Mirrors the CLI POC (chroma-core/foundation #97): after ensuring each
source collection, /init attaches the server-side function via
SysDb::create_attached_function, with the wiki collection as output.

- Attachment name `{source}_to_wiki`; operator `http_generate`
  (configurable); params carry the modal `endpoint_url`,
  `source_collection`, and `source_kind`.
- New FoundationConfig fields: function_name, function_endpoint_url,
  min_records_for_invocation (defaults mirror the POC + the chroma
  frontend's 100-record default). Output dimension is already hardcoded
  to 1024 in /init (chroma #7127), so no seed_output_collection step is
  needed.
- Idempotent: AlreadyExists / CollectionAlreadyHasFunction are treated
  as success so /init stays safe to call repeatedly.

Mirrors the CLI POC (chroma-core/foundation #97): after ensuring each
source collection, /init attaches the server-side function via
SysDb::create_attached_function, with the wiki collection as output.

- Attachment name `{source}_to_wiki`; operator `http_generate`
  (configurable); params carry the modal `endpoint_url`,
  `source_collection`, and `source_kind`.
- New FoundationConfig fields: function_name, function_endpoint_url,
  min_records_for_invocation (defaults mirror the POC + the chroma
  frontend's 100-record default). Output dimension is already hardcoded
  to 1024 in /init (chroma #7127), so no seed_output_collection step is
  needed.
- Idempotent: AlreadyExists / CollectionAlreadyHasFunction are treated
  as success so /init stays safe to call repeatedly.

…7134)

> **Draft.** Stacked on #7133 (the worker change that *reads* the
chunk-sibling flag). Merge #7133 first, then rebase this onto main.

## Summary

Extends the foundation `/init` endpoint to mirror the CLI POC
(chroma-core/foundation #97), so `/init` is the single bootstrap for a
team's foundation workspace. On top of the existing wiki +
wiki_revisions creation, `/init` now:

1. **Ensures the source collections** (slack, notion; configurable via
`CHROMA_FOUNDATION__SOURCE_COLLECTIONS`).
2. **Sets `chroma:group_chunk_siblings = true`** on each source
collection so the worker's `PartitionOperator` (#7133) keeps a job's
chunk records in one partition — the ordering the end-of-job marker
relies on (ADR 0001 §6).
3. **Attaches the foundation function** to each source collection via
`SysDb::create_attached_function`, with the wiki collection as output —
the server-side equivalent of the POC's HTTP attach.

## Function attach (mirrors POC #97)

- Attachment name `{source}_to_wiki`; operator `http_generate`
(configurable).
- `params`: `{ endpoint_url, source_collection, source_kind }` —
`endpoint_url` defaults to the modal URL from the POC;
`source_collection`/`source_kind` are the source name.
- `min_records_for_invocation` defaults to 100 (matches the chroma
frontend default).
- **No `seed_output_collection` step** — per @HammadB, the output
dimension is already hardcoded to 1024 in `/init`'s collection creation
(chroma #7127, already on main).
- **Idempotent**: `AlreadyExists` / `CollectionAlreadyHasFunction` are
treated as success, so `/init` stays safe to call repeatedly.

## Shared constant

The chunk-sibling flag key is promoted to
`chroma_types::CHROMA_GROUP_CHUNK_SIBLINGS_KEY` so the reader (worker
`PartitionOperator`) and writer (`/init`) share one definition;
`partition_log.rs` re-exports it.

## Wiki collections deliberately untouched

Wiki/wiki_revisions are the function's *output* — no chunk-sibling flag,
no attach. The marker mechanism operates on the source/input side.

## Caveat: get-or-create idempotency

`/init` uses get-or-create for collections. If a source collection
**already exists** without the flag (e.g. created by an earlier upload),
the metadata isn't retroactively updated. `/init` must run before the
first upload (it's the bootstrap). The function attach is independently
idempotent. Pre-existing source collections would need a one-off
metadata backfill — out of scope here.

## Test plan

- [x] `cargo check -p foundation-api`, `cargo check -p chroma-types`
pass.
- [x] `cargo test -p foundation-api --lib routes::init` — 4/4 pass.
- [ ] **CI must run the worker suite** — the `partition_log.rs`
re-export couldn't be compiled locally (Homebrew rustc 1.94.1 vs pinned
1.92.0; `wal3` fails under 1.94.1 independent of this change).
- [ ] End-to-end (post-#7133-merge): `/init` → source collections carry
the flag + have `http_generate` attached → uploads chunk into them →
attached function runs and observes the end-of-job marker last.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>