Release v0.24.0: Claude Haiku tag suggestions on propose-RFC (#27)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -23,6 +23,170 @@ skip versions are the composition of each intervening adjacent
 release's steps in order — no A-to-B path is pre-computed beyond
 that.
 
+## 0.24.0 — 2026-05-28
+
+**Minor — one new secret required before this version serves tag
+suggestions; no schema migration; no behavior change for deployments
+that do not bind the key.** Roadmap item #27: as a contributor fills in
+the propose-RFC form, the backend asks Claude Haiku to recommend tags
+drawn from the collection's existing tag set, surfaced as clickable
+suggestion chips. Shipped from driver session 0025.0. This is the §9.1
+"Slice 2" AI-suggested chips that the propose modal has carried a
+deferred placeholder for since Slice 1.
+
+- **`POST /api/rfcs/suggest-tags`** (contributor-gated, per-user
+  rate-limited). Takes the partial draft (`title`, `pitch`,
+  `use_case`) and returns `{ "suggestions": [{ "tag", "confidence" },
+  …] }`. The model is constrained to the corpus's existing tags — v1
+  tags are free-form chip input, so "the taxonomy" is the de-facto set
+  of distinct tags the existing RFCs carry. The model MUST NOT invent
+  tags; taxonomy extension is a deliberate out-of-scope follow-up.
+- **Always Claude Haiku, for cost.** Tag suggestion uses Haiku
+  regardless of the `ENABLED_MODELS` chat-picker universe, via the new
+  `providers.construct_haiku()` factory. There is no RFC slug at propose
+  time, so the §6.7 per-RFC funder credential path does not apply — the
+  surface runs on the operator's own `ANTHROPIC_API_KEY`.
+- **Degrades to silence, never error.** No key bound, an empty corpus,
+  an empty draft, a rate-limited caller, or an unparseable model reply
+  all yield an empty list; the propose modal hides its suggestion row,
+  and the rest of the app is unaffected. So a deployment that does not
+  set the key sees no change at all.
+- **Privacy disclosure.** The modal carries an inline note that the
+  draft text is sent to Anthropic to generate the suggestions. This is
+  required for honesty (the text leaves the deployment before the RFC
+  is submitted); cookie-consent does not gate it because the user has
+  actively typed into a draft surface. The exact wording wants a
+  counsel pass before OHM's deploy, per the #22 drafting discipline.
+- **Frontend.** `ProposeModal` debounce-posts the draft (700 ms, with a
+  stale-response guard); suggestion chips are clickable and add to the
+  tag list (nothing auto-applies). `api.suggestTags()` is forgiving —
+  any non-OK response resolves to `[]`.
+
+Tests: 11 new (`test_tag_suggest_vertical.py`) — contributor-gating,
+universe-constrained filtering, no-key / empty-corpus / rate-limit
+paths, plus units for the universe gather, the tolerant reply parser,
+the max cap, the empty-draft short-circuit, and provider-failure
+fallback. Full suite 351 green.
+
+Upgrade steps:
+
+1. You **MUST** bind `ANTHROPIC_API_KEY` for the suggestion surface to
+   work. On OHM this is an operator gesture — the key never touches the
+   conversation. Set it from your own terminal via stdin (so the bytes
+   never land in shell history):
+
+   ```bash
+   printf '%s' "$(pbpaste)" | .venv/bin/ohm-rfc-app-flotilla \
+       secret set ohm-rfc-app ANTHROPIC_API_KEY
+   ```
+
+   (The §18 chat stack already reads this same key, so a deployment
+   that has chat configured **MAY** already have it bound — confirm with
+   `flotilla secret list ohm-rfc-app`.) If the key is absent the app
+   still boots and serves normally; tag suggestions are simply
+   unavailable until it is set.
+2. You **MAY** tune the per-user rate limit via `TAG_SUGGEST_RATE_MAX`
+   (default 30) and `TAG_SUGGEST_RATE_WINDOW_SECONDS` (default 60). The
+   defaults apply when unset.
+3. You **SHOULD** have counsel review the modal's disclosure wording
+   before exposing the surface to users, per the #22 drafting
+   discipline — the copy is honest as written, but the legal review is
+   the right call for any "your text is sent to a third party" notice.
+
+## 0.23.0 — 2026-05-28
+
+Roadmap item #29: signing in lands the user on their most recently
+viewed app state instead of the empty-state home view. Shipped from
+driver session 0022.0. Per-user, server-side, on by default; first-ever
+sign-ins still land on home.
+
+1. **Server-side last-state.** A new `user_session_state` table holds one
+   row per user: `last_route TEXT`, `last_route_state TEXT` (light view
+   state encoded as JSON — SQLite has no native JSONB — never draft-buffer
+   contents), `resume_enabled INTEGER NOT NULL DEFAULT 1`, and
