feat(search): support multiple folders in the semantic-search path filter

Extend the ADR-027 Phase 2 path filter from a single path_prefix to a
list of folders. The new normalize_path_prefixes() helper is the single
source of truth for trimming, dropping blanks, and de-duplicating, and
folds the legacy single path_prefix into the list for backward
compatibility.

build_base_filter_conditions() adds one MatchText to the must clause for
a single folder (unchanged shape) and OR-s multiple folders via a nested
Filter(should=[...]) so a file under any selected folder matches while
still AND-ing against the ACL/doc_type/date conditions.

path_prefixes is threaded through every search surface: the
nc_semantic_search MCP tool, the visualization API (JSON body), and the
viz route (CSV query param). The Astrolabe frontend folder picker that
produces these lists ships in a companion astrolabe PR.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/ADR-027-rich-search-filters.md

@@ -68,7 +68,7 @@ Filters can only be applied to fields that exist in the Qdrant payload (built in
 |---|---|---|---|
 | Modified-date range | `modified_at` | `int` (Unix ts) | ✅ **Ready** — value present on every point; needs a payload index (added in Phase 1, no content re-index) |
 | Document type | `doc_type` | keyword-indexed `str` | ✅ Implemented |
-| Directory / path | `file_path` (files only) | `str` | ✅ **Ready (Phase 2)** — value present on file points; TEXT payload index added (no content re-index), filtered with `MatchText` |
+| Directory / path | `file_path` (files only) | `list[str]` (multi-folder) | ✅ **Implemented (Phase 2)** — TEXT payload index (no content re-index); one or more folders filtered with `MatchText`, multiple OR-ed via nested `Filter(should=...)`; picked from the native folder browser |
 | Tags | — | — | ❌ **Not indexed** — no `tags` field is written during scanning |
 | Category (notes) | — | — | ❌ Not in payload — fetched from the Notes API at verify time only |
 
