diff --git a/TESTING.md b/TESTING.md
index 1fb6a93b..7b1cb16d 100644
--- a/TESTING.md
+++ b/TESTING.md
@@ -2443,10 +2443,38 @@ Recorded deviations on this page:
   view" filters are active, and plain "Filters" otherwise; the text is its accessible
   name, so the count is spoken. The concept has no indicator, and without one a Tags
   filter set by Tags & categories Browse was invisible on the shelf. The Library counts
-  Tags; Images counts Source, Folder, Media and Tags (each once). The toolbar category is
+  Tags, Folder and Tag match (D150); Images counts Source, Folder, Media and Tags (each once). The toolbar category is
   not a Refine filter and is not counted. The caption's count is a `role="status"`
   region, written only when it changes and kept shown while the shelf reloads, so
   Load more and scrolling never re-announce it.
+- **D150** (#444, cutover #334): "Refine this view" on the Library holds the concept
+  Filters dialog's **Folder** ("All output folders", then each folder below an output
+  root as a tree built by path segment (each folder directly under its own parent,
+  case variants as distinct siblings, siblings case-insensitive then exact), indented
+  by depth, read from `GET /prompt_manager/library/options?include=folders`
+  when the dialog opens; the chosen folder stays listed even when the list lacks it) and
+  **Tags**, plus **Tag match** ("All of these tags" / "Any of these tags" / "Prompts without tags", D149) drawn as the
+  concept's own select; the concept's "Prompt evidence" and prototype note are absent.
+  `GET /prompt_manager/library` takes `folder` (`/`-joined; `\` is a separator only on
+  Windows, on POSIX it is part of a folder's name as the listing shows it; `.`, `..`,
+  empty segments and, on Windows, drives are 400) and `tag_mode` (`all` default, `any`, `untagged` from D149), and echoes
+  both; a client whose non-default value is not echoed (an un-restarted older server)
+  shows the read error, never the unfiltered shelf. A folder keeps a parent with one
+  linked image (`generated_images.prompt_id`) in it or below it under any spelling of
+  any output root (the root as configured or detected and after `realpath`, so a
+  symlinked output folder works): `file_path` (`normcase(normpath(abspath))`) is
+  compared with prefixes built by the same normalization, so case folding is the
+  platform's own, including non-ASCII on Windows. The folder is an outer AND around the
+  parent and pair arms; Any puts one `t.name IN (...)` in each arm, so a card matches
+  when the parent or one active pair carries any tag (text and category still AND
+  inside each arm); with one tag Any equals All. Filters counts Tags, Folder and a Tag
+  match other than All (D44). Saved Library views store `tag_mode` (`all|any|untagged`) and
+  `folder` (text 1024); older rows read the defaults. Tests:
+  `tests/test_library_folders.py` (pure prefixes and names with `posixpath`/`ntpath`,
+  drive, UNC, non-ASCII, symlinked root, the any-tag union), `test_api_library.py`,
+  `test_saved_views.py`, the library-state and saved-views JS units, and
+  `tests/browser/workspace-library-filters.spec.mjs` (behavior, the Refine dialog against
+  the concept Filters dialog, artifact captures). Windows: run `portability.yml` on the PR.
 
 `tests/browser/library-concept.spec.mjs` compares the shelf (#249 E3) on the
 concept-shaped fixture, which creates the concept's prompts last to first so Recently
@@ -6637,12 +6665,12 @@ Deploying this backend needs a ComfyUI restart (Python and route changes).
 
 `#/tags` ("Tags & categories", page title "Tags") is a native workspace route; it no
 longer hands off to the legacy tag manager. That page stays reachable from Overview's
-"Open existing tag manager" card for multi-tag AND/OR browsing (tag search and sort
-and the untagged entry moved here with D149, #444); bulk prompt delete stays on the
-legacy admin page (bulk tags: the Prompt library's selection bar, D151). A
-prompt's category is changed in the Prompt library editor, on many prompts at once with
-the Prompt library's selection bar (D148, #437), or with the legacy admin page's "Set
-Category" (both `POST /prompt_manager/bulk/category`);
+"Open existing tag manager" card for its own page; tag search and sort, the untagged
+entry (D149) and multi-tag OR (the Library's Tag match, D150) moved to the workspace
+(#444); bulk prompt delete stays on the legacy admin page (bulk tags: the Prompt
+library's selection bar, D151). A prompt's category is changed in the Prompt library
+editor, on many prompts at once with the Prompt library's selection bar (D148, #437), or
+with the legacy admin page's "Set Category" (both `POST /prompt_manager/bulk/category`);
 the Images selection bar's Set category sets images' own categories only (D140, #332),
 and Manage category renames a value on prompts, recipes and images together (D144). The screen consumes only the `/prompt_manager/vocabulary/*` routes
 above and adds no route, so PR B needed no ComfyUI restart; D149 (#444) adds read
@@ -6715,10 +6743,10 @@ fixture-only tags after the concept's sample tags.
   counted every prompt without `prompt_tags` and hid the entry at 0; this row always
   shows) and echoes `search` and `sort`. Browse opens the Library with `tag_mode=untagged`
   (`GET /prompt_manager/library`, echoed as `tag_mode`; with a `tag` it is 400): "Filters ·
-  1", and Refine this view adds **Tag match** after Tags ("All of these tags" / "Prompts
+  1", and Refine this view adds **Tag match** after Tags ("All of these tags" / "Any of these tags" (D150) / "Prompts
   without tags", the latter disables Tags and drops them on Apply). A client whose request
   the server did not echo (an un-restarted older server) shows the read error with Retry,
-  never an unfiltered list. Saved Library views store `tag_mode` (`all|untagged`, default
+  never an unfiltered list. Saved Library views store `tag_mode` (`all|any|untagged`, default
   `all`); untagged with tags is refused on write and reads back as `all`; an older build
   opens an untagged view as the whole Library. The concept comparison holds the row to the
   concept's first category row, its top to the concept table's offset, the table to that
diff --git a/database/library.py b/database/library.py
index ec684527..49f18ac9 100644
--- a/database/library.py
+++ b/database/library.py
@@ -5,6 +5,7 @@ import sqlite3
 from collections.abc import Iterator
 from contextlib import contextmanager
 
+from .library_folders import folder_condition, list_library_folders
 from .library_tokens import library_edit_token
 
 _ELIGIBLE = """(EXISTS(SELECT 1 FROM prompt_pairs ep WHERE ep.positive_prompt_id=p.id)
@@ -121,6 +122,9 @@ def _archive(value: str) -> str:
     return ARCHIVE_SCOPES[value]
 
 
+# How the Tags filter matches (#444): every tag (AND), any of them (OR), or
+# parents without any tag.
+TAG_MODES = ("all", "any", "untagged")
 # A parent that no tag's Browse returns (#444 "Untagged prompts"): no tag of its
 # own and no active pair carrying one. The vocabulary's untagged count uses it too.
 UNTAGGED = (
@@ -128,8 +132,6 @@ UNTAGGED = (
     "AND NOT EXISTS(SELECT 1 FROM prompt_pairs up JOIN prompt_pair_tags upt "
     "ON upt.pair_id=up.id WHERE up.positive_prompt_id=p.id AND up.archived=0)"
 )
-# How the Tags filter matches: every tag (AND), or parents without any tag.
-TAG_MODES = ("all", "untagged")
 
 
 def _tag_mode(tag_mode: object, tags: list[str]) -> str:
@@ -140,8 +142,33 @@ def _tag_mode(tag_mode: object, tags: list[str]) -> str:
     return tag_mode
 
 
+def _tag_conditions(tags: list[str], any_tag: bool) -> tuple[list, list, list]:
+    """Parent-arm and pair-arm tag conditions and the tags' parameters."""
+    parent_exists = (
+        "EXISTS(SELECT 1 FROM prompt_tags pt JOIN tags t ON t.id=pt.tag_id "
+        "WHERE pt.prompt_id=p.id AND t.name{test})"
+    )
+    pair_exists = (
+        "EXISTS(SELECT 1 FROM prompt_pair_tags pt JOIN tags t ON t.id=pt.tag_id "
+        "WHERE pt.pair_id=pp.id AND t.name{test})"
+    )
+    if any_tag and tags:
+        # One condition per arm: the card, or one active pair, carries any tag.
+        test = " IN (" + ",".join("?" for _ in tags) + ")"
+        return [parent_exists.format(test=test)], [pair_exists.format(test=test)], tags
+    return (
+        [parent_exists.format(test="=?") for _ in tags],
+        [pair_exists.format(test="=?") for _ in tags],
+        tags,
+    )
+
+
 def _filter(
-    text: str, category: str | None, tags: list[str], tag_mode: str = "all"
+    text: str,
+    category: str | None,
+    tags: list[str],
+    tag_mode: str = "all",
+    folder_prefixes: list[str] | None = None,
 ) -> tuple[str, list]:
     if not isinstance(text, str) or len(text) > 500:
         raise ValueError("Search text must be a string of at most 500 characters")
@@ -153,7 +180,8 @@ def _filter(
         or any(not isinstance(tag, str) or not tag or len(tag) > 200 for tag in tags)
     ):
         raise ValueError("Invalid library tags")
-    untagged = _tag_mode(tag_mode, tags) == "untagged"
+    mode = _tag_mode(tag_mode, tags)
+    untagged = mode == "untagged"
     parent, pair, parent_params, pair_params = [], ["pp.archived=0"], [], []
     if text:
         parent.append("(p.text LIKE ? ESCAPE '\\' OR ls.title LIKE ? ESCAPE '\\')")
@@ -168,17 +196,11 @@ def _filter(
         pair.append("pp.category=?")
         parent_params.append(category)
         pair_params.append(category)
-    for tag in tags:
-        parent.append(
-            "EXISTS(SELECT 1 FROM prompt_tags pt JOIN tags t ON t.id=pt.tag_id "
-            "WHERE pt.prompt_id=p.id AND t.name=?)"
-        )
-        pair.append(
-            "EXISTS(SELECT 1 FROM prompt_pair_tags pt JOIN tags t ON t.id=pt.tag_id "
-            "WHERE pt.pair_id=pp.id AND t.name=?)"
-        )
-        parent_params.append(tag)
-        pair_params.append(tag)
+    parent_tags, pair_tags, tag_params = _tag_conditions(tags, mode == "any")
+    parent.extend(parent_tags)
+    pair.extend(pair_tags)
+    parent_params.extend(tag_params)
+    pair_params.extend(tag_params)
     condition = (
         "("
         + (" AND ".join(parent) or "1=1")
@@ -194,7 +216,13 @@ def _filter(
         # A whole-card condition: inside the parent-or-pair OR an untagged pair
         # would let a tagged parent through.
         condition = f"({condition}) AND {UNTAGGED}"
-    return f"({_ELIGIBLE}) AND ({condition})", [*parent_params, *pair_params]
+    params = [*parent_params, *pair_params]
+    if folder_prefixes:
+        # A whole-card condition around both arms: images link to the parent.
+        folder, folder_params = folder_condition(folder_prefixes)
+        condition = f"({condition}) AND {folder}"
+        params.extend(folder_params)
+    return f"({_ELIGIBLE}) AND ({condition})", params
 
 
 class LibraryOperations:
@@ -278,6 +306,7 @@ class LibraryOperations:
         category: str | None = None,
         tags: list[str] | None = None,
         tag_mode: str = "all",
+        folder_prefixes: list[str] | None = None,
         sort: str = "newest",
         limit: int = 40,
         after: dict | None = None,
@@ -285,7 +314,9 @@ class LibraryOperations:
         _limit(limit)
         if sort not in _ORDERS:
             raise ValueError("Unknown library sort order")
-        where, params = _filter(text, category, [] if tags is None else tags, tag_mode)
+        where, params = _filter(
+            text, category, [] if tags is None else tags, tag_mode, folder_prefixes
+        )
         if after is not None:
             if (
                 not isinstance(after, dict)
@@ -351,6 +382,7 @@ class LibraryOperations:
         category: str | None = None,
         tags: list[str] | None = None,
         tag_mode: str = "all",
+        folder_prefixes: list[str] | None = None,
         sort: str = "newest",
         limit: int = 40,
         after: dict | None = None,
@@ -364,6 +396,7 @@ class LibraryOperations:
                 category=category,
                 tags=tags,
                 tag_mode=tag_mode,
+                folder_prefixes=folder_prefixes,
                 sort=sort,
                 limit=limit,
                 after=after,
@@ -494,9 +527,13 @@ class LibraryOperations:
             "categories": [row["category"] for row in rows],
         }
 