+   `last_updated_at`. Per-user (not per-device), matching the
+   "go to where I was last" intent.
+2. **Route-change capture.** A new frontend hook (`frontend/src/lib/
+   useLastState.js`) debounce-posts the current route + light state to
+   `PUT /api/me/last-state` for authenticated users only; anonymous
+   sessions are a no-op. The handler upserts the user's row and no-ops
+   when `resume_enabled` is 0.
+3. **Sign-in redirect.** The stored `last_route` (+ decoded state +
+   `resume_enabled`) is folded onto the existing `/api/auth/me` payload
+   (no new GET endpoint), so the frontend reads it on boot. On a hard
+   sign-in landing (app booted on `/`), the app redirects to the stored
+   route. The redirect is gated on the #21-Part-C Amplitude `identify`
+   having fired (`identifyReady`), preserving identify-then-track
+   ordering — the first event on the resumed route carries the user_id.
+4. **Edge cases.** Stale routes (an RFC since withdrawn or now
+   unreadable) are a graceful no-op — existing routing falls through to
+   the catalog/empty-state. Opt-out ships at the column level
+   (`resume_enabled`); the profile-settings toggle UI is a follow-up.
+   Stored state is route + light view state only, never draft contents
+   (documented in `SPEC.md` §6.8).
+
+Migration `022_user_session_state.sql` creates the table. No new
+environment variables, overlay keys, or secrets.
+
+Upgrade steps:
+
+1. Deployments **MUST** apply database migrations; `022_user_session_state.sql`
+   runs automatically on next boot (the migration runner globs
+   `backend/migrations/*.sql` and applies any not yet recorded in
+   `schema_migrations`). The migration is additive — a new table — and
+   requires no data backfill.
+2. No new environment variables, overlay keys, or secrets. No operator
+   action beyond the standard `flotilla deploy ohm-rfc-app`.
+
+## 0.22.0 — 2026-05-28
+
+Roadmap item #26: an optional **"What will you be using this for?"**
+field on both propose surfaces. Shipped from driver session 0022.0.
+Additive and backward-compatible — no behavior changes for anyone who
+leaves the field blank.
+
+1. **Propose-RFC modal.** Below the required "Why is this RFC needed?"
+   field (`pitch`) sits a new optional **"What will you be using this
+   RFC for?"** textarea. "Needed" is the abstract justification; "using
+   it for" is the concrete ground-truth use case — captured without
+   being forced.
+2. **Propose-PR modal.** Below the required "Why is this change needed?"
+   field (`description`) sits a new optional **"What will you be using
+   this change for?"** textarea.
+3. **Display.** The RFC view (`RFCView` / `ProposalView`) and PR review
+   view (`PRView`) render the captured use case alongside the existing
+   "why" text, with a muted "left blank" treatment when absent.
+4. **Persistence (deployment note).** In this deployment the framework's
+   `rfcs` / PR surfaces are the Gitea-backed cache tables `cached_rfcs`
+   / `cached_prs`, rebuilt by the reconciler. Because the propose write
+   path is endpoint → Gitea → reconcile (and the reconciler doesn't
+   carry the new field), the durable home is a canonical, reconcile-proof
+   side table `proposed_use_cases` (keyed by `(scope, pr_number)`) that
+   the propose/open endpoints write directly and the view endpoints read
+   back. The literal nullable `proposed_use_case` columns named by the
+   roadmap are also added to `cached_rfcs` / `cached_prs` for parity and
+   any future reconciler that learns to carry the field. NULL/blank use
+   cases simply never write a side-table row — absence is "left blank".
+
+Migration `021_proposed_use_case.sql` adds the two cache columns
+(`ALTER TABLE … ADD COLUMN proposed_use_case TEXT`), the
+`proposed_use_cases` canonical table, and its lookup indexes. The
+reconciler's upsert (`ON CONFLICT DO UPDATE`) sets only known columns,
+so the added cache columns survive reconciles. Backend validators accept
+the field as NULL/omitted (no required-validation) with an 8000-char cap
+matching the existing PR `description` bound; blank/whitespace is treated
+as absent.
+
+Upgrade steps:
+
+1. Deployments **MUST** apply database migrations; `021_proposed_use_case.sql`
+   runs automatically on next boot (the migration runner globs
+   `backend/migrations/*.sql` and applies any not yet recorded in
+   `schema_migrations`). The migration is additive — nullable cache
+   columns plus a new table — and requires no data backfill.
+2. No new environment variables, overlay keys, or secrets. No operator
+   action beyond the standard `flotilla deploy ohm-rfc-app`.
+
 ## 0.21.0 — 2026-05-28
 
