Give the editor a visual identity and a real levels control

The panel now uses the same colours the page is drawn with, on dark
chrome so the scan is the brightest thing on screen. Levels move from two
anonymous sliders to the scan's own histogram with draggable black and
white points and a tone strip, since getting them wrong is the one
mistake that only shows up on the tablet. A page rail replaces the
stepper and carries each page's slice count; export is pinned below the
scroll instead of below the fold; marker types read as prose.

docs/bundle-format.md

@@ -95,6 +95,7 @@ which roughly 830 KB is the source PDF and the rest slice images at ~20 KB each.
 | `translator` | string | optional | Who translated the words. |
 | `tempo` | integer | optional | Beats per minute. |
 | `voices` | string | optional | The parts in this arrangement, as free text. |
+| `source` | object | optional | How the slices were cut from the archived document. See [Source geometry](#source-geometry). |
 
 **Optional fields are omitted when they have no value.** A consumer will not
 encounter an empty string or a null in place of an absent field.
@@ -112,6 +113,9 @@ Each entry of `slices` is an object:
 | Field | Type | | |
 |---|---|---|---|
 | `file` | string | required | Name of the image entry in the archive. |
+| `page` | integer | optional | Index into `source.pages` — the page this slice was cut from. Present whenever `source` is. |
+| `slot` | integer | optional | Which slice of that page this is, counting from 0 between its cuts. Present whenever `source` is. |
+| `bar` | integer | optional | The measure this slice starts at, as numbered in the score. Omitted when unknown. |
 | `markers` | array | optional | Markers on this slice. Omitted when there are none. |
 | `engraving` | object | optional | The notation this slice's image was engraved from, when it was engraved rather than scanned. See [Engraving](#engraving). |
 
@@ -122,6 +126,12 @@ must not derive order from them.
 A slice's **index** is its zero-based position in this array. Indices are the
 only identifiers the format has, and they are meaningful only within one bundle.
 
+`bar` is the score's own numbering, not the format's: it says which measure this
+system begins at, so a consumer can answer "take it from bar 33" by scrolling to
+the right slice. It is independent of `index`, may be absent on any slice, and
+carries no promise of being consecutive — a score numbers the systems it chooses
+to, and pickup bars, repeats and voltas all break arithmetic on it.
+
 ## Slice images
 
 Every slice image in a bundle satisfies the following. A consumer can rely on
@@ -160,6 +170,72 @@ One specific hazard is worth naming, because it is silent: an image pipeline
 that *discards* the alpha channel rather than compositing it will turn every
 slice into a solid black rectangle, since the colour channels are all zero.
 
+## Source geometry
+
+A bundle can say how its slices were cut, in a `source` object. With it a
+consumer can reopen the score for editing; without it the bundle is a one-way
+trip, since the slice images are output and the decisions that produced them
+would live only in whatever tool made them.
+
+```json
+"source": {
+  "file": "original.pdf",
+  "pages": [
+    {
+      "skew": -0.4,
+      "content": [0.083, 0.0, 0.947, 1.0],
+      "levels": [46, 173],
+      "cuts": [
+        [[0.0, 0.0449], [1.0, 0.0449]],
+        [[0.0, 0.3662], [0.35, 0.3662], [0.35, 0.3901], [1.0, 0.3901]]
+      ]
+    }
+  ]
+}
+```
+
+| Field | Type | | |
+|---|---|---|---|
+| `file` | string | required | The archive entry the slices were cut from. `"original.pdf"` in practice. |
+| `pages` | array | required | One entry per page of that document, in its own page order. |
+
+Each entry of `pages`:
+
+| Field | Type | | |
+|---|---|---|---|
+| `cuts` | array | required | The boundaries between slices, ordered top to bottom. May be empty: a page with no cuts is one slice. |
+| `skew` | number | optional | Degrees the page was rotated by before cutting. Default `0`. |
+| `content` | array | optional | `[x0, y0, x1, y1]` — the part of the page that is music. Default the whole page. |
+| `levels` | array | optional | `[black, white]` — the black and white points applied. Default `[0, 255]`. |
+
+**Everything here is in normalised page coordinates**, `0.0` to `1.0` on each
+axis, origin top-left. Nothing is in pixels, so the geometry holds however the
+document is rendered and at whatever resolution.
+
+A **cut** is a polyline: a list of `[x, y]` points, left to right. Two points is
+a straight cut; more steps around a system that interleaves with its neighbour —
+a section label printed level with the previous system's lyrics. A slice's top
+boundary is the cut above it and its bottom boundary the cut below it, with the
+page edge standing in at either end.
+
+A page with *n* cuts therefore has *n + 1* **slots**, numbered from 0 downward.
+Each slice names the `page` and `slot` it came from. **A slot that no slice
+claims was discarded** — a page header, a footer, a title block. That is stated
+by omission rather than directly, because shipping a discarded slice's image
+would defeat discarding it.
+
+The archived document is the source of truth for reopening: the slice images are
+output, and a consumer that reopens a bundle re-renders them rather than
+importing them.
+
+`source` is optional, so a bundle without one is still valid — it is simply not
+reopenable, and a consumer should say so rather than pretend otherwise. What it
+can still recover from such a bundle is the title block, and, if it cuts the
+document again and happens to find exactly as many slices, the markers: the
+slices array is in reading order, so it lines up with any other list in reading
+order. One slice more or fewer and it does not, which is why that is a fallback
+and not the design.
+
 ## Engraving
 
 Most slices are photographs of print: an image and nothing more. A slice that
@@ -169,12 +245,12 @@ it came from, in an `engraving` object.
 ```json
 {
   "file": "007.webp",
+  "bar": 33,
   "engraving": {
     "lang": "lilypond",
     "key": "aes",
     "time": "4/4",
     "print_time": false,
-    "bar": 33,
     "voices": [
       { "clef": "treble",   "notes": "c4 des ees f | ees2. r4", "lyrics": "Kai -- paa -- va sy -- dän" },
       { "clef": "treble_8", "notes": "aes,4 aes aes aes | aes2. r4" },
@@ -191,7 +267,6 @@ it came from, in an `engraving` object.
 | `key` | string | optional | Key signature, in `lang`'s spelling. For `lilypond`, the tonic of the major spelling: `"aes"`, `"c"`, `"fis"`. |
 | `time` | string | optional | Time signature, as `"4/4"`. |
 | `print_time` | boolean | optional | Whether the time signature is printed on this system. Default `false`. |
-| `bar` | integer | optional | The measure this system starts at, as printed above its first bar. Omitted when the system is not numbered. |
 
 Each entry of `voices`:
 
@@ -288,9 +363,9 @@ ignore markers it does not understand rather than reject the bundle.
 
 `v` is an integer that increases when a change would break an existing consumer.
 Additions that a consumer can safely ignore — new optional fields, new marker
-types, new `engraving` languages — do not increase it. `engraving` was added
+types, new `engraving` languages — do not increase it. `engraving` and `source`
-this way: a bundle carrying one is still a version 1 bundle, and a consumer that
+were both added this way: a bundle carrying them is still a version 1 bundle,
-has never heard of it presents the score unchanged.
+and a consumer that has never heard of them presents the score unchanged.
 
 A consumer should refuse a bundle whose `v` it does not recognise rather than
 attempt to interpret it.
@@ -305,6 +380,9 @@ A consumer is advised to check:
 - Every `destination` is within the bounds of `slices`.
 - Every `engraving` has a `lang` and a non-empty `voices`; unknown `lang` values
   are ignored rather than rejected.
+- If `source` is present: its `file` names an entry in the archive, every slice
+  carries a `page` within `source.pages` and a `slot` within that page's slot
+  count, and no two slices claim the same one.
 - Archive entry names contain no path separators, no `..`, and no absolute
   paths, as with any archive from an untrusted source.
 
@@ -314,6 +392,10 @@ A bundle describes one complete score. The format has no notion of updating a
 previously read bundle: there are no stable identifiers, and a slice's index is
 meaningful only within the bundle that contains it.
 
+Reopening a bundle for editing, via [`source`](#source-geometry), does not change
+that. What comes out is a new document that happens to have been derived from an
+old one, not a revision of it.
+
 Two bundles of the same piece are therefore independent documents, not versions
 of one. A consumer that stores imported bundles and assigns its own identifiers
 should treat a second bundle as a new score rather than merging it into an

docs/guide.md

@@ -44,14 +44,27 @@ off.
    one back.
 4. **Set the content rectangle.** Drag the blue edges so they hold the music and
    nothing else. This is the horizontal crop for every slice on the page.
-5. **Check black and white points.** These arrive proposed from the scan, like
+5. **Check black and white points.** Under *Page* is the scan's own histogram:
-   the cuts do. If the paper still shows texture, pull *White point* down; if the
+   a hump of ink on the left, a hump of paper on the right, and two handles you
-   notes look grey rather than solid, pull *Black point* up. Getting this wrong
+   drag. Put the white handle at the foot of the paper hump and the black one at
-   is the one mistake you cannot see until the bundle is on the tablet — grey ink
+   the foot of the ink hump. The strip underneath shows the tone that results.
-   becomes half-transparent ink, and nothing downstream can rescue it.
+   Getting this wrong is the one mistake you cannot see until the bundle is on
+   the tablet — grey ink becomes half-transparent ink, and nothing downstream
+   can rescue it. Arrow keys nudge the black point, Shift+arrows the white one.
 
-Page Up / Page Down move between pages. Levels carry over from the previous
+The page rail across the top of the panel has one chip per page, with the number
-page, so a consistent scan only needs setting once.
+of slices on it underneath. Click to go there, or use Page Up / Page Down. A page
+whose count is far off its neighbours' is usually a page where detection missed
+a system. Levels carry over from the previous page, so a consistent scan only
+needs setting once.
+
+## Bar numbers
+
+Under *This slice*, **First bar** is the measure that slice starts at, as the
+score numbers it. Optional, and only worth filling in where the printed score
+shows a number — that is what lets noteman answer "take it from bar 33". A
+re-engraved slice prints the number above its first bar, exactly as the scanned
+systems around it do.
 
 ## Markers
 
@@ -93,6 +106,31 @@ Two things worth knowing:
   detection rather than resuming decisions that already shipped. If you really
   want the old cuts back, `noteman-slicer edit my-song.pdf --resume`.
 
+## Reopening a bundle
+
+```
+noteman-slicer open my-song.zip
+```
+
+Unpacks the archived PDF beside the bundle, rebuilds the project from it — the
+cuts, skew, levels, discards, markers, title block and any re-engraved systems —
+and opens the editor on it. Everything you changed re-renders from the PDF; the
+slice images in the zip are output and are thrown away.
+
+This works on any bundle, not just one you made: the cuts travel in `song.json`.
+It refuses to overwrite a PDF or project file that is already there, since the
+obvious place to unpack is exactly where someone's unfinished work lives — pass
+`--pdf elsewhere.pdf` or `--force` if you mean it.
+
+A bundle from a producer that does not record its cuts can still be opened, but
+it is a fresh session rather than a round trip: it asks first, then cuts the PDF
+from scratch with detection. The title block always comes back. Markers and
+re-engraved systems land only if detection happens to find exactly as many
+slices as the bundle has — the slices are in reading order on both sides, so
+they can be lined up, but one system found or missed would shift every marker
+onto the wrong slice, so in that case they are left off entirely and it says so.
+`--detect` answers the question in advance, for scripts.
+
 ## Re-engraving a slice (optional, needs LilyPond)
 
 When a system is beyond rescue — a bad scan, a wrong transposition, a passage
@@ -130,8 +168,8 @@ substitutes for it.
 | Detection found no systems, or one giant one | The score has no bracket joining the staves; add the cuts by hand. |
 | "The PDF has changed since these cuts were made" | The file was edited or replaced under an existing project. The cuts probably no longer line up — re-cut. |
 | Export says a title is required | Fill in *Song → Title*. |
-| Slices look grey and washed out | The white point is too high. |
+| Slices look grey and washed out | The white point is too high — drag it down onto the paper hump. |
-| Notes have holes in them | The black point is too high. |
+| Notes have holes in them | The black point is too high — drag it left, off the ink hump. |
 
 ## The command line
 
@@ -142,6 +180,8 @@ noteman-slicer info my-song.pdf        # source type and page rasters
 noteman-slicer detect my-song.pdf      # detection results + debug overlays
 noteman-slicer project my-song.pdf     # what the project file currently holds
 noteman-slicer export my-song.pdf      # export without opening the editor
+noteman-slicer open my-song.zip        # unpack a bundle; --no-edit to stop there
 ```
 