-    def get_library_options(self) -> dict:
+    def get_library_options(self, folder_roots=None) -> dict:
+        """Categories; with *folder_roots* (root spellings) also ``folders``."""
         with self.library_snapshot() as (conn, epoch, _ceiling):
-            return self._get_library_options(conn, epoch)
+            result = self._get_library_options(conn, epoch)
+            if folder_roots is not None:
+                result["folders"] = list_library_folders(conn, folder_roots, _ELIGIBLE)
+            return result
 
     def get_library_previews(self, positive_ids: list[int]) -> dict[int, list[dict]]:
         """Read at most two links per parent in one bounded page query."""
diff --git a/database/library_folders.py b/database/library_folders.py
new file mode 100644
index 00000000..48d10f7d
--- /dev/null
+++ b/database/library_folders.py
@@ -0,0 +1,114 @@
+"""Library output-folder filter (#444): folder names, root prefixes and listing.
+
+A folder is a ``/``-joined path relative to an output root, as Images' folder
+filter and the legacy ``/prompt_manager/subfolders`` name them. A parent
+matches a folder when one of its linked images (``generated_images.prompt_id``,
+the link its previews and image count read) lies in that folder or below it,
+under any spelling of any output root.
+
+Matching compares ``generated_images.file_path``, which is always
+``normcase(normpath(abspath(path)))`` (``models.normalize_image_path``), with
+prefixes built by the same normalization here, so case folding is the
+platform's own on both sides (Windows folds non-ASCII too, unlike SQLite's
+``lower()``) and the comparison is an exact ``substr`` with no wildcards.
+"""
+
+import os
+import sqlite3
+
+_MAX_FOLDER = 1024
+_MAX_PREFIXES = 64
+
+
+def normalize_folder(value: object, pathmod=os.path) -> str:
+    """The folder as ``a/b``, outer slashes dropped; empty means no filter.
+
+    ``/`` always separates. ``\\`` separates only on Windows (``ntpath``): on
+    POSIX it is an ordinary character of a folder's name, and the listing
+    (``relative_folder``) names such a folder with it, so both agree.
+    ``.``/``..``/empty segments, control characters and (on Windows) a drive
+    are refused: the value only ever names a folder below a root.
+    """
+    if not isinstance(value, str) or len(value) > _MAX_FOLDER:
+        raise ValueError(f"folder must be text of at most {_MAX_FOLDER} characters")
+    windows = pathmod.sep == "\\"
+    folder = (value.replace("\\", "/") if windows else value).strip("/")
+    if not folder:
+        return ""
+    parts = folder.split("/")
+    if (
+        any(part in ("", ".", "..") for part in parts)
+        or (windows and ":" in parts[0])
+        or any(ord(char) < 32 or ord(char) == 127 for char in folder)
+    ):
+        raise ValueError("folder must be a folder below an output root")
+    return folder
+
+
+def _base(root: object, pathmod) -> str:
+    return pathmod.normcase(pathmod.normpath(str(root)))
+
+
+def folder_prefixes(roots, folder: str, pathmod=os.path) -> list[str]:
+    """One ``file_path`` prefix per root spelling for a normalized folder."""
+    prefixes = []
+    for root in roots:
+        joined = pathmod.join(_base(root, pathmod), *folder.split("/"))
+        prefix = pathmod.normcase(pathmod.normpath(joined)) + pathmod.sep
+        if prefix not in prefixes:
+            prefixes.append(prefix)
+    if not prefixes or len(prefixes) > _MAX_PREFIXES:
+        raise ValueError("No output folder to filter by")
+    return prefixes
+
+
+def folder_condition(prefixes: list[str]) -> tuple[str, list]:
+    """A condition on alias ``p``: one linked image under any prefix."""
+    tests = " OR ".join("substr(fg.file_path,1,?)=?" for _ in prefixes)
+    params = [value for prefix in prefixes for value in (len(prefix), prefix)]
+    return (
+        "EXISTS(SELECT 1 FROM generated_images fg WHERE fg.prompt_id=p.id "
+        f"AND ({tests}))",
+        params,
+    )
+
+
+def relative_folder(image_path: str, roots, pathmod=os.path) -> str | None:
+    """The folder of *image_path* below the first root spelling holding it.
+
+    The spelling of the stored path is kept (its case on Windows); ``None``
+    for an image directly in a root or outside every root.
+    """
+    directory = pathmod.normpath(pathmod.dirname(image_path))
+    folded = pathmod.normcase(directory)
+    for root in roots:
+        base = _base(root, pathmod)
+        start = base if base.endswith(pathmod.sep) else base + pathmod.sep
+        if not folded.startswith(start):
+            continue
+        # normcase keeps the length for ordinary names; else show the folded form.
+        rest = (directory if len(directory) == len(folded) else folded)[len(start) :]
+        parts = rest.split(pathmod.sep)
+        if any(part in ("", ".", "..") for part in parts):
+            return None
+        return "/".join(parts)
+    return None
+
+
+def list_library_folders(
+    conn: sqlite3.Connection, roots, eligible: str, pathmod=os.path
+) -> list[str]:
+    """Every folder (and ancestor) holding an image of an eligible parent."""
+    folders = set()
+    for (image_path,) in conn.execute(
+        "SELECT DISTINCT g.image_path FROM generated_images g "
+        "JOIN prompts p ON p.id=g.prompt_id WHERE " + eligible
+    ):
+        if not isinstance(image_path, str) or not image_path:
+            continue
+        folder = relative_folder(image_path, roots, pathmod)
+        if folder is None:
+            continue
+        parts = folder.split("/")
+        folders.update("/".join(parts[:index]) for index in range(1, len(parts) + 1))
+    return sorted(folders, key=lambda value: (value.casefold(), value))
diff --git a/database/saved_views.py b/database/saved_views.py
index 9fad284c..9d691f43 100644
--- a/database/saved_views.py
+++ b/database/saved_views.py
@@ -33,8 +33,9 @@ MAX_TAG_LENGTH = 50
 _IMAGE_SORTS = ("newest", "oldest", "name", "name-desc", "rating")
 _LIBRARY_SORTS = ("newest", "oldest", "name", "rating")
 _MEDIA = ("all", "image", "video")
-# How a Library view's Tags match (#444): every tag, or parents without tags.
-_TAG_MODES = ("all", "untagged")
+# How a Library view's Tags match (#444): every tag, any of them, or parents
+# without tags ("untagged" never goes with tags; the listing refuses both).
+_TAG_MODES = ("all", "any", "untagged")
 _CONTROL = re.compile(r"[\x00-\x1f\x7f]")
 _SOURCE = re.compile(r"all|0|[1-9][0-9]{0,8}")
 # A collection id as the listing's ``collection`` query takes it (#331): none
@@ -69,8 +70,9 @@ _STATE_FIELDS = {
         "category": ("text", 100, ""),
         "sort": ("choice", _LIBRARY_SORTS, "newest"),
         "tags": ("tags", None, ()),
-        # #444: "untagged" never goes with tags (the listing refuses both).
+        # #444: the Tags match and the output folder (relative, "/"-joined).
         "tag_mode": ("choice", _TAG_MODES, "all"),
+        "folder": ("text", 1024, ""),
     },
 }
 
diff --git a/py/api/library.py b/py/api/library.py
index 5bd4e973..be699e70 100644
--- a/py/api/library.py
+++ b/py/api/library.py
@@ -21,9 +21,11 @@ from .pairs import pair_response
 try:
     from ...database.library import ARCHIVE_SCOPES
     from ...database.library_commands import LibraryCommandError
+    from ...database.library_folders import folder_prefixes, normalize_folder
 except ImportError:
     from database.library import ARCHIVE_SCOPES
     from database.library_commands import LibraryCommandError
+    from database.library_folders import folder_prefixes, normalize_folder
 
 _SECRET = os.urandom(32)
 
@@ -283,13 +285,47 @@ class LibraryRoutesMixin:
         outputs = list(self._get_all_output_dirs())
         return self._media_roots(outputs), len(outputs)
 
+    def _library_root_spellings(self) -> list[str]:
+        """Every spelling of each output root (#444 folder filter): the
+        validated, resolved root and each configured or detected path that
+        resolves to it, so images saved through a symlinked root match."""
+        from ..config import GalleryConfig
+
+        roots = [str(root) for root in self._get_all_output_dirs()]
+        candidates = [
+            *GalleryConfig.MONITORING_DIRECTORIES,
+            self._find_comfyui_output_dir(),
+            *self._comfyui_output_dir_list(),
+        ]
+        spellings = []
+        for root in roots:
+            for value in (root, *candidates):
+                if not value or not isinstance(value, (str, os.PathLike)):
+                    continue
+                value = str(value)
+                same = value == root or os.path.normcase(
+                    os.path.realpath(value)
+                ) == os.path.normcase(root)
+                if same and value not in spellings:
+                    spellings.append(value)
+        return spellings
+
     @pair_response
     async def get_library_options(self, request: web.Request) -> web.Response:
-        result = await self._run_in_executor(self.db.get_library_options)
+        include = request.query.get("include", "")
+        if include not in ("", "folders"):
+            raise ValueError("include must be empty or 'folders'")
+        if include:
+            # Folders are read only when Refine opens (a walk of linked paths).
+            roots = await self._run_in_executor(self._library_root_spellings)
+            result = await self._run_in_executor(self.db.get_library_options, roots)
+        else:
+            result = await self._run_in_executor(self.db.get_library_options)
         return web.json_response({"success": True, **result})
 
