diff --git a/nextcloud_mcp_server/api/visualization.py b/nextcloud_mcp_server/api/visualization.py
index 2b0650c1..242c7c13 100644
--- a/nextcloud_mcp_server/api/visualization.py
+++ b/nextcloud_mcp_server/api/visualization.py
@@ -23,10 +23,8 @@ from nextcloud_mcp_server.api.management import (
     _parse_int_param,
     _sanitize_error_for_client,
     _validate_query_string,
-    extract_bearer_token,
     validate_token_and_get_user,
 )
-from nextcloud_mcp_server.client import NextcloudClient
 from nextcloud_mcp_server.config import get_settings
 from nextcloud_mcp_server.embedding.service import get_embedding_service
 from nextcloud_mcp_server.search import (
@@ -34,6 +32,10 @@ from nextcloud_mcp_server.search import (
     SemanticSearchAlgorithm,
 )
 from nextcloud_mcp_server.search.context import get_chunk_with_context
+from nextcloud_mcp_server.vector.oauth_sync import (
+    NotProvisionedError,
+    get_user_client_basic_auth,
+)
 from nextcloud_mcp_server.vector.placeholder import get_placeholder_filter
 from nextcloud_mcp_server.vector.qdrant_client import get_qdrant_client
 from nextcloud_mcp_server.vector.visualization import compute_pca_coordinates
@@ -512,11 +514,6 @@ async def get_chunk_context(request: Request) -> JSONResponse:
         # Convert doc_id to int if possible (most IDs are int)
         doc_id_val: str | int = int(doc_id) if doc_id.isdigit() else doc_id
 
-        # Get bearer token for client initialization
-        token = extract_bearer_token(request)
-        if not token:
-            raise ValueError("Missing token")
-
         # Get Nextcloud host from OAuth context
         oauth_ctx = request.app.state.oauth_context
         nextcloud_host = oauth_ctx.get("config", {}).get("nextcloud_host", "")
@@ -524,10 +521,19 @@ async def get_chunk_context(request: Request) -> JSONResponse:
         if not nextcloud_host:
             raise ValueError("Nextcloud host not configured")
 
-        # Initialize authenticated Nextcloud client
-        async with NextcloudClient.from_token(
-            base_url=nextcloud_host, token=token, username=user_id
-        ) as nc_client:
+        # Use the user's stored app password for Nextcloud calls.
+        # The OAuth bearer is only used to authenticate Astrolabe → MCP Server;
+        # MCP Server → Nextcloud always uses the app password provisioned
+        # during the authorization step.
+        try:
+            nc_client = await get_user_client_basic_auth(user_id, nextcloud_host)
+        except NotProvisionedError as e:
+            return JSONResponse(
+                {"success": False, "error": str(e)},
+                status_code=401,
+            )
+
+        async with nc_client:
             chunk_context = await get_chunk_with_context(
                 nc_client=nc_client,
                 user_id=user_id,
@@ -687,11 +693,6 @@ async def get_pdf_preview(request: Request) -> JSONResponse:
         except ValueError as e:
             return JSONResponse({"success": False, "error": str(e)}, status_code=400)
 
-        # Get bearer token for WebDAV authentication
-        token = extract_bearer_token(request)
-        if not token:
-            raise ValueError("Missing token")
-
         # Get Nextcloud host from OAuth context
         oauth_ctx = request.app.state.oauth_context
         nextcloud_host = oauth_ctx.get("config", {}).get("nextcloud_host", "")
@@ -699,10 +700,19 @@ async def get_pdf_preview(request: Request) -> JSONResponse:
         if not nextcloud_host:
             raise ValueError("Nextcloud host not configured")
 
-        # Download PDF via WebDAV using user's token
-        async with NextcloudClient.from_token(
-            base_url=nextcloud_host, token=token, username=user_id
-        ) as nc_client:
+        # Use the user's stored app password for Nextcloud calls.
+        # The OAuth bearer is only used to authenticate Astrolabe → MCP Server;
+        # MCP Server → Nextcloud always uses the app password provisioned
+        # during the authorization step.