 UX-polish wave. Roadmap items #31 (comprehensive UX polish — foundation

SPEC.md

@@ -714,6 +714,47 @@ The lighter half ships the structural shape — frontmatter, consent,
 resolution, revocation. The heavier half ships the runtime
 hardening.
 
+### 6.8 Sign-in state resume (roadmap item #29, v0.23.0)
+
+Signing in lands the user back on their most recently-viewed app
+state instead of always on the empty-state home view. The model is
+**per-user**, not per-device — the safe default the roadmap calls
+for: a sign-in on any device resumes the most-recently-recorded
+route. A per-device split and a profile-settings toggle UI are
+follow-ups; v0.23.0 ships the column-level opt-out flag
+(`resume_enabled`, default on) and the default-on behavior.
+
+**Storage.** A single row per user in `user_session_state`
+(migration 022): `user_id` (PK, FK → `users.id`, cascade-delete),
+`last_route` (TEXT, the frontend pathname), `last_route_state`
+(TEXT, JSON-encoded — SQLite has no native JSONB, so JSON-as-TEXT
+matches how the app stores every other JSON blob), `resume_enabled`
+(INTEGER, default 1), and `last_updated_at`.
+
+**Wiring.** A debounced (~1s) frontend route-change hook posts the
+current route to `PUT /api/me/last-state` for authenticated users
+(anonymous: no-op). The stored `last_route` is folded onto the
+existing `/api/auth/me` payload (no extra round-trip); on sign-in,
+after the §21-Part-C Amplitude `identify` fires, the frontend
+`navigate()`s to it. The identify-then-redirect ordering is
+preserved: the redirect is gated on identify having fired.
+
+**Stale state.** If the stored route is an RFC since withdrawn or
+one the user lost rights to read, the redirect is a graceful no-op:
+`navigate(last_route)` lands on whatever that route renders today,
+and the existing routing already falls through to the
+catalog/empty-state for a missing/unreadable RFC. No special-casing
+on the server.
+
+**Privacy (binding).** The stored state is **route + light view
+state ONLY** — scroll anchors, open-tab selection, filter chips, and
+the like. It **MUST NOT** carry draft-buffer contents, PR/comment
+draft text, or any user-typed content. The frontend never sends such
+content; the `last_route_state` column comment in migration 022 and
+this paragraph are the contract. Resume state is purposely cheap to
+discard: a deliberate "clear" (or `resume_enabled = 0`) drops the
+user back to today's empty-state behavior.
+
 ---
 
 ## 7. The left pane

VERSION

@@ -1 +1 @@
-0.21.0
+0.24.0

backend/.env.example

@@ -38,10 +38,22 @@ GITEA_WEBHOOK_SECRET=change-me-to-a-shared-secret
 # Comma-separated list of provider keys to enable. Per the §19.2
 # per-RFC-model topic, this is app-wide until that topic lands.
 ENABLED_MODELS=claude
+# ANTHROPIC_API_KEY also powers the §9.1 propose-RFC tag suggestions
+# (roadmap #27) — that surface always uses Claude Haiku for cost,
+# independent of ENABLED_MODELS. With no key set, tag suggestions are
+# simply unavailable (the modal hides the row); the rest of the app is
+# unaffected.
 ANTHROPIC_API_KEY=
 GOOGLE_API_KEY=
 OPENAI_API_KEY=
 
+# --- Tag suggestions (§9.1 / roadmap #27) ---
+# Per-user rate limit on the suggest-tags endpoint (cost backstop; the
+# modal debounces and the endpoint is contributor-gated). Optional —
+# these defaults apply when unset.
+TAG_SUGGEST_RATE_MAX=30
+TAG_SUGGEST_RATE_WINDOW_SECONDS=60
+
 # --- Email (§15.4) ---
 # Leave SMTP_HOST unset to use the stdout fallback — the integration
 # tests rely on it, and a dev environment without a real SMTP provider

backend/app/api.py

@@ -39,6 +39,7 @@ from . import (
     notify,
     philosophy,
     providers as providers_mod,
+    tag_suggest,
 )
 from .bot import Bot
 from .config import Config
@@ -51,6 +52,22 @@ class ProposeBody(BaseModel):
     slug: str = Field(min_length=1, max_length=80)
     pitch: str = Field(min_length=1)
     tags: list[str] = Field(default_factory=list)
+    # Roadmap #26: optional "What will you be using this RFC for?" — the
+    # concrete ground-truth use case, distinct from the `pitch`'s abstract
+    # "why is this needed." Optional (NULL/omitted accepted), no minimum,
+    # generous cap matching the pitch's free-text body bound.
+    proposed_use_case: str | None = Field(default=None, max_length=8000)
+
+
+class SuggestTagsBody(BaseModel):
+    # Roadmap #27: the partial propose-RFC draft, sent as the user types
+    # (debounced on the frontend). All fields optional — suggestions
+    # refine as the draft fills in. `pitch` is the "why is this needed"
+    # rationale; `use_case` is the #26 optional ground-truth field.
+    # Bounds mirror the propose body's free-text caps.
+    title: str = Field(default="", max_length=200)
+    pitch: str = Field(default="", max_length=8000)
+    use_case: str = Field(default="", max_length=8000)
 
 
 class DeclineBody(BaseModel):
@@ -62,6 +79,18 @@ class FunderCredentialBody(BaseModel):
     api_key: str = Field(min_length=1, max_length=2048)
 