     @pair_response
     async def list_library(self, request: web.Request) -> web.Response:
+        folder = normalize_folder(request.query.get("folder", ""))
         options = {
             "text": request.query.get("text", ""),
             "category": request.query.get("category"),
@@ -299,21 +335,34 @@ class LibraryRoutesMixin:
         }
         limit = _page_limit(request)
         cursor = request.query.get("cursor")
+        roots = (
+            await self._run_in_executor(self._library_root_spellings) if folder else []
+        )
+        prefixes = folder_prefixes(roots, folder) if folder else None
 
         def read() -> tuple[dict, dict]:
             with self.db.library_snapshot(include_ceiling=True) as snapshot:
                 conn, epoch, ceiling = snapshot
+                # The folder and the roots it was resolved under join the scope.
                 scope = _scope(
-                    {"kind": "parents", "projection": 2, "epoch": epoch, **options}
+                    {
+                        "kind": "parents",
+                        "projection": 2,
+                        "epoch": epoch,
+                        **options,
+                        **({"folder": folder, "roots": roots} if folder else {}),
+                    }
                 )
                 result = self.db._list_library(
                     conn,
                     epoch,
                     ceiling,
                     **options,
+                    folder_prefixes=prefixes,
                     limit=limit,
                     after=_decode(cursor, scope),
                 )
+                result["folder"] = folder
                 records = self.db.get_library_previews(
                     [parent["id"] for parent in result["items"]]
                 )
diff --git a/tests/browser/workspace-library-filters.spec.mjs b/tests/browser/workspace-library-filters.spec.mjs
new file mode 100644
index 00000000..2dbb7101
--- /dev/null
+++ b/tests/browser/workspace-library-filters.spec.mjs
@@ -0,0 +1,143 @@
+// #444 (D150): the Library's output-folder filter and multi-tag OR in "Refine this view", against the real server, and
+// the Refine dialog against the concept's Filters dialog (app.js:1345-1352).
+import {writeFile} from 'node:fs/promises';
+import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
+import {test,expect} from './fixtures.mjs';
+import {captureCanonicalState} from './history-canonical-comparison.mjs';
+import {inventoryOf,diffInventory} from './library-editor-canonical-comparison.mjs';
+
+const route='/prompt_manager/workspace#/library';
+const concept='/__test__/canonical/workspace';
+const cards=page=>page.locator('article[data-prompt-id]');
+const card=(page,text)=>cards(page).filter({has:page.getByText(text,{exact:true})});
+const toolbar=page=>page.locator('#workspace-main search.toolbar');
+const filtersButton=page=>toolbar(page).getByRole('button',{name:/^Filters(?: · \d)?$/});
+const refine=page=>page.getByRole('dialog',{name:'Refine this view',exact:true});
+const folder=page=>refine(page).getByRole('combobox',{name:'Folder',exact:true});
+const tags=page=>refine(page).getByRole('textbox',{name:'Tags',exact:true});
+const match=page=>refine(page).getByRole('combobox',{name:'Tag match',exact:true});
+const apply=page=>refine(page).getByRole('button',{name:'Apply filters',exact:true});
+const caption=page=>page.locator('#workspace-main .section-caption > span').first();
+
+test.beforeEach(async({page,request,browserName})=>{
+    await startCoverage(page,browserName);await expect(await request.post('/__test__/reset',{data:{native_library:true}})).toBeOK();
+    page.libraryErrors=[];page.on('pageerror',error=>page.libraryErrors.push(error.message));
+});
+test.afterEach(async({page,browserName})=>{await saveCoverage(page,browserName);expect(page.libraryErrors).toEqual([]);});
+
+async function open(page) {
+    await page.goto(route);await expect(caption(page)).toHaveText(/^3 positive prompts · /);
+}
+/** Open Refine and wait for the folder list it reads on opening. */
+async function openRefine(page) {
+    const folders=page.waitForResponse(item=>new URL(item.url()).pathname==='/prompt_manager/library/options'&&new URL(item.url()).searchParams.get('include')==='folders');
+    await filtersButton(page).click();await expect(refine(page)).toBeVisible();await folders;
+}
+
+test('Refine offers Folder, Tags and Tag match; a folder narrows the shelf to prompts with images there',async({page})=>{
+    await open(page);await openRefine(page);
+    await expect(refine(page).locator('.field label')).toHaveText(['Folder','Tags','Tag match']);
+    // Both roots hold a "shared" folder; the root's own images name no folder.
+    await expect(folder(page).locator('option')).toHaveText(['All output folders','shared']);
+    await expect(match(page).locator('option')).toHaveText(['All of these tags','Any of these tags','Prompts without tags']);
+    await folder(page).selectOption('shared');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^1 positive prompt · /);
+    await expect(cards(page)).toHaveCount(1);await expect(card(page,'Cat portrait')).toHaveCount(1);
+    await expect(filtersButton(page)).toHaveText('Filters · 1');
+    await openRefine(page);await expect(folder(page)).toHaveValue('shared');
+    await refine(page).getByRole('button',{name:'Clear filters',exact:true}).click();
+    await expect(caption(page)).toHaveText(/^3 positive prompts · /);await expect(filtersButton(page)).toHaveText('Filters');
+});
+
+test('Tag match Any shows every prompt carrying one of the tags; changing only the match applies it',async({page})=>{
+    await open(page);await openRefine(page);
+    await tags(page).fill('cats, dogs');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^0 positive prompts · /);await expect(filtersButton(page)).toHaveText('Filters · 1');
+    await openRefine(page);await match(page).selectOption('any');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^2 positive prompts · /);
+    await expect(cards(page)).toHaveCount(2);await expect(card(page,'Cat portrait')).toHaveCount(1);await expect(card(page,'Dog landscape')).toHaveCount(1);
+    await expect(filtersButton(page)).toHaveText('Filters · 2');
+});
+
+test('a saved view keeps its folder and tag match',async({page})=>{
+    await open(page);await openRefine(page);
+    await folder(page).selectOption('shared');await tags(page).fill('cats, dogs');await match(page).selectOption('any');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^1 positive prompt · /);
+    await toolbar(page).getByRole('button',{name:'Save view',exact:true}).click();
+    const save=page.getByRole('dialog',{name:'Save this view',exact:true});
+    await save.getByRole('textbox',{name:'View name',exact:true}).fill('Shared cats or dogs');
+    const created=page.waitForResponse(item=>new URL(item.url()).pathname==='/prompt_manager/saved-views'&&item.request().method()==='POST');
+    await save.getByRole('button',{name:'Save',exact:true}).click();
+    const body=(await created).request().postDataJSON();
+    expect(body.state).toMatchObject({folder:'shared',tag_mode:'any',tags:['cats','dogs']});
+    await page.goto('about:blank');await open(page);
+    await page.getByRole('navigation',{name:'Saved views',exact:true}).getByRole('link',{name:'Shared cats or dogs',exact:true}).click();
+    await expect(caption(page)).toHaveText(/^1 positive prompt · /);await expect(filtersButton(page)).toHaveText('Filters · 3');
+});
+
+test('a chosen folder missing from the folder list stays listed and chosen in Refine',async({page})=>{
+    await open(page);await openRefine(page);await folder(page).selectOption('shared');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^1 positive prompt · /);
+    // The folder has no image any more as far as the list knows (or the read failed): Apply must not drop it.
+    await page.route('**/prompt_manager/library/options?include=folders',route=>route.fulfill({json:{success:true,library_epoch:'x',categories:[],folders:[]}}));
+    await openRefine(page);
+    await expect(folder(page).locator('option')).toHaveText(['All output folders','shared']);await expect(folder(page)).toHaveValue('shared');
+    await apply(page).click();await expect(caption(page)).toHaveText(/^1 positive prompt · /);await expect(filtersButton(page)).toHaveText('Filters · 1');
+});
+
+// Live B1: the server's flat list sorts full paths as text ("-" and "_" before "/"); Refine shows each folder directly
+// under its own parent and keeps case variants apart.
+test('the Folder list nests each folder under its exact parent',async({page})=>{
+    const folders=['CCC','CCC/mabes9sans-dataset','CCC/mabes9sans-dataset-v1','CCC/mabes9sans-dataset/mabes9sans-dataset_IMG_GEN',
+        'FLUX','FLUX/2025-12-11','flux','flux/images','flux-klein','kiko','kiko-v6','kiko/char'].sort();
+    await page.route('**/prompt_manager/library/options?include=folders',route=>route.fulfill({json:{success:true,library_epoch:'x',categories:[],folders}}));
+    await open(page);await openRefine(page);
+    const I='\u00a0\u00a0';
+    await expect(folder(page).locator('option')).toHaveText(['All output folders','CCC',`${I}mabes9sans-dataset`,`${I}${I}mabes9sans-dataset_IMG_GEN`,
+        `${I}mabes9sans-dataset-v1`,'FLUX',`${I}2025-12-11`,'flux',`${I}images`,'flux-klein','kiko',`${I}char`,'kiko-v6']);
+    expect(await folder(page).locator('option').evaluateAll(nodes=>nodes.map(node=>node.value))).toEqual(['','CCC','CCC/mabes9sans-dataset',
+        'CCC/mabes9sans-dataset/mabes9sans-dataset_IMG_GEN','CCC/mabes9sans-dataset-v1','FLUX','FLUX/2025-12-11','flux','flux/images','flux-klein',
+        'kiko','kiko/char','kiko-v6']);
+});
+
+test('an older server that ignores the folder shows an error with Retry, never the whole shelf',async({page})=>{
+    await open(page);
+    await page.route('**/prompt_manager/library?*',async route=>{
+        const response=await route.fetch();const body=await response.json();delete body.folder;delete body.tag_mode;
+        await route.fulfill({response,json:body});
+    });
+    await openRefine(page);await folder(page).selectOption('shared');await apply(page).click();
+    await expect(page.locator('#workspace-main').getByText('Prompt library could not be loaded. Retry.')).toBeVisible();
+    await expect(cards(page)).toHaveCount(0);
+});
+
+// D150: the Refine dialog is the concept's Filters dialog: its Folder select and Tags input, plus Tag match drawn as the
+// concept's own select; the concept's "Prompt evidence" (no data yet) and its prototype note are not shown.
+function mapFiltersDialog(reference,{folders,matchOptions}) {
+    const [conceptFolder,,conceptTags]=reference.fields;
+    return {...reference,
+        fields:[{...conceptFolder,options:folders},{...conceptTags},{...conceptFolder,label:'Tag match',options:matchOptions}],
+        small:[],
+        // Production's Apply reads "Apply filters" (Images and Library share it, #249).
+        actions:{...reference.actions,buttons:reference.actions.buttons.map(item=>item.text==='Apply tag filter'?{...item,text:'Apply filters'}:item)}};
+}
+for(const [width,height] of [[1600,1100],[390,844]])for(const theme of ['dark','light'])test(`Refine dialog matches the concept Filters dialog ${width} ${theme} (D150)`,async({page},testInfo)=>{
+    await page.setViewportSize({width,height});
+    await page.goto('about:blank');await page.goto(`${concept}#library`);await page.getByRole('combobox',{name:'Theme',exact:true}).selectOption(theme);
+    await page.locator('#main').getByRole('button',{name:'Filters',exact:true}).click();await expect(page.locator('#modal')).toBeVisible();
+    const reference=await page.locator('#modal').evaluate(inventoryOf);
+    await captureCanonicalState(page,testInfo,`concept-filters-${width}-${theme}`,'#modal');
+    await open(page);await page.getByRole('combobox',{name:'Theme',exact:true}).selectOption(theme);await openRefine(page);
+    await expect(folder(page).locator('option')).toHaveCount(2);
+    const actual=await refine(page).evaluate(inventoryOf);
+    await captureCanonicalState(page,testInfo,`production-refine-${width}-${theme}`,'dialog[open]');
+    const expected=mapFiltersDialog(reference,{folders:[['','All output folders'],['shared','shared']],matchOptions:[['all','All of these tags'],['any','Any of these tags'],['untagged','Prompts without tags']]});
+    const path=testInfo.outputPath('refine-inventory.json');await writeFile(path,JSON.stringify({reference,actual},null,2));
+    await testInfo.attach('refine-inventory',{path,contentType:'application/json'});
+    expect(reference.fields.map(item=>item.label)).toEqual(['Folder','Prompt evidence','Tags']);
+    expect(diffInventory(expected,actual)).toEqual([]);
+    await refine(page).getByRole('button',{name:'Close dialog',exact:true}).click();
+    await openRefine(page);await folder(page).selectOption('shared');await tags(page).fill('cats, dogs');await match(page).selectOption('any');await apply(page).click();
+    await expect(caption(page)).toHaveText(/^1 positive prompt · /);await page.mouse.move(0,0);
+    await captureCanonicalState(page,testInfo,`production-library-folder-any-${width}-${theme}`,'#workspace-main');
+});
diff --git a/tests/browser/workspace-library.spec.mjs b/tests/browser/workspace-library.spec.mjs
index 685eab8d..a2ba6187 100644
--- a/tests/browser/workspace-library.spec.mjs
+++ b/tests/browser/workspace-library.spec.mjs
@@ -155,7 +155,8 @@ test('Retry re-reads a failed category list with the shelf',async({page})=>{
     await page.locator('#workspace-main search.toolbar').getByRole('button',{name:'Filters',exact:true}).click();
     await refine(page).getByRole('button',{name:'Apply filters',exact:true}).click();await expect(refine(page)).toHaveCount(0);
     const search=page.getByRole('searchbox',{name:'Search workspace',exact:true});await search.fill(' ');
-    await page.waitForTimeout(400);expect(reads).toEqual([]);await expect(cards(page)).toHaveCount(3);
+    // Only the folder list Refine reads on opening (D150), never the shelf.
+    await page.waitForTimeout(400);expect(reads).toEqual(['/prompt_manager/library/options']);await expect(cards(page)).toHaveCount(3);
 });
 