+        try:
+            nc_client = await get_user_client_basic_auth(user_id, nextcloud_host)
+        except NotProvisionedError as e:
+            return JSONResponse(
+                {"success": False, "error": str(e)},
+                status_code=401,
+            )
+
+        async with nc_client:
             pdf_bytes, _ = await nc_client.webdav.read_file(file_path)
 
         # Check file size limit (50 MB)
diff --git a/nextcloud_mcp_server/auth/viz_routes.py b/nextcloud_mcp_server/auth/viz_routes.py
index fe45327d..d072c373 100644
--- a/nextcloud_mcp_server/auth/viz_routes.py
+++ b/nextcloud_mcp_server/auth/viz_routes.py
@@ -34,6 +34,10 @@ from nextcloud_mcp_server.search import (
     SemanticSearchAlgorithm,
 )
 from nextcloud_mcp_server.search.context import get_chunk_with_context
+from nextcloud_mcp_server.vector.oauth_sync import (
+    NotProvisionedError,
+    get_user_client_basic_auth,
+)
 from nextcloud_mcp_server.vector.pca import PCA
 from nextcloud_mcp_server.vector.placeholder import get_placeholder_filter
 from nextcloud_mcp_server.vector.qdrant_client import get_qdrant_client
@@ -554,12 +558,28 @@ async def chunk_context_endpoint(request: Request) -> JSONResponse:
         # Convert doc_id to int (all document types use int IDs)
         doc_id_int = int(doc_id)
 
-        # Get authenticated Nextcloud client
-        # Use context expansion module to fetch chunk with surrounding context
-        async with await _get_authenticated_client_for_userinfo(request) as nc_client:
+        user_id = request.user.display_name
+        settings = get_settings()
+        nextcloud_host = settings.nextcloud_host
+        if not nextcloud_host:
+            raise RuntimeError("Nextcloud host not configured")
+
+        # Use the user's stored app password for Nextcloud calls.
+        # The session cookie only authenticates the browser → MCP Server hop;
+        # MCP Server → Nextcloud always uses the app password provisioned
+        # during the authorization step.
+        try:
+            nc_client = await get_user_client_basic_auth(user_id, nextcloud_host)
+        except NotProvisionedError as e:
+            return JSONResponse(
+                {"success": False, "error": str(e)},
+                status_code=401,
+            )
+
+        async with nc_client:
             chunk_context = await get_chunk_with_context(
                 nc_client=nc_client,
-                user_id=request.user.display_name,  # User ID from auth
+                user_id=user_id,
                 doc_id=doc_id_int,
                 doc_type=doc_type,
                 chunk_start=start,
diff --git a/tests/integration/test_astrolabe_chunk_context.py b/tests/integration/test_astrolabe_chunk_context.py
new file mode 100644
index 00000000..201ca49d
--- /dev/null
+++ b/tests/integration/test_astrolabe_chunk_context.py
@@ -0,0 +1,294 @@
+"""Integration test for the chunk-context HTTP path in multi-user BasicAuth mode.
+
+Cross-system interface test: Tests the MCP server's /api/v1/chunk-context
+handler via the Astrolabe PHP app (/apps/astrolabe/api/chunk-context). Astrolabe
+source lives in ./third_party/astrolabe (submodule) and is installed during
+test setup by app-hooks/post-installation/20-install-astrolabe-app.sh.
+
+Regression test: Prior to this test, `get_chunk_context` in
+nextcloud_mcp_server/api/visualization.py forwarded the OAuth bearer token
+directly to Nextcloud via NextcloudClient.from_token(...). In multi-user
+BasicAuth deployments, Nextcloud doesn't validate that bearer on the Notes
+API, so the handler returned 404 (wrapped by Astrolabe as 500). This test
+exercises the full chain:
+
+    browser session → astrolabe → MCP server (OAuth bearer) →
+        get_user_client_basic_auth → Nextcloud (app password BasicAuth) → note
+
+so a regression to from_token-style auth would surface as a 500/404 from
+Astrolabe instead of a 200 with chunk_text.
