feat: add --mode strip to remove the OCR text layer without rasterizing

Adds a processing mode that removes the invisible (render mode 3) OCR text
layer in place. Unlike `--ocr-engine none --force-ocr`, it does not
rasterize the page, so images and visible content are preserved unchanged
and the output is smaller rather than larger. Options that require
rasterization or OCR (--deskew, --clean, --sidecar, etc.) are rejected.

Only invisible text is removed; text drawn as visible glyphs under an
opaque image (some OCR engines, and OCRmyPDF v2.2 and earlier) cannot be
removed this way, as documented.

Closes #1435.

src/ocrmypdf/_graft.py

@@ -342,6 +342,14 @@ class OcrGrafter:
             ocr_tree: OCR tree for fpdf2 renderer.
             autorotate_correction: Orientation correction in degrees (0, 90, 180, 270).
         """
+        if self.context.options.mode == ProcessingMode.strip_text:
+            # Strip mode: remove the invisible OCR text layer in place without
+            # rasterizing or grafting anything. Honor --pages if specified.
+            options = self.context.options
+            if not options.pages or pageno in options.pages:
+                strip_invisible_text(self.pdf_base, self.pdf_base.pages[pageno])
+            return
+
         if ocr_output and ocr_tree:
             raise ValueError(
                 'Cannot specify both ocr_output and ocr_tree for fpdf2 renderer'

src/ocrmypdf/_options.py

@@ -43,12 +43,16 @@ class ProcessingMode(StrEnum):
     - ``force``: Rasterize all content and run OCR regardless of existing text
     - ``skip``: Skip OCR on pages that already have text
     - ``redo``: Re-OCR pages, stripping old invisible text layer
+    - ``strip``: Remove the invisible OCR text layer in place; do not OCR
     """
 
     default = 'default'
     force = 'force'
     skip = 'skip'
     redo = 'redo'
+    # User-facing value is '--mode strip'; the member is named strip_text to
+    # avoid shadowing str.strip on this str-based enum.
+    strip_text = 'strip'
 
 
 class TaggedPdfMode(StrEnum):
@@ -79,8 +83,7 @@ def _resolve_page_token(token: str, total_pages: int | None) -> int:
     if token.lower() == 'end':
         if total_pages is None:
             raise BadArgsError(
-                "'end' was used in --pages but the total page count is not yet "
-                "known"
+                "'end' was used in --pages but the total page count is not yet known"
             )
         return total_pages
     return int(token)

src/ocrmypdf/_pipeline.py

@@ -334,6 +334,11 @@ def is_ocr_required(page_context: PageContext) -> bool:
     pageinfo = page_context.pageinfo
     options = page_context.options
 
+    if options.mode == ProcessingMode.strip_text:
+        # Strip mode removes the OCR text layer in place; it never rasterizes
+        # or runs OCR. The stripping happens in OcrGrafter.graft_page.
+        return False
+
     ocr_required = True
 
     if options.pages and pageinfo.pageno not in options.pages:

src/ocrmypdf/_validation.py

@@ -17,7 +17,7 @@ import pikepdf
 
 from ocrmypdf._defaults import DEFAULT_ROTATE_PAGES_THRESHOLD
 from ocrmypdf._exec import unpaper
-from ocrmypdf._options import OcrOptions
+from ocrmypdf._options import OcrOptions, ProcessingMode
 from ocrmypdf._plugin_manager import OcrmypdfPluginManager
 from ocrmypdf.exceptions import (
     BadArgsError,
@@ -118,8 +118,36 @@ def check_options_preprocessing(options: OcrOptions) -> None:
         )
 
 
+def check_options_strip(options: OcrOptions) -> None:
+    """Reject options that cannot apply in strip mode.
+
+    ``--mode strip`` removes the OCR text layer in place without rasterizing or
+    running OCR, so image-processing and OCR-output options have no effect.
+    """
+    if options.mode != ProcessingMode.strip_text:
+        return
+    incompatible = {
+        '--deskew': options.deskew,
+        '--clean': options.clean,
+        '--clean-final': options.clean_final,
+        '--remove-background': options.remove_background,
+        '--rotate-pages': options.rotate_pages,
+        '--oversample': options.oversample,
+        '--remove-vectors': options.remove_vectors,
+        '--sidecar': options.sidecar,
+    }
+    used = sorted(name for name, value in incompatible.items() if value)
+    if used:
+        raise BadArgsError(
+            "--mode strip removes the OCR text layer without rasterizing or "
+            "running OCR, so these options have no effect and are not allowed: "
+            f"{', '.join(used)}"
+        )
+
+
 def _check_plugin_invariant_options(options: OcrOptions) -> None:
     check_platform()
+    check_options_strip(options)
     check_options_sidecar(options)
     check_options_preprocessing(options)
 

src/ocrmypdf/cli.py

@@ -327,7 +327,11 @@ Online documentation is located at:
         "'default' errors if text is found. "
         "'force' rasterizes all content and runs OCR (same as --force-ocr). "
         "'skip' skips pages with existing text (same as --skip-text). "
-        "'redo' re-OCRs pages, replacing old invisible text (same as --redo-ocr).",
+        "'redo' re-OCRs pages, replacing old invisible text (same as --redo-ocr). "
+        "'strip' removes the invisible OCR text layer without rasterizing or "
+        "running OCR, producing a smaller file; only text drawn as invisible "
+        "(render mode 3) is removed, so text from some OCR engines cannot be "
+        "removed this way.",
     )
     # Legacy flags for backward compatibility - these set the mode internally
     ocrsettings.add_argument(