 test('failed library reads retry while late search responses cannot overwrite newer results',async({page})=>{
@@ -200,7 +201,7 @@ test('library toolbar matches the concept and tags live in Refine this view',asy
     // D44: the active Tags filter shows on the button; the category is the toolbar's own and is not counted.
     await expect(toolbar.getByRole('button')).toHaveText(['Save view','Filters · 1']);
     await toolbar.getByRole('button',{name:'Filters · 1',exact:true}).click();
-    await expect(refine(page).locator('.field label')).toHaveText(['Tags','Tag match']);await expect(refine(page).getByRole('textbox',{name:'Tags',exact:true})).toHaveValue('studio');
+    await expect(refine(page).locator('.field label')).toHaveText(['Folder','Tags','Tag match']);await expect(refine(page).getByRole('textbox',{name:'Tags',exact:true})).toHaveValue('studio');
     await refine(page).getByRole('button',{name:'Clear filters',exact:true}).click();await expect(refine(page)).toHaveCount(0);
     await expect(toolbar.getByRole('button',{name:'Filters',exact:true})).toBeFocused();
     await expect(page.getByRole('combobox',{name:'Filter by category',exact:true})).toHaveValue('');await expect(cards(page)).toHaveCount(3);
diff --git a/tests/browser/workspace-saved-views.spec.mjs b/tests/browser/workspace-saved-views.spec.mjs
index 26a2c1be..1b216a4d 100644
--- a/tests/browser/workspace-saved-views.spec.mjs
+++ b/tests/browser/workspace-saved-views.spec.mjs
@@ -208,7 +208,7 @@ test('a view stored under older rules still lists and opens with its usable valu
     await raw({ page: 'library', name: '', state: JSON.stringify({ q: 'dog', sort: 'name-desc' }) });
     expect(await listed(request)).toEqual([
         { id: imagesId, page: 'images', name: 'Old cats', state: { ...IMAGE_DEFAULTS, q: 'cat' } },
-        expect.objectContaining({ page: 'library', name: 'Saved view', state: { q: 'dog', category: '', sort: 'newest', tags: [], tag_mode: 'all' } }),
+        expect.objectContaining({ page: 'library', name: 'Saved view', state: { q: 'dog', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' } }),
     ]);
     // A state that is no JSON object is never listed, and its link behaves like a missing view.
     const corruptId = await raw({ page: 'images', name: 'Corrupt', state: '{not json' });
@@ -233,7 +233,7 @@ test('a view stored under older rules still lists and opens with its usable valu
 // D153 (#447): the workspace no longer offers "Highest rated"; the API still stores such a view as it was saved.
 test('a view saved under Highest rated opens on Recently added on Images and the Library', async ({ page, request }) => {
     const images = await create(request, { page: 'images', name: 'Rated cats', state: { ...IMAGE_DEFAULTS, q: 'cat', sort: 'rating' } });
-    const library = await create(request, { page: 'library', name: 'Rated dogs', state: { q: 'dog', category: '', sort: 'rating', tags: [], tag_mode: 'all' } });
+    const library = await create(request, { page: 'library', name: 'Rated dogs', state: { q: 'dog', category: '', sort: 'rating', tags: [], tag_mode: 'all', folder: '' } });
     expect((await listed(request)).map(view => view.state.sort)).toEqual(['rating', 'rating']);
     const listings = [];
     page.on('request', item => {
@@ -257,7 +257,7 @@ test('a view saved under Highest rated opens on Recently added on Images and the
 
 test('leaving a saved view returns Images and the Library to their own last state (#249 M2)', async ({ page, request }) => {
     const dogs = await create(request, { page: 'images', name: 'Dogs', state: { ...IMAGE_DEFAULTS, q: 'dogs' } });
-    const cats = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all' } });
+    const cats = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' } });
     await page.goto(`${workspace}#/images`);
     await search(page).fill('cat');
     await expect(imageCards(page)).toHaveCount(1);
@@ -300,7 +300,7 @@ test('a toolbar change while sources load keeps the saved Source and Folder (#24
 });
 
 test('a saved view left while its list or rename is pending leaves the next page alone', async ({ page, request }) => {
-    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all' } });
+    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' } });
     let releaseList = () => {};
     const holdList = async () => {
         const held = new Promise(resolve => { releaseList = resolve; });
@@ -348,7 +348,7 @@ test('an unknown saved view opens Images, and a failed listing offers Retry', as
     await expect(page).toHaveURL(/#\/images$/);
     await expect(main(page).getByRole('heading', { level: 1 })).toHaveText('Images');
 
-    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all' } });
+    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' } });
     let failing = true;
     await page.route(`**${API}`, route => failing && route.request().method() === 'GET'
         ? route.fulfill({ status: 500, contentType: 'application/json', body: '{"success":false,"error":"down"}' })
@@ -539,7 +539,7 @@ test('Edit renames an open view, and deletes it only after confirming inside the
 });
 
 test('a deleted Library view returns to the Library, and failed edits say so', async ({ page, request }) => {
-    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all' } });
+    const view = await create(request, { page: 'library', name: 'Cats', state: { q: 'cat', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' } });
     await page.goto(`${workspace}#/saved/${view.id}`);
     await expect(heading(page)).toHaveText('Cats');
     const edit = main(page).locator('.heading-actions > button').first();
diff --git a/tests/js/workspace-library-state.test.js b/tests/js/workspace-library-state.test.js
index f765a729..a31063d0 100644
--- a/tests/js/workspace-library-state.test.js
+++ b/tests/js/workspace-library-state.test.js
@@ -104,6 +104,20 @@ test('archived variant reads use their own scope and cursor without changing the
  const active=[];const plain=createLibraryDetail({api:{get:async url=>{active.push(url);return {positive:item(1),variants:[]};}},onChange:()=>{}});await plain.load(1);assert.equal(new URL(active[0],'https://x').searchParams.has('archive'),false);
  assert.throws(()=>createLibraryDetail({api:{},onChange:()=>{},archive:'parents'}));
 });
+test('tag mode any and a folder are sent, echoed and validated (#444)',async()=>{
+ const {createLibraryStream,LIBRARY_TAG_MODES}=await source;assert.deepEqual(LIBRARY_TAG_MODES,['all','any','untagged']);
+ const calls=[];const pending=[{...page([item(1)]),tag_mode:'any',folder:'2026/Aug'},{...page([item(2)]),tag_mode:'all',folder:''},page([item(3)]),{...page([item(4)]),tag_mode:'all'}];
+ const s=createLibraryStream({api:{get:async(url)=>{calls.push(new URL(url,'https://x').searchParams);return pending.shift();}}});
+ assert.equal(await s.reset({tags:['a','b'],tagMode:'any',folder:'2026/Aug'}),1);
+ assert.equal(calls[0].get('tag_mode'),'any');assert.equal(calls[0].get('folder'),'2026/Aug');assert.deepEqual(calls[0].getAll('tag'),['a','b']);
+ // An older server that ignored them answers without the echo: an error, never the unfiltered shelf.
+ assert.equal(await s.reset({tags:['a','b'],tagMode:'any',folder:'2026/Aug'}),0);assert.ok(s.state.error instanceof TypeError);
+ // The defaults send neither, so they need no echo.
+ assert.equal(await s.reset({tagMode:'all',folder:''}),1);assert.equal(calls[2].has('tag_mode'),false);assert.equal(calls[2].has('folder'),false);
+ assert.equal(await s.reset({folder:'x'}),0);assert.ok(s.state.error instanceof TypeError,'a folder without its echo is refused');
+ await assert.rejects(s.reset({tagMode:'or'}),TypeError);await assert.rejects(s.reset({folder:3}),TypeError);
+ assert.equal(calls.length,4);s.dispose();
+});
 test('tag mode untagged is sent, echoed and never combined with tags (#444)',async()=>{
  const {createLibraryStream}=await source;const calls=[];const pending=[{...page([item(1)]),tag_mode:'untagged'},page([item(2)]),page([item(3)])];
  const s=createLibraryStream({api:{get:async(url)=>{calls.push(url);return pending.shift();}}});
@@ -112,7 +126,7 @@ test('tag mode untagged is sent, echoed and never combined with tags (#444)',asy
  assert.equal(await s.reset({tagMode:'untagged'}),0);assert.ok(s.state.error instanceof TypeError);assert.deepEqual(s.state.items,[]);
  // The default sends no tag_mode, so it needs no echo.
  assert.equal(await s.reset({tagMode:'all'}),1);assert.equal(new URL(calls[2],'https://x').searchParams.has('tag_mode'),false);
- await assert.rejects(s.reset({tagMode:'untagged',tags:['a']}),TypeError);await assert.rejects(s.reset({tagMode:'none'}),TypeError);
+ await assert.rejects(s.reset({tagMode:'untagged',tags:['a']}),TypeError);await assert.rejects(s.reset({tagMode:'or'}),TypeError);
  assert.equal(calls.length,3);s.dispose();
 });
 test('the stream keeps the first page\'s storage epoch and refuses a later page from another one (#437)',async()=>{
@@ -131,3 +145,28 @@ test('the shelf no longer sorts by rating (D153)',async()=>{
  assert.throws(()=>createLibraryStream({api:{get:async()=>page([])},restore:{filters:{sort:'rating'},state:{}}}),/Invalid library sort/);
  for(const sort of ['newest','oldest','name']) assert.equal(await s.reset({sort}),0);s.dispose();
 });
+test('Refine › Folder nests each folder under its exact parent, by path segment (#444 live B1)',async()=>{
+ const {libraryFolderOptions}=await source;assert.equal(typeof libraryFolderOptions,'function');
+ const I='  ';
+ // The server's flat list sorts full paths as text, so "-" and "_" land before "/" (live report shapes).
+ const folders=['CCC','CCC/mabes9sans-dataset','CCC/mabes9sans-dataset-v1','CCC/mabes9sans-dataset/mabes9sans-dataset_IMG_GEN',
+  'FLUX','FLUX/2025-12-11','flux','flux/images','flux-klein','illustrious','illustrious-base','illustrious/2026-10-26','illustrious/training',
+  'illustrious/training/a','kiko','kiko-v6','kiko/char','kiko/XXX','QWEN','QWEN/x','Qwen','Qwen/y','Qwen-Training','Video','Video/v','video'].sort();
+ const options=libraryFolderOptions(folders);
+ assert.deepEqual(options[0],['','All output folders']);
+ assert.deepEqual(options.slice(1),[
+  ['CCC','CCC'],['CCC/mabes9sans-dataset',`${I}mabes9sans-dataset`],['CCC/mabes9sans-dataset/mabes9sans-dataset_IMG_GEN',`${I}${I}mabes9sans-dataset_IMG_GEN`],
+  ['CCC/mabes9sans-dataset-v1',`${I}mabes9sans-dataset-v1`],
+  ['FLUX','FLUX'],['FLUX/2025-12-11',`${I}2025-12-11`],['flux','flux'],['flux/images',`${I}images`],['flux-klein','flux-klein'],
+  ['illustrious','illustrious'],['illustrious/2026-10-26',`${I}2026-10-26`],['illustrious/training',`${I}training`],['illustrious/training/a',`${I}${I}a`],
+  ['illustrious-base','illustrious-base'],
+  ['kiko','kiko'],['kiko/char',`${I}char`],['kiko/XXX',`${I}XXX`],['kiko-v6','kiko-v6'],
+  ['QWEN','QWEN'],['QWEN/x',`${I}x`],['Qwen','Qwen'],['Qwen/y',`${I}y`],['Qwen-Training','Qwen-Training'],
+  ['Video','Video'],['Video/v',`${I}v`],['video','video'],
+ ]);
+ // Every parent precedes its children directly; a chosen folder missing from the list is kept, with its parents.
+ assert.deepEqual(libraryFolderOptions(['a'],'a/b/c').slice(1),[['a','a'],['a/b',`${I}b`],['a/b/c',`${I}${I}c`]]);
+ assert.deepEqual(libraryFolderOptions([],''),[['','All output folders']]);
+ // A POSIX folder whose name holds a backslash is one segment.
+ assert.deepEqual(libraryFolderOptions(['Metadata\\Klein_4b Wildcard Run']).slice(1),[['Metadata\\Klein_4b Wildcard Run','Metadata\\Klein_4b Wildcard Run']]);
+});
diff --git a/tests/js/workspace-saved-views.test.js b/tests/js/workspace-saved-views.test.js
index 72435079..bb9e0a50 100644
--- a/tests/js/workspace-saved-views.test.js
+++ b/tests/js/workspace-saved-views.test.js
@@ -5,7 +5,7 @@ const assert = require('node:assert/strict');
 const source = import('../../web/js/workspace/saved-views.mjs');
 