@@ -186,19 +186,30 @@ express:
     it on the answer path. When demand appears it can be threaded through using exactly the same
     parameter + `parse_modified_timestamp` pattern; doing it now would add an unused parameter and
     widen the change for no user-visible gain.
-- **Phase 2 — directory / path (implemented).** Add a `path_prefix` parameter threaded through the
-  same shared contract (`build_base_filter_conditions` → `FieldCondition(key="file_path",
-  match=MatchText(text=path_prefix))`), and a `file_path` **TEXT** payload index in
+- **Phase 2 — directory / path (implemented).** Threaded through the same shared contract
+  (`build_base_filter_conditions`) and backed by a `file_path` **TEXT** payload index in
   `_PAYLOAD_INDEX_FIELDS` (no content re-index — `file_path` is already on every file point).
   `MatchText` semantics differ by backend: **server Qdrant** tokenizes (AND-of-tokens, so
   `/Projects/Reports` matches files whose path contains both the `Projects` and `Reports` tokens),
   while **local/embedded qdrant-client** matches by substring containment — both serve folder
   scoping, neither is a strict left-anchored prefix (a future strict-prefix would need an indexed
   ancestor-path array, i.e. a re-index, so it stays out of Phase 2). Because `file_path` is only
-  written for `doc_type == "file"`, a non-empty `path_prefix` implicitly restricts results to
-  files; the frontend uses a native path text input enabled only when the **Files** doc type is in
-  scope (rather than `NcFilePicker`, to avoid a hard `@nextcloud/vue` component-version dependency —
-  same rationale as the date inputs). A blank value is treated as "no filter".
+  written for `doc_type == "file"`, a non-empty path filter implicitly restricts results to files.
+  - **Multi-folder (list-valued).** The filter accepts **one or more** folders via a
+    `path_prefixes: list[str]` parameter (the original single `path_prefix` is retained for
+    backward compatibility and folded into the list by `normalize_path_prefixes`, which trims,
+    drops blanks, and de-dupes). `build_base_filter_conditions` adds a single `MatchText` to the
+    `must` clause for one folder, and OR-s multiple folders via a nested `Filter(should=[...])` so a
+    file under **any** selected folder matches while still AND-ing against the ACL/doc_type/date
+    conditions. Every search surface parses the list: the MCP tool (`nc_semantic_search`), the
+    visualization API (JSON body), and the viz route (CSV query param).
+  - **Frontend uses the native folder picker.** Instead of a free-text path input, the Astrolabe
+    app opens Nextcloud's server-side folder browser via `getFilePickerBuilder()` from
+    `@nextcloud/dialogs` (already a dependency — no `@nextcloud/vue` component-version coupling),
+    configured directory-only + multi-select. Picked folders are real, validated server paths
+    (no typos), rendered as removable chips, and sent as a comma-separated `path_prefixes` list. The
+    Astrolabe PHP `ApiController`/`McpServerClient` forward the list to the MCP server. The control
+    is enabled only when the **Files** doc type is in scope; an empty selection means "no filter".
 - **Phase 3 — tags (and optionally category).** Add a `tags: list[str]` payload field in
   `processor.py`, propagate Nextcloud system tags during scanning, trigger a re-index, then wire
   `NcSelectTags` (`MatchAny` over tags). Re-index cost lives here, isolated from the cheap wins.
@@ -214,7 +225,9 @@ The Astrolabe app adds filter controls to the existing collapsible advanced pane
   specific `@nextcloud/vue` component version (`NcDateTimePicker` / `NcChip` remain a later option);
   this matches the component's existing native `<input type="range">` controls.
 - Doc types → existing checkbox grid, now also echoed as chips.
-- (Phase 2/3) path → `NcFilePicker`; tags → `NcSelectTags :fetch-tags`.
+- (Phase 2) path → native folder picker (`getFilePickerBuilder` from `@nextcloud/dialogs`),
+  multi-select, rendered as one removable chip per folder. (Phase 3) tags → `NcSelectTags
+  :fetch-tags`.
 
 Dates cross the wire as **RFC 3339 / ISO 8601 strings** (e.g. `"2026-01-01T00:00:00Z"`) — the format
 Nextcloud's date pickers and Unified Search use. The MCP/HTTP boundary parses RFC 3339 (and bare

nextcloud_mcp_server/api/visualization.py

@@ -31,7 +31,10 @@ from nextcloud_mcp_server.search import (
     BM25HybridSearchAlgorithm,
     SemanticSearchAlgorithm,
 )
-from nextcloud_mcp_server.search.access_filter import list_accessible_owners
+from nextcloud_mcp_server.search.access_filter import (
+    list_accessible_owners,
+    normalize_path_prefixes,
+)
 from nextcloud_mcp_server.search.context import (
     get_chunk_bbox_and_page_from_qdrant,
     get_chunk_with_context,
@@ -225,8 +228,21 @@ async def unified_search(request: Request) -> JSONResponse:
         include_pca = body.get("include_pca", False)
         include_chunks = body.get("include_chunks", True)
         doc_types = body.get("doc_types")  # Optional filter
-        # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter.
-        path_prefix = (body.get("path_prefix") or "").strip() or None
+        # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter. Accept a
+        # path_prefixes list (multi-folder) alongside the legacy single
+        # path_prefix; normalize drops blanks and de-dupes.
+        _path_prefixes_raw = body.get("path_prefixes")
+        if isinstance(_path_prefixes_raw, list):
+            _path_prefixes_list = _path_prefixes_raw
+        elif isinstance(_path_prefixes_raw, str):
+            _path_prefixes_list = _path_prefixes_raw.split(",")
+        else:
+            # Ignore any other JSON shape (number, object, null) rather than
+            # blowing up on .split — the legacy path_prefix still applies.
+            _path_prefixes_list = []
+        path_prefixes = normalize_path_prefixes(
+            body.get("path_prefix"), _path_prefixes_list
+        )
 