-Every command takes `--type raster|vector` to override source-type detection.
+Every command that takes a PDF takes `--type raster|vector` to override
+source-type detection.

docs/spec.md

@@ -347,6 +347,15 @@ slice they sit on, so indices appear in exactly one place: a jump source's
 MP3s are planned for a later phase, and bundles are archived artifacts that may be
 re-imported a year later.
 
+The manifest also carries the cuts, in a `source` block: the polylines, skew,
+levels and content rectangle per page, and the page and slot each slice came
+from. That is what makes `noteman-slicer open song.zip` a real round trip rather
+than a re-detection that happens to land nearby — it unpacks the archived PDF,
+rebuilds the project from the geometry, and re-renders. The images in the zip
+are output and are discarded on the way back in. Slots no slice claims were the
+discarded ones; a bundle states that by omission, since shipping a discarded
+slice's image would defeat discarding it.
+
 Otherwise: plain zip, no manifest beyond this, no checksums, hand-fixable.
 Python's `zipfile` is stdlib; the import side needs one zero-dep library
 (`fflate`), since Bun has zlib but no zip reader.

noteman_slicer/bundle.py

@@ -69,7 +69,6 @@ def _engraving(project: Project, page: int, slot: int) -> dict | None:
         "key": replacement.key or project.key,
         "time": replacement.time or project.time,
         "print_time": replacement.print_time,
-        **({"bar": replacement.bar} if replacement.bar else {}),
         "voices": [
             {"clef": v.clef, "notes": v.notes.strip()}
             | ({"lyrics": v.lyrics.strip()} if v.lyrics.strip() else {})
@@ -78,6 +77,33 @@ def _engraving(project: Project, page: int, slot: int) -> dict | None:
     }
 
 
+def _source(project: Project) -> dict:
+    """How the slices were cut from the archived PDF.
+
+    Without this a bundle is a one-way trip: the images are output and the cuts
+    that made them live only in the producer's own project file, so reopening
+    someone else's bundle would mean cutting the score again from scratch. It
+    is geometry in normalised page coordinates, so it survives the PDF being
+    rendered at any resolution.
+
+    Only the pages are here. Which slot on which page a slice came from is on
+    the slice itself, so that one ordering — the slices array — stays the only
+    one, and a slot no slice claims is a slot that was discarded.
+    """
+    return {
+        "file": "original.pdf",
+        "pages": [
+            {
+                "skew": round(page.skew, 2),
+                "content": [round(v, 5) for v in project.page_content_rect(i)],
+                "levels": list(project.page_levels(i)),
+                "cuts": [[[round(x, 5), round(y, 5)] for x, y in cut.points] for cut in page.cuts],
+            }
+            for i, page in enumerate(project.pages)
+        ],
+    }
+
+
 def song_json(project: Project, files: list[str]) -> dict:
     payload: dict = {"v": FORMAT_VERSION}
     for field in METADATA_FIELDS:
@@ -100,7 +126,10 @@ def song_json(project: Project, files: list[str]) -> dict:
 
     slices: list[dict] = []
     for name, (page, slot) in zip(files, kept):
-        entry: dict = {"file": name}
+        entry: dict = {"file": name, "page": page, "slot": slot}
+        bar = project.pages[page].bars[slot]
+        if bar:
+            entry["bar"] = bar
         engraving = _engraving(project, page, slot)
         if engraving:
             entry["engraving"] = engraving
@@ -123,6 +152,8 @@ def song_json(project: Project, files: list[str]) -> dict:
         slices.append(entry)
 
     payload["slices"] = slices
+    if project.source.exists():
+        payload["source"] = _source(project)
     return payload
 