 
+class LastStateBody(BaseModel):
+    # v0.23.0 / roadmap item #29: server-side sign-in state resume.
+    # `route` is a frontend pathname the user was last on (bounded so a
+    # hostile client can't stuff arbitrary blobs through). `state` is an
+    # optional bag of *light* view state (scroll anchors, open tab,
+    # filter chips). PRIVACY: it MUST NOT carry draft-buffer contents —
+    # the frontend only ever sends ephemeral view state, and the column
+    # comment in migration 022 + SPEC §6.2 are the binding contract.
+    route: str = Field(min_length=1, max_length=2048)
+    state: dict[str, Any] | None = None
+
+
 class BetaRequestBody(BaseModel):
     # v0.8.0 — captured on the first OTC sign-in. All three fields are
     # required so the admin queue has a coherent triage shape.
@@ -349,6 +378,28 @@ def make_router(
         )
         has_passcode = bool(row and row["passcode_hash"])
         passcode_set_at = row["passcode_set_at"] if (row and has_passcode) else None
+        # v0.23.0 / item #29: fold the sign-in-resume state onto the
+        # same round-trip the frontend already makes on boot. When
+        # resume is disabled (resume_enabled = 0) we hand back a null
+        # route so the client never redirects; the stored row stays put
+        # so re-enabling later resumes the last-known route.
+        state_row = db.conn().execute(
+            "SELECT last_route, last_route_state, resume_enabled "
+            "FROM user_session_state WHERE user_id = ?",
+            (user.user_id,),
+        ).fetchone()
+        resume_enabled = bool(state_row["resume_enabled"]) if state_row else True
+        last_route = (
+            state_row["last_route"]
+            if (state_row and resume_enabled)
+            else None
+        )
+        last_route_state = None
+        if state_row and resume_enabled and state_row["last_route_state"]:
+            try:
+                last_route_state = json.loads(state_row["last_route_state"])
+            except (ValueError, TypeError):
+                last_route_state = None
         return {
             "authenticated": True,
             "user": {
@@ -365,6 +416,10 @@ def make_router(
                 "needs_profile": needs_profile,
                 "has_passcode": has_passcode,
                 "passcode_set_at": passcode_set_at,
+                # v0.23.0 / item #29 — sign-in state resume.
+                "resume_enabled": resume_enabled,
+                "last_route": last_route,
+                "last_route_state": last_route_state,
             },
         }
 
@@ -434,6 +489,52 @@ def make_router(
             notify.fan_out_new_beta_request(requester_user_id=user.user_id)
         return {"ok": True}
 
+    # ---------------------------------------------------------------
+    # v0.23.0 (§6.2, roadmap item #29): server-side sign-in state
+    # resume. The frontend debounce-posts the user's current route +
+    # a small bag of light view state here on every route change; the
+    # next sign-in reads `last_route` off `/api/auth/me` and redirects.
+    #
+    # Per-user (NOT per-device) — one row per user, keyed on user_id.
+    # `resume_enabled` is the opt-out flag (default on); when it's 0
+    # this endpoint no-ops so a user who turned resume off doesn't keep
+    # silently rewriting their stored route. PRIVACY: the body carries
+    # route + light state ONLY, never draft-buffer contents (migration
+    # 022 column comment + SPEC §6.2 are the binding contract).
+    #
+    # `require_user` (not `require_contributor`) — a pending/granted
+    # distinction is irrelevant for "remember where I was", and a
+    # pending user navigating read-only surfaces should still resume.
+    # Anonymous callers get the 401 `require_user` raises.
+    # ---------------------------------------------------------------
+
+    @router.put("/api/me/last-state")
+    async def put_last_state(body: LastStateBody, request: Request) -> dict[str, Any]:
+        user = auth.require_user(request)
+        # Respect the opt-out: if a row already exists with resume
+        # disabled, leave it untouched and report the no-op. A first-
+        # ever POST (no row yet) defaults to enabled and stores.
+        existing = db.conn().execute(
+            "SELECT resume_enabled FROM user_session_state WHERE user_id = ?",
+            (user.user_id,),
+        ).fetchone()
+        if existing is not None and not existing["resume_enabled"]:
+            return {"ok": True, "stored": False}
+        state_json = json.dumps(body.state) if body.state is not None else None
+        db.conn().execute(
+            """
+            INSERT INTO user_session_state
+                (user_id, last_route, last_route_state, last_updated_at)
+            VALUES (?, ?, ?, datetime('now'))
+            ON CONFLICT(user_id) DO UPDATE SET
+                last_route = excluded.last_route,
+                last_route_state = excluded.last_route_state,
+                last_updated_at = excluded.last_updated_at
+            """,
+            (user.user_id, body.route, state_json),
+        )
+        return {"ok": True, "stored": True}
+
     # ---------------------------------------------------------------
     # v0.11.0: trust device for 30 days (§6.2, roadmap item #9).
     #
@@ -557,12 +658,36 @@ def make_router(
         ).fetchone()
         if row is None:
             raise HTTPException(404, "Not found")
-        return _serialize_rfc(row)
+        payload = _serialize_rfc(row)
+        # Roadmap #26: surface the optional propose-time use case on the
+        # RFC view. The idea PR closes on merge, but the canonical row in
+        # `proposed_use_cases` persists; look it up by slug (the latest
+        # 'rfc'-scope row for this slug). NULL == "left blank".
+        uc = db.conn().execute(
+            """
+            SELECT use_case FROM proposed_use_cases
+             WHERE scope = 'rfc' AND rfc_slug = ?
+             ORDER BY id DESC LIMIT 1
+            """,
+            (slug,),
+        ).fetchone()
+        payload["proposed_use_case"] = uc["use_case"] if uc else None
+        return payload
 
     # ---------------------------------------------------------------
     # §7.3 / §9.3: pending ideas
     # ---------------------------------------------------------------
 
