# Session 0022.1 — Transcript
> Parent: SESSION-0022.0-TRANSCRIPT-…md
> Date: 2026-05-28
> Goal: implement roadmap #26 (optional use-case field) as rfc-app v0.22.0 feature code
> Outcome: **Shipped to branch `feature/v0.22.0-usecase-field` (commit 7c6c906). Optional `proposed_use_case` field added to propose-RFC + propose-PR surfaces end-to-end. Backend 336 passed (332 baseline + 4 new), frontend build green.**

## Pre-session state
- Worktree `/Users/benstull/git/rfc-app-v0.22.0-usecase`, branch `feature/v0.22.0-usecase-field` based on main @ 2ac20b1 (Merge feature/v0.21.0-ux-polish).
- migrations 001–020 present (no 016 — gap predates this work). 021 reserved for me.
- Baseline: 332 backend tests.

## Turn-by-turn arc
1. Explored the propose surfaces. **Key finding: the roadmap's mental model doesn't match the architecture.** The roadmap names "the rfcs table" and "the PR-metadata table" for a new column, but:
   - The propose-RFC "Why is this RFC needed?" field is named `pitch` (frontend `ProposeModal.jsx` + `ProposeBody.pitch` in `api.py`), serialized into the RFC entry **body** and the Gitea PR description. Truth is Gitea, not a DB row.
   - The propose-PR surface (`PRModal.jsx` + `OpenPRBody` in `api_prs.py`) has a single free-text `description` field — that IS the "why is this change needed" the roadmap refers to. Also Gitea-truth.
   - `cached_rfcs` / `cached_prs` (002_cache.sql) are **caches**, rebuilt from Gitea by `cache.py`'s reconciler. The write path is endpoint → Gitea → reconcile. Since `cache.py` (which I may NOT edit) doesn't carry a `proposed_use_case` field, a cache column alone would always read NULL after a propose/open.
2. **Decision:** added the nullable cache columns per the roadmap's literal shape (migration 021), AND a dedicated canonical, reconcile-proof side table `proposed_use_cases` (scope ∈ {'rfc','pr'}, keyed by pr_number, UNIQUE(scope,pr_number)) that my endpoint code writes directly and the read endpoints query. The side table is the true source read at view time; cache columns are mirrored for parity / future reconciler use. This keeps everything inside my file ownership (no `cache.py`/`db.py`/`entry.py` edits).
3. Backend wiring:
   - `ProposeBody` + `OpenPRBody` gain `proposed_use_case: str | None = Field(default=None, max_length=8000)` (8000 matches the existing PR description bound; pitch is unbounded but 8000 is generous).
   - `propose_rfc` (api.py ~line 700) writes the side-table row + mirrors onto `cached_prs` after `cache.refresh_meta_pulls`, only when the stripped value is non-empty (blank/whitespace == "left blank", no row).
   - `open_pr` (api_prs.py, after `_refresh_after_pr_write`) does the same for scope 'pr'.
   - Reads: `_proposal_use_case` helper feeds `list_proposals` + `get_proposal`; `get_rfc` looks up by slug (latest 'rfc' row, since the idea PR closes on merge); `_pr_use_case` (module fn) feeds `get_pr`.
4. Frontend: `api.js` (`proposeRFC`, `openPR` send `proposed_use_case` or null); `ProposeModal.jsx` + `PRModal.jsx` add optional textareas below the existing required fields with "(optional)" labels and field-help; `ProposalView.jsx`, `RFCView.jsx` (main view only), `PRView.jsx` render with muted italic "left blank" treatment when null. Reused existing classes (`entry-body`, `field-help`, `pr-description`) + inline component-scoped styles only — no App.css/index.css/tokens.css edits.
5. Tests: 4 new tests in `test_proposed_use_case_vertical.py` reusing FakeGitea/seed helpers. All green on first run. Full suite 336 passed.
6. Frontend build initially failed on missing `VITE_APP_NAME` (deployment overlay var, not in the worktree) — re-ran `npm run build` with `VITE_APP_NAME`/`VITE_BETA_CONTACT` set inline; built clean. No .env committed.

## Cut state
- Branch `feature/v0.22.0-usecase-field` @ **7c6c906**.
- Files changed: backend/app/api.py, backend/app/api_prs.py, frontend/src/api.js, frontend/src/components/{ProposeModal,PRModal,ProposalView,RFCView,PRView}.jsx, + NEW backend/migrations/021_proposed_use_case.sql, + NEW backend/tests/test_proposed_use_case_vertical.py.
- Migration number: 021.
- Backend: 336 passed (332 baseline + 4 new). Frontend: build green.

## What the driver needs to know
- **CHANGELOG `Upgrade steps:` proposal:** `none — additive nullable column + new side table, migration 021 auto-applies on deploy (run_migrations globs migrations/*.sql).`
- **CHANGELOG entry summary:** "#26: Optional 'What will you be using this for?' capture on the propose-RFC and propose-PR surfaces. New optional `proposed_use_case` free-text field alongside the existing required justification on both modals; persisted, returned, and displayed (with a muted 'left blank' treatment when absent). New migration 021; new canonical `proposed_use_cases` table."
- **api.py regions I edited (merge-overlap awareness vs 0022.2):**
  - `ProposeBody` class (~line 49).
  - `propose_rfc` endpoint — the block right after `await cache.refresh_meta_pulls(...)` / before `return {"pr_number": ...}` (~line 707).
  - `list_proposals` + `get_proposal` (~lines 566–640): added `_proposal_use_case` nested helper + a `proposed_use_case` key in each return.
  - `get_rfc` (~line 558): changed `return _serialize_rfc(row)` into a payload + slug lookup.
  - I did NOT touch `_serialize_rfc` / `_entry_payload` / `_serialize_rfc` list-builder (the catalog `list_rfcs` loop is untouched).
- **api_prs.py:** `OpenPRBody` (~line 42), `open_pr` (post-refresh block), `get_pr` return dict (added one key), new module-level `_pr_use_case` before `_pr_capabilities`.
- **Architectural note for the driver:** the roadmap's "rfcs table / PR-metadata table column" framing was reconciled against the real Gitea-truth + cache-mirror architecture by adding a dedicated `proposed_use_cases` canonical table (the durable source) plus the literal cache columns. If a future change teaches `cache.py`'s reconciler to carry the field, the cache columns are ready; until then the side table is authoritative. No `cache.py`/`db.py` edits were needed or made.

## §19.2 candidates surfaced
- none. (Possible future: teach the reconciler to round-trip propose-time metadata through a Gitea trailer so the cache columns become self-sufficient and the side table can be retired — but that's speculative and out of scope.)