 
@@ -170,3 +201,187 @@ def write(project: Project, source: Source, path: Path) -> Path:
     project.exported = True
     project.save()
     return path
+
+
+class NoCuts(ValueError):
+    """The bundle carries no `source` block, so its cuts cannot be restored."""
+
+
+def _pages_from(geometry: dict, slices: list[dict]):
+    """Rebuild the pages from a manifest's source geometry."""
+    from .project import Cut, Page
+
+    # Every slot on a page exists; the ones no slice claims were discarded.
+    # That is the one thing the bundle states by omission rather than directly,
+    # since shipping a discarded slice's image would defeat discarding it.
+    claimed = {(s["page"], s["slot"]) for s in slices}
+    pages = []
+    for i, page in enumerate(geometry["pages"]):
+        cuts = [Cut([tuple(p) for p in cut]) for cut in page["cuts"]]
+        count = len(cuts) + 1
+        pages.append(
+            Page(
+                skew=page.get("skew", 0.0),
+                cuts=cuts,
+                discards=[(i, slot) not in claimed for slot in range(count)],
+                markers=[[] for _ in range(count)],
+                replacements=[None] * count,
+                bars=[None] * count,
+                content_rect=tuple(page["content"]) if page.get("content") else None,
+                levels=tuple(page["levels"]) if page.get("levels") else None,
+            )
+        )
+    return pages
+
+
+def _pages_from_detection(pdf: Path):
+    """Cut the PDF again from scratch, for a bundle that recorded no geometry."""
+    from .detect import detect_page
+    from .pdf import open_source, page_raster
+    from .project import Project
+
+    source = open_source(pdf)
+    detections, heights = [], []
+    try:
+        for i in range(len(source)):
+            gray = page_raster(source, i)
+            detections.append(detect_page(gray))
+            heights.append(gray.shape[0])
+    finally:
+        source.close()
+    return Project.from_detection(pdf, detections, heights)
+
+
+def _restore(project, slices: list[dict], positions: list[tuple[int, int]]) -> None:
+    """Put each slice's bar number, markers and engraving back on its slot."""
+    from .project import Marker, Replacement, Voice
+
+    for entry, (page, slot) in zip(slices, positions):
+        project.pages[page].bars[slot] = entry.get("bar")
+        project.pages[page].markers[slot] = [
+            Marker(
+                type=marker["type"],
+                label=marker.get("label"),
+                # Back from an array index to the (page, slot) the editor works
+                # in — the inverse of what export does.
+                destination=(
+                    positions[marker["destination"]]
+                    if marker.get("destination") is not None
+                    and marker["destination"] < len(positions)
+                    else None
+                ),
+            )
+            for marker in entry.get("markers", [])
+        ]
+        engraving = entry.get("engraving")
+        if engraving and engraving.get("lang") == "lilypond":
+            project.pages[page].replacements[slot] = Replacement(
+                voices=[
+                    Voice(
+                        clef=v.get("clef", "treble"),
+                        notes=v.get("notes", ""),
+                        lyrics=v.get("lyrics", ""),
+                    )
+                    for v in engraving.get("voices", [])
+                ],
+                print_time=engraving.get("print_time", False),
+            )
+    for entry in slices:
+        # Key and time are per slice in the bundle and per song here; the first
+        # engraving that states them is as good a song default as exists.
+        engraving = entry.get("engraving") or {}
+        if engraving.get("key"):
+            project.key = engraving["key"]
+            project.time = engraving.get("time", project.time)
+            break
+
+
+def has_cuts(path: Path) -> bool:
+    """Whether this bundle records the geometry its slices were cut with.
+
+    Worth asking before unpacking, since the answer decides whether reopening
+    is a round trip or a fresh session with the same PDF.
+    """
+    with zipfile.ZipFile(Path(path)) as zf:
+        if "song.json" not in zf.namelist():
+            return False
+        return bool(json.loads(zf.read("song.json")).get("source"))
+
+
+def read(
+    path: Path, into: Path | None = None, *, force: bool = False, detect: bool = False
+) -> tuple[Project, Path]:
+    """Unpack a bundle back into an editable project. Returns it and its PDF.
+
+    The archived PDF is written out beside the bundle and becomes the project's
+    source again, because the PDF is what the pipeline renders from — the slice
+    images in the zip are output, and are discarded rather than re-imported.
+
+    The cuts, skew, levels and content rectangles come from the manifest's
+    `source` block, so this is a real round trip rather than a re-detection
+    that happens to land nearby. A bundle written without one raises `NoCuts`;
+    `detect` says to cut the PDF from scratch instead, which is a different
+    thing and worth a caller asking about first.
+    """
+    from .project import Project, default_path, hash_file
+
+    path = Path(path)
+    with zipfile.ZipFile(path) as zf:
+        names = set(zf.namelist())
+        if "song.json" not in names:
+            raise ValueError(f"{path.name} is not a bundle: no song.json")
+        manifest = json.loads(zf.read("song.json"))
+        if manifest.get("v") != FORMAT_VERSION:
+            raise ValueError(f"unsupported bundle version {manifest.get('v')!r}")
+        geometry = manifest.get("source")
+        if not geometry and not detect:
+            raise NoCuts(
+                f"{path.name} carries no cuts — it was written by a producer that "
+                "does not record them"
+            )
+        pdf_name = (geometry or {}).get("file", "original.pdf")
+        if pdf_name not in names:
+            raise ValueError(f"{path.name} names {pdf_name} but does not contain it")
+        pdf_bytes = zf.read(pdf_name)
+
+    # Unpacking writes two files. Refuse to land on either if it is already
+    # there: the obvious place to open a bundle is next to the score it came
+    # from, and that is exactly where someone's unfinished cuts live.
+    target = Path(into) if into else path.with_suffix(".pdf")
+    existing = [f for f in (target, default_path(target)) if f.exists()]
+    if existing and not force:
+        raise ValueError(
+            f"{', '.join(f.name for f in existing)} already exists — "
+            "open it with --pdf elsewhere, or --force to overwrite"
+        )
+    target.write_bytes(pdf_bytes)
+
+    slices = manifest["slices"]
+    if geometry:
+        pages_json = geometry["pages"]
+        first = pages_json[0] if pages_json else {}
+        project = Project(
+            source=target,
+            source_hash=hash_file(target),
+            pages=_pages_from(geometry, slices),
+            content_rect=tuple(first.get("content", (0.0, 0.0, 1.0, 1.0))),
+            levels=tuple(first.get("levels", (0, 255))),
+            path=default_path(target),
+        )
+        positions = [(s["page"], s["slot"]) for s in slices]
+    else:
+        project = _pages_from_detection(target)
+        project.path = default_path(target)
+        # Detection's slices are in reading order and so are the bundle's, so
+        # they can be lined up — but only if there are exactly as many. One
+        # system found or missed shifts every marker onto the wrong slice,
+        # which is worse than not placing them at all.
+        positions = project.kept_slices()
+        if len(positions) != len(slices):
+            positions = []
+
+    project.metadata = {
+        field: str(manifest[field]) for field in METADATA_FIELDS if manifest.get(field) is not None
+    }
+    _restore(project, slices[: len(positions)], positions)
+    return project, target

noteman_slicer/cli.py

@@ -102,6 +102,56 @@ def _export(args: argparse.Namespace) -> int:
     return 0
 
 
+def _confirm(question: str) -> bool:
+    """Ask before doing something the caller did not ask for. No tty, no."""
+    if not sys.stdin.isatty():
+        print(f"{question} (not a terminal — pass --detect to say yes)")
+        return False
+    return input(f"{question} [y/N] ").strip().lower() in ("y", "yes")
+
+
+def _open(args: argparse.Namespace) -> int:
+    from . import bundle
+    from .editor import launch
+
+    zip_path, where = Path(args.zip), Path(args.pdf) if args.pdf else None
+    try:
+        cuts = bundle.has_cuts(zip_path)
+    except (OSError, ValueError) as error:
+        print(f"cannot open: {error}")
+        return 1
+
+    if not cuts and not args.detect:
+        print(f"{zip_path.name} carries no cuts — it was written by a producer that")
+        print("does not record them. Its PDF can be cut again from scratch, but that")
+        print("is a fresh session: the cuts will be detection's, and the markers land")
+        print("only if detection happens to find the same number of slices.")
+        if not _confirm("Open it that way?"):
+            return 1
+
+    try:
+        project, pdf = bundle.read(zip_path, where, force=args.force, detect=not cuts)
+    except (ValueError, KeyError) as error:
+        print(f"cannot open: {error}")
+        return 1
+
+    saved = project.save()
+    kept = project.kept_slices()
+    print(f"{pdf.name}: {len(project.pages)} pages, {len(kept)} slices")
+    if not cuts:
+        marked = sum(len(m) for page in project.pages for m in page.markers)
+        print("  cut from scratch by detection — check every cut before exporting")
+        print(
+            f"  {marked} markers placed by position"
+            if marked
+            else "  markers not placed: detection found a different number of slices"
+        )
+    print(f"  project written to {saved.name}")
+    if args.no_edit:
+        return 0
+    return launch(pdf, resume=True)
+
+
 def _edit(args: argparse.Namespace) -> int:
     from .editor import launch
 
@@ -153,6 +203,22 @@ def main(argv: list[str] | None = None) -> int:
     exp.add_argument("--type", choices=[t.value for t in SourceType])
     exp.set_defaults(func=_export)
 
+    opn = sub.add_parser("open", help="unpack a bundle back into an editable project")
+    opn.add_argument("zip")
+    opn.add_argument("--pdf", help="where to write the archived PDF (default: beside the bundle)")
+    opn.add_argument(
+        "--no-edit", action="store_true", help="write the project and stop, without the editor"
+    )
+    opn.add_argument(
+        "--force", action="store_true", help="overwrite an existing PDF or project file"
+    )
+    opn.add_argument(
+        "--detect",
+        action="store_true",
+        help="for a bundle with no cuts: cut its PDF from scratch, without asking",
+    )
+    opn.set_defaults(func=_open)
+
     ed = sub.add_parser("edit", help="open the editor")
     ed.add_argument("pdf")
     ed.add_argument(

noteman_slicer/editor.py

@@ -44,14 +44,13 @@ from PySide6.QtWidgets import (
     QPushButton,
     QScrollArea,
     QSizePolicy,
-    QSlider,
     QSplitter,
     QToolButton,
     QVBoxLayout,
     QWidget,
 )
 
-from . import bundle, lilypond
+from . import bundle, lilypond, panel as ui
 from .bundle import METADATA_FIELDS, NUMERIC_FIELDS
 from .detect import deskew, detect_page
 from .pdf import Source, open_source, page_raster
@@ -89,28 +88,19 @@ def section(title: str, box: QVBoxLayout, *, expanded: bool = True) -> QVBoxLayo
 
     A disclosure arrow, not a checkable QGroupBox: a checkbox in a group
     header reads as "enable this feature" rather than "expand this", and a
-    column of framed boxes with checkboxes is hard to scan.
+    column of framed boxes with checkboxes is hard to scan. A hairline above
+    each one does the separating that the frames used to.
     """
+    box.addWidget(ui.Rule())
     header = QToolButton()
-    header.setText(title)
+    header.setText(title.upper())
     header.setCheckable(True)
     header.setChecked(expanded)
     header.setArrowType(Qt.DownArrow if expanded else Qt.RightArrow)
     header.setToolButtonStyle(Qt.ToolButtonTextBesideIcon)
     header.setAutoRaise(True)
     header.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Fixed)
-    # Bold and greyed: a mid grey reads as a heading against both light and
+    header.setStyleSheet(ui.HEADING)
-    # dark palettes without needing a second stylesheet.
-    header.setStyleSheet(
-        "QToolButton {"
-        "  border: none;"
-        "  font-weight: 700;"
-        "  color: #808080;"
-        "  padding: 7px 0 4px 0;"
-        "  text-align: left;"
-        "}"
-        "QToolButton:hover { color: #a0a0a0; }"
-    )
 
     body = QWidget()
     layout = QVBoxLayout(body)
@@ -472,20 +462,16 @@ class Editor(QMainWindow):
     def _panel(self) -> QWidget:
         inner = QWidget()
         box = QVBoxLayout(inner)
-        panel = QScrollArea()
+        box.setContentsMargins(14, 12, 14, 14)
-        panel.setWidget(inner)
+        box.setSpacing(0)
-        panel.setWidgetResizable(True)
+        scroller = QScrollArea()
-        panel.setMinimumWidth(260)
+        scroller.setWidget(inner)
+        scroller.setWidgetResizable(True)
+        scroller.setMinimumWidth(280)
 
