-- Roadmap #26 (rfc-app v0.22.0): the optional "What will you be using
-- this for?" capture on the two propose surfaces.
--
-- The roadmap's framing names "the rfcs table" and "the PR-metadata
-- table" for a `proposed_use_case TEXT NULL` column. In this deployment
-- those two surfaces are the cache tables `cached_rfcs` and `cached_prs`
-- (002_cache.sql). We add the nullable column to each, matching the
-- existing naming convention (no NOT NULL, no default — NULL is the
-- "left blank" sentinel the view surfaces render tastefully).
--
-- BUT: those tables are *cache*, rebuilt from Gitea by the §4.1
-- reconciler (cache.py). The reconciler's INSERT...ON CONFLICT DO UPDATE
-- sets only the columns it knows about, so an unlisted column is
-- preserved on the update path — yet a propose/open never *writes* the
-- column through the cache (the write path is endpoint -> Gitea ->
-- reconcile, and the reconciler does not carry this field). So the cache
-- column alone would always read NULL.
--
-- The durable home is therefore a dedicated app-truth table the propose
-- /open endpoints write directly (keyed by the PR number, which is the
-- stable identity for both idea PRs and rfc_branch PRs) and the view
-- endpoints read back. This is not cache — it is canonical and survives
-- any reconcile. The cache columns are added too for parity with the
-- roadmap's literal shape and for any future reconciler that learns to
-- carry the field, but the side table is the source of truth read at
-- view time.

ALTER TABLE cached_rfcs ADD COLUMN proposed_use_case TEXT;
ALTER TABLE cached_prs ADD COLUMN proposed_use_case TEXT;

-- Canonical, reconcile-proof store. One row per propose/open that
-- supplied a use case. `scope` distinguishes the propose-RFC surface
-- ('rfc') from the propose-PR-against-an-RFC surface ('pr'); `pr_number`
-- is the join key the endpoints already have in hand. NULL/omitted use
-- cases simply never write a row here, so absence == "left blank".
CREATE TABLE proposed_use_cases (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    scope           TEXT NOT NULL CHECK (scope IN ('rfc', 'pr')),
    rfc_slug        TEXT NOT NULL,
    pr_number       INTEGER NOT NULL,
    use_case        TEXT NOT NULL,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (scope, pr_number)
);

CREATE INDEX idx_proposed_use_cases_lookup ON proposed_use_cases (scope, pr_number);
CREATE INDEX idx_proposed_use_cases_slug ON proposed_use_cases (scope, rfc_slug);