 const IMAGE_DEFAULTS = { q: '', category: '', sort: 'newest', source: 'all', folder: '', media: 'all', tags: [], favorites: false, collection: '' };
-const LIBRARY_DEFAULTS = { q: '', category: '', sort: 'newest', tags: [], tag_mode: 'all' };
+const LIBRARY_DEFAULTS = { q: '', category: '', sort: 'newest', tags: [], tag_mode: 'all', folder: '' };
 
 test('a saved state always holds every page key and keeps only values its page accepts', async () => {
     const { normalizeViewState, SAVED_VIEW_PAGES } = await source;
@@ -31,8 +31,8 @@ test('a saved state always holds every page key and keeps only values its page a
     assert.deepEqual(normalizeViewState('images', { ...full, q: 'x'.repeat(501), folder: 7, tags: Array(21).fill('t') }),
         { ...full, q: '', folder: '', tags: [] });
     assert.deepEqual(normalizeViewState('images', { ...full, category: 'bad\u0007', tags: [' '] }), { ...full, category: '', tags: [] });
-    // Library has no source, folder or media, and no Name Z–A.
-    assert.deepEqual(normalizeViewState('library', { ...full, sort: 'name-desc' }), { q: 'castle', category: 'Portraits', sort: 'newest', tags: ['moody', 'fog'], tag_mode: 'all' });
+    // Library has no source or media, and no Name Z–A; its folder (#444) is the Library's own.
+    assert.deepEqual(normalizeViewState('library', { ...full, sort: 'name-desc' }), { q: 'castle', category: 'Portraits', sort: 'newest', tags: ['moody', 'fog'], tag_mode: 'all', folder: 'a/b' });
     assert.deepEqual(normalizeViewState('library', { sort: 'oldest' }), { ...LIBRARY_DEFAULTS, sort: 'oldest' });
     // The returned tags are a copy.
     const tags = ['one'];
@@ -62,7 +62,7 @@ test('the listing keeps usable views in order and normalizes their state', async
         { id: 1, page: 'images', name: 'Videos', state: { media: 'video', source: '9' } },
     ] });
     assert.deepEqual(views, [
-        { id: 3, page: 'library', name: 'Neon', state: { q: 'neon', category: '', sort: 'name', tags: [], tag_mode: 'all' } },
+        { id: 3, page: 'library', name: 'Neon', state: { q: 'neon', category: '', sort: 'name', tags: [], tag_mode: 'all', folder: '' } },
         { id: 1, page: 'images', name: 'Videos', state: { ...IMAGE_DEFAULTS, media: 'video', source: '9' } },
     ]);
     assert.equal(parseSavedView(null), null);
@@ -84,8 +84,8 @@ test('page filters and saved states convert both ways', async () => {
     assert.equal(imagesViewState({ ...filters, collection: undefined }).collection, '');
     assert.equal(imagesViewState({ ...filters, collection: 7 }).collection, '7');
     assert.equal(imagesViewState({ ...filters, favorites: undefined }).favorites, false);
-    const shelf = { text: 'neon', category: 'Cities', sort: 'oldest', tags: ['night'], tagMode: 'all' };
-    assert.deepEqual(libraryViewState(shelf), { q: 'neon', category: 'Cities', sort: 'oldest', tags: ['night'], tag_mode: 'all' });
+    const shelf = { text: 'neon', category: 'Cities', sort: 'oldest', tags: ['night'], tagMode: 'any', folder: '2026' };
+    assert.deepEqual(libraryViewState(shelf), { q: 'neon', category: 'Cities', sort: 'oldest', tags: ['night'], tag_mode: 'any', folder: '2026' });
     assert.deepEqual(libraryFilters(libraryViewState(shelf)), shelf);
 });
 
@@ -216,16 +216,27 @@ test('a state over the API 4 KB cap is refused before anything is sent (#249 M5)
     assert.deepEqual(api.calls, []);
 });
 
-test('a Library view keeps its tag match, and untagged never travels with tags (#444)', async () => {
+test('a Library view keeps its tag match and folder; an old view reads the defaults (#444)', async () => {
+    const { normalizeViewState, libraryFilters } = await source;
+    assert.deepEqual(normalizeViewState('library', { tag_mode: 'any', folder: '2026/Aug' }), { ...LIBRARY_DEFAULTS, tag_mode: 'any', folder: '2026/Aug' });
+    assert.deepEqual(normalizeViewState('library', { tag_mode: 'or', folder: 'x'.repeat(1025) }), LIBRARY_DEFAULTS);
+    assert.deepEqual(libraryFilters({ q: 'a' }), { text: 'a', category: '', sort: 'newest', tags: [], tagMode: 'all', folder: '' });
+});
+
+test('a Library view keeps untagged, and untagged never travels with tags (#444)', async () => {
     const { normalizeViewState, libraryFilters, libraryViewState } = await source;
     assert.equal(normalizeViewState('library', { tag_mode: 'untagged' }).tag_mode, 'untagged');
-    assert.equal(normalizeViewState('library', { tag_mode: 'any' }).tag_mode, 'all');
     assert.deepEqual(normalizeViewState('library', { tags: ['a'], tag_mode: 'untagged' }), { ...LIBRARY_DEFAULTS, tags: ['a'] });
-    const shelf = { text: '', category: '', sort: 'newest', tags: [], tagMode: 'untagged' };
+    const shelf = { text: '', category: '', sort: 'newest', tags: [], tagMode: 'untagged', folder: '' };
     assert.equal(libraryViewState(shelf).tag_mode, 'untagged');
     assert.deepEqual(libraryFilters(libraryViewState(shelf)), shelf);
 });
 
+test('a shelf without the #444 filters saves their defaults', async () => {
+    const { libraryViewState } = await source;
+    assert.deepEqual(libraryViewState({ text: '', category: '', sort: 'newest', tags: [] }), LIBRARY_DEFAULTS);
+});
+
 test('a view saved under the retired Highest rated sort opens on Recently added (D153)', async () => {
     const { normalizeViewState, imagesFilters, libraryFilters } = await source;
     assert.equal(normalizeViewState('images', { sort: 'rating' }).sort, 'newest');
diff --git a/tests/test_api_library.py b/tests/test_api_library.py
index 6239b611..e457a2cd 100644
--- a/tests/test_api_library.py
+++ b/tests/test_api_library.py
@@ -123,6 +123,72 @@ class TestLibraryAPI(ImageAPITestCase):
             },
         )
 