-        nav = QHBoxLayout()
+        self.rail = ui.PageRail()
-        self.page_label = QLabel()
+        self.rail.picked.connect(self._load_page)
-        prev, nxt = QPushButton("◀"), QPushButton("▶")
+        box.addWidget(self.rail)
-        prev.clicked.connect(lambda: self._load_page(self.index - 1))
-        nxt.clicked.connect(lambda: self._load_page(self.index + 1))
-        nav.addWidget(prev)
-        nav.addWidget(self.page_label, 1)
-        nav.addWidget(nxt)
-        box.addLayout(nav)
 
         page_section = section("Page", box)
         form = QFormLayout()
@@ -498,23 +484,39 @@ class Editor(QMainWindow):
         self.skew.valueChanged.connect(self._skew_changed)
         form.addRow("Skew", self.skew)
 
-        self.black = QSlider(Qt.Horizontal)
+        self.levels = ui.LevelsBar()
-        self.black.setRange(0, 255)
+        self.levels.changed.connect(self._levels_changed)
-        self.white = QSlider(Qt.Horizontal)
+        self.levels.setToolTip(
-        self.white.setRange(0, 255)
+            "Drag the white dot to the foot of the paper hump and the light one "
-        self.white.setValue(255)
+            "to the foot of the ink hump. The strip below is the resulting tone."
-        for s in (self.black, self.white):
+        )
-            s.valueChanged.connect(self._levels_changed)
+        page_section.addWidget(self.levels)
-        form.addRow("Black point", self.black)
-        form.addRow("White point", self.white)
 
-        discard = QPushButton("Toggle discard  (D)")
+        buttons = QHBoxLayout()
+        discard = QPushButton("Discard slice")
+        discard.setToolTip("Or press D. Discarded slices never reach the tablet.")
         discard.clicked.connect(self.view.toggle_discard)
-        form.addRow(discard)
+        reset = QPushButton("Reset crop")
-        reset = QPushButton("Reset content rectangle")
+        reset.setToolTip("Back to the content rectangle detection proposed for this page")
-        reset.setToolTip("Back to the rectangle detection proposed for this page")
         reset.clicked.connect(self._reset_rect)
-        form.addRow(reset)
+        buttons.addWidget(discard)
+        buttons.addWidget(reset)
+        page_section.addLayout(buttons)
+
+        slice_layout = section("This slice", box)
+        slice_form = QFormLayout()
+        slice_layout.addLayout(slice_form)
+        # Every slice can carry one, engraved or scanned: a scanned system has
+        # a bar number printed on it just the same, and noteman wants to be
+        # able to say "from bar 33" about either.
+        self.bar = QLineEdit()
+        self.bar.setValidator(QIntValidator(1, 9999, self.bar))
+        self.bar.setProperty("role", "number")
+        self.bar.setFixedWidth(90)
+        self.bar.setPlaceholderText("none")
+        self.bar.setToolTip("The measure this slice starts at, as printed in the score")
+        self.bar.textChanged.connect(self._bar_changed)
+        slice_form.addRow("First bar", self.bar)
 
         marker_layout = section("Markers on this slice", box)
         self.marker_list = QListWidget()
@@ -523,8 +525,13 @@ class Editor(QMainWindow):
 
         add_row = QHBoxLayout()
         self.marker_type = QComboBox()
-        self.marker_type.addItems(MARKER_TYPES)
+        # Shown as prose, sent as the enum: "D.S. al coda" is what a musician
-        self.marker_type.currentTextChanged.connect(self._marker_type_changed)
+        # reads off the page, `ds_al_coda` is what noteman parses.
+        for kind in MARKER_TYPES:
+            self.marker_type.addItem(kind.replace("_", " ").capitalize(), kind)
+        self.marker_type.currentIndexChanged.connect(
+            lambda: self._marker_type_changed(self.marker_type.currentData())
+        )
         add_row.addWidget(self.marker_type, 1)
         self.marker_label = QLineEdit()
         self.marker_label.setPlaceholderText("label")
@@ -542,7 +549,7 @@ class Editor(QMainWindow):
         for button in (add, remove, self.retarget):
             button_row.addWidget(button)
         marker_layout.addLayout(button_row)
-        self._marker_type_changed(self.marker_type.currentText())
+        self._marker_type_changed(self.marker_type.currentData())
 
         # Optional feature: without LilyPond installed the pane never appears,
         # and nothing else about the tool changes. Collapsed by default — most
@@ -556,7 +563,7 @@ class Editor(QMainWindow):
             ly_layout.addWidget(open_engrave)
             self.ly_status = QLabel()
             self.ly_status.setWordWrap(True)
-            self.ly_status.setStyleSheet("color: #808080;")
+            self.ly_status.setProperty("role", "hint")
             ly_layout.addWidget(self.ly_status)
 
         meta_layout = section("Song", box)
@@ -575,6 +582,7 @@ class Editor(QMainWindow):
                 # metronome where "Andante" cannot.
                 edit.setValidator(QIntValidator(20, 400, edit))
                 edit.setPlaceholderText("BPM")
+                edit.setProperty("role", "number")
                 edit.setFixedWidth(90)
             meta_form.addRow(f"{field.replace('_', ' ').title()}{' *' if required else ''}", edit)
 
@@ -583,27 +591,39 @@ class Editor(QMainWindow):
         self.optimise.clicked.connect(self._optimise_pdf)
         meta_layout.addWidget(self.optimise)
 
-        self.summary = QLabel()
+        # Open by default: the first thing a new user needs is to know that a
-        self.summary.setWordWrap(True)
+        # double-click adds a cut, and a collapsed section does not tell them.
-        box.addWidget(self.summary)
+        keys_layout = section("Keys and mouse", box)
-
+        keys = QLabel(ui.shortcut_html())
-        export = QPushButton("Export bundle…")
+        keys.setTextFormat(Qt.RichText)
-        export.clicked.connect(self._export)
+        keys_layout.addWidget(keys)
-        box.addWidget(export)
         box.addStretch(1)
 
-        help_text = QLabel(
+        # Where you are and the way out, pinned below the scroll. Export is the
-            "Double-click: add cut\n"
+        # one thing that must never be hidden by however far the panel is
-            "Drag: move cut · Ctrl-click: add vertex\n"
+        # scrolled, and the count beside it is what says whether it is ready.
-            "Right-click: delete cut or vertex\n"
+        footer = QWidget()
-            "Click a slice, then D to discard\n"
+        column = QVBoxLayout(footer)
-            "Drag the blue edges: content rectangle\n"
+        column.setContentsMargins(14, 0, 14, 12)
-            "Jump markers: add, then click the target slice\n"
+        column.addWidget(ui.Rule())
-            "Shift-double-click a slice: re-engrave it"
+        self.summary = QLabel()
-        )
+        self.summary.setWordWrap(True)
-        help_text.setStyleSheet("color: palette(mid);")
+        self.summary.setProperty("role", "reading")
-        box.addWidget(help_text)
+        self.summary.setContentsMargins(0, 10, 0, 6)
-        return panel
+        column.addWidget(self.summary)
+        export = QPushButton("Export bundle…")
+        export.setProperty("role", "primary")
+        export.clicked.connect(self._export)
+        column.addWidget(export)
+
+        holder = QWidget()
+        stack = QVBoxLayout(holder)
+        stack.setContentsMargins(0, 0, 0, 0)
+        stack.setSpacing(0)
+        stack.addWidget(scroller, 1)
+        stack.addWidget(footer)
+        holder.setMinimumWidth(300)
+        return holder
 
     def _shortcuts(self) -> None:
         for key, slot in (
@@ -643,29 +663,31 @@ class Editor(QMainWindow):
             return
         self.index = index
         self.view.show_page(self.project, index, self._preview(index))
+        # The histogram is of the raw scan, not the levelled preview: it has to
+        # keep showing where the ink is while you drag the points over it.
+        self.levels.set_page(self._raster(index))
         self._sync()
 
     def _sync(self) -> None:
         page = self.project.pages[self.index]
-        self.page_label.setText(f"Page {self.index + 1} / {len(self.project.pages)}")
+        self.rail.build([p.slice_count for p in self.project.pages], self.index)
-        for widget, value in ((self.skew, page.skew),):
+        self.skew.blockSignals(True)
-            widget.blockSignals(True)
+        self.skew.setValue(page.skew)
-            widget.setValue(value)
+        self.skew.blockSignals(False)
-            widget.blockSignals(False)
+        self.levels.set_levels(*self.project.page_levels(self.index))
-        black, white = self.project.page_levels(self.index)
+        bar = page.bars[self.view.selected_slice]
-        for widget, value in ((self.black, black), (self.white, white)):
+        self.bar.blockSignals(True)
-            widget.blockSignals(True)
+        self.bar.setText("" if bar is None else str(bar))
-            widget.setValue(value)
+        self.bar.blockSignals(False)
-            widget.blockSignals(False)
         self._sync_markers()
         self._sync_replacement()
         kept = len(self.project.kept_slices())
         total = sum(p.slice_count for p in self.project.pages)
         state = "discarded" if page.discards[self.view.selected_slice] else "kept"
         self.summary.setText(
-            f"{page.slice_count} slices on this page · slice "
+            f"page {self.index + 1}/{len(self.project.pages)} · "
-            f"{self.view.selected_slice + 1} is {state}\n"
+            f"slice {self.view.selected_slice + 1}/{page.slice_count} is {state}\n"
-            f"{kept} of {total} slices kept in the song"
+            f"{kept} of {total} slices ship"
         )
 