+"""
+
+import base64
+import json
+import logging
+import re
+import time
+import uuid
+
+import anyio
+import httpx
+import pytest
+
+from tests.conftest import create_mcp_client_session
+from tests.integration.test_astrolabe_multi_user_background_sync import (
+    complete_astrolabe_authorization,
+    login_to_nextcloud,
+)
+from tests.integration.test_astrolabe_plotly_visualization import wait_for_vector_sync
+
+logger = logging.getLogger(__name__)
+
+pytestmark = [pytest.mark.integration, pytest.mark.multi_user_basic]
+
+
+def _build_basic_auth_header(username: str, password: str) -> str:
+    credentials = base64.b64encode(f"{username}:{password}".encode()).decode("utf-8")
+    return f"Basic {credentials}"
+
+
+async def _poll_astrolabe_search_for_note(
+    page,
+    unique_term: str,
+    note_id,
+    csrf_headers: dict,
+    timeout_seconds: int = 60,
+) -> dict:
+    """Poll Astrolabe's search endpoint until `note_id` shows up in results.
+
+    `wait_for_vector_sync` only waits for the total indexed count to grow —
+    it does not guarantee that *this specific* document is visible yet
+    (observed on nc32 where deck-card seed data indexes first and the new
+    note arrives in Qdrant a few seconds later). Poll until the unique term
+    returns our note, or fail loudly with the last response we saw.
+    """
+    deadline = time.monotonic() + timeout_seconds
+    last_results: list | None = None
+    attempts = 0
+    while time.monotonic() < deadline:
+        attempts += 1
+        search_resp = await page.request.get(
+            f"http://localhost:8080/apps/astrolabe/api/search"
+            f"?query={unique_term}&algorithm=hybrid&limit=5&include_pca=false",
+            headers=csrf_headers,
+        )
+        assert search_resp.ok, (
+            f"Astrolabe search failed on attempt {attempts}: "
+            f"{search_resp.status} {await search_resp.text()}"
+        )
+        search_data = await search_resp.json()
+        assert search_data.get("success"), (
+            f"Astrolabe search returned error on attempt {attempts}: {search_data}"
+        )
+        last_results = search_data.get("results") or []
+        note_result = next(
+            (
+                r
+                for r in last_results
+                if r.get("doc_type") == "note" and str(r.get("id")) == str(note_id)
+            ),
+            None,
+        )
+        if note_result is not None:
+            logger.info(
+                f"Note {note_id} surfaced in Astrolabe search after {attempts} "
+                f"attempts (~{attempts * 2}s)"
+            )
+            return note_result
+        await anyio.sleep(2)
+
+    raise AssertionError(
+        f"Note {note_id} with unique term '{unique_term}' did not surface in "
+        f"Astrolabe search within {timeout_seconds}s ({attempts} attempts). "
+        f"Last {len(last_results or [])} results: {last_results}"
+    )
+
+
+@pytest.mark.timeout(300)
+async def test_chunk_context_endpoint_uses_app_password(
+    browser,
+    test_users_setup,
+    configure_astrolabe_for_mcp_server,
+):
+    """Astrolabe /api/chunk-context must return 200 with populated chunk_text.
+
+    Covers the regression where the MCP handler used BearerAuth against
+    Nextcloud instead of BasicAuth with the stored app password.