+    async def test_folder_filter_lists_and_matches_prompts_by_output_folder(self):
+        deep = self._save_prompt("deep")
+        top = self._save_prompt("top")
+        other = self._save_prompt("other")
+        self._save_prompt("no images")
+        for prompt, parts in ((deep, ("a", "b")), (top, ("a",)), (other, ("ab",))):
+            path = make_png(self.output_dir.joinpath(*parts, f"{prompt}.png"))
+            self.api.db.link_image_to_prompt(prompt, str(path))
+        response, options = await self.get("/options", include="folders")
+        self.assertEqual(response.status, 200)
+        self.assertEqual(options["folders"], ["a", "a/b", "ab"])
+        _, plain = await self.get("/options")
+        self.assertNotIn("folders", plain)
+        _, first = await self.get(folder="a", limit=1)
+        self.assertEqual((first["total"], first["folder"]), (2, "a"))
+        # Outer slashes are dropped (a backslash separates only on Windows).
+        outer = "\\a\\" if os.name == "nt" else "/a/"
+        _, second = await self.get(folder=outer, limit=1, cursor=first["next_cursor"])
+        self.assertEqual(
+            sorted([first["items"][0]["text"], second["items"][0]["text"]]),
+            ["deep", "top"],
+        )
+        _, all_rows = await self.get()
+        self.assertEqual((all_rows["total"], all_rows["folder"]), (4, ""))
+        for params in (
+            {"folder": "a/../ab"},
+            *([{"folder": "C:/x"}] if os.name == "nt" else []),
+            {"folder": "b", "cursor": first["next_cursor"]},
+            {"cursor": first["next_cursor"]},
+        ):
+            response, result = await self.get(limit=1, **params)
+            self.assertEqual(response.status, 400, params)
+            self.assertEqual(result["success"], False)
+        response, _ = await self.get("/options", include="tags")
+        self.assertEqual(response.status, 400)
+
+    @unittest.skipIf(os.name == "nt", "a backslash is a separator on Windows")
+    async def test_a_posix_folder_name_with_a_backslash_filters_its_prompts(self):
+        prompt = self._save_prompt("klein")
+        name = "Metadata\\Klein_4b Wildcard Run"
+        path = make_png(self.output_dir / name / "x.png")
+        self.api.db.link_image_to_prompt(prompt, str(path))
+        _, options = await self.get("/options", include="folders")
+        self.assertIn(name, options["folders"])
+        _, result = await self.get(folder=name)
+        self.assertEqual((result["total"], result["folder"]), (1, name))
+
+    async def test_any_tag_mode_is_sent_through_and_echoed(self):
+        self._save_prompt("a only", tags=["a"])
+        self._save_prompt("b only", tags=["b"])
+        self._save_prompt("neither")
+        _, result = await self.get(tag=["a", "b"], tag_mode="any")
+        self.assertEqual(result["tag_mode"], "any")
+        self.assertEqual(
+            sorted(i["text"] for i in result["items"]), ["a only", "b only"]
+        )
+        _, both = await self.get(tag=["a", "b"])
+        self.assertEqual((both["total"], both["tag_mode"]), (0, "all"))
+        _, first = await self.get(tag=["a", "b"], tag_mode="any", limit=1)
+        response, _ = await self.get(
+            tag=["a", "b"], limit=1, cursor=first["next_cursor"]
+        )
+        self.assertEqual(response.status, 400)
+        response, _ = await self.get(tag_mode="or")
+        self.assertEqual(response.status, 400)
+
     async def test_variant_cursor_is_positive_scoped_and_required_limits_are_bounded(
         self,
     ):
diff --git a/tests/test_library_folders.py b/tests/test_library_folders.py
new file mode 100644
index 00000000..a49359fa
--- /dev/null
+++ b/tests/test_library_folders.py
@@ -0,0 +1,243 @@
+"""#444: the Library's output-folder filter and multi-tag OR."""
+
+import ntpath
+import os
+import posixpath
+import tempfile
+import unittest
+from pathlib import Path
+
+from database.library_folders import (
+    folder_prefixes,
+    normalize_folder,
+    relative_folder,
+)
+from database.operations import PromptDatabase
+from utils.hashing import generate_prompt_hash
+
+
+class TestFolderNames(unittest.TestCase):
+    def test_normalize_strips_outer_slashes_on_both_flavors(self):
+        for flavor in (posixpath, ntpath):
+            with self.subTest(flavor=flavor.__name__):
+                self.assertEqual(normalize_folder("", flavor), "")
+                self.assertEqual(normalize_folder("/", flavor), "")
+                self.assertEqual(normalize_folder("/a/b/", flavor), "a/b")
+                self.assertEqual(normalize_folder("..foo/b", flavor), "..foo/b")
+
+    def test_a_backslash_separates_only_on_windows(self):
+        # Live B1: on POSIX a backslash is part of a folder name, as listed.
+        name = "Metadata\\Klein_4b Wildcard Run"
+        self.assertEqual(normalize_folder(name, posixpath), name)
+        self.assertEqual(
+            normalize_folder("2026\\08-Aug\\", posixpath), "2026\\08-Aug\\"
+        )
+        self.assertEqual(
+            normalize_folder(name, ntpath), "Metadata/Klein_4b Wildcard Run"
+        )
+        self.assertEqual(normalize_folder("2026\\08-Aug\\", ntpath), "2026/08-Aug")
+        # A colon names a drive only on Windows.
+        self.assertEqual(normalize_folder("a:b/c", posixpath), "a:b/c")
+
+    def test_normalize_refuses_anything_but_a_folder_below_a_root(self):
+        for flavor, value in (
+            *(
+                (flavor, value)
+                for flavor in (posixpath, ntpath)
+                for value in ("a/../b", "./a", "a//b", "a\x00b", 3, "x" * 1025)
+            ),
+            (ntpath, "C:/x"),
+            (ntpath, "c:"),
+            (ntpath, "a\\..\\b"),
+        ):
+            with self.subTest(flavor=flavor.__name__, value=value):
+                with self.assertRaises(ValueError):
+                    normalize_folder(value, flavor)
+
+    def test_the_default_flavor_is_the_platform_path_module(self):
+        self.assertEqual(normalize_folder("a\\b"), normalize_folder("a\\b", os.path))
+
+    def test_posix_prefixes_are_exact_and_end_in_a_separator(self):
+        self.assertEqual(
+            folder_prefixes(["/out", "/data/out/"], "a/b", posixpath),
+            ["/out/a/b/", "/data/out/a/b/"],
+        )
+        self.assertEqual(folder_prefixes(["/"], "a", posixpath), ["/a/"])
+        self.assertEqual(
+            folder_prefixes(["/out", "/out/"], "a", posixpath), ["/out/a/"]
+        )
+        with self.assertRaises(ValueError):
+            folder_prefixes([], "a", posixpath)
+
+    def test_windows_prefixes_fold_case_including_non_ascii(self):
+        self.assertEqual(
+            folder_prefixes(["C:\\ComfyUI\\Output"], "Ä/Sub", ntpath),
+            ["c:\\comfyui\\output\\ä\\sub\\"],
+        )
+        self.assertEqual(folder_prefixes(["D:\\"], "x", ntpath), ["d:\\x\\"])
+        self.assertEqual(
+            folder_prefixes(["\\\\Server\\Share\\Out"], "a", ntpath),
+            ["\\\\server\\share\\out\\a\\"],
+        )
+        # The stored file_path is normcase(normpath(abspath)), the same fold.
+        stored = ntpath.normcase(ntpath.normpath("C:/ComfyUI/output/Ä/sub/x.png"))
+        self.assertTrue(
+            stored.startswith(
+                folder_prefixes(["C:/ComfyUI/Output"], "ä/SUB", ntpath)[0]
+            )
+        )
+
+    def test_relative_folder_keeps_the_stored_spelling(self):
+        self.assertEqual(
+            relative_folder("/out/2026/Aug/x.png", ["/out"], posixpath), "2026/Aug"
+        )
+        self.assertIsNone(relative_folder("/out/x.png", ["/out"], posixpath))
+        self.assertIsNone(relative_folder("/outside/x.png", ["/out"], posixpath))
+        self.assertIsNone(relative_folder("/output2/a/x.png", ["/out"], posixpath))
+        self.assertEqual(
+            relative_folder("/out/..foo/x.png", ["/out"], posixpath), "..foo"
+        )
+        self.assertEqual(
+            relative_folder("C:\\Out\\Ä\\Sub\\x.png", ["c:\\out"], ntpath), "Ä/Sub"
+        )
+        self.assertEqual(relative_folder("D:\\a\\x.png", ["D:\\"], ntpath), "a")
+
+
+class TestLibraryFolderAndAnyTag(unittest.TestCase):
+    def setUp(self):
+        self.temp = tempfile.TemporaryDirectory()
+        base = Path(os.path.realpath(self.temp.name))
+        self.root = base / "output"
+        self.root.mkdir()
+        self.db = PromptDatabase(str(base / "folders.db"))
+
+    def tearDown(self):
+        try:
+            self.db.close_all()
+        finally:
+            self.temp.cleanup()
+
+    def save(self, text, **metadata):
+        return self.db.save_prompt(
+            text, prompt_hash=generate_prompt_hash(text), **metadata
+        )
+
+    def link(self, prompt_id, *parts):
+        path = self.root.joinpath(*parts)
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_bytes(b"x")
+        self.db.link_image_to_prompt(prompt_id, str(path))
+
+    def texts(self, **options):
+        return sorted(item["text"] for item in self.db.list_library(**options)["items"])
+
+    def in_folder(self, folder, roots=None):
+        return self.texts(
+            folder_prefixes=folder_prefixes(roots or [str(self.root)], folder)
+        )
+
+    def test_folder_matches_its_descendants_only(self):
+        self.link(self.save("deep"), "a", "b", "x.png")
+        self.link(self.save("top"), "a", "y.png")
+        self.link(self.save("sibling"), "ab", "z.png")
+        self.link(self.save("literal"), "100%_off", "w.png")
+        self.save("no images")
+        self.assertEqual(self.in_folder("a"), ["deep", "top"])
+        self.assertEqual(self.in_folder("a/b"), ["deep"])
+        self.assertEqual(self.in_folder("ab"), ["sibling"])
+        self.assertEqual(self.in_folder("100%_off"), ["literal"])
+        self.assertEqual(self.in_folder("1"), [])
+        cut = self.db.list_library(
+            folder_prefixes=folder_prefixes([str(self.root)], "a"), limit=1
+        )
+        self.assertEqual(cut["total"], 2)
+
+    def test_folder_combines_with_text_category_and_tags(self):
+        self.link(self.save("red cat", category="Art", tags=["cat"]), "a", "1.png")
+        self.link(self.save("red dog", category="Art", tags=["dog"]), "a", "2.png")
+        self.link(self.save("red bird", category="Art", tags=["cat"]), "b", "3.png")
+        prefixes = folder_prefixes([str(self.root)], "a")
+        self.assertEqual(
+            self.texts(folder_prefixes=prefixes, tags=["cat"]), ["red cat"]
+        )
+        self.assertEqual(
+            self.texts(folder_prefixes=prefixes, text="dog", category="Art"),
+            ["red dog"],
+        )
+
+    @unittest.skipIf(os.name == "nt", "symlinks need privileges on Windows")
+    def test_folder_listing_and_match_through_a_symlinked_root(self):
+        link = self.root.parent / "linked"
+        os.symlink(self.root, link)
+        prompt = self.save("via link")
+        (self.root / "a").mkdir()
+        (self.root / "a" / "x.png").write_bytes(b"x")
+        self.db.link_image_to_prompt(prompt, str(link / "a" / "x.png"))
+        spellings = [str(self.root), str(link)]
+        self.assertEqual(self.in_folder("a", spellings), ["via link"])
+        self.assertEqual(self.in_folder("a", [str(self.root)]), [])
+        self.assertEqual(self.db.get_library_options(spellings)["folders"], ["a"])
+
+    @unittest.skipIf(os.name == "nt", "a backslash is a separator on Windows")
+    def test_a_posix_folder_with_a_backslash_lists_and_filters_alike(self):
+        name = "Metadata\\Klein_4b Wildcard Run"
+        self.link(self.save("klein"), name, "x.png")
+        self.link(self.save("other"), "Metadata", "y.png")
+        listed = self.db.get_library_options([str(self.root)])["folders"]
+        self.assertEqual(listed, ["Metadata", name])
+        self.assertEqual(self.in_folder(normalize_folder(name)), ["klein"])
+        self.assertEqual(self.in_folder(normalize_folder("Metadata")), ["other"])
+
+    def test_folder_listing_offers_ancestors_and_skips_outside_images(self):
+        self.link(self.save("deep"), "2026", "08-Aug", "x.png")
+        self.link(self.save("root image"), "y.png")
+        outside = Path(self.temp.name) / "elsewhere" / "z.png"
+        outside.parent.mkdir()
+        outside.write_bytes(b"x")
+        self.db.link_image_to_prompt(self.save("outside"), str(outside))
+        options = self.db.get_library_options([str(self.root)])
+        self.assertEqual(options["folders"], ["2026", "2026/08-Aug"])
+        self.assertNotIn("folders", self.db.get_library_options())
+
+    def test_folder_combines_with_untagged(self):
+        self.link(self.save("plain in a"), "a", "1.png")
+        self.link(self.save("tagged in a", tags=["t"]), "a", "2.png")
+        self.link(self.save("plain in b"), "b", "3.png")
+        prefixes = folder_prefixes([str(self.root)], "a")
+        self.assertEqual(
+            self.texts(folder_prefixes=prefixes, tag_mode="untagged"), ["plain in a"]
+        )
+
+    def test_any_tag_mode_is_the_union_across_parent_and_pair(self):
+        self.save("parent a", tags=["a"])
+        self.save("parent b", tags=["b"])
+        self.save("both", tags=["a", "b"])
+        self.save("neither", tags=["c"])
+        self.db.save_prompt_pair("pair b", "noise", tags=["b"])
+        split = self.save("split", tags=["a"])
+        self.db.save_prompt_pair("split", "split noise", tags=["b"])
+        archived = self.db.save_prompt_pair("archived b", "old", tags=["b"])
+        self.db.archive_prompt_pair(archived)
+        self.assertIsInstance(split, int)
+        self.assertEqual(
+            self.texts(tags=["a", "b"], tag_mode="any"),
+            ["both", "pair b", "parent a", "parent b", "split"],
+        )
+        self.assertEqual(self.texts(tags=["a", "b"], tag_mode="all"), ["both"])
+        self.assertEqual(self.texts(tags=["a", "b"]), ["both"])
+        for tags in (["a"], ["b"], ["c"]):
+            self.assertEqual(
+                self.texts(tags=tags, tag_mode="any"), self.texts(tags=tags)
+            )
+        self.assertEqual(
+            self.texts(tags=["a", "b"], tag_mode="any", text="parent"),
+            ["parent a", "parent b"],
+        )
+        self.assertEqual(self.texts(tag_mode="any"), self.texts())
+        for mode in ("none", None, "ANY"):
+            with self.subTest(mode=mode), self.assertRaises(ValueError):
+                self.db.list_library(tag_mode=mode)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/test_saved_views.py b/tests/test_saved_views.py
index d5cdc565..010c64cb 100644
--- a/tests/test_saved_views.py
+++ b/tests/test_saved_views.py
@@ -48,6 +48,7 @@ LIBRARY_STATE = {
     "sort": "rating",
     "tags": [],
     "tag_mode": "untagged",
+    "folder": "2026/Aug",
 }
 IMAGES_DEFAULTS = {
     "q": "",
@@ -66,6 +67,7 @@ LIBRARY_DEFAULTS = {
     "sort": "newest",
     "tags": [],
     "tag_mode": "all",
+    "folder": "",
 }
 # A row saved by an older build: no favorites key, a retired key, a sort
 # that is no longer offered and an over-long folder.
@@ -242,14 +244,15 @@ class TestSavedViewsApi(ImageAPITestCase):
         for sort in ("newest", "oldest", "name", "rating"):
             await self.create(
                 page="library",
-                state={"sort": sort, "tags": ["a b"], "tag_mode": "all"},
+                state={"sort": sort, "tags": ["a b"], "tag_mode": "all", "folder": ""},
             )
-        untagged = await self.create(
-            page="library", state={"tags": [], "tag_mode": "untagged"}
-        )
-        self.assertEqual(untagged["state"]["tag_mode"], "untagged")
+        for mode in ("untagged", "any"):
+            view = await self.create(
+                page="library", state={"tags": [], "tag_mode": mode}
+            )
+            self.assertEqual(view["state"]["tag_mode"], mode)
         _, listed = await self.send("GET")
-        self.assertEqual(len(listed["views"]), 21)
+        self.assertEqual(len(listed["views"]), 22)
 