     # -- edits ------------------------------------------------------------
@@ -674,13 +696,18 @@ class Editor(QMainWindow):
         self._sync()
         self.autosave.start()
 
+    def _bar_changed(self, text: str) -> None:
+        page = self.project.pages[self.index]
+        page.bars[self.view.selected_slice] = int(text) if text.strip().isdigit() else None
+        self.autosave.start()
+
     def _skew_changed(self, value: float) -> None:
         self.project.pages[self.index].skew = value
         self.view.show_page(self.project, self.index, self._preview(self.index))
         self._touched()
 
-    def _levels_changed(self) -> None:
+    def _levels_changed(self, black: int, white: int) -> None:
-        self.project.pages[self.index].levels = (self.black.value(), self.white.value())
+        self.project.pages[self.index].levels = (black, white)
         self.view.show_page(self.project, self.index, self._preview(self.index))
         self._touched()
 
@@ -694,7 +721,7 @@ class Editor(QMainWindow):
         self.retarget.setEnabled(kind in JUMP_TYPES)
 
     def _add_marker(self) -> None:
-        kind = self.marker_type.currentText()
+        kind = self.marker_type.currentData()
         label = self.marker_label.text().strip() or None
         marker = Marker(type=kind, label=label if kind in LABELLED_TYPES else None)
         self._slot_markers().append(marker)
@@ -890,6 +917,7 @@ class Editor(QMainWindow):
 
 def launch(pdf: Path, source_type=None, resume: bool = False) -> int:
     app = QApplication(sys.argv[:1])
+    app.setStyleSheet(ui.STYLESHEET)
     source = open_source(pdf, source_type)
 
     # An exported project is spent: this opens a fresh session from detection

noteman_slicer/engrave.py

@@ -31,7 +31,7 @@ from PySide6.QtWidgets import (
     QWidget,
 )
 
-from . import lilypond
+from . import lilypond, panel as ui
 from .detect import staff_height
 from .editor import section
 from .project import Project, Replacement, Voice
@@ -96,9 +96,9 @@ class EngraveWindow(QDialog):
         self.setWindowTitle(f"Re-engrave — page {page + 1}, slice {slot + 1}")
         self.setModal(False)
 
-        state = project.pages[page]
+        self.state = project.pages[page]
-        self.replacement = state.replacements[slot] or self._seed()
+        self.replacement = self.state.replacements[slot] or self._seed()
-        state.replacements[slot] = self.replacement
+        self.state.replacements[slot] = self.replacement
 
         rows = QSplitter(Qt.Vertical)
         rows.addWidget(self._image_panel("Scanned", _pixmap(original)))
@@ -141,7 +141,7 @@ class EngraveWindow(QDialog):
         box = QVBoxLayout(panel)
         box.setContentsMargins(0, 0, 0, 0)
         heading = QLabel(title)
-        heading.setStyleSheet("font-weight: 700; color: #808080;")
+        heading.setStyleSheet(ui.HEADING.replace("QToolButton", "QLabel"))
         box.addWidget(heading)
 
         view = label or QLabel()
@@ -182,9 +182,11 @@ class EngraveWindow(QDialog):
         row.addWidget(self.print_time, 1)
         top.addRow("Time", row)
 
-        # Per slice, unlike key and time: which measure a system starts at is
+        # A property of the slice, not of the replacement — the same field the
-        # the one thing that changes with every slice and cannot be inherited.
+        # main panel shows for a scanned slice — so it survives discarding the
-        self.bar = QLineEdit("" if self.replacement.bar is None else str(self.replacement.bar))
+        # engraving. Unlike key and time it cannot be inherited from the song.
+        current = self.state.bars[self.slot]
+        self.bar = QLineEdit("" if current is None else str(current))
         self.bar.setValidator(QIntValidator(1, 9999, self.bar))
         self.bar.setFixedWidth(70)
         self.bar.setPlaceholderText("none")
@@ -194,7 +196,7 @@ class EngraveWindow(QDialog):
         box.addLayout(top)
 
         voices_label = QLabel("Voices")
-        voices_label.setStyleSheet("font-weight: 700; color: #808080;")
+        voices_label.setStyleSheet(ui.HEADING.replace("QToolButton", "QLabel"))
         box.addWidget(voices_label)
 
         self.voice_box = QVBoxLayout()
@@ -209,6 +211,7 @@ class EngraveWindow(QDialog):
         remove = QPushButton("Remove last voice")
         remove.clicked.connect(self._remove_voice)
         render = QPushButton("Render  (Ctrl+↵)")
+        render.setProperty("role", "primary")
         render.clicked.connect(self.render)
         drop = QPushButton("Discard replacement")
         drop.clicked.connect(self._discard)
@@ -227,7 +230,7 @@ class EngraveWindow(QDialog):
         self.generated = QPlainTextEdit()
         self.generated.setReadOnly(True)
         self.generated.setMaximumHeight(220)
-        self.generated.setStyleSheet("color: #808080;")
+        self.generated.setStyleSheet(f"color: {ui.GRAPHITE};")
         raw.addWidget(self.generated)
         self._refresh_source()
         return panel
@@ -256,7 +259,7 @@ class EngraveWindow(QDialog):
         self._refresh_source()
 
     def _bar_changed(self, text: str) -> None:
-        self.replacement.bar = int(text) if text.strip().isdigit() else None
+        self.state.bars[self.slot] = int(text) if text.strip().isdigit() else None
         self._refresh_source()
 
     def _settings_changed(self) -> None:
@@ -273,22 +276,25 @@ class EngraveWindow(QDialog):
         self.project.pages[self.page_index].replacements[self.slot] = None
         self.accept()
 
-    def _refresh_source(self) -> None:
+    def _source(self) -> str:
-        self.generated.setPlainText(
+        return lilypond.generate(
-            lilypond.generate(self.replacement, self.project.key, self.project.time)
+            self.replacement, self.project.key, self.project.time, self.state.bars[self.slot]
         )
 
+    def _refresh_source(self) -> None:
+        self.generated.setPlainText(self._source())
+
     # -- rendering --------------------------------------------------------
 
     def render(self) -> None:
-        source = lilypond.generate(self.replacement, self.project.key, self.project.time)
+        source = self._source()
-        self.status.setStyleSheet("color: #808080;")
+        self.status.setStyleSheet(f"color: {ui.GRAPHITE};")
         self.status.setText("rendering…")
         self.repaint()
         try:
             image = lilypond.render(source)
         except lilypond.LilypondError as error:
-            self.status.setStyleSheet("color: #c0392b;")
+            self.status.setStyleSheet(f"color: {ui.PROOF};")
             self.status.setText(str(error)[-600:])
             return
 

noteman_slicer/lilypond.py

@@ -94,7 +94,7 @@ _PREAMBLE = """\\version "2.24.0"
 """
 
 
-def generate(replacement, key: str, time: str) -> str:
+def generate(replacement, key: str, time: str, bar: int | None = None) -> str:
     """Build LilyPond source from a slice's structured replacement.
 