+    def _proposal_use_case(pr_number: int) -> str | None:
+        """Roadmap #26: read the optional use case for an idea PR from the
+        canonical side table. Returns None when none was supplied (the
+        "left blank" sentinel the frontend renders tastefully)."""
+        row = db.conn().execute(
+            "SELECT use_case FROM proposed_use_cases WHERE scope = 'rfc' AND pr_number = ?",
+            (pr_number,),
+        ).fetchone()
+        return row["use_case"] if row else None
+
     @router.get("/api/proposals")
     async def list_proposals() -> dict[str, Any]:
         rows = db.conn().execute(
@@ -582,6 +707,7 @@ def make_router(
                     "description": r["description"],
                     "opened_by": r["opened_by"],
                     "opened_at": r["opened_at"],
+                    "proposed_use_case": _proposal_use_case(r["pr_number"]),
                 }
                 for r in rows
             ]
@@ -630,6 +756,7 @@ def make_router(
             "opened_at": row["opened_at"],
             "entry": entry_payload,
             "affordances": affordances,
+            "proposed_use_case": _proposal_use_case(pr_number),
         }
 
     # ---------------------------------------------------------------
@@ -706,8 +833,55 @@ def make_router(
         # cache write is idempotent.)
         await cache.refresh_meta_pulls(config, gitea)
 
+        # Roadmap #26: persist the optional use case to the canonical,
+        # reconcile-proof side table keyed by the idea PR number. NULL/
+        # blank simply writes no row (absence == "left blank"). Done after
+        # the refresh so the cache row exists; the mirror onto cached_prs
+        # keeps the cache column in parity for any read that uses it.
+        use_case = (payload.proposed_use_case or "").strip()
+        if use_case:
+            db.conn().execute(
+                """
+                INSERT INTO proposed_use_cases (scope, rfc_slug, pr_number, use_case)
+                VALUES ('rfc', ?, ?, ?)
+                ON CONFLICT(scope, pr_number) DO UPDATE SET use_case = excluded.use_case
+                """,
+                (slug, pr["number"], use_case),
+            )
+            db.conn().execute(
+                "UPDATE cached_prs SET proposed_use_case = ? WHERE pr_kind = 'idea' AND pr_number = ?",
+                (use_case, pr["number"]),
+            )
+
         return {"pr_number": pr["number"], "slug": slug}
 
+    # ---------------------------------------------------------------
+    # §9.1 Slice 2 (roadmap #27): Claude Haiku tag suggestions as the
+    # propose-RFC fields fill in. The modal debounce-posts the partial
+    # draft; we constrain Haiku to the corpus's existing tag set and
+    # return a short ranked list of clickable chips. Gated to
+    # contributors (same gate as propose) so the cost surface is bounded
+    # to people who can actually file an RFC; rate-limited per user as a
+    # backstop. Degrades to an empty list (no error) when no Anthropic
+    # key is bound, the corpus has no tags yet, or the draft is empty —
+    # so the modal simply shows nothing extra.
+    # ---------------------------------------------------------------
+
+    @router.post("/api/rfcs/suggest-tags")
+    async def suggest_rfc_tags(payload: SuggestTagsBody, request: Request) -> dict[str, Any]:
+        user = auth.require_contributor(request)
+        if not tag_suggest.rate_limit_ok(user.user_id):
+            raise HTTPException(429, "Too many tag-suggestion requests; please slow down.")
+        provider = tag_suggest.haiku_provider(config)
+        if provider is None:
+            return {"suggestions": []}
+        universe = tag_suggest.gather_tag_universe()
+        draft = tag_suggest.Draft(
+            title=payload.title, pitch=payload.pitch, use_case=payload.use_case
+        )
+        suggestions = tag_suggest.suggest(provider, draft, universe)
+        return {"suggestions": suggestions}
+
     # ---------------------------------------------------------------
     # §9.3: merge / decline / withdraw an idea PR
     # ---------------------------------------------------------------

backend/app/api_prs.py

@@ -42,6 +42,11 @@ RFC_FILE_PATH = "RFC.md"
 class OpenPRBody(BaseModel):
     title: str = Field(min_length=1, max_length=240)
     description: str = Field(max_length=8000)
+    # Roadmap #26: optional "What will you be using this change for?" —
+    # the concrete ground-truth use case sibling to the required
+    # "why is this change needed" (the `description`). Optional, generous
+    # cap matching the description bound.
+    proposed_use_case: str | None = Field(default=None, max_length=8000)
 
 
 class PRDescriptionBody(BaseModel):
@@ -173,6 +178,26 @@ def make_router(
             raise HTTPException(502, f"Gitea: {e.detail}")
 
         await _refresh_after_pr_write(rfc)
+
+        # Roadmap #26: persist the optional use case to the canonical,
+        # reconcile-proof side table keyed by the PR number. Blank/omitted
+        # writes no row (absence == "left blank"). The mirror onto
+        # cached_prs keeps the cache column in parity.
+        use_case = (body.proposed_use_case or "").strip()
+        if use_case:
+            db.conn().execute(
+                """
+                INSERT INTO proposed_use_cases (scope, rfc_slug, pr_number, use_case)
+                VALUES ('pr', ?, ?, ?)
+                ON CONFLICT(scope, pr_number) DO UPDATE SET use_case = excluded.use_case
+                """,
+                (slug, pr["number"], use_case),
+            )
+            db.conn().execute(
+                "UPDATE cached_prs SET proposed_use_case = ? WHERE rfc_slug = ? AND pr_number = ?",
+                (use_case, slug, pr["number"]),
+            )
+
         return {"pr_number": pr["number"], "slug": slug, "branch": branch}
 
