feat(qdrant): add tenant-scoped point storage for ingestion

Why:
- Ingested chunks need to become searchable Qdrant points before the upload
  response returns, with tenant/domain isolation and a safe re-ingestion
  story per ADR-0001/0017.

Changes:
- src/application/points/: index_chunks() is the sole entry point, owning
  payload construction, batched/bounded-concurrency upserts
  (upsert_concurrency semaphore), and a soft-delete sweep for points a
  shorter re-ingestion leaves behind. The sweep runs only after every upsert
  in the attempt succeeds, so a failed attempt can leave a stale prefix but
  never removes content from a working index.
- PointStorage port (application/ports/) + QdrantPointStorage adapter
  (infrastructure/qdrant/points.py), keeping the qdrant_client SDK out of
  application code per ADR-0015.
- FakePointStorage test double for exercising the ordering/idempotency
  guarantees without a real Qdrant.

src/application/points/indexing.py

@@ -0,0 +1,203 @@
+"""The one caller-facing entry point for indexing embedded chunks (ADR-0001, ADR-0017).
+
+`index_chunks` is the only version of this step callers should reach for. It
+owns the whole composition a correct upsert needs:
+
+- building ADR-0001's payload for every chunk, with `tenant_id`/`domain` taken
+  from server-derived context;
+- offloading that (and the per-chunk content hashing) to a thread, since it is
+  blocking CPU work (ADR-0017);
+- batching at `QDRANT_UPSERT_BATCH_SIZE` inside ADR-0001's 64-256 band;
+- bounding in-flight batches with an `asyncio.Semaphore` rather than an
+  unbounded `gather` (ADR-0017);
+- running the soft-delete sweep for a shortened file **only after every batch
+  has succeeded**.
+
+That last ordering is the point, not an implementation detail — see
+`_deactivate_stale` below. `build_chunk_payload` and `_batches` stay internal;
+pushing that composition onto every call site is exactly the obligation a deep
+module absorbs once (CLAUDE.md, "prefer deep modules").
+"""
+
+import asyncio
+import uuid
+from collections.abc import Sequence
+from dataclasses import dataclass
+from datetime import UTC, datetime
+
+from anyio import CapacityLimiter, to_thread
+
+from src.application.ingestion.errors import PointIndexingError
+from src.application.ingestion.models import EmbeddedChunk
+from src.application.points.models import ChunkPoint
+from src.application.points.payload import build_chunk_payload
+from src.application.ports.embedding import DenseEmbedder, SparseEmbedder
+from src.application.ports.point_storage import PointStorage
+from src.config import QdrantSettings
+
+
+@dataclass(frozen=True)
+class IndexingResult:
+    """What one indexing pass wrote.
+
+    `points_upserted` counts points written, not points *created* — a
+    deterministic-id upsert cannot distinguish an insert from an overwrite, so
+    the ingestion job reports this as `points_created` and leaves
+    `points_updated` at zero rather than guessing.
+    """
+
+    points_upserted: int
+    points_soft_deleted: int
+
+
+def _embedding_model_version(
+    dense_embedders: Sequence[DenseEmbedder], sparse_embedder: SparseEmbedder
+) -> str:
+    """Compose the `embedding_model_version` payload value (ADR-0001).
+
+    Sorted so the string is stable regardless of the order the embedders were
+    wired in — an unstable value would make "which chunks need re-embedding?"
+    unanswerable, which is the field's only reason to exist.
+    """
+    versions = sorted(
+        [embedder.model_version for embedder in dense_embedders] + [sparse_embedder.model_version]
+    )
+    return "+".join(versions)
+
+
+def _batches(points: Sequence[ChunkPoint], size: int) -> list[Sequence[ChunkPoint]]:
+    return [points[i : i + size] for i in range(0, len(points), size)]
+
+
+def _build_points(
+    embedded: Sequence[EmbeddedChunk],
+    *,
+    tenant_id: uuid.UUID,
+    domain: str,
+    file_id: uuid.UUID,
+    source_filename: str,
+    source_type: str,
+    actor: str,
+    embedding_model_version: str,
+    indexed_at: datetime,
+) -> list[ChunkPoint]:
+    """Blocking: hashes every chunk's content. Always called through a thread."""
+    return [
+        ChunkPoint(
+            point_id=item.chunk.chunk_id,
+            dense=item.dense,
+            sparse=item.sparse,
+            payload=build_chunk_payload(
+                item.chunk,
+                tenant_id=tenant_id,
+                domain=domain,
+                file_id=file_id,
+                source_filename=source_filename,
+                source_type=source_type,
+                actor=actor,
+                embedding_model_version=embedding_model_version,
+                indexed_at=indexed_at,
+            ),
+        )
+        for item in embedded
+    ]
+
+
+async def _upsert_bounded(
+    storage: PointStorage, batch: Sequence[ChunkPoint], *, semaphore: asyncio.Semaphore
+) -> None:
+    async with semaphore:
+        try:
+            await storage.upsert_points(batch)
+        except Exception as exc:
+            raise PointIndexingError(f"upserting {len(batch)} points failed: {exc}") from exc
+
+
+async def _deactivate_stale(
+    storage: PointStorage,
+    *,
+    tenant_id: uuid.UUID,
+    file_id: uuid.UUID,
+    from_chunk_index: int,
+    actor: str,
+    deleted_at: datetime,
+) -> int:
+    """Soft-delete points left over from a longer previous version of this file.
+
+    Chunk indices are contiguous from 0, so "index >= the new chunk count" is
+    exactly the set of points the new version no longer produces.
+
+    This runs **only after every upsert has succeeded**, and that ordering is
+    what keeps a failed attempt from damaging a working index. ADR-0001's
+    deterministic point ids mean a re-ingestion overwrites in place, so literal
+    atomic replacement is not available; what *is* guaranteed is that a failed
+    attempt never removes content (it can only leave a prefix updated), and that
+    a retry converges to the correct state. See ADR-0017.
+    """
+    try:
+        return await storage.deactivate_points_from_index(
+            tenant_id=tenant_id,
+            file_id=file_id,
+            from_chunk_index=from_chunk_index,
+            deleted_at=deleted_at,
+            updated_by=actor,
+        )
+    except Exception as exc:
+        raise PointIndexingError(f"soft-deleting stale points failed: {exc}") from exc
+
+
+async def index_chunks(
+    embedded: Sequence[EmbeddedChunk],
+    *,
+    storage: PointStorage,
+    tenant_id: uuid.UUID,
+    domain: str,
+    file_id: uuid.UUID,
+    source_filename: str,
+    source_type: str,
+    actor: str,
+    dense_embedders: Sequence[DenseEmbedder],
+    sparse_embedder: SparseEmbedder,
+    settings: QdrantSettings,
+    thread_limiter: CapacityLimiter,
+) -> IndexingResult:
+    """Upsert every embedded chunk as a tenant-scoped point, then sweep leftovers.
+
+    Raises `PointIndexingError` (502) if any batch or the sweep fails.
+    """
+    if not embedded:
+        return IndexingResult(points_upserted=0, points_soft_deleted=0)
+
+    indexed_at = datetime.now(UTC)
+    points = await to_thread.run_sync(
+        lambda: _build_points(
+            embedded,
+            tenant_id=tenant_id,
+            domain=domain,
+            file_id=file_id,
+            source_filename=source_filename,
+            source_type=source_type,
+            actor=actor,
+            embedding_model_version=_embedding_model_version(dense_embedders, sparse_embedder),
+            indexed_at=indexed_at,
+        ),
+        limiter=thread_limiter,
+    )
+
+    semaphore = asyncio.Semaphore(settings.upsert_concurrency)
+    await asyncio.gather(
+        *(
+            _upsert_bounded(storage, batch, semaphore=semaphore)
+            for batch in _batches(points, settings.upsert_batch_size)
+        )
+    )
+
+    soft_deleted = await _deactivate_stale(
+        storage,
+        tenant_id=tenant_id,
+        file_id=file_id,
+        from_chunk_index=len(points),
+        actor=actor,
+        deleted_at=indexed_at,
+    )
+    return IndexingResult(points_upserted=len(points), points_soft_deleted=soft_deleted)