Add HANDOFF.md — session summary v3.1.0/v2.0.0

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

HANDOFF.md

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+# HANDOFF.md
+
+Current state of the comic compression toolchain as of 2026-06-28.
+
+## Repositories
+
+| Repo | Branch | Latest commit |
+|------|--------|---------------|
+| `comic-compress-new` (CLI) | main | `94f3fab` |
+| `iMGcompress-core` (library) | master | `a03d0e5` |
+| `iMGcompress` (GUI) | master | `7b7021a` |
+
+## What was done in this session (v3.1.0 / v2.0.0)
+
+### NuGet package updates (all three projects)
+- SharpCompress `0.42` → `0.49.1` (CVE GHSA-6c8g-7p36-r338 fixed)
+- Magick.NET-Q8-x64 → `14.14.0` (multiple CVEs fixed)
+- Imazen.WebP → `11.0.0`
+- Imageflow.AllPlatforms + Imageflow.Net → `0.15.1`
+- iTextSharp → `5.5.13.5`, itext → `9.6.0`
+- McMaster.Extensions.CommandLineUtils → `5.1.0`
+- System.Drawing.Common → `10.0.9`
+
+### SharpCompress 0.49 breaking API migration (`iMGcompress-core`)
+- `ReaderFactory.Open` → `OpenReader(stream, new ReaderOptions())`
+- `RarArchive/ZipArchive.Open` → `OpenArchive(filename, new ReaderOptions())`
+- `ZipArchive.Create()` → `CreateArchive()`
+- `SaveTo(path, CompressionType)` → `SaveTo(path, new ZipWriterOptions(CompressionType))`
+- Return type `ZipArchive` → `IWritableArchive<ZipWriterOptions>`
+- Removed `using ZstdSharp` (internalized in 0.49)
+
+### Parallel within-archive compression (`iMGcompress-core`, `-P` flag)
+- New `ProcessArchivePAR2` + `CompressEntrySync` in `Compressor.cs`
+- Batched 3-phase design: sequential read → `Parallel.For` (`ProcessorCount/2` threads) → sequential write
+- Ordering guaranteed by indexed pre-allocated result slots
+- Measured speedup: **~3.4–5×** vs serial on i7-12700KF (10 batch size)
+- Memory bounded per batch; logs strictly in original entry order from write phase
+
+### MemoryStream pre-sizing (`iMGcompress-core`)
+- All `new MemoryStream()` → `new MemoryStream(entry.Size > 0 ? (int)entry.Size : 4096)`
+- Eliminates buffer-doubling reallocations on all 9 allocation sites in `Compressor.cs`
+
+### CLI fixes and new flags (`ComicCompress`)
+- Fixed missing `OnExecuteAsync` — app was throwing `InvalidOperationException` on launch
+- Added `-w|--new-webp`: use Imageflow encoder (experimental; benchmarked 8–15% slower than Imazen.WebP)
+- Added `-P|--par-archive`: enable parallel within-archive compression
+
+### GUI (`iMGcompress`)
+- Added `checkBox_parArchive` (flat-button, location `382,231`, TabIndex 14)
+- Default ON for COMIX and COMIX+PDF modes; OFF for IMAGE and ZEBRA
+- Wired into `FileProcessor.ProcessorFlags` constructor
+- Version bumped to `2.0.0 (28/06/2026)`
+
+### Other
+- Added `CLAUDE.md` to `comic-compress-new` with build commands and architecture notes
+
+## Current versions
+
+- CLI (`ComicCompress`): `3.1.0 (28/06/2026)` — see `Program.cs`
+- GUI (`iMGcompress`): `2.0.0 (28/06/2026)` — see `MGCompress.cs`
+
+## Known state / open items
+
+- **Imageflow encoder** (`-w` flag) is wired and working but consistently slower than Imazen.WebP across all tested archive sizes. Kept as an experimental path only.
+- **`libwebp.dll`** must be present alongside the executable — it is checked into the repo root of both `comic-compress-new` and `iMGcompress-core`.
+- The GUI runs single-threaded on the UI thread (`button_start_Click` is synchronous). Long jobs block the window. Not addressed in this session.