     # -------------------------------------------------------------------
@@ -300,6 +325,7 @@ def make_router(
             "pr_number": pr_number,
             "title": pr_row["title"],
             "description": pr_row["description"],
+            "proposed_use_case": _pr_use_case(pr_number),
             "state": pr_row["state"],
             "opened_by": pr_row["opened_by"],
             "opened_at": pr_row["opened_at"],
@@ -762,6 +788,17 @@ def _can_edit_pr_text(rfc, pr_row, viewer) -> bool:
     return _can_withdraw(rfc, pr_row, viewer)
 
 
+def _pr_use_case(pr_number: int) -> str | None:
+    """Roadmap #26: the optional propose-PR use case from the canonical
+    side table, or None when the change was opened without one ("left
+    blank")."""
+    row = db.conn().execute(
+        "SELECT use_case FROM proposed_use_cases WHERE scope = 'pr' AND pr_number = ?",
+        (pr_number,),
+    ).fetchone()
+    return row["use_case"] if row else None
+
+
 def _pr_capabilities(rfc, pr_row, viewer) -> dict:
     return {
         "can_merge": _can_merge(rfc, viewer) and pr_row["state"] == "open",

backend/app/providers.py

@@ -184,6 +184,21 @@ def load_providers(env: dict) -> dict[str, BaseProvider]:
     return providers
 
 
+def construct_haiku(api_key: str) -> AnthropicProvider:
+    """A dedicated Claude Haiku provider, independent of the
+    `ENABLED_MODELS` chat-picker universe.
+
+    The §9.1 tag-suggestion surface (roadmap #27) always wants the
+    cheap + fast model regardless of which models the operator surfaces
+    in the §8.12 picker, so it constructs Haiku directly from the
+    operator's Anthropic key rather than going through `load_providers`.
+    The model id is sourced from the same `_CLAUDE_VARIANTS` table the
+    picker uses, so a model-string bump lands in one place.
+    """
+    model, name = _CLAUDE_VARIANTS["claude-haiku"]
+    return AnthropicProvider(api_key=api_key, model=model, display_name=name)
+
+
 def load_from_config(config) -> dict[str, BaseProvider]:
     """Convenience adapter so callers can pass our Config dataclass directly."""
     env = {