+    """
+    await configure_astrolabe_for_mcp_server(
+        mcp_server_internal_url="http://mcp-multi-user-basic:8000",
+        mcp_server_public_url="http://localhost:8003",
+    )
+
+    username = "alice"
+    password = test_users_setup[username]["password"]
+    note_id = None
+    unique_term = f"chunk_ctx_test_{uuid.uuid4().hex[:8]}"
+
+    context = await browser.new_context(ignore_https_errors=True)
+    page = await context.new_page()
+
+    try:
+        await login_to_nextcloud(page, username, password)
+        auth_result = await complete_astrolabe_authorization(page, username, password)
+        assert auth_result["step1"], "OAuth authorization did not complete"
+        assert auth_result["step2"], "App password provisioning did not complete"
+
+        auth_header = _build_basic_auth_header(username, password)
+        async with create_mcp_client_session(
+            url="http://localhost:8003/mcp",
+            headers={"Authorization": auth_header},
+            client_name="Alice Chunk Context Test",
+        ) as mcp_client:
+            initial_sync = await mcp_client.call_tool("nc_get_vector_sync_status", {})
+            if initial_sync.isError:
+                pytest.skip("Vector sync not enabled on mcp-multi-user-basic")
+            initial_count = json.loads(initial_sync.content[0].text).get(
+                "indexed_count", 0
+            )
+
+            note_body = (
+                f"# Chunk Context Regression Test\n\n"
+                f"This document exists to verify that the chunk-context HTTP "
+                f"endpoint can re-fetch it after indexing. "
+                f"Unique marker: {unique_term}.\n\n"
+                f"Paragraph two exists so there is a plausible surrounding "
+                f"context to slice. Lorem ipsum dolor sit amet, consectetur "
+                f"adipiscing elit."
+            )
+            note_response = await mcp_client.call_tool(
+                "nc_notes_create_note",
+                {
+                    "title": f"Chunk Context Test {unique_term}",
+                    "content": note_body,
+                    "category": "Test",
+                },
+            )
+            assert not note_response.isError, f"Create note failed: {note_response}"
+            note_id = json.loads(note_response.content[0].text).get("id")
+            assert note_id is not None
+
+            sync_complete, status = await wait_for_vector_sync(
+                mcp_client, initial_count, timeout_seconds=90
+            )
+            assert sync_complete, f"Vector sync did not complete: {status}"
+
+        # Use the browser's session to drive Astrolabe end-to-end, the way a
+        # real user would: this exercises astrolabe's OAuth token retrieval
+        # and the MCP server's handler under a real bearer. Nextcloud's
+        # controllers require a CSRF token (`requesttoken` header) that the
+        # rendered SPA picks up from `OC.requestToken`; direct page.request
+        # calls don't get it for free, so we load an Astrolabe page and
+        # forward the token on each subsequent API call.
+        await page.goto(
+            "http://localhost:8080/apps/astrolabe/", wait_until="networkidle"
+        )
+        request_token = await page.evaluate("window.OC && OC.requestToken")
+        assert request_token, (
+            "Could not read OC.requestToken from Astrolabe page — is the user logged in?"
+        )
+        csrf_headers = {"requesttoken": request_token}
+
+        note_result = await _poll_astrolabe_search_for_note(
+            page=page,
+            unique_term=unique_term,
+            note_id=note_id,
+            csrf_headers=csrf_headers,
+            timeout_seconds=60,
+        )
+        start = note_result.get("chunk_start_offset")
+        end = note_result.get("chunk_end_offset")
+        assert start is not None and end is not None, (
+            f"Search result missing chunk offsets: {note_result}"
+        )
+
+        chunk_resp = await page.request.get(
+            "http://localhost:8080/apps/astrolabe/api/chunk-context",
+            params={
+                "doc_type": "note",
+                "doc_id": str(note_id),
+                "start": str(start),
+                "end": str(end),
+            },
+            headers=csrf_headers,
+        )
+        assert chunk_resp.status == 200, (
+            f"chunk-context returned {chunk_resp.status}, body: "
+            f"{await chunk_resp.text()}"
+        )
+        chunk_data = await chunk_resp.json()
+        assert chunk_data.get("success") is True, f"Response: {chunk_data}"
+        chunk_text = chunk_data.get("chunk_text") or ""
+        assert chunk_text, f"Empty chunk_text in response: {chunk_data}"
+        # The unique marker is in the indexed body, so it must appear in the
+        # chunk text or in the surrounding context.
