fix(vector): tighten get_chunk_bbox_and_page_from_qdrant doc_id to str

🔴 Blocking finding from PR #773 latest review:
`get_chunk_bbox_and_page_from_qdrant` (`search/context.py:199`) still
declared `doc_id: int | str` and passed the raw value into
`MatchValue(value=doc_id)` at lines 239 and 256 without `str()`
coercion. After this branch's startup backfill normalises every Qdrant
`doc_id` payload to a string, an `int` filter would silently match zero
points — the function would return `(None, None)` instead of the
chunk bbox / page, and PDF highlight overlays would fail in production.

Take option 2 from the reviewer's two suggestions (annotation
tightening over inline coercion): the producer side of this PR has
already narrowed every other `doc_id` annotation to `str`, so this
function is the last hold-out. Pushing the contract into the type
system means `ty` will catch any future regression at the call site.

Production callers in `api/visualization.py` and `auth/viz_routes.py`
already pass `doc_id` (str) verbatim after the recent merge with
master's chunk_index-first refactor, so no caller-side changes needed.

Update the 9 calls in `tests/unit/test_chunk_bbox_helper.py` to use
string literals (`"42"` / `"99"` / `"1"`) instead of integers. The
mock doesn't validate `MatchValue` value types, so the tests passed
with stale int doc_ids today — but they were exercising a path
production no longer takes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/search/context.py

@@ -198,7 +198,7 @@ async def _get_deck_metadata_from_qdrant(
 
 async def get_chunk_bbox_and_page_from_qdrant(
     user_id: str,
-    doc_id: int | str,
+    doc_id: str,
     chunk_index: int | None,
     chunk_start: int,
     chunk_end: int,
@@ -214,7 +214,11 @@ async def get_chunk_bbox_and_page_from_qdrant(
 
     Args:
         user_id: User ID who owns the document
-        doc_id: Document ID (int for file/note, str for some doc types)
+        doc_id: Document ID — always a string. Producers stringify their
+            native ID before writing to Qdrant so the keyword payload
+            index on ``doc_id`` matches every point regardless of source
+            doc_type. An ``int`` filter against the str-indexed payload
+            would silently match zero points.
         chunk_index: Zero-based chunk index, or None to use offset fallback
         chunk_start: Character offset where chunk starts (used when
             chunk_index is None)

tests/unit/test_chunk_bbox_helper.py

@@ -58,7 +58,7 @@ class TestIndexedPath:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,
@@ -84,7 +84,7 @@ class TestOffsetFallbackPath:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="bob",
-                doc_id=99,
+                doc_id="99",
                 chunk_index=None,
                 chunk_start=500,
                 chunk_end=600,
@@ -105,7 +105,7 @@ class TestOffsetFallbackPath:
         with ctx, caplog.at_level("WARNING"):
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="bob",
-                doc_id=99,
+                doc_id="99",
                 chunk_index=None,
                 chunk_start=0,
                 chunk_end=100,
@@ -124,7 +124,7 @@ class TestPayloadShape:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=1,
+                doc_id="1",
                 chunk_index=0,
                 chunk_start=0,
                 chunk_end=10,
@@ -143,7 +143,7 @@ class TestPayloadShape:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,
@@ -157,7 +157,7 @@ class TestPayloadShape:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,
@@ -171,7 +171,7 @@ class TestPayloadShape:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,
@@ -188,7 +188,7 @@ class TestPayloadShape:
         with ctx:
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,
@@ -205,7 +205,7 @@ class TestExceptionHandling:
         with ctx, caplog.at_level("WARNING"):
             result = await get_chunk_bbox_and_page_from_qdrant(
                 user_id="alice",
-                doc_id=42,
+                doc_id="42",
                 chunk_index=3,
                 chunk_start=0,
                 chunk_end=100,