         if not query:
             return JSONResponse({"results": [], "total_found": 0})
@@ -268,7 +284,7 @@ async def unified_search(request: Request) -> JSONResponse:
                                 accessible_owners=owners,
                                 modified_after=modified_after,
                                 modified_before=modified_before,
-                                path_prefix=path_prefix,
+                                path_prefixes=path_prefixes,
                             )
                         )
                 # Sort, then cap to a fixed over-fetch budget before the result
@@ -288,7 +304,7 @@ async def unified_search(request: Request) -> JSONResponse:
                     accessible_owners=owners,
                     modified_after=modified_after,
                     modified_before=modified_before,
-                    path_prefix=path_prefix,
+                    path_prefixes=path_prefixes,
                 )
             return results
 
@@ -440,8 +456,21 @@ async def vector_search(request: Request) -> JSONResponse:
         limit = min(body.get("limit", 10), 50)  # Enforce max limit
         include_pca = body.get("include_pca", True)
         doc_types = body.get("doc_types")  # Optional list of document types
-        # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter.
-        path_prefix = (body.get("path_prefix") or "").strip() or None
+        # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter. Accept a
+        # path_prefixes list (multi-folder) alongside the legacy single
+        # path_prefix; normalize drops blanks and de-dupes.
+        _path_prefixes_raw = body.get("path_prefixes")
+        if isinstance(_path_prefixes_raw, list):
+            _path_prefixes_list = _path_prefixes_raw
+        elif isinstance(_path_prefixes_raw, str):
+            _path_prefixes_list = _path_prefixes_raw.split(",")
+        else:
+            # Ignore any other JSON shape (number, object, null) rather than
+            # blowing up on .split — the legacy path_prefix still applies.
+            _path_prefixes_list = []
+        path_prefixes = normalize_path_prefixes(
+            body.get("path_prefix"), _path_prefixes_list
+        )
         # ADR-027 modified-date range filter. Accepts RFC 3339 / ISO 8601
         # datetimes or Unix seconds; normalized to int Unix seconds. None ⇒ open.
         try:
@@ -507,7 +536,7 @@ async def vector_search(request: Request) -> JSONResponse:
                                 accessible_owners=owners,
                                 modified_after=modified_after,
                                 modified_before=modified_before,
-                                path_prefix=path_prefix,
+                                path_prefixes=path_prefixes,
                             )
                         )
                 # Sort merged results by score and limit
@@ -522,7 +551,7 @@ async def vector_search(request: Request) -> JSONResponse:
                     accessible_owners=owners,
                     modified_after=modified_after,
                     modified_before=modified_before,
-                    path_prefix=path_prefix,
+                    path_prefixes=path_prefixes,
                 )
             return results
 

nextcloud_mcp_server/auth/viz_routes.py

@@ -33,7 +33,10 @@ from nextcloud_mcp_server.search import (
     BM25HybridSearchAlgorithm,
     SemanticSearchAlgorithm,
 )
-from nextcloud_mcp_server.search.access_filter import list_accessible_owners
+from nextcloud_mcp_server.search.access_filter import (
+    list_accessible_owners,
+    normalize_path_prefixes,
+)
 from nextcloud_mcp_server.search.context import (
     get_chunk_bbox_and_page_from_qdrant,
     get_chunk_with_context,
@@ -144,8 +147,14 @@ async def vector_visualization_search(request: Request) -> JSONResponse:
     doc_types_param = request.query_params.get("doc_types", "")
     doc_types = doc_types_param.split(",") if doc_types_param else None
 
-    # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter.
-    path_prefix = (request.query_params.get("path_prefix") or "").strip() or None
+    # ADR-027 Phase 2 path filter (files only); blank ⇒ no filter. Accept a
+    # comma-separated path_prefixes list (multi-folder) plus the legacy single
+    # path_prefix; normalize_path_prefixes drops blanks and de-dupes.
+    path_prefix = request.query_params.get("path_prefix")
+    path_prefixes = normalize_path_prefixes(
+        path_prefix,
+        (request.query_params.get("path_prefixes") or "").split(","),
+    )
 
