chatbot_v3/docs/adr/0002-chunk-crud-and-search-api.md

# 0002. Chunk CRUD and payload/keyword search API

## Status

Accepted

Route naming note: ADR-0008 owns the REST API surface and renames the
indicative endpoint examples in this ADR from `/chunks/...` to `/points/...`.
The CRUD semantics, Qdrant primitives, payload schema, soft-delete behavior,
and tenant-isolation rules in this ADR remain accepted.

## Context

Beyond bulk ingestion ([0001](0001-ingestion-pipeline-and-collection-schema.md)),
we need FastAPI endpoints for direct, fine-grained management of individual
chunks: create a single chunk, update a chunk's content/vectors/payload,
delete chunks (by ID or in bulk by filter), and list/search chunks by keyword
and payload metadata (tenant, domain, file, etc.) — independent of the
semantic hybrid retrieval used by the AI agent (ADR-0003).

This pipeline operates on the same collection and payload schema defined in
ADR-0001, and Qdrant's Points API already provides the primitives needed —
there's no need for a custom data layer on top.

## Decision

Expose a thin FastAPI layer directly over Qdrant's Points API, operating on
the `chunks` collection and payload schema from ADR-0001:

| Operation | FastAPI endpoint (indicative) | Qdrant primitive |
|---|---|---|
| Create a point | `POST /points` | upsert (single point) |
| Update a point's vectors/content | `PUT /points/{point_id}` | upsert (`update_only` mode) |
| Partially update payload | `PATCH /points/{point_id}/payload` | `set_payload` / `overwrite_payload` |
| Delete one point | `DELETE /points/{point_id}` | delete by ID |
| Delete many points | `DELETE /points?file_id=...` | delete by filter |
| List/paginate points, in order | `GET /points?file_id=...` | `scroll` with filter + pagination, `order_by: order_id` |
| Reorder/insert a point | `PATCH /points/{point_id}/order` | `set_payload` on `order_id` only |
| Count points | `GET /points/count` | `count` |
| Keyword search | `GET /points/search?q=...` | full-text payload index on `content` (match, not semantic) |
| Bulk multi-op edits | `POST /points/batch` | Qdrant `points/batch` |

### Ordering and reordering

Chunks belonging to a `file_id` are listed via `scroll` ordered by the
mutable `order_id` payload field (ADR-0001) — this is what lets the frontend
display and let a backend user modify chunk order. Because `order_id` is a
fractional float key rather than a sequential integer position, moving or
inserting a chunk only requires assigning it a new value between its two new
neighbors — no renumbering of siblings, and no effect on the chunk's stable
point ID (which is derived from the immutable `chunk_index`, not `order_id`).

`PATCH /points/{point_id}/order` does more than set one field, though: since
ADR-0001 also maintains `previous_chunk_id`/`next_chunk_id` pointers for O(1)
adjacency lookups, a single reorder touches **up to four chunks** in one
`points/batch` call:
1. The moved chunk: new `order_id`, new `previous_chunk_id`/`next_chunk_id`.
2. Its old neighbors: re-link their `previous_chunk_id`/`next_chunk_id` to
   skip over the moved chunk.
3. Its new neighbors: re-link them to point at the moved chunk.

The same fix-up applies to insert (new chunk) and delete (soft-deleted chunk
— see below) operations: any operation that changes a chunk's position or
removes it from the sequence must atomically update the neighbors' pointers
in the same `points/batch` request, or `previous_chunk_id`/`next_chunk_id`
go stale.

### Keyword search is not semantic search

`GET /points/search` matches against the full-text payload index on
`content` (and structured filters on `tenant_id`, `domain`, `file_id`,
etc.) — it is filter/match-based keyword search, not embedding-based
retrieval. This is deliberately distinct from the hybrid dense+sparse
retrieval used by the AI agent in ADR-0003; the two "search" concepts serve
different callers (a human/admin managing chunks vs. an agent retrieving
context) and should not be conflated in the API or in future discussion.