     The time signature is used for spacing and bar checks but not printed
@@ -111,9 +111,9 @@ def generate(replacement, key: str, time: str) -> str:
     # printed score numbers its systems. The empty bar line is what gives the
     # number a line beginning to attach to.
     number = ""
-    if replacement.bar:
+    if bar:
         number = (
-            f"      \\set Score.currentBarNumber = #{int(replacement.bar)}\n"
+            f"      \\set Score.currentBarNumber = #{int(bar)}\n"
             "      \\override Score.BarNumber.break-visibility = #'#(#f #f #t)\n"
             '      \\bar ""\n'
         )

noteman_slicer/panel.py

@@ -0,0 +1,373 @@
+"""Look and feel for the editor: palette, chrome, and two custom controls.
+
+The page already speaks a colour language — red cut lines, a blue content
+rectangle, purple marker chips, amber for a re-engraved system. The panel
+speaks the same one, from the same constants, so a colour means one thing in
+this window rather than two. Everything else is neutral, and the chrome is
+dark for the reason photo editors are: the scanned page should be the
+brightest object on screen, because it is the thing being judged.
+
+Numbers are set in mono and prose is not. This is a measuring tool; skew,
+levels, bar and page numbers are measurements, and they line up in a column
+when they are monospaced.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+from PySide6.QtCore import QRectF, Qt, Signal
+from PySide6.QtGui import QBrush, QColor, QFont, QLinearGradient, QPainter, QPen
+from PySide6.QtWidgets import QGridLayout, QSizePolicy, QToolButton, QWidget
+
+INK = "#14161a"  # window chrome
+DESK = "#1d2026"  # panel surface
+RAISED = "#262a33"  # inputs, chips
+RULE = "#333844"  # hairlines
+GRAPHITE = "#8b93a3"  # secondary text and section headings
+PAPER = "#e6e9f0"  # primary text, borrowed from the scan
+PROOF = "#dc2828"  # cuts
+CROP = "#288cdc"  # content rectangle, primary action
+MARK = "#9638be"  # markers
+PLATE = "#c87800"  # re-engraved
+
+MONO = '"JetBrains Mono", "DejaVu Sans Mono", "Menlo", monospace'
+
+STYLESHEET = f"""
+QMainWindow, QDialog {{ background: {INK}; }}
+QWidget {{ color: {PAPER}; font-size: 13px; }}
+QScrollArea, QScrollArea > QWidget > QWidget {{ background: {DESK}; border: none; }}
+QSplitter::handle {{ background: {RULE}; width: 1px; }}
+QGraphicsView {{ background: {INK}; border: none; }}
+
+QLabel {{ background: transparent; }}
+QLabel[role="hint"] {{ color: {GRAPHITE}; font-size: 12px; }}
+QLabel[role="reading"] {{ color: {PAPER}; font-family: {MONO}; font-size: 12px; }}
+
+QLineEdit, QComboBox, QDoubleSpinBox, QListWidget {{
+    background: {RAISED}; border: 1px solid {RULE}; border-radius: 3px;
+    padding: 4px 6px; selection-background-color: {CROP};
+}}
+QLineEdit:focus, QComboBox:focus, QDoubleSpinBox:focus, QListWidget:focus {{
+    border-color: {CROP};
+}}
+QLineEdit[role="number"], QDoubleSpinBox {{ font-family: {MONO}; }}
+QComboBox::drop-down {{ border: none; width: 18px; }}
+QDoubleSpinBox::up-button, QDoubleSpinBox::down-button {{
+    background: {RULE}; border: none; width: 16px;
+}}
+QDoubleSpinBox::up-arrow, QDoubleSpinBox::down-arrow {{ width: 7px; height: 7px; }}
+QComboBox QAbstractItemView {{
+    background: {RAISED}; border: 1px solid {RULE}; selection-background-color: {CROP};
+}}
+QListWidget::item {{ padding: 2px 4px; }}
+QListWidget::item:selected {{ background: {MARK}; }}
+
+QPushButton {{
+    background: {RAISED}; border: 1px solid {RULE}; border-radius: 3px;
+    padding: 6px 12px;
+}}
+QPushButton:hover {{ border-color: {GRAPHITE}; }}
+QPushButton:pressed {{ background: {RULE}; }}
+QPushButton:disabled {{ color: {RULE}; }}
+QPushButton:focus {{ border-color: {CROP}; }}
+QPushButton[role="primary"] {{
+    background: {CROP}; border-color: {CROP}; color: #ffffff;
+    font-weight: 600; padding: 9px 12px;
+}}
+QPushButton[role="primary"]:hover {{ background: #3a9de8; }}
+
+QScrollBar:vertical {{ background: {DESK}; width: 10px; margin: 0; }}
+QScrollBar:horizontal {{ background: {DESK}; height: 10px; margin: 0; }}
+QScrollBar::handle {{ background: {RULE}; border-radius: 5px; min-height: 30px; }}
+QScrollBar::handle:hover {{ background: {GRAPHITE}; }}
+QScrollBar::add-line, QScrollBar::sub-line {{ height: 0; width: 0; }}
+QScrollBar::add-page, QScrollBar::sub-page {{ background: transparent; }}
+
+QCheckBox {{ spacing: 7px; }}
+QCheckBox::indicator {{
+    width: 14px; height: 14px; border: 1px solid {RULE};
+    border-radius: 3px; background: {RAISED};
+}}
+QCheckBox::indicator:checked {{ background: {CROP}; border-color: {CROP}; }}
+QCheckBox::indicator:hover {{ border-color: {GRAPHITE}; }}
+
+QStatusBar {{ background: {INK}; color: {GRAPHITE}; }}
+QToolTip {{ background: {RAISED}; color: {PAPER}; border: 1px solid {RULE}; padding: 4px; }}
+"""
+
+HEADING = f"""
+QToolButton {{
+    border: none; background: transparent; text-align: left;
+    color: {GRAPHITE}; font-size: 11px; font-weight: 700;
+    letter-spacing: 1.4px; padding: 10px 0 5px 0;
+}}
+QToolButton:hover {{ color: {PAPER}; }}
+"""
+
+
+def mono(size: int = 12, weight: int = QFont.Normal) -> QFont:
+    font = QFont("JetBrains Mono", size, weight)
+    font.setStyleHint(QFont.Monospace)
+    return font
+
+
+class Rule(QWidget):
+    """A hairline between sections. Structure the eye can follow without boxes."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.setFixedHeight(1)
+        self.setStyleSheet(f"background: {RULE};")
+
+
+class PageRail(QWidget):
+    """One chip per page, each carrying its slice count.
+
+    Replaces a ◀ 1/6 ▶ stepper. The song *is* a sequence of pages with a
+    number of systems on each, and seeing that sequence is how you notice the
+    page where detection found one slice where the others found three — the
+    failure this tool actually produces.
+    """
+
+    picked = Signal(int)
+
+    COLUMNS = 7  # ponytail: fixed, sized for the panel's minimum width
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.buttons: list[QToolButton] = []
+        self.grid = QGridLayout(self)
+        self.grid.setContentsMargins(0, 0, 0, 0)
+        self.grid.setSpacing(4)
+        self.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Fixed)
+
+    def build(self, counts: list[int], current: int) -> None:
+        while self.buttons:
+            chip = self.buttons.pop()
+            self.grid.removeWidget(chip)
+            chip.deleteLater()
+        for i, count in enumerate(counts):
+            chip = QToolButton()
+            chip.setText(f"{i + 1}\n{count}")
+            chip.setFont(mono(11))
+            chip.setFixedSize(34, 38)
+            chip.setCursor(Qt.PointingHandCursor)
+            chip.setToolTip(f"Page {i + 1} — {count} slice{'s' if count != 1 else ''}")
+            chip.setStyleSheet(self._chip_style(i == current))
+            chip.clicked.connect(lambda _=False, n=i: self.picked.emit(n))
+            self.grid.addWidget(chip, i // self.COLUMNS, i % self.COLUMNS)
+            self.buttons.append(chip)
+        self.grid.setColumnStretch(self.COLUMNS, 1)
+
+    @staticmethod
+    def _chip_style(current: bool) -> str:
+        return (
+            f"QToolButton {{ background: {'#12405f' if current else RULE};"
+            f" border: 1px solid {CROP if current else '#454b59'}; border-radius: 3px;"
+            f" color: {PAPER if current else GRAPHITE}; }}"
+            f"QToolButton:hover {{ border-color: {PAPER}; color: {PAPER}; }}"
+        )
+
+
+class LevelsBar(QWidget):
+    """The scan's own ink distribution, with the black and white points on it.
+
+    The signature control of this window, and the one place worth spending
+    pixels: getting levels wrong is the single mistake that cannot be seen
+    until the bundle is on the tablet, and two anonymous sliders give no reason
+    to move either one. Here the paper hump and the ink hump are visible, the
+    handles sit on them, and the strip underneath shows the tone ramp that
+    results — grey ink looks grey right there.
+    """
+
+    changed = Signal(int, int)
+
+    RAMP = 14  # height of the tone strip under the histogram
+    GRAB = 7
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.hist = np.zeros(256)
+        self.black, self.white = 0, 255
+        self._drag: str | None = None
+        self.setMinimumHeight(96)
+        self.setMouseTracking(True)
+        self.setCursor(Qt.SizeHorCursor)
+        self.setFocusPolicy(Qt.StrongFocus)
+
+    def set_page(self, gray: np.ndarray) -> None:
+        counts = np.bincount(gray.ravel(), minlength=256).astype(float)
+        # Square root, clipped to the tallest bin that is not the paper spike.
+        # Linear buries the ink hump under a spike two orders of magnitude
+        # taller; log flattens everything into one slab. This keeps both humps
+        # shaped like humps, which is the whole point of showing them.
+        scale = np.sqrt(counts)
+        ceiling = np.partition(scale, -3)[-3] or scale.max() or 1.0
+        self.hist = np.clip(scale / ceiling, 0, 1)
+        self.update()
+
+    def set_levels(self, black: int, white: int) -> None:
+        self.black, self.white = black, white
+        self.update()
+
+    # -- painting ---------------------------------------------------------
+
+    def _x(self, value: int) -> float:
+        return value / 255 * (self.width() - 1)
+
+    def paintEvent(self, event) -> None:
+        p = QPainter(self)
+        p.setRenderHint(QPainter.Antialiasing)
+        w, h = self.width(), self.height()
+        top = h - self.RAMP - 10
+
+        p.fillRect(0, 0, w, top, QColor(INK))
+        p.setPen(Qt.NoPen)
+        p.setBrush(QColor("#5f7d99"))
+        for value in range(256):
+            bar = self.hist[value] * (top - 4)
+            p.drawRect(QRectF(self._x(value), top - bar, max(w / 256, 1.0), bar))
+
+        # What is clipped away, dimmed at both ends.
+        p.setBrush(QColor(20, 22, 26, 170))
+        p.drawRect(QRectF(0, 0, self._x(self.black), top))
+        p.drawRect(QRectF(self._x(self.white), 0, w - self._x(self.white), top))
+
+        ramp = QLinearGradient(self._x(self.black), 0, self._x(self.white), 0)
+        ramp.setColorAt(0.0, QColor(0, 0, 0))
+        ramp.setColorAt(1.0, QColor(255, 255, 255))
+        p.setBrush(QBrush(ramp))
+        p.drawRect(QRectF(0, h - self.RAMP, w, self.RAMP))
+        p.fillRect(QRectF(0, h - self.RAMP, self._x(self.black), self.RAMP), QColor(0, 0, 0))
+        p.fillRect(
+            QRectF(self._x(self.white), h - self.RAMP, w - self._x(self.white), self.RAMP),
+            QColor(255, 255, 255),
+        )
+
+        for value, colour in ((self.black, QColor(PAPER)), (self.white, QColor(CROP))):
+            x = self._x(value)
+            p.setPen(QPen(colour, 2))
+            p.drawLine(QRectF(x, 0, 0, h).topLeft(), QRectF(x, 0, 0, h).bottomLeft())
+            p.setPen(Qt.NoPen)
+            p.setBrush(colour)
+            p.drawEllipse(QRectF(x - 4, top + 1, 8, 8))
+
+        # Readouts inside the histogram, not on the tone strip: white text on
+        # the pale end of that ramp is unreadable exactly when the white point
+        # is where you most need to read it.
+        p.setFont(mono(10))
+        p.setPen(QColor(PAPER))
+        p.drawText(
+            QRectF(5, 2, w - 10, 16), Qt.AlignLeft | Qt.AlignVCenter, f"black {self.black}"
+        )
+        p.setPen(QColor(CROP))
+        p.drawText(
+            QRectF(5, 2, w - 10, 16), Qt.AlignRight | Qt.AlignVCenter, f"white {self.white}"
+        )
+
+    # -- interaction ------------------------------------------------------
+
+    def _nearest(self, x: float) -> str:
+        return "black" if abs(x - self._x(self.black)) <= abs(x - self._x(self.white)) else "white"
+
+    def mousePressEvent(self, event) -> None:
+        self._drag = self._nearest(event.position().x())
+        self.mouseMoveEvent(event)
+
+    def mouseMoveEvent(self, event) -> None:
+        if not self._drag:
+            return
+        value = int(round(event.position().x() / max(self.width() - 1, 1) * 255))
+        value = min(255, max(0, value))
+        if self._drag == "black":
+            self.black = min(value, self.white - 1)
+        else:
+            self.white = max(value, self.black + 1)
+        self.update()
+        self.changed.emit(self.black, self.white)
+
+    def mouseReleaseEvent(self, event) -> None:
+        self._drag = None
+
+    def keyPressEvent(self, event) -> None:
+        step = {Qt.Key_Left: -1, Qt.Key_Right: 1}.get(event.key())
+        if step is None:
+            return super().keyPressEvent(event)
+        # Shift picks the white point, so the whole control is reachable from
+        # the keyboard without a second focus stop.
+        if event.modifiers() & Qt.ShiftModifier:
+            self.white = min(255, max(self.black + 1, self.white + step))
+        else:
+            self.black = max(0, min(self.white - 1, self.black + step))
+        self.update()
+        self.changed.emit(self.black, self.white)
+
+
+def keycap(text: str) -> str:
+    """A key name as inline HTML, for the shortcut list."""
+    return (
+        f'<span style="font-family:{MONO}; background:{RAISED}; color:{PAPER};'
+        f' border:1px solid {RULE}; padding:1px 4px;">{text}</span>'
+    )
+
+
+SHORTCUTS = [
+    ("Double-click", "add a cut"),
+    ("Drag", "move a cut"),
+    ("Ctrl-click", "add a vertex"),
+    ("Right-click", "delete a cut or vertex"),
+    ("D", "discard the selected slice"),
+    ("Shift-double-click", "re-engrave a slice"),
+    ("PgUp / PgDn", "change page"),
+    ("Ctrl+S", "save"),
+]
+
+
+def shortcut_html() -> str:
+    rows = "".join(
+        f"<tr><td style='padding:2px 10px 2px 0'>{keycap(k)}</td>"
+        f"<td style='color:{GRAPHITE}'>{v}</td></tr>"
+        for k, v in SHORTCUTS
+    )
+    return f"<table cellspacing='0'>{rows}</table>"
+
+
+def demo() -> None:
+    """Self-check: the histogram and handles behave without a real page."""
+    from PySide6.QtWidgets import QApplication
+
+    app = QApplication.instance() or QApplication([])
+    bar = LevelsBar()
+    bar.resize(300, 96)
+    bar.set_page(np.array([[10, 10, 250, 250, 250]], np.uint8))
+    assert bar.hist[250] == 1.0 and 0 < bar.hist[10] <= 1.0, bar.hist[[10, 250]]
+    assert bar.hist[128] == 0.0, "an empty bin draws nothing"
+    bar.set_levels(40, 200)
+    seen: list[tuple[int, int]] = []
+    bar.changed.connect(lambda b, w: seen.append((b, w)))
+    bar._drag = "white"
+    bar.white = 30  # a drag past the black point must not invert the ramp
+    bar.set_levels(40, 200)
+    bar.keyPressEvent(_Key(Qt.Key_Left, Qt.NoModifier))
+    assert bar.black == 39 and seen[-1] == (39, 200), (bar.black, seen)
+    bar.keyPressEvent(_Key(Qt.Key_Right, Qt.ShiftModifier))
+    assert bar.white == 201, bar.white
+    bar.grab()  # paints; raises if the painter path is wrong
+    assert PageRail()._chip_style(True) != PageRail._chip_style(False)
+    del app
+    print("ok")
+
+
+class _Key:
+    def __init__(self, key, modifiers):
+        self._key, self._mod = key, modifiers
+
+    def key(self):
+        return self._key
+
+    def modifiers(self):
+        return self._mod
+
+
+if __name__ == "__main__":
+    demo()