     # Parse ADR-027 modified-date range filter. Accepts RFC 3339 / ISO 8601
     # datetimes or Unix seconds; normalized to int Unix seconds. Absent ⇒
@@ -235,7 +244,7 @@ async def vector_visualization_search(request: Request) -> JSONResponse:
                         accessible_owners=accessible_owners,
                         modified_after=modified_after,
                         modified_before=modified_before,
-                        path_prefix=path_prefix,
+                        path_prefixes=path_prefixes,
                     )
                 all_results.extend(unverified_results)
             else:
@@ -258,7 +267,7 @@ async def vector_visualization_search(request: Request) -> JSONResponse:
                             accessible_owners=accessible_owners,
                             modified_after=modified_after,
                             modified_before=modified_before,
-                            path_prefix=path_prefix,
+                            path_prefixes=path_prefixes,
                         )
                     all_results.extend(unverified_results)
                 # Sort by score, then cap to the same limit*2 over-fetch budget

nextcloud_mcp_server/search/access_filter.py

@@ -27,6 +27,7 @@ from __future__ import annotations
 import logging
 import time
 from collections import OrderedDict
+from collections.abc import Iterable
 from typing import Any, Protocol
 
 from qdrant_client.models import (
@@ -189,6 +190,43 @@ def build_ownership_filter(
     return Filter(should=conditions)
 
 
+def normalize_path_prefixes(
+    path_prefix: str | None = None,
+    path_prefixes: Iterable[str] | None = None,
+) -> list[str]:
+    """Merge the legacy single ``path_prefix`` and list ``path_prefixes`` into
+    one clean, de-duplicated list of folder filters.
+
+    Blank/whitespace entries are dropped (an empty UI field must mean "no
+    filter", not "match everything"), surrounding whitespace is stripped, and
+    order is preserved while removing duplicates. Accepting both inputs keeps
+    the pre-ADR-027-Phase-2 single-value contract working while callers migrate
+    to the multi-folder list.
+
+    Args:
+        path_prefix: Legacy single folder filter (deprecated; folded into the
+            returned list).
+        path_prefixes: Zero or more folder filters.
+
+    Returns:
+        Ordered, de-duplicated list of non-empty folder filters (possibly empty).
+    """
+    raw: list[str] = []
+    if path_prefix:
+        raw.append(path_prefix)
+    if path_prefixes:
+        raw.extend(path_prefixes)
+
+    seen: set[str] = set()
+    cleaned: list[str] = []
+    for value in raw:
+        stripped = value.strip()
+        if stripped and stripped not in seen:
+            seen.add(stripped)
+            cleaned.append(stripped)
+    return cleaned
+
+
 def build_base_filter_conditions(
     user_id: str,
     accessible_owners: list[str] | None = None,
@@ -196,6 +234,7 @@ def build_base_filter_conditions(
     modified_after: int | None = None,
     modified_before: int | None = None,
     path_prefix: str | None = None,
+    path_prefixes: list[str] | None = None,
 ) -> list[Condition]:
     """Build the common ``must`` conditions shared by every search algorithm.
 
@@ -211,7 +250,10 @@ def build_base_filter_conditions(
     2. ``build_ownership_filter(...)`` — ACL-aware ``owner_id``/``user_id`` scope.
     3. ``doc_type`` exact match — only when ``doc_type`` is truthy.
     4. ``modified_at`` range — only when at least one bound is given.
-    5. ``file_path`` text match — only when ``path_prefix`` is given.
+    5. ``file_path`` text match — only when a path filter is given. One folder
+       adds a single ``MatchText`` to ``must``; multiple folders are OR-ed via a
+       nested ``Filter(should=[...])`` so a file under *any* selected folder
+       matches.
 