+        combined = (
+            chunk_text
+            + chunk_data.get("before_context", "")
+            + chunk_data.get("after_context", "")
+        )
+        assert re.search(re.escape(unique_term), combined), (
+            f"Unique term {unique_term} missing from chunk+context: "
+            f"chunk_text={chunk_text!r}, before={chunk_data.get('before_context')!r}, "
+            f"after={chunk_data.get('after_context')!r}"
+        )
+    finally:
+        try:
+            if note_id is not None:
+                auth_header = _build_basic_auth_header(username, password)
+                async with create_mcp_client_session(
+                    url="http://localhost:8003/mcp",
+                    headers={"Authorization": auth_header},
+                    client_name="Alice Chunk Context Cleanup",
+                ) as mcp_client:
+                    await mcp_client.call_tool(
+                        "nc_notes_delete_note", {"note_id": note_id}
+                    )
+        except Exception as cleanup_err:
+            logger.warning(f"Cleanup failed for note {note_id}: {cleanup_err}")
+        await context.close()
+
+
+@pytest.mark.timeout(60)
+async def test_chunk_context_endpoint_requires_authentication():
+    """Direct HTTP hit at /api/v1/chunk-context without a bearer must 401."""
+    async with httpx.AsyncClient() as client:
+        response = await client.get(
+            "http://localhost:8003/api/v1/chunk-context",
+            params={
+                "doc_type": "note",
+                "doc_id": "1",
+                "start": "0",
+                "end": "10",
+            },
+        )
+        assert response.status_code == 401, (
+            f"Expected 401 without auth, got {response.status_code}: {response.text}"
+        )
+
+
+@pytest.mark.timeout(60)
+async def test_chunk_context_endpoint_rejects_invalid_bearer():
+    """A syntactically-valid-but-unverifiable bearer must not 500.
+
+    The NotProvisionedError path (handler reached but no stored app password)
+    is covered by the corresponding unit test. This check guards the other
+    rejection path: token validation fails upfront at
+    `validate_token_and_get_user`, which must turn into a clean 401/404 from
+    the HTTP layer, not an opaque 500.
+    """
+    async with httpx.AsyncClient() as client:
+        response = await client.get(
+            "http://localhost:8003/api/v1/chunk-context",
+            params={
+                "doc_type": "note",
+                "doc_id": "1",
+                "start": "0",
+                "end": "10",
+            },
+            headers={"Authorization": "Bearer invalid.token.value"},
+        )
+        assert response.status_code in (401, 404), (
+            f"Expected 401/404 for invalid bearer, got {response.status_code}: "
+            f"{response.text}"
+        )
diff --git a/tests/unit/test_management_chunk_context_endpoint.py b/tests/unit/test_management_chunk_context_endpoint.py
new file mode 100644
index 00000000..e387a91a
--- /dev/null
+++ b/tests/unit/test_management_chunk_context_endpoint.py
@@ -0,0 +1,279 @@
+"""
+Unit tests for Management API chunk-context endpoint.
+
+Tests the /api/v1/chunk-context endpoint focusing on:
+- Parameter validation (doc_type, doc_id, start, end, context)
+- OAuth token validation
+- Nextcloud credential path (must use get_user_client_basic_auth, not
+  NextcloudClient.from_token — see regression in api/visualization.py)
+- Error handling (missing params, invalid ranges, missing credentials)
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+from starlette.applications import Starlette
+from starlette.routing import Route
+from starlette.testclient import TestClient
+
+from nextcloud_mcp_server.api.visualization import get_chunk_context
+from nextcloud_mcp_server.vector.oauth_sync import NotProvisionedError
+
+pytestmark = pytest.mark.unit
+
+
+def create_test_app():
+    """Create a test Starlette app with the chunk-context endpoint."""
+    app = Starlette(
+        routes=[
+            Route("/api/v1/chunk-context", get_chunk_context, methods=["GET"]),
+        ]
+    )
+    app.state.oauth_context = {"config": {"nextcloud_host": "http://localhost:8080"}}
+    return app
+
+
+def _make_mock_chunk_context(chunk_text="chunk", before="before", after="after"):
+    """Mock the ChunkContext dataclass with enough fields for the handler."""