backend/app/tag_suggest.py

@@ -0,0 +1,244 @@
+"""Roadmap #27 — Claude Haiku tag suggestions for the propose-RFC modal.
+
+A cheap, fast assist: given the partial RFC draft a user is typing, ask
+Claude Haiku to recommend tags drawn ONLY from the tags already in use
+across the corpus. v1 has no curated tag list — tags are free-form chip
+input (§9.1) — so "the taxonomy" is the de-facto set of distinct tags
+the existing RFCs already carry. The model is constrained to that set
+and MUST NOT invent new tags; taxonomy extension (letting the model
+propose genuinely new tags) is a deferred follow-up per the roadmap.
+
+Why Haiku specifically: cost. Picking a few reasonable tags from a known
+set is well within Haiku's range, and the modal fires this repeatedly as
+the user types, so the per-call price has to stay small.
+
+The whole surface degrades to silence rather than error: no Anthropic
+key, no provider, an empty corpus, a rate-limited caller, an empty
+draft, or an unparseable model reply all yield an empty suggestion list.
+The propose modal hides its suggestion row on an empty list, so the
+fallback is simply the existing free-form chip input with nothing extra
+shown.
+"""
+from __future__ import annotations
+
+import json
+import logging
+import os
+import time
+from dataclasses import dataclass
+
+from . import db
+from .providers import BaseProvider, construct_haiku
+
+log = logging.getLogger(__name__)
+
+# Bound the universe handed to the model so a large corpus can't blow up
+# the prompt size (and the cost). The most-common tags matter most.
+_UNIVERSE_CAP = 200
+
+# How many suggestions we ever return to the modal.
+DEFAULT_MAX_SUGGESTIONS = 6
+
+
+@dataclass
+class Draft:
+    """The partial propose-RFC draft. `pitch` is the "why is this needed"
+    rationale; `use_case` is the #26 optional ground-truth field."""
+
+    title: str = ""
+    pitch: str = ""
+    use_case: str = ""
+
+    def is_empty(self) -> bool:
+        return not (self.title.strip() or self.pitch.strip() or self.use_case.strip())
+
+
+def haiku_provider(config) -> BaseProvider | None:
+    """Construct a dedicated Claude Haiku provider from the operator's
+    Anthropic key, or return None when no key is configured.
+
+    None means "suggestions unavailable" — the caller returns an empty
+    list and the modal shows nothing. This is the seam tests monkeypatch
+    to inject a fake provider without a real key. There is no RFC slug at
+    propose time, so the §6.7 per-RFC funder path deliberately does not
+    apply: tag suggestion always runs on the operator's own key.
+    """
+    key = getattr(config, "anthropic_api_key", "") or ""
+    if not key:
+        return None
+    return construct_haiku(key)
+
+
+def gather_tag_universe(cap: int = _UNIVERSE_CAP) -> list[str]:
+    """Every distinct tag in use across the cached corpus, most-common
+    first (ties broken alphabetically for determinism), capped.
+
+    This is the universe the model is constrained to. An empty corpus
+    yields an empty list, which short-circuits suggestion to silence.
+    """
+    rows = db.conn().execute("SELECT tags_json FROM cached_rfcs").fetchall()
+    counts: dict[str, int] = {}
+    for r in rows:
+        try:
+            tags = json.loads(r["tags_json"] or "[]")
+        except (ValueError, TypeError):
+            continue
+        if not isinstance(tags, list):
+            continue
+        for t in tags:
+            if not isinstance(t, str):
+                continue
+            tag = t.strip()
+            if tag:
+                counts[tag] = counts.get(tag, 0) + 1
+    ranked = sorted(counts, key=lambda t: (-counts[t], t.lower()))
+    return ranked[:cap]
+
+
+# ---------------------------------------------------------------------------
+# Rate limiting — in-process, per-user sliding window.
+#
+# Cost control, not security: the `require_contributor` gate already
+# bounds callers to authenticated beta users, and the modal debounces.
+# This is the backstop against a stuck/abusive client hammering the
+# endpoint. In-memory is sufficient (single-process uvicorn on the VM)
+# and resets on restart, which is fine for a cost guard.
+# ---------------------------------------------------------------------------
+
+_CALLS: dict[int, list[float]] = {}
+
+
+def _rate_config() -> tuple[int, float]:
+    try:
+        max_calls = int(os.environ.get("TAG_SUGGEST_RATE_MAX", "30"))
+    except ValueError:
+        max_calls = 30
+    try:
+        window = float(os.environ.get("TAG_SUGGEST_RATE_WINDOW_SECONDS", "60"))
+    except ValueError:
+        window = 60.0
+    return max_calls, window
+
+
+def rate_limit_ok(user_id: int, *, now: float | None = None) -> bool:
+    """True if this call is within the per-user window; records the call.
+    `now` is injectable for tests (defaults to a monotonic clock)."""
+    max_calls, window = _rate_config()
+    t = time.monotonic() if now is None else now
+    calls = _CALLS.setdefault(user_id, [])
+    cutoff = t - window
+    calls[:] = [c for c in calls if c > cutoff]
+    if len(calls) >= max_calls:
+        return False
+    calls.append(t)
+    return True
+
+
+def reset_rate_limits() -> None:
+    """Test seam — clear the in-process window state."""
+    _CALLS.clear()
+
+
+# ---------------------------------------------------------------------------
+# Prompt + parse.
+# ---------------------------------------------------------------------------
+
+_SYSTEM = (
+    "You suggest topic tags for a draft RFC — a structured proposal "
+    "document in a collection. You are given the draft's title, its "
+    "rationale, an optional use case, and the exact set of tags already "
+    "in use across the collection. Choose the tags from that set that "
+    "best fit the draft.\n"
+    "Rules:\n"
+    "- Choose ONLY from the provided tag set. Never invent a tag.\n"
+    "- Order best-fit first. Omit weak fits rather than padding the list.\n"
+    "- Return at most {max} tags.\n"
+    "Respond with ONLY a JSON array, no prose, of the form:\n"
+    '[{{"tag": "<exact tag from the set>", "confidence": <number between 0 and 1>}}]\n'
+    "If no tag in the set fits the draft, return []."
+)
+
+
+def _build_messages(draft: Draft, universe: list[str], max_suggestions: int):
+    system = _SYSTEM.format(max=max_suggestions)
+    parts: list[str] = []
+    if draft.title.strip():
+        parts.append(f"Title: {draft.title.strip()[:300]}")
+    if draft.pitch.strip():
+        parts.append(f"Why this RFC is needed:\n{draft.pitch.strip()[:4000]}")
+    if draft.use_case.strip():
+        parts.append(f"What it will be used for:\n{draft.use_case.strip()[:4000]}")
+    parts.append(
+        "Tags already in use (choose only from these):\n" + ", ".join(universe)
+    )
+    return system, [{"role": "user", "content": "\n\n".join(parts)}]
+
+
+def _extract_json_array(text: str):
+    start = text.find("[")
+    end = text.rfind("]")
+    if start == -1 or end == -1 or end < start:
+        return None
+    try:
+        return json.loads(text[start : end + 1])
+    except ValueError:
+        return None
+
+
+def parse_reply(text: str, universe: list[str], max_suggestions: int) -> list[dict]:
+    """Parse the model reply into a clean, universe-constrained list.
+
+    Tolerant of the model returning bare strings or objects, extra prose
+    around the JSON, unknown/invented tags (dropped), duplicate tags
+    (deduped), and missing/garbage confidences (defaulted + clamped).
+    """
+    data = _extract_json_array(text or "")
+    if not isinstance(data, list):
+        return []
+    # Map back to the canonical spelling in the universe, case-insensitively,
+    # so a model that lowercases a tag still resolves to the real one.
+    canonical = {t.lower(): t for t in universe}
+    out: list[dict] = []
+    seen: set[str] = set()
+    for item in data:
+        if isinstance(item, dict):
+            raw = item.get("tag")
+            conf = item.get("confidence")
+        elif isinstance(item, str):
+            raw, conf = item, None
+        else:
+            continue
+        if not isinstance(raw, str):
+            continue
+        tag = canonical.get(raw.strip().lower())
+        if tag is None or tag in seen:
+            continue
+        try:
+            c = float(conf) if conf is not None else 0.5
+        except (ValueError, TypeError):
+            c = 0.5
+        c = max(0.0, min(1.0, c))
+        out.append({"tag": tag, "confidence": round(c, 3)})
+        seen.add(tag)
+        if len(out) >= max_suggestions:
+            break
+    return out
+
+
+def suggest(
+    provider: BaseProvider,
+    draft: Draft,
+    universe: list[str],
+    max_suggestions: int = DEFAULT_MAX_SUGGESTIONS,
+) -> list[dict]:
+    """Orchestrate one suggestion call. Returns [] for an empty draft or
+    empty universe (no model call), and for any provider/parse failure."""
+    if draft.is_empty() or not universe:
+        return []
+    system, history = _build_messages(draft, universe, max_suggestions)
+    try:
+        text = provider.send(system, history)
+    except Exception as exc:  # provider/network failure → silent empty
+        log.warning("tag-suggest provider failed: %s", exc)
+        return []
+    return parse_reply(text, universe, max_suggestions)