     async def test_write_requires_the_collection_key(self):
         # #331 D140: a view saved on a collection page keeps the collection id.
@@ -694,13 +697,24 @@ class TestSavedViewsSchema(unittest.TestCase):
                 )
         self.assertEqual(normalize_state("history", {}), {})
 
-    def test_library_tag_mode_is_kept_and_never_paired_with_tags(self):
-        # A row from before #444 has no tag_mode: it opens matching every tag.
+    def test_library_tag_mode_and_folder_are_kept_with_defaults_for_old_rows(self):
+        # A row from before #444 has neither key.
         old = {"q": "", "category": "", "sort": "rating", "tags": ["a"]}
         self.assertEqual(normalize_state("library", old), {**LIBRARY_DEFAULTS, **old})
         self.assertEqual(
-            normalize_state("library", {"tag_mode": "any"}), LIBRARY_DEFAULTS
+            normalize_state("library", {"tag_mode": "or", "folder": 3}),
+            LIBRARY_DEFAULTS,
         )
+        for mode in ("all", "any", "untagged"):
+            self.assertEqual(
+                normalize_state("library", {"tag_mode": mode})["tag_mode"], mode
+            )
+        with self.assertRaises(SavedViewInvalid):
+            encode_state("library", {**LIBRARY_STATE, "tag_mode": "or"})
+        with self.assertRaises(SavedViewInvalid):
+            encode_state("library", {**LIBRARY_STATE, "folder": "x" * 1025})
+
+    def test_library_untagged_is_never_paired_with_tags(self):
         # Never written by this build: the tags win, as the listing refuses both.
         self.assertEqual(
             normalize_state("library", {"tags": ["a"], "tag_mode": "untagged"}),
@@ -708,8 +722,6 @@ class TestSavedViewsSchema(unittest.TestCase):
         )
         with self.assertRaises(SavedViewInvalid):
             encode_state("library", {**LIBRARY_STATE, "tags": ["a"]})
-        with self.assertRaises(SavedViewInvalid):
-            encode_state("library", {**LIBRARY_STATE, "tag_mode": "none"})
 