+    ctx = MagicMock()
+    ctx.chunk_text = chunk_text
+    ctx.before_context = before
+    ctx.after_context = after
+    ctx.has_before_truncation = False
+    ctx.has_after_truncation = False
+    ctx.page_number = None
+    ctx.chunk_index = 0
+    ctx.total_chunks = 1
+    return ctx
+
+
+def _make_mock_nc_client():
+    """Mock NextcloudClient that supports `async with`."""
+    mock_client = MagicMock()
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=None)
+    return mock_client
+
+
+class TestChunkContextParameterValidation:
+    """Tests for parameter validation in the chunk-context endpoint."""
+
+    def test_missing_params_returns_400(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            return_value=("testuser", True),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            # Missing end
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=0",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            assert response.status_code == 400
+            data = response.json()
+            assert data["success"] is False
+            assert "required parameters" in data["error"].lower()
+
+    def test_end_less_than_or_equal_start_returns_400(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            return_value=("testuser", True),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=100&end=100",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            assert response.status_code == 400
+            data = response.json()
+            assert data["success"] is False
+            assert "end must be greater than start" in data["error"].lower()
+
+    def test_non_numeric_start_returns_400(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            return_value=("testuser", True),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=abc&end=10",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            assert response.status_code == 400
+
+
+class TestChunkContextTokenValidation:
+    """Tests for OAuth token validation."""
+
+    def test_missing_token_returns_401(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            side_effect=ValueError("Missing Authorization header"),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=0&end=10"
+            )
+            assert response.status_code == 401
+            data = response.json()
+            assert data["error"] == "Unauthorized"
+
+    def test_invalid_token_returns_401(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            side_effect=Exception("Token expired"),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=0&end=10",
+                headers={"Authorization": "Bearer invalid-token"},
+            )
+            assert response.status_code == 401
+
+
+class TestChunkContextCredentialPath:
+    """Regression tests: the handler MUST use get_user_client_basic_auth.
+
+    The earlier bug (reproduced in homelab 2026-04-22) forwarded the OAuth
+    bearer directly to Nextcloud via NextcloudClient.from_token. That works in
+    single-user env-BasicAuth mode but fails with 401 in multi-user BasicAuth
+    mode because Nextcloud won't validate that bearer on the Notes API.
+    """
+
+    def test_successful_fetch_uses_app_password_client(self):
+        """Handler must build its NC client via get_user_client_basic_auth and
+        return the chunk text from get_chunk_with_context."""
+        mock_nc_client = _make_mock_nc_client()
+        mock_ctx = _make_mock_chunk_context(
+            chunk_text="hello world",
+            before="before the chunk",
+            after="after the chunk",
+        )
+
+        with (
+            patch(
+                "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+                new_callable=AsyncMock,
+                return_value=("testuser", True),
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
+                return_value=mock_nc_client,
+            ) as mock_basic_auth,
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_chunk_with_context",
+                new_callable=AsyncMock,
+                return_value=mock_ctx,
+            ),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=42&start=0&end=11",
+                headers={"Authorization": "Bearer test-token"},
+            )
+
+            assert response.status_code == 200
+            data = response.json()
+            assert data["success"] is True
+            assert data["chunk_text"] == "hello world"
+            assert data["before_context"] == "before the chunk"
+            assert data["after_context"] == "after the chunk"
+
+            # Regression guard: credential resolution must go through the
+            # app-password helper, not NextcloudClient.from_token.
+            mock_basic_auth.assert_awaited_once_with(
+                "testuser", "http://localhost:8080"
+            )
+
+    def test_not_provisioned_returns_401(self):
+        """If the user has no stored app password, the handler must surface
+        NotProvisionedError as a clean 401 (not 500)."""
+        with (
+            patch(
+                "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+                new_callable=AsyncMock,
+                return_value=("testuser", True),
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
+                side_effect=NotProvisionedError(
+                    "User testuser has not provisioned an app password."