     Args:
         user_id: Querying user.
@@ -220,10 +262,13 @@ def build_base_filter_conditions(
         doc_type: Optional single document-type filter.
         modified_after: Inclusive lower bound on ``modified_at`` (Unix seconds).
         modified_before: Inclusive upper bound on ``modified_at`` (Unix seconds).
-        path_prefix: Optional folder/path filter on the ``file_path`` payload
-            field (ADR-027 Phase 2). Implemented with ``MatchText`` against the
-            text-indexed ``file_path``. ``file_path`` is only written for
-            ``doc_type == "file"`` points, so a non-empty ``path_prefix``
+        path_prefix: Deprecated single folder/path filter; folded into
+            ``path_prefixes``. Kept for backward compatibility.
+        path_prefixes: Optional folder/path filters on the ``file_path`` payload
+            field (ADR-027 Phase 2). Each is implemented with ``MatchText``
+            against the text-indexed ``file_path`` and multiple folders are
+            OR-ed together. ``file_path`` is only written for
+            ``doc_type == "file"`` points, so any non-empty path filter
             implicitly restricts results to files. NOTE the match semantics
             differ by backend: server Qdrant tokenizes (AND-of-tokens, so
             ``"/Projects/Reports"`` matches files whose path contains both the
@@ -255,9 +300,23 @@ def build_base_filter_conditions(
             )
         )
 
-    if path_prefix:
+    # One folder ⇒ a single ``must`` condition (the original Phase 2 shape).
+    # Multiple folders ⇒ OR them in a nested ``Filter(should=...)`` so a file
+    # under any selected folder matches, while still AND-ing against the other
+    # ``must`` conditions (ACL, doc_type, date).
+    folders = normalize_path_prefixes(path_prefix, path_prefixes)
+    if len(folders) == 1:
         conditions.append(
-            FieldCondition(key="file_path", match=MatchText(text=path_prefix))
+            FieldCondition(key="file_path", match=MatchText(text=folders[0]))
+        )
+    elif len(folders) > 1:
+        conditions.append(
+            Filter(
+                should=[
+                    FieldCondition(key="file_path", match=MatchText(text=folder))
+                    for folder in folders
+                ]
+            )
         )
 
     return conditions

nextcloud_mcp_server/search/algorithms.py

@@ -300,6 +300,7 @@ class SearchAlgorithm(ABC):
         modified_after: int | None = None,
         modified_before: int | None = None,
         path_prefix: str | None = None,
+        path_prefixes: list[str] | None = None,
         **kwargs: Any,
     ) -> list[SearchResult]:
         """Execute search with the given parameters.
@@ -321,10 +322,13 @@ class SearchAlgorithm(ABC):
                 ``accessible_owners`` (ADR-027). ``None`` ⇒ open-ended.
             modified_before: Optional inclusive upper bound on ``modified_at``
                 (Unix seconds, UTC). ``None`` ⇒ open-ended.
-            path_prefix: Optional folder/path filter on the ``file_path`` payload
-                field (ADR-027 Phase 2). Only ``doc_type == "file"`` points carry
-                ``file_path``, so a non-empty value implicitly restricts results
-                to files. ``None`` ⇒ no path filter.
+            path_prefix: Deprecated single folder/path filter; folded into
+                ``path_prefixes``. Kept for backward compatibility.
+            path_prefixes: Optional folder/path filters on the ``file_path``
+                payload field (ADR-027 Phase 2), OR-ed together. Only
+                ``doc_type == "file"`` points carry ``file_path``, so any
+                non-empty value implicitly restricts results to files. ``None``
+                or empty ⇒ no path filter.
             **kwargs: Algorithm-specific parameters
 