### Delete is soft by default

`DELETE /points/{point_id}` and `DELETE /points?file_id=...` set
`is_active: false` and `deleted_at` (via `set_payload`) rather than removing
the point from Qdrant — consistent with ADR-0001's soft-delete fields. This
keeps deleted points available for audit and lets `GET /points` and
`GET /points/search` filter them out by default (`is_active: true` implied
unless the caller explicitly asks to include inactive chunks). A hard delete
(actual point removal, e.g. `points/delete`) is available separately for
compliance-driven purges, not as the default CRUD behavior. Either way, the
deleted chunk's `previous_chunk_id`/`next_chunk_id` neighbors are relinked to
point at each other in the same `points/batch` call, so context-window
expansion (ADR-0003) never walks into a deactivated or removed chunk.

### Tenant isolation

Every endpoint (read and write) has its `tenant_id` filter injected
server-side from the authenticated request context — never accepted as
client-supplied input in the request body or query string. This is
non-negotiable: it's the same isolation boundary ADR-0001 relies on for
multitenancy, and it must hold for every code path that touches the
collection, not just ingestion.

### Concurrency

Updates use the `version` payload field (from ADR-0001) together with
Qdrant's `update_filter`, giving an optimistic-concurrency-style guard
against races between a concurrent ingestion re-run (ADR-0001) and a manual
edit through this API.

### Re-ingestion versus manual edits

A file can be re-uploaded after someone has hand-edited one of its points
through this API. **The newly ingested file wins.** Ingestion is authoritative
for the content of the file it ingested; a manual edit is a correction that
survives only until the source document is replaced.

Concretely:

- A point that still exists in the new version (same `file_id` +
  `chunk_index`, hence the same deterministic point ID) is **overwritten in
  place**. Ingestion performs a read-check-write so `version` is incremented
  from whatever the manual edit left it at, rather than reset to `1`.
- A point from the previous ingestion that is **absent** from the new version
  is flagged `is_active: false` with `deleted_at` set. It is never removed
  from Qdrant — the soft-delete rule above applies to re-ingestion exactly as
  it applies to `DELETE`.
- A manually created point (`POST /points`) is assigned a `chunk_index` past
  the ingested range, so the same sweep deactivates it on the next upload of
  its file. This is the intended consequence of "the new file wins", not an
  accident of the sweep's bounds.

Because the point ID is derived from the immutable `chunk_index`, an
overwritten point cannot hold both the manual edit and the new file's content.
The clobbered content is therefore recorded in `point_audit_events`
(ADR-0009) as a `reingest_overwrite` operation carrying `before_version`, so
the edit is recoverable from the audit trail even though it is no longer a
live point.

Rejected alternative: preserving manual edits by having ingestion skip points
with `version > 1`. It breaks the guarantee that a successful upload leaves
Qdrant matching the uploaded document, and it needs a second, separate rule
for edited points that no longer exist in the new version — two divergent
notions of authority over one file.

### Re-embedding on content edit

`PUT /points/{point_id}` can change `content`, which leaves the stored
vectors stale unless they're recomputed. When `content` changes, the point
is **re-embedded inline**, reusing the same async embedding ports and
batch/semaphore bounds ingestion uses ([0017](0017-synchronous-ingestion-in-the-request-path.md)),
for parity between the two write paths. When `content` is unchanged, the
edit applies only the supplied vector/payload fields and skips re-embedding
entirely. Failure modes on this path reuse ingestion's status codes: `502`
on embedder failure, `504` if the edit's embedding step exceeds the same
timeout budget class as ingestion. The `version` guard (`update_filter`)
still applies to the write — re-embedding happens before the guarded write,
not instead of it, so a stale-version edit still fails with `409` rather
than re-embedding for nothing.

Rejected alternatives: requiring the caller to supply vectors when content
changes (pushes model knowledge onto the client, and is easy to get subtly
wrong); marking the point stale for background re-embedding later (needs
background work, which ADR-0017 currently rules out for this slice).

