uploads read per-part and downloads stream each range straight to disk.
• Failed multipart uploads are now aborted server-side (previously the Rust engine leaked incomplete multipart uploads on failure).
• Progress events, response shapes, and single-part paths are unchanged.

Fixed: Python engine "token is malformed" on AWS S3

• When a profile had no session token, the Python engine serialized JSON null to the literal string "None" and sent it as x-amz-security-token, which AWS rejects with "the provided token is malformed or otherwise invalid". Session tokens are now only passed to the client when actually present, matching the other engines.

Inspector tools now run natively on the selected engine

• "Put test data" and "Delete all" are real implementations in all four engines instead of Python-script stubs: put-testdata creates the configured objects/versions with a bounded worker pool; delete-all pages through object versions (falling back to plain listing where versioning is unsupported), batch-deletes with configurable batch size, workers, and delay, and reports counts, durations, and failures.
• Tool labels changed from "put-testdata.py"/"delete-all.py" to "put-testdata"/"delete-all"; whatever engine is selected performs the work.

UI: anchored, downward-opening select menus

• All dropdown selectors (endpoint profile, backend engine, default engine, inspector placement, endpoint type, AWS region, filter/sort modes, page and copy-destination selectors) use a new shared AppSelectField widget.
• Menus now open anchored directly beneath the field and animate downward (fade + top-aligned expansion); when there is not enough room below, they flip and open upward from the field instead. The selected item is highlighted with a check mark and scrolled into view.

UI: more compact desktop layout

• Reduced desktop chrome: header margins/padding 14→12, outer panel padding 14→12, panel gaps 10→8, bucket panel width 300→272, inspector section dividers 28→16, lifecycle card padding 12→10, resize handles 14→10.
• Desktop list tiles are now dense with compact visual density by default.