         Returns:

nextcloud_mcp_server/search/bm25_hybrid.py

@@ -75,6 +75,7 @@ class BM25HybridSearchAlgorithm(SearchAlgorithm):
         modified_after: int | None = None,
         modified_before: int | None = None,
         path_prefix: str | None = None,
+        path_prefixes: list[str] | None = None,
         **kwargs: Any,
     ) -> list[SearchResult]:
         """
@@ -100,8 +101,11 @@ class BM25HybridSearchAlgorithm(SearchAlgorithm):
                 seconds, UTC); ``None`` ⇒ open-ended (ADR-027).
             modified_before: Inclusive upper bound on ``modified_at`` (Unix
                 seconds, UTC); ``None`` ⇒ open-ended (ADR-027).
-            path_prefix: Folder/path filter on ``file_path`` (files only);
-                ``None`` ⇒ no path filter (ADR-027 Phase 2).
+            path_prefix: Deprecated single folder filter; folded into
+                ``path_prefixes`` (ADR-027 Phase 2).
+            path_prefixes: Folder/path filters on ``file_path`` (files only),
+                OR-ed together; ``None``/empty ⇒ no path filter (ADR-027
+                Phase 2).
             **kwargs: Additional parameters (score_threshold override)
 
         Returns:
@@ -152,6 +156,7 @@ class BM25HybridSearchAlgorithm(SearchAlgorithm):
             modified_after=modified_after,
             modified_before=modified_before,
             path_prefix=path_prefix,
+            path_prefixes=path_prefixes,
         )
 
         query_filter = Filter(must=filter_conditions)

nextcloud_mcp_server/search/semantic.py

@@ -55,6 +55,7 @@ class SemanticSearchAlgorithm(SearchAlgorithm):
         modified_after: int | None = None,
         modified_before: int | None = None,
         path_prefix: str | None = None,
+        path_prefixes: list[str] | None = None,
         **kwargs: Any,
     ) -> list[SearchResult]:
         """Execute semantic search using vector similarity.
@@ -79,8 +80,11 @@ class SemanticSearchAlgorithm(SearchAlgorithm):
                 seconds, UTC); ``None`` ⇒ open-ended (ADR-027).
             modified_before: Inclusive upper bound on ``modified_at`` (Unix
                 seconds, UTC); ``None`` ⇒ open-ended (ADR-027).
-            path_prefix: Folder/path filter on ``file_path`` (files only);
-                ``None`` ⇒ no path filter (ADR-027 Phase 2).
+            path_prefix: Deprecated single folder filter; folded into
+                ``path_prefixes`` (ADR-027 Phase 2).
+            path_prefixes: Folder/path filters on ``file_path`` (files only),
+                OR-ed together; ``None``/empty ⇒ no path filter (ADR-027
+                Phase 2).
             **kwargs:
                 - score_threshold (float): override the instance default
 
@@ -122,6 +126,7 @@ class SemanticSearchAlgorithm(SearchAlgorithm):
             modified_after=modified_after,
             modified_before=modified_before,
             path_prefix=path_prefix,
+            path_prefixes=path_prefixes,
         )
 