### `order_id` gap exhaustion

Repeatedly inserting into the same gap between two neighbors eventually
exhausts float precision (ADR-0001's known limitation). This slice does
**not** ship a renormalize endpoint. Instead, any operation that assigns a
new fractional `order_id` between two neighbors (insert, reorder) computes
the resulting gap and:

- logs a structured warning (`points.order_id.gap_low`) with `file_id` and
  the two neighbor point IDs once the gap falls under a defined safety
  threshold, so the condition is observable before it becomes uninsertable;
- **rejects** the write with `409` and a distinct error code if the
  computed gap is no longer representable (would collapse to one of the two
  neighbor values), instead of silently applying an imprecise value.

Recovering from an exhausted gap is a manual data-fix operation covered by
the operator runbook, not an endpoint this slice builds — deferring the
renormalize primitive is acceptable, silently producing an unrepresentable
gap is not.

### `POST /points/batch` semantics

Batch requests are **all-or-nothing**, capped at **100 operations per
request**. The service layer validates every operation's `version`
precondition before applying any of them; if any operation's precondition
fails, the whole request is rejected with `409` and nothing is applied — no
partially-applied batch ever reaches Qdrant. This follows directly from the
`version`-guard rule above applied at the batch level, and from the
pointer-relinking rule (a reorder/insert/delete's neighbor updates must land
in the same `points/batch` call, and a partial relink is a defect): partial
application of a batch is exactly the failure mode that would produce a
stale pointer chain. The 100-operation cap is independent of ADR-0001's
64–256-point bulk-ingestion batch sizing — that number is about upload
throughput; this one bounds an admin/manual edit request to something that
comfortably finishes inside a normal request timeout.

## Consequences

### Positive
- Reuses the exact collection/schema from ADR-0001 — no parallel data model
  to keep in sync.
- Thin mapping to Qdrant primitives keeps the API predictable and easy to
  extend as new filter/sort needs arise.
- Clear separation from ADR-0003's semantic search avoids API consumers
  confusing "find chunks matching this filter" with "retrieve chunks relevant
  to this query."

### Negative
- Keyword search here is limited to what Qdrant's full-text payload index
  supports — no stemming/synonym handling beyond what that index offers.
- Optimistic concurrency via `version` requires every writer (ingestion and
  this API) to consistently read-check-write; a writer that skips this can
  silently clobber concurrent edits.
- Inline re-embedding puts embedder latency and `502`/`504` failure modes on
  an admin content edit, not just on ingestion — an edit that only intended
  to fix a typo pays the same embedding cost as a fresh chunk.
- Deferring the `order_id` renormalize endpoint means a file whose gaps are
  genuinely exhausted has no automated recovery in this slice; an operator
  must intervene by hand until that endpoint exists.
- All-or-nothing batch semantics mean one stale operation in a 100-operation
  batch fails the entire request, even when the other 99 operations are
  independent and would have succeeded on their own.

## Alternatives Considered

- **Separate keyword-search infrastructure (e.g. Elasticsearch)**: rejected —
  Qdrant's native full-text payload index already covers filter-style keyword
  search on `content`, and adding a second search system would duplicate data
  and infrastructure for no clear benefit at current scale.
- **Client-supplied `tenant_id` in request body**: rejected — trusting
  client input for the isolation boundary is a direct multitenancy security
  risk; it must come from server-side auth context.
- **Caller-supplied vectors on content edit**: rejected — pushes embedding
  model knowledge onto the client and makes it easy to silently desync
  vectors from content.
- **Mark-stale-and-re-embed-later on content edit**: rejected for this
  slice — needs background work, which ADR-0017 currently rules out.
- **Renormalize `order_id` automatically within this slice**: rejected —
  nothing in current scope has hit gap exhaustion; building the primitive
  now is speculative. Revisit if the logged warning starts firing in
  practice.
- **Partial-success batch semantics (per-operation status)**: rejected —
  a partially-applied batch is exactly the failure mode that leaves the
  pointer chain (`previous_chunk_id`/`next_chunk_id`) inconsistent, which
  this ADR treats as a defect, not a degraded-but-acceptable outcome.