     def test_validation_errors_are_saved_view_invalid(self):
         for call in (
diff --git a/web/js/workspace/library-state.mjs b/web/js/workspace/library-state.mjs
index bb4e4d98..596f82f7 100644
--- a/web/js/workspace/library-state.mjs
+++ b/web/js/workspace/library-state.mjs
@@ -12,18 +12,22 @@ function parameters(filters,limit) {
     for(const tag of filters.tags || []) if(tag.trim()) query.append('tag',tag.trim());
     const sort=filters.sort || 'newest';
     if(!['newest','oldest','name'].includes(sort)) throw new TypeError('Invalid library sort');
-    // #444: how Tags match; `untagged` lists parents no tag's Browse returns and never goes with tags.
-    const tagMode=filters.tagMode ?? 'all';
+    // #444: how Tags match (every tag, any of them, or parents no tag's Browse returns, which never goes with tags) and
+    // the output folder below a root.
+    const tagMode=filters.tagMode ?? 'all',folder=filters.folder ?? '';
     if(!LIBRARY_TAG_MODES.includes(tagMode) || (tagMode==='untagged' && query.has('tag'))) throw new TypeError('Invalid library tag mode');
+    if(typeof folder!=='string' || folder.length>1024) throw new TypeError('Invalid library folder');
     if(tagMode!=='all') query.set('tag_mode',tagMode);
+    if(folder) query.set('folder',folder);
     query.set('sort',sort);return query;
 }
 /** The Library's tag match values (#444); the first is the default, sent as no parameter. */
-export const LIBRARY_TAG_MODES=Object.freeze(['all','untagged']);
+export const LIBRARY_TAG_MODES=Object.freeze(['all','any','untagged']);
 // `variant_total` is the filtered parents' active negative variants (the concept caption's "M negative variants").
 function validatePage(page,cursor,query) {
-    // A tag match the server did not echo was not applied (an older server): never show the whole shelf as filtered.
+    // A tag match or folder the server did not echo was not applied (an older server): never show the whole shelf as filtered.
     if(query?.has('tag_mode') && page?.tag_mode!==query.get('tag_mode')) throw new TypeError('Unconfirmed library tag mode');
+    if(query?.has('folder') && page?.folder!==query.get('folder')) throw new TypeError('Unconfirmed library folder');
     if(!page || !Array.isArray(page.items) || page.items.some(item=>!parent(item)) || !Number.isSafeInteger(page.total) || page.total<0 || !Number.isSafeInteger(page.variant_total) || page.variant_total<0 || typeof page.has_more!=='boolean' || !(page.next_cursor===null || (typeof page.next_cursor==='string' && page.next_cursor.length)) || page.has_more!==(page.next_cursor!==null) || (page.has_more && cursor===page.next_cursor)) throw new TypeError('Invalid library page');
 }
 export function createLibraryStream({api,onChange=()=>{},restore}) {
@@ -121,3 +125,28 @@ export function libraryWindow(count,columns,top,height,focused=-1) {
     if(focused>=0 && focused<count) keep.add(Math.floor(focused/columns));
     return [...keep].sort((a,b)=>a-b).flatMap(row=>Array.from({length:columns},(_,column)=>row*columns+column).filter(index=>index<count));
 }
+
+const byFolderName=(a,b)=>{const x=a.toLowerCase(),y=b.toLowerCase();return x<y?-1:x>y?1:a<b?-1:a>b?1:0;};
+/**
+ * Refine › Folder options (#444 D150): the concept's "All output folders" first, then the folders as a tree built by
+ * path segment, so each folder sits directly under its own parent (never under a longer sibling such as `kiko-v6`) and
+ * folders differing only in case stay distinct siblings. Siblings sort case-insensitively, then by exact spelling. A
+ * label is the last segment indented by depth (the legacy admin select). The chosen folder is kept even when the list
+ * lacks it, with its parents.
+ */
+export function libraryFolderOptions(folders,current='') {
+    const root=new Map();
+    for(const folder of current?[...folders,current]:folders) {
+        let level=root;
+        for(const segment of folder.split('/')) {if(!level.has(segment)) level.set(segment,new Map());level=level.get(segment);}
+    }
+    const options=[['','All output folders']];
+    (function walk(level,prefix,depth) {
+        for(const segment of [...level.keys()].sort(byFolderName)) {
+            const path=prefix?`${prefix}/${segment}`:segment;
+            options.push([path,`${'\u00a0\u00a0'.repeat(depth)}${segment}`]);
+            walk(level.get(segment),path,depth+1);
+        }
+    })(root,'',0);
+    return options;
+}
diff --git a/web/js/workspace/library.mjs b/web/js/workspace/library.mjs
index e57169fc..82c12dc2 100644
--- a/web/js/workspace/library.mjs
+++ b/web/js/workspace/library.mjs
@@ -2,7 +2,7 @@ import {createScope,createButton} from '../shared/toolkit/core.js';
 import {createPromptSender} from './prompt-sender.mjs';
 import {mountPromptBlocks} from './prompt-inspector.mjs';
 import {mountImages} from './images.mjs';
-import {createLibraryStream,createLibraryDetail,libraryPromptRoles,LIBRARY_TAG_MODES} from './library-state.mjs';
+import {createLibraryStream,createLibraryDetail,libraryPromptRoles,LIBRARY_TAG_MODES,libraryFolderOptions} from './library-state.mjs';
 import {promptRoles} from './prompt-blocks.mjs';
 import {createLibraryEditor,showWorkspaceToast} from './library-editor.mjs';
 import {createLibraryEditorController} from './library-editor-state.mjs';
@@ -31,8 +31,8 @@ const metadataDrafts=new Map();
 const archivedVisible=new Map();
 // The concept's sorts first, then the Library's appended Oldest first (D14); D153 (#447) drops "Highest rated".
 const LIBRARY_SORTS=Object.freeze([['newest','Recently added'],['name','Name A–Z'],['oldest','Oldest first']]);
-// Refine › Tag match (#444 D149), in LIBRARY_TAG_MODES order.
-const TAG_MATCH_OPTIONS=Object.freeze([['all','All of these tags'],['untagged','Prompts without tags']]);
+// Refine › Tag match (#444 D149, D150), in LIBRARY_TAG_MODES order.
+const TAG_MATCH_OPTIONS=Object.freeze([['all','All of these tags'],['any','Any of these tags'],['untagged','Prompts without tags']]);
 // A card's focusable controls in order: the D148 selection checkbox, then its buttons (#437).
 const CARD_CONTROLS='button, input[type="checkbox"]';
 const CATEGORIES_FAILED='Categories could not be loaded. Open the Prompt library again to retry.';
@@ -85,9 +85,9 @@ export function onLibraryWrite(listener) {
  * with the existing Library filters, and the heading takes focus as after a save.
  */
 export function browseLibrary(filters) {
-    const {text='',category='',tags=[],sort='newest',tagMode='all'}=filters || {};
-    if(typeof text!=='string' || typeof category!=='string' || !Array.isArray(tags) || tags.some(tag=>typeof tag!=='string') || typeof sort!=='string' || !LIBRARY_TAG_MODES.includes(tagMode)) throw new TypeError('Invalid Library filters');
-    shelfVisit={filters:{text,category,tags:[...tags],sort,tagMode},anchor:null};
+    const {text='',category='',tags=[],sort='newest',tagMode='all',folder=''}=filters || {};
+    if(typeof text!=='string' || typeof category!=='string' || !Array.isArray(tags) || tags.some(tag=>typeof tag!=='string') || typeof sort!=='string' || !LIBRARY_TAG_MODES.includes(tagMode) || typeof folder!=='string') throw new TypeError('Invalid Library filters');
+    shelfVisit={filters:{text,category,tags:[...tags],sort,tagMode,folder},anchor:null};
     focusHeadingOnMount=true;window.location.hash='#/library';
 }
 /** Remember the selection a reconciled save names, so the destination history opens on it once. */
@@ -160,16 +160,16 @@ export function mountLibrary(main,api,parentScope,{positiveId,savedState=null,on
         const visit=saved?null:shelfVisit, mountedGeneration=writeGeneration;
         // An invalidated visit keeps only filters and anchor: the stream restarts and heights are measured again.
         const restorable=visit?.state?visit:null;
-        const filters={text:'',category:'',tags:[],sort:'newest',tagMode:'all',...visit?.filters,...saved};
+        const filters={text:'',category:'',tags:[],sort:'newest',tagMode:'all',folder:'',...visit?.filters,...saved};
         // D153: a sort the shelf no longer offers (an older "Highest rated" visit) reads as Recently added.
         if(!LIBRARY_SORTS.some(([value])=>value===filters.sort)) filters.sort='newest';
         const section=el('section',undefined,'library-shelf');section.setAttribute('aria-label','Prompt library');
         // The shared concept toolbar (app.js toolbar(), a347–360): Tags live in "Refine this view" (D14), no Refresh (D15).
         // Its own scope, disposed after the visit is saved: removing it first would shorten the page and clamp scrollY.
         const toolbarScope=createScope();
-        // D44: Filters reads "Filters · N" while Refine filters (from Refine or a Browse) narrow the shelf: Tags, and a
-        // Tag match other than All (#444 D149).
-        const refinements=()=>(filters.tags.length?1:0)+(filters.tagMode!=='all'?1:0);
+        // D44: Filters reads "Filters · N" while Refine filters (from Refine or a Browse) narrow the shelf: Tags, a Folder
+        // and a Tag match other than All (#444 D149, D150) each count once.
+        const refinements=()=>(filters.tags.length?1:0)+(filters.folder?1:0)+(filters.tagMode!=='all'?1:0);
         const toolbar=mountToolbar(section,{scope:toolbarScope,categories:filters.category?[filters.category]:[],sorts:LIBRARY_SORTS,
             value:{q:filters.text,category:filters.category,sort:filters.sort},activeFilters:refinements(),onChange:applyToolbar,onFilters:openFilters,
             onSaveView:trigger=>{const value=toolbar.value();onSaveView(trigger,libraryViewState({...filters,text:value.q.trim(),category:value.category,sort:value.sort}));}});
@@ -216,7 +216,7 @@ export function mountLibrary(main,api,parentScope,{positiveId,savedState=null,on
         // Nothing follows the grid in the concept; the legacy Library stays one click away on Overview (spec §5).
         continuation.append(message,retry,more);section.append(optionsStatus,exportStatus,selection.element,caption,grid,continuation);main.append(section);
         const cards=new Map(), rowNodes=new Map(), spacers=new Map(), heights=new Map(), pendingMeasurements=new Map();
-        let state,frame=0,loadFrame=0,observer,optionsRequest,focusOverride=-1;
+        let state,frame=0,loadFrame=0,observer,optionsRequest,folderRequest,focusOverride=-1;
         const columns=()=>window.innerWidth>=1700?3:window.innerWidth<=700?1:2;
         const readInlineSize=()=>Math.round(grid.getBoundingClientRect().width*64)/64;
         let inlineSize=readInlineSize(), columnCount=columns(), layout={rows:[],height:0}, dirty=true, items, indexesById=new Map();
@@ -423,17 +423,26 @@ export function mountLibrary(main,api,parentScope,{positiveId,savedState=null,on
             if(Object.entries(next).every(([key,item])=>filters[key]===item)) return;
             Object.assign(filters,next);reset();
         }
-        /** "Refine this view" with the Library's extra filters, Tags (D14) and Tag match (D149); Clear also clears the toolbar category. */
+        /**
+         * "Refine this view" with the Library's filters: the concept's Folder (#444 D150, its options read when the dialog
+         * opens), Tags (D14) and Tag match (D149, D150); Clear also clears the toolbar category.
+         */
         function openFilters(trigger) {
-            openRefineDialog({scope,trigger,fields:[{key:'tags'},{key:'tagMode',options:TAG_MATCH_OPTIONS}],
-                values:{tags:filters.tags.join(', '),tagMode:filters.tagMode},onApply:applyRefinement,
-                onClear:cleared=>{toolbar.setValue({category:cleared.category});applyRefinement(cleared);}});
+            const refine=openRefineDialog({scope,trigger,fields:[{key:'folder',options:libraryFolderOptions([],filters.folder)},{key:'tags'},
+                {key:'tagMode',options:TAG_MATCH_OPTIONS}],values:{folder:filters.folder,tags:filters.tags.join(', '),tagMode:filters.tagMode},
+                onApply:applyRefinement,onClear:cleared=>{toolbar.setValue({category:cleared.category});applyRefinement(cleared);}});
+            folderRequest?.abort();const request=folderRequest=new AbortController();
+            // A failed read leaves "All output folders" and the current folder; nothing else depends on it.
+            api.get('/prompt_manager/library/options?include=folders',{signal:request.signal}).then(data=>{
+                if(scope.signal.aborted || folderRequest!==request || !Array.isArray(data?.folders) || data.folders.some(folder=>typeof folder!=='string')) return;
+                refine.setOptions('folder',libraryFolderOptions(data.folders,filters.folder));
+            },()=>{});
         }
-        function applyRefinement({tags,tagMode='all',category=filters.category}) {
+        function applyRefinement({tags,tagMode='all',folder='',category=filters.category}) {
             // "Prompts without tags" takes no Tags (the dialog disables them).
             const next=tagMode==='untagged'?[]:[...new Set(tags.split(',').map(tag=>tag.trim()).filter(Boolean))];
-            if(category===filters.category && tagMode===filters.tagMode && next.length===filters.tags.length && next.every((tag,index)=>tag===filters.tags[index])) return;
-            filters.category=category;filters.tags=next;filters.tagMode=tagMode;reset();
+            if(category===filters.category && tagMode===filters.tagMode && folder===filters.folder && next.length===filters.tags.length && next.every((tag,index)=>tag===filters.tags[index])) return;
+            filters.category=category;filters.tags=next;filters.tagMode=tagMode;filters.folder=folder;reset();
         }
         scope.listen(more,'click',()=>stream.loadMore());
         // Retry also re-reads a category list that failed (D15: Refresh is gone).
@@ -446,7 +455,7 @@ export function mountLibrary(main,api,parentScope,{positiveId,savedState=null,on
             // A write while mounted makes this stream stale: keep only what still means something.
             // A saved view is not the plain shelf, so it never replaces the Library return state (#249 M2, as Favorites).
             if(!saved) shelfVisit=mountedGeneration!==writeGeneration?{filters:savedFilters,anchor:savedAnchor}:state?{filters:savedFilters,state,scrollY:window.scrollY,layout:{inlineSize,columns:columnCount,heights:[...heights],anchor:savedAnchor}}:null;
-            toolbarScope.dispose();stream.dispose();optionsRequest?.abort();observer?.disconnect();measurementObserver?.disconnect();cancelAnimationFrame(frame);cancelAnimationFrame(loadFrame);for(const card of cards.values())removeCard(card);cards.clear();});
+            toolbarScope.dispose();stream.dispose();optionsRequest?.abort();folderRequest?.abort();observer?.disconnect();measurementObserver?.disconnect();cancelAnimationFrame(frame);cancelAnimationFrame(loadFrame);for(const card of cards.values())removeCard(card);cards.clear();});
         loadCategories();if(restorable) {render(stream.state);if(restorable.state.loading || restorable.state.error)stream.loadMore();} else reset();
     }
 
diff --git a/web/js/workspace/saved-views.mjs b/web/js/workspace/saved-views.mjs
index 664bc4f0..4711c332 100644
--- a/web/js/workspace/saved-views.mjs
+++ b/web/js/workspace/saved-views.mjs
@@ -47,8 +47,9 @@ const FIELDS = Object.freeze({
     }),
     library: Object.freeze({
         q: text(500), category: text(100), sort: choice(['newest', 'oldest', 'name'], 'newest'), tags,
-        // #444: how the Tags match; 'untagged' never goes with tags (the listing refuses both).
-        tag_mode: choice(['all', 'untagged'], 'all'),
+        // #444: how the Tags match ('untagged' never goes with tags; the listing refuses both) and the output folder
+        // ('/'-joined, below a root).
+        tag_mode: choice(['all', 'any', 'untagged'], 'all'), folder: text(1024),
     }),
 });
 
@@ -117,11 +118,12 @@ export function imagesViewState(filters) {
 /** Library shelf filters (library.mjs `filters`) from a saved state, and the state of the current filters. */
 export function libraryFilters(state) {
     const view = normalizeViewState('library', state);
-    return { text: view.q, category: view.category, sort: view.sort, tags: view.tags, tagMode: view.tag_mode };
+    return { text: view.q, category: view.category, sort: view.sort, tags: view.tags, tagMode: view.tag_mode, folder: view.folder };
 }
 export function libraryViewState(filters) {
     return normalizeViewState('library', { q: filters.text, category: filters.category, sort: filters.sort, tags: filters.tags,
-        tag_mode: filters.tagMode ?? 'all' });
+        // A filter the shelf lacks (undefined) takes its key's default in normalizeViewState.
+        tag_mode: filters.tagMode, folder: filters.folder });
 }
 
 /**
diff --git a/web/js/workspace/workspace-dialogs.mjs b/web/js/workspace/workspace-dialogs.mjs
index 8df9f351..9b114335 100644
--- a/web/js/workspace/workspace-dialogs.mjs
+++ b/web/js/workspace/workspace-dialogs.mjs
@@ -24,7 +24,7 @@
 import { createButton, createSwitch } from '../shared/toolkit/core.js';
 import { noun } from './plural.mjs';
 
-// `tagMode` (#444, D149): the Library's Tag match select after Tags; its `untagged` value disables Tags.
+// `tagMode` (#444, D149, D150): the Library's Tag match select after Tags; its `untagged` value disables Tags.
 const FIELD_LABELS = Object.freeze({ source: 'Source', folder: 'Folder', media: 'Media', tags: 'Tags', tagMode: 'Tag match' });
 const FIELD_ORDER = Object.keys(FIELD_LABELS);