backend/migrations/021_proposed_use_case.sql

@@ -0,0 +1,47 @@
+-- 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);

backend/migrations/022_user_session_state.sql

@@ -0,0 +1,54 @@
+-- v0.23.0 / roadmap item #29: server-side sign-in state resume.
+--
+-- Track each authenticated user's last-viewed route + a small bag of
+-- "light" component state so that the *next* sign-in can land the user
+-- back where they left off, rather than always dropping them on the
+-- empty-state home view.
+--
+-- Storage shape (one row per user — per-user, NOT per-device, per the
+-- #29 "safe default"):
+--
+--   * `user_id` — PRIMARY KEY and FK into users(id) with cascade on
+--     delete. INTEGER to match users.id (INTEGER PRIMARY KEY
+--     AUTOINCREMENT). A deleted user automatically loses their stored
+--     resume state. One row per user means a later sign-in on any
+--     device resumes the most-recently-recorded route — the per-user
+--     model the roadmap asks for.
+--
+--   * `last_route` — the frontend pathname the user was last on
+--     (e.g. "/rfc/open-human-model"). TEXT, nullable until the first
+--     route-change POST lands. NEVER contains draft-buffer contents —
+--     it is a route only. See SPEC §6.2 "Sign-in state resume
+--     (privacy)".
+--
+--   * `last_route_state` — a JSON-encoded bag of *light* component
+--     state (scroll anchors, open-tab selection, filter chips, etc.).
+--     SQLite has no native JSONB; we store JSON as TEXT exactly as the
+--     rest of the app stores its JSON blobs (json.dumps / json.loads,
+--     cf. permission_events.details, actions.details). Nullable.
+--     PRIVACY INVARIANT: this column MUST NOT carry draft-buffer text,
+--     PR bodies, comment drafts, or any user-typed content — only
+--     ephemeral view state safe to replay. The PUT handler is the
+--     enforcement point; the column comment is the contract.
+--
+--   * `resume_enabled` — the per-user opt-out flag. 1 (default) means
+--     "resume me where I left off"; 0 means "always land on home". The
+--     PUT handler no-ops the upsert when this is 0, and the read path
+--     refuses to hand back a stored route when this is 0. A
+--     profile-settings toggle UI to flip this is a follow-up (the
+--     column + default-on behavior ship now); see CHANGELOG v0.23.0.
+--
+--   * `last_updated_at` — TEXT timestamp, app convention
+--     `datetime('now')`, matching device_trust.last_seen_at /
+--     users.last_seen_at. Refreshed on every successful upsert.
+--
+-- No new env vars. The debounce interval for the frontend route-change
+-- POST is a frontend constant (~1s), not a server knob.
+
+CREATE TABLE user_session_state (
+    user_id          INTEGER PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    last_route       TEXT,
+    last_route_state TEXT,                        -- JSON-encoded light state, nullable
+    resume_enabled   INTEGER NOT NULL DEFAULT 1,
+    last_updated_at  TEXT NOT NULL DEFAULT (datetime('now'))
+);

backend/tests/test_proposed_use_case_vertical.py

@@ -0,0 +1,161 @@
+"""End-to-end vertical for roadmap #26 (rfc-app v0.22.0): the optional
+"What will you be using this for?" capture on the two propose surfaces.
+
+Reuses the FakeGitea + session helpers from test_propose_vertical.py and
+the active-RFC seed from test_rfc_view_vertical.py. Proves:
+
+  (a) propose-RFC persists and returns `proposed_use_case` when supplied,
+      and the value survives onto the merged super-draft's RFC view;
+  (b) propose-RFC accepts a NULL / omitted use case ("left blank");
+  (c) propose-PR persists and returns `proposed_use_case` when supplied,
+      and accepts a NULL / omitted one.
+"""
+from __future__ import annotations
+
+from test_propose_vertical import (  # noqa: F401
+    FakeGitea,
+    app_with_fake_gitea,
+    provision_user_row,
+    sign_in_as,
+    tmp_env,
+)
+from test_pr_flow_vertical import _cut_branch_and_accept_change
+from test_rfc_view_vertical import SEED_BODY, seed_active_rfc
+
+
+# ---------------------------------------------------------------------------
+# propose-RFC
+# ---------------------------------------------------------------------------
+
+
+def test_propose_rfc_persists_and_returns_use_case(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        provision_user_row(user_id=1, login="ben", role="owner")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor", email="alice@test")
+
+        r = client.post("/api/rfcs/propose", json={
+            "title": "Open Human Model",
+            "slug": "open-