+                ),
+            ),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=0&end=10",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            assert response.status_code == 401
+            data = response.json()
+            assert data["success"] is False
+            assert "app password" in data["error"].lower()
+
+    def test_chunk_fetch_returns_none_yields_404(self):
+        """When get_chunk_with_context returns None (doc missing / offsets
+        out of range), the handler reports 404 with a structured error body."""
+        mock_nc_client = _make_mock_nc_client()
+
+        with (
+            patch(
+                "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+                new_callable=AsyncMock,
+                return_value=("testuser", True),
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
+                return_value=mock_nc_client,
+            ),
+            patch(
+                "nextcloud_mcp_server.api.visualization.get_chunk_with_context",
+                new_callable=AsyncMock,
+                return_value=None,
+            ),
+        ):
+            app = create_test_app()
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=999&start=0&end=10",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            assert response.status_code == 404
+            data = response.json()
+            assert data["success"] is False
+            assert "failed to fetch chunk context" in data["error"].lower()
+
+
+class TestChunkContextConfigErrors:
+    """Tests for configuration failure paths."""
+
+    def test_missing_nextcloud_host_config(self):
+        with patch(
+            "nextcloud_mcp_server.api.visualization.validate_token_and_get_user",
+            new_callable=AsyncMock,
+            return_value=("testuser", True),
+        ):
+            app = create_test_app()
+            app.state.oauth_context = {"config": {"nextcloud_host": ""}}
+            client = TestClient(app)
+            response = client.get(
+                "/api/v1/chunk-context?doc_type=note&doc_id=1&start=0&end=10",
+                headers={"Authorization": "Bearer test-token"},
+            )
+            # Handler wraps ValueError via _sanitize_error_for_client → 500
+            assert response.status_code == 500
diff --git a/tests/unit/test_management_pdf_preview_endpoint.py b/tests/unit/test_management_pdf_preview_endpoint.py
index b0e80079..02e1deb3 100644
--- a/tests/unit/test_management_pdf_preview_endpoint.py
+++ b/tests/unit/test_management_pdf_preview_endpoint.py
@@ -72,10 +72,6 @@ class TestPdfPreviewParameterValidation:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             client = TestClient(app)
@@ -97,10 +93,6 @@ class TestPdfPreviewParameterValidation:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             client = TestClient(app)
@@ -130,10 +122,6 @@ class TestPdfPreviewParameterValidation:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             client = TestClient(app)
@@ -163,10 +151,6 @@ class TestPdfPreviewParameterValidation:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             client = TestClient(app)
@@ -240,11 +224,8 @@ class TestPdfPreviewRendering:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -289,11 +270,8 @@ class TestPdfPreviewRendering:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -329,11 +307,8 @@ class TestPdfPreviewRendering:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -368,11 +343,8 @@ class TestPdfPreviewRendering:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -412,11 +384,8 @@ class TestPdfPreviewEdgeCases:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -442,10 +411,6 @@ class TestPdfPreviewEdgeCases:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             # Override with empty config
@@ -481,11 +446,8 @@ class TestPdfPreviewEdgeCases:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -523,11 +485,8 @@ class TestPdfPreviewEdgeCases:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -560,10 +519,6 @@ class TestPdfPreviewSecurityValidation:
                 new_callable=AsyncMock,
                 return_value=("testuser", True),
             ),
-            patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
         ):
             app = create_test_app()
             client = TestClient(app)
@@ -610,11 +565,8 @@ class TestPdfPreviewSecurityValidation:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -652,11 +604,8 @@ class TestPdfPreviewSecurityValidation:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):
@@ -696,11 +645,8 @@ class TestPdfPreviewSecurityValidation:
                 return_value=("testuser", True),
             ),
             patch(
-                "nextcloud_mcp_server.api.visualization.extract_bearer_token",
-                return_value="test-token",
-            ),
-            patch(
-                "nextcloud_mcp_server.client.NextcloudClient.from_token",
+                "nextcloud_mcp_server.api.visualization.get_user_client_basic_auth",
+                new_callable=AsyncMock,
                 return_value=mock_nc_client,
             ),
         ):