---
id: clarify-session-spec-details
name: Clarify Sessions Spec — Part Types, Slug, Indexing, Nesting
status: completed
depends_on: []
scope: narrow
risk: trivial
impact: component
level: implementation
---

## Description

Five closely related documentation gaps in `sessions.md` that affect implementers:

1. **S07**: `FilePartData[]` is referenced in ToolState (`sessions.md:132`) but never defined. Clarify whether it's the same as the `file` part type's data shape.

2. **S08**: The AI SDK UIMessage part type mapping (`sessions.md:145-152`) covers 6 types but omits `step-finish`, `patch`, `snapshot`, `compaction`, `agent`. Document whether these are excluded from the UIMessage view or add mappings.

3. **S09**: `sessions.slug` generation strategy is undocumented. Is it human-provided, auto-generated, or random? This matters for API design and uniqueness enforcement.

4. **S10**: A composite index `(session_id, type)` on parts would support queries like "all tool-call parts in session X." Document whether this index is needed or whether existing indexes suffice.

5. **S11**: The `agent` part type implies sub-agent delegation which might need nesting, but parts have no `parentId`. Document whether parts are flat or nesting might be needed.

## Acceptance Criteria

- [ ] `FilePartData` type defined or cross-referenced in sessions.md
- [ ] Omitted AI SDK part types (`step-finish`, `patch`, `snapshot`, `compaction`, `agent`) explicitly documented as excluded or mapped
- [ ] `sessions.slug` generation strategy documented (human-provided vs auto-generated)
- [ ] Parts `(session_id, type)` index considered and either added or documented as unnecessary
- [ ] Flat vs nested parts semantics documented — if nesting may be needed, note it as a future concern
- [ ] All changes in `sessions.md`; `table-reference.md` updated if indexes change

## References

- docs/reviews/storage-architecture-review-2026-04-21.md#S07
- docs/reviews/storage-architecture-review-2026-04-21.md#S08
- docs/reviews/storage-architecture-review-2026-04-21.md#S09
- docs/reviews/storage-architecture-review-2026-04-21.md#S10
- docs/reviews/storage-architecture-review-2026-04-21.md#S11
- docs/architecture/storage/sessions.md

## Notes

> To be filled by implementation agent

## Summary

> To be filled on completion