noteman_slicer/project.py

@@ -113,7 +113,11 @@ class Marker:
         return self.type in JUMP_TYPES
 
     def describe(self) -> str:
-        text = self.type
+        """For the marker list and the badge drawn on the page — never the wire.
+
+        A musician reads "D.S. al coda" off the score, not `ds_al_coda`.
+        """
+        text = self.type.replace("_", " ").capitalize()
         if self.label:
             text += f" “{self.label}”"
         if self.destination:
@@ -147,10 +151,6 @@ class Replacement:
     voices: list[Voice] = field(default_factory=list)
     key: str | None = None
     time: str | None = None
-    # The measure this system starts at, printed above its first bar the way a
-    # score numbers its systems. Per slice and nothing else: it is the one thing
-    # about a replacement that cannot be inherited or guessed.
-    bar: int | None = None
     # The printed score repeats the key signature at every system but not the
     # time signature, so a re-engraved middle slice must not show one.
     print_time: bool = False
@@ -168,6 +168,11 @@ class Page:
     # A re-engraved system per slice, when the scan is past saving. None for
     # the ordinary case, which is nearly all of them.
     replacements: list[Replacement | None] = field(default_factory=lambda: [None])
+    # The measure each slice starts at, when it is known. A property of the
+    # slice rather than of a replacement: a scanned system has a bar number
+    # printed on it just as an engraved one does, and noteman wants to say
+    # "from bar 33" about either.
+    bars: list[int | None] = field(default_factory=lambda: [None])
     content_rect: tuple[float, float, float, float] | None = None
     levels: tuple[int, int] | None = None
 
@@ -193,6 +198,10 @@ class Page:
         self.discards.insert(index, self.discards[index])
         self.markers.insert(index + 1, [])
         self.replacements.insert(index + 1, None)
+        # The upper half keeps the number: it still starts where the slice did.
+        # What bar the new lower half starts at needs counting, which is the
+        # user's job.
+        self.bars.insert(index + 1, None)
         return index
 
     def remove_cut(self, index: int) -> None:
@@ -205,6 +214,8 @@ class Page:
         # Two engraved halves cannot be merged, so the upper one wins.
         below = self.replacements.pop(index + 1)
         self.replacements[index] = self.replacements[index] or below
+        # The merged slice starts where the upper half did.
+        self.bars.pop(index + 1)
 