         # ACL pre-filter (design §11), opt-in via ACL_PREFILTER_ENABLED and OFF

nextcloud_mcp_server/server/semantic.py

@@ -32,7 +32,10 @@ from nextcloud_mcp_server.models.semantic import (
 from nextcloud_mcp_server.observability.metrics import (
     instrument_tool,
 )
-from nextcloud_mcp_server.search.access_filter import list_accessible_owners
+from nextcloud_mcp_server.search.access_filter import (
+    list_accessible_owners,
+    normalize_path_prefixes,
+)
 from nextcloud_mcp_server.search.bm25_hybrid import BM25HybridSearchAlgorithm
 from nextcloud_mcp_server.search.context import get_chunk_with_context
 from nextcloud_mcp_server.search.verification import verify_search_results
@@ -88,6 +91,7 @@ def configure_semantic_tools(mcp: FastMCP):
             str | None,
             Field(
                 description=(
+                    "Deprecated single-folder filter; prefer path_prefixes. "
                     "Restrict to files under this folder/path "
                     "(e.g. '/Projects/Reports'). Matches the file_path of "
                     "indexed files only, so setting it implicitly limits "
@@ -95,6 +99,18 @@ def configure_semantic_tools(mcp: FastMCP):
                 ),
             ),
         ] = None,
+        path_prefixes: Annotated[
+            list[str] | None,
+            Field(
+                description=(
+                    "Restrict to files under any of these folders/paths "
+                    "(e.g. ['/Projects/Reports', '/Shared/Specs']). Folders are "
+                    "OR-ed together. Matches the file_path of indexed files "
+                    "only, so setting it implicitly limits results to files. "
+                    "None or empty = no path filter."
+                ),
+            ),
+        ] = None,
     ) -> SemanticSearchResponse:
         """
         Search Nextcloud content using BM25 hybrid search with cross-app support.
@@ -127,9 +143,12 @@ def configure_semantic_tools(mcp: FastMCP):
             modified_before: Only return documents whose last-modified time is at or before this
                 instant. Same formats as modified_after. None = no upper bound (default). Must be
                 >= modified_after when both are supplied.
-            path_prefix: Restrict to files under this folder/path (e.g. "/Projects/Reports").
-                Matches the file_path of indexed files only — setting it implicitly limits results
-                to files. None = no path filter (default).
+            path_prefix: Deprecated single-folder filter; prefer path_prefixes. Restrict to files
+                under this folder/path (e.g. "/Projects/Reports"). Folded into path_prefixes.
+            path_prefixes: Restrict to files under any of these folders/paths (OR-ed), e.g.
+                ["/Projects/Reports", "/Shared/Specs"]. Matches the file_path of indexed files
+                only — setting it implicitly limits results to files. None/empty = no path filter
+                (default).
 
         Returns:
             SemanticSearchResponse with matching documents ranked by fusion scores.
@@ -200,11 +219,10 @@ def configure_semantic_tools(mcp: FastMCP):
                 )
             )
 
-        # Treat a blank/whitespace path_prefix as "no filter" so an empty UI
-        # field doesn't filter out every result (ADR-027 Phase 2).
-        path_prefix = path_prefix.strip() if path_prefix else None
-        if not path_prefix:
-            path_prefix = None
+        # Merge the legacy single path_prefix and the path_prefixes list into one
+        # cleaned list, dropping blank/whitespace entries so an empty UI field
+        # doesn't filter out every result (ADR-027 Phase 2).
+        folder_prefixes = normalize_path_prefixes(path_prefix, path_prefixes)
 
         # Expand the caller's identity to every owner whose content they
         # have read access to via Nextcloud shares. Lets a user find files
@@ -252,7 +270,7 @@ def configure_semantic_tools(mcp: FastMCP):
                     accessible_owners=accessible_owners,
                     modified_after=modified_after_ts,
                     modified_before=modified_before_ts,
-                    path_prefix=path_prefix,
+                    path_prefixes=folder_prefixes,
                 )
                 all_results.extend(unverified_results)
             else:
@@ -280,7 +298,7 @@ def configure_semantic_tools(mcp: FastMCP):
                         accessible_owners=accessible_owners,
                         modified_after=modified_after_ts,
                         modified_before=modified_before_ts,
-                        path_prefix=path_prefix,
+                        path_prefixes=folder_prefixes,
                     )
                     all_results.extend(unverified_results)
 

tests/unit/search/test_access_filter.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 from unittest.mock import AsyncMock
 
 import pytest
-from qdrant_client.models import FieldCondition, MatchText, Range
+from qdrant_client.models import FieldCondition, Filter, MatchText, Range
 
 from nextcloud_mcp_server.search import access_filter
 from nextcloud_mcp_server.search.access_filter import (
@@ -13,6 +13,7 @@ from nextcloud_mcp_server.search.access_filter import (
     build_ownership_filter,
     clear_accessible_owners_cache,
     list_accessible_owners,
+    normalize_path_prefixes,
 )
 
