merge(harness): extend GTC parity harness with GUI cells

Brings GTC-6 onto main: tests/gtc/parity_harness.sh gains a GUI
suite driven by the gated integration_gtc_wan_segmented cargo test
binary, with five new band-gated cells covering provider_download_file
segmented downloads (SFTP/S3/FTP), AeroSync segmented downloads
(sync_download_transfer), and cross-profile DAG transfers.

Bands chosen 2026-05-20 (user-confirmed conservative profile):
  gui-single-sftp     2.0..5.0
  gui-single-s3       1.8..5.0
  gui-single-ftp      1.8..5.0
  gui-sync-sftp       1.8..4.0
  gui-cross-sftp-s3   2.5..5.0

New CLI flags: --suite cli|gui|all, --gui-only, --gui-cells LIST,
--band KEY:F:C now accepts gui-* keys.

Out of scope (documented in tests/gtc/README.md): FTP GUI batch path
(no-double-pool invariant), rclone_crypt overlay, AeroVault overlay.

Closes the GTC filone (GTC-0..GTC-6).

Co-Authored-By: aeroftp[bot] <aeroftp[bot]@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

tests/gtc/README.md

@@ -25,18 +25,32 @@ filone. See:
 ## Usage
 
 ```bash
-# Default run: all five protocols, CLI surfaces only (GTC-0 scope)
+# Default: CLI surfaces only (back-compat). Five protocols, segments-1
+# / segments-n / parallel-n cells per protocol.
 tests/gtc/parity_harness.sh
 
-# Subset for fast iteration
+# CLI subset for fast iteration
 tests/gtc/parity_harness.sh --protocols sftp,s3
 
+# GUI surfaces only (cargo-test driven)
+tests/gtc/parity_harness.sh --suite gui
+# equivalent shortcut
+tests/gtc/parity_harness.sh --gui-only
+
+# Full matrix: CLI + GUI in one run
+tests/gtc/parity_harness.sh --suite all
+
+# Subset of GUI cells
+tests/gtc/parity_harness.sh --suite gui \
+    --gui-cells gui-single-sftp,gui-cross-sftp-s3
+
 # Dry-run: generate corpus, write plan, do not transfer
 tests/gtc/parity_harness.sh --dry-run
 
-# Override band (per-protocol speedup floor/ceiling, picks the
-# tighter of spec vs flag)
+# Override band (per-protocol speedup floor/ceiling for CLI cells, OR
+# per-cell-key for GUI cells; repeatable)
 tests/gtc/parity_harness.sh --band sftp:2.0:5.0
+tests/gtc/parity_harness.sh --suite gui --band gui-single-sftp:2.2:4.5
 ```
 
 The run id is the UTC timestamp at start (`YYYYMMDDTHHMMSSZ`). Output
@@ -46,14 +60,55 @@ appended to
 `docs/dev/roadmap/APPENDIX-GUI-TRANSFER-CONVERGENCE/baselines/legacy-floor.csv`
 the first time it's recorded.
 
-## What is and is not exercised in GTC-0
+## CLI cells (GTC-0 scope)
 
 In: `cli-segments-1` (legacy single-stream baseline),
 `cli-segments-n` (DAG range), `cli-parallel-n` (DAG batch),
 byte-identity assertions, exit-code shape per CLI.
 
-Out: `gui-single`/`gui-batch`/`gui-sync`/`gui-cross`. Those surfaces
-are still legacy per the pin and would just re-measure
-`cli-segments-1` while paying the Tauri IPC setup cost. They get
-added in GTC-1 as the first surface (Panel batch) actually starts
-using DAG.
+| protocol | floor | ceiling |
+|----------|-------|---------|
+| sftp     | 1.5   | 6.0     |
+| ftp      | 1.5   | 5.0     |
+| ftps     | 1.3   | 5.0     |
+| s3       | 2.0   | 6.0     |
+| webdav   | 1.3   | 4.0     |
+
+## GUI cells (GTC-6, added 2026-05-20)
+
+GUI surfaces don't run through `aeroftp-cli`: they're driven via the
+gated `integration_gtc_wan_segmented.rs` cargo test binary which
+exercises each GUI Tauri entry-point directly against the axpbuntu
+lab. The harness invokes the corresponding test fn, parses the
+single-line summary it emits on stderr, and produces one parity cell.
+
+Test binary requirements (same as the cargo integration suite):
+- axpbuntu lab credentials in the vault (admin SFTP + FTP + S3/MinIO).
+- ~64 MiB free at `$TMPDIR` for the round-trip files.
+- WAN reachability to `49.13.171.110` (no firewall blocking SSH/FTP/S3).
+
+| cell key            | engine                            | protocol  | floor | ceiling | rationale                                       |
+|---------------------|-----------------------------------|-----------|-------|---------|-------------------------------------------------|
+| `gui-single-sftp`   | `provider_download_file`+ segs    | sftp      | 2.0   | 5.0     | Empirical median 2.98x on axpbuntu, 64 MiB.     |
+| `gui-single-s3`     | `provider_download_file`+ segs    | s3 (MinIO)| 1.8   | 5.0     | HttpClonePool overhead on small slices.         |
+| `gui-single-ftp`    | `provider_download_file`+ segs    | ftp       | 1.8   | 5.0     | FtpConnectionPool reuse + REST/RETR.            |
+| `gui-sync-sftp`     | `sync_download_transfer` (GTC-3)  | sftp      | 1.8   | 4.0     | AeroSync overlay narrows ceiling vs. raw.       |
+| `gui-cross-sftp-s3` | `transfer_orchestrator::execute_batch` (GTC-4) | sftp -> s3 | 2.5 | 5.0   | DAG fan-out across two providers, 4x16 MiB.     |
+
+Bands are policy decisions taken 2026-05-20 (closure of GTC-5,
+user-confirmed conservative profile). They protect against:
+1. Regressions below the empirical median minus WAN jitter (floor).
+2. Anomalous "too good" runs from caching / fixture corruption (ceiling).
+
+Override on the command line with `--band <cell-key>:<floor>:<ceiling>`.
+
+### Out of GTC-6 scope
+
+- `gui-batch-sftp` / `gui-batch-s3`: the FTP GUI batch path runs on
+  `FtpDownloadExecutor`, not the `ProviderDownloadExecutor` that the
+  segments engine targets (no-double-pool invariant). It would
+  re-measure the legacy floor (0.9 .. 1.2x) and is excluded by design.
+- `rclone_crypt_*` downloads: full-buffer-in-memory path, doesn't
+  touch the segmented helper. Wiring requires a separate slice that
+  also has to handle decrypt streaming.
+- AeroVault overlay extract: same family as crypt, same exclusion.