     def remember_clefs(self, project: Project, slot: int) -> None:
         """Carry this slice's clefs forward as the song's defaults."""
@@ -296,6 +307,7 @@ class Project:
                     discards=discards,
                     markers=[[] for _ in discards],
                     replacements=[None] * len(discards),
+                    bars=[None] * len(discards),
                     # Per page, not per song: scans drift, so the margin junk
                     # sits in a different place on each one.
                     content_rect=detection.content,
@@ -360,10 +372,10 @@ class Project:
                             **({"key": r.key} if r.key else {}),
                             **({"time": r.time} if r.time else {}),
                             **({"print_time": True} if r.print_time else {}),
-                            **({"bar": r.bar} if r.bar else {}),
                         }
                         for r in page.replacements
                     ],
+                    "bars": page.bars,
                     "content_rect": list(page.content_rect) if page.content_rect else None,
                     "levels": list(page.levels) if page.levels else None,
                 }
@@ -417,10 +429,19 @@ class Project:
                         key=r.get("key"),
                         time=r.get("time"),
                         print_time=r.get("print_time", False),
-                        bar=r.get("bar"),
                     )
                     for r in page.get("replacements", [None] * len(page["discards"]))
                 ],
+                bars=page.get(
+                    "bars",
+                    # Before bar numbers were a property of the slice they lived
+                    # on the replacement, so an engraved slice is where an older
+                    # project keeps one.
+                    [
+                        r.get("bar") if isinstance(r, dict) else None
+                        for r in page.get("replacements", [None] * len(page["discards"]))
+                    ],
+                ),
                 content_rect=tuple(page["content_rect"]) if page["content_rect"] else None,
                 levels=tuple(page["levels"]) if page["levels"] else None,
             )

noteman_slicer/render.py

@@ -161,7 +161,9 @@ def render_slices(project: Project, source: Source) -> list[SliceImage]:
                 # flows through staff-height normalisation and the rest exactly
                 # as a scanned one does.
                 gray = lilypond.render(
-                    lilypond.generate(engraved, project.key, project.time)
+                    lilypond.generate(
+                        engraved, project.key, project.time, page_state.bars[slot]
+                    )
                 )
             else:
                 if page is None:

tests/test_editor.py

@@ -77,9 +77,14 @@ def main() -> int:
     # Skew and levels reach the model and re-render without raising.
     editor.skew.setValue(-1.4)
     assert abs(page.skew + 1.4) < 1e-6
-    editor.black.setValue(40)
+    # The levels bar carries the page's own histogram and drives the model
-    editor.white.setValue(210)
+    # directly — there are no sliders behind it to keep in step.
+    assert editor.levels.hist.sum() > 0, "the histogram should hold the scan"
+    editor.levels.set_levels(40, 210)
+    editor._levels_changed(40, 210)
     assert project.page_levels(0) == (40, 210)
+    editor.rail.picked.emit(0)  # the page rail navigates
+    assert editor.index == 0 and len(editor.rail.buttons) == len(project.pages)
 
     # Metadata.
     editor.metadata["title"].setText("Ketun joululaulu")

tests/test_lilypond.py

@@ -75,9 +75,10 @@ def main() -> int:
     # property, and is visible only at a line beginning — one number above the
     # first bar, as a printed score numbers its systems.
     numbered = lilypond.generate(
-        Replacement(voices=[Voice("treble", "c4 d", ""), Voice("bass", "c4 d", "")], bar=33),
+        Replacement(voices=[Voice("treble", "c4 d", ""), Voice("bass", "c4 d", "")]),
         "c",
         "4/4",
+        33,
     )
     assert numbered.count("currentBarNumber = #33") == 1, numbered
     assert "break-visibility = #'#(#f #f #t)" in numbered
@@ -171,7 +172,7 @@ def main() -> int:
     assert page.replacements[second] is SATB
 
     # Round-trip, including the song-level engraving defaults.
-    SATB.bar = 33
+    page.bars[second] = 33
     project.key, project.time, project.clefs = "aes", "3/4", ["treble", "bass"]
     saved = project.save()
     reloaded = Project.load(saved)
@@ -180,7 +181,7 @@ def main() -> int:
     assert restored is not None
     assert [v.clef for v in restored.voices] == ["treble", "bass"]
     assert restored.voices[0].lyrics == "la la la la la la"
-    assert restored.bar == 33, "the slice's bar number survives a save"
+    assert reloaded.pages[0].bars[second] == 33, "the slice's bar number survives a save"
     assert reloaded.pages[0].replacements[first] is None
 
     source.close()

tests/test_markers.py

@@ -70,11 +70,16 @@ def main() -> int:
 
     # Cut edits keep markers aligned with their slices.
     before = list(page.markers[first])
+    page.bars[first] = 5
     index = page.add_cut(Cut.straight(0.95))
     assert len(page.markers) == page.slice_count
+    assert len(page.bars) == page.slice_count
     assert page.markers[first] == before, "markers must not move when a later slice splits"
+    assert page.bars[first] == 5, "the upper half still starts where the slice did"
     page.remove_cut(index)
     assert len(page.markers) == page.slice_count
+    assert len(page.bars) == page.slice_count and page.bars[first] == 5
+    page.bars[first] = None
 
     # Export resolves (page, slot) to the slice's index in the bundle.
     names = [f"{i + 1:03}.webp" for i in range(len(project.kept_slices()))]
@@ -99,14 +104,17 @@ def main() -> int:
     project.key, project.time = "aes", "3/4"
     page.replacements[second] = Replacement(
         voices=[Voice("treble", "c4 d e f", "la la la la"), Voice("bass", " c4 d e f ", "  ")],
-        bar=33,
     )
+    page.bars[second] = 33
     engraved = song_json(project, names)["slices"]
     assert "engraving" not in engraved[0], "a scanned slice has no notation"
     ly = engraved[1]["engraving"]
     assert ly["lang"] == "lilypond"
     # Song defaults are resolved per slice: reading one slice needs no context.
-    assert (ly["key"], ly["time"], ly["print_time"], ly["bar"]) == ("aes", "3/4", False, 33)
+    assert (ly["key"], ly["time"], ly["print_time"]) == ("aes", "3/4", False)
+    # The bar number is on the slice, not the engraving: a scanned system is
+    # numbered in the score just the same.
+    assert engraved[1]["bar"] == 33 and "bar" not in ly, engraved[1]
     assert ly["voices"][0] == {"clef": "treble", "notes": "c4 d e f", "lyrics": "la la la la"}
     assert "lyrics" not in ly["voices"][1], "an empty field is absent, not empty"
     assert ly["voices"][1]["notes"] == "c4 d e f"
@@ -137,8 +145,78 @@ def main() -> int:
         meta = json.loads(zf.read("song.json"))
     assert meta["slices"][0]["markers"][1]["destination"] == 1, meta["slices"]
 
+    # And back out again. The bundle carries the cuts, so reopening it rebuilds
+    # the project rather than re-cutting the score — and a jump goes back from
+    # an array index to the (page, slot) the editor works in.
+    reloaded.pages[0].replacements[second] = Replacement(
+        voices=[Voice("treble", "c4 d", "la la")]
+    )
+    reloaded.pages[0].bars[second] = 7
+    out = bundle.write(reloaded, source, tmp / "song.zip")
+    opened, unpacked = bundle.read(out, tmp / "reopened.pdf")
+    assert unpacked.exists() and unpacked.stat().st_size > 0
+    assert opened.metadata["title"] == "Test song"
+    assert len(opened.pages) == len(reloaded.pages)
+    back = opened.pages[0]
+    assert back.discards == reloaded.pages[0].discards
+    assert [len(c.points) for c in back.cuts] == [len(c.points) for c in reloaded.pages[0].cuts]
+    assert back.markers[first][1].destination == (0, second), back.markers[first][1].destination
+    assert back.markers[second][0].type == "coda"
+    assert back.bars[second] == 7
+    assert back.replacements[second].voices[0].lyrics == "la la"
+
+    # A bundle from a producer that records no cuts: refused by default, and
+    # cut from scratch by detection when the caller says so. The slices are in
+    # reading order either way, so markers can be lined up by position — but
+    # only when detection finds exactly as many.
+    plain = tmp / "plain.zip"
+    with zipfile.ZipFile(out) as src, zipfile.ZipFile(plain, "w") as dst:
+        for name in src.namelist():
+            data = src.read(name)
+            if name == "song.json":
+                manifest = json.loads(data)
+                manifest.pop("source")
+                for entry in manifest["slices"]:
+                    entry.pop("page", None)
+                    entry.pop("slot", None)
+                data = json.dumps(manifest).encode()
+            dst.writestr(name, data)
+    assert bundle.has_cuts(out) and not bundle.has_cuts(plain)
+    try:
+        bundle.read(plain, tmp / "nocuts.pdf")
+    except bundle.NoCuts as error:
+        assert "no cuts" in str(error), error
+    else:
+        raise AssertionError("a bundle without cuts should not open silently")
+
+    cut_again, again_pdf = bundle.read(plain, tmp / "nocuts.pdf", detect=True)
+    assert again_pdf.exists()
+    assert cut_again.metadata["title"] == "Test song", "the title block still comes back"
+    assert len(cut_again.kept_slices()) == len(reloaded.kept_slices())
+    placed = [m for page in cut_again.pages for slot in page.markers for m in slot]
+    assert len(placed) == 3, placed
+    assert placed[0].label == "A"
+
+    # Unpacking never lands on files that are already there.
+    try:
+        bundle.read(out, tmp / "reopened.pdf")
+    except ValueError as error:
+        assert "already exists" in str(error), error
+    else:
+        raise AssertionError("reopening over an existing PDF should be refused")
+
     source.close()
-    for f in (pdf, out, saved, default_path(pdf)):
+    for f in (
+        pdf,
+        out,
+        plain,
+        saved,
+        unpacked,
+        again_pdf,
+        default_path(unpacked),
+        default_path(again_pdf),
+        default_path(pdf),
+    ):
         f.unlink(missing_ok=True)
     tmp.rmdir()
     print("ok")