 
@@ -270,6 +271,67 @@ class TestBuildBaseFilterConditions:
             isinstance(c, FieldCondition) and c.key == "file_path" for c in conditions
         )
 
+    @staticmethod
+    def _path_should_texts(conditions) -> set[str] | None:
+        """Return the file_path texts from the nested OR Filter, or None if no
+        such filter is present. Ignores the ownership Filter (which ORs
+        user_id/owner_id, not file_path)."""
+        for cond in conditions:
+            if not isinstance(cond, Filter) or not cond.should:
+                continue
+            if all(
+                isinstance(c, FieldCondition) and c.key == "file_path"
+                for c in cond.should
+            ):
+                return {
+                    c.match.text
+                    for c in cond.should
+                    if isinstance(c, FieldCondition) and isinstance(c.match, MatchText)
+                }
+        return None
+
+    @pytest.mark.unit
+    def test_multiple_path_prefixes_or_in_nested_should(self) -> None:
+        # Two+ folders must OR together: a single nested Filter(should=[...]) is
+        # appended (not two must conditions, which would AND and match nothing).
+        conditions = build_base_filter_conditions(
+            "alice", None, path_prefixes=["/Projects", "/Archive"]
+        )
+        assert self._path_should_texts(conditions) == {"/Projects", "/Archive"}
+        # No bare file_path FieldCondition in must for the multi-folder case.
+        assert not any(
+            isinstance(c, FieldCondition) and c.key == "file_path" for c in conditions
+        )
+
+    @pytest.mark.unit
+    def test_path_prefix_and_path_prefixes_merge_and_dedupe(self) -> None:
+        # Legacy single + list inputs merge; duplicates collapse so a folder
+        # passed both ways yields two distinct conditions, not three.
+        conditions = build_base_filter_conditions(
+            "alice",
+            None,
+            path_prefix="/Projects",
+            path_prefixes=["/Projects", "/Archive"],
+        )
+        assert self._path_should_texts(conditions) == {"/Projects", "/Archive"}
+
+    @pytest.mark.unit
+    def test_single_effective_prefix_uses_flat_must_condition(self) -> None:
+        # When dedupe/blank-stripping leaves exactly one folder, keep the
+        # original flat MatchText in must rather than a one-element should.
+        conditions = build_base_filter_conditions(
+            "alice", None, path_prefixes=["/Projects", "  ", "/Projects"]
+        )
+        # The only nested Filter should be ownership, never a path OR.
+        assert self._path_should_texts(conditions) is None
+        path_conds = [
+            c
+            for c in conditions
+            if isinstance(c, FieldCondition) and c.key == "file_path"
+        ]
+        assert len(path_conds) == 1
+        assert path_conds[0].match.text == "/Projects"
+
     @pytest.mark.unit
     def test_all_filters_compose(self) -> None:
         # placeholder + ownership + doc_type + modified_at range + file_path = 5.
@@ -282,3 +344,18 @@ class TestBuildBaseFilterConditions:
             path_prefix="/Projects",
         )
         assert len(conditions) == 5
+
+
+class TestNormalizePathPrefixes:
+    @pytest.mark.unit
+    def test_empty_inputs_return_empty_list(self) -> None:
+        assert normalize_path_prefixes(None, None) == []
+        assert normalize_path_prefixes("", []) == []
+        assert normalize_path_prefixes("   ", ["", "  "]) == []
+
+    @pytest.mark.unit
+    def test_strips_dedupes_and_preserves_order(self) -> None:
+        result = normalize_path_prefixes(
+            " /Projects ", ["/Archive", "/Projects", "  ", "/Specs"]
+        )
+        assert result == ["/Projects", "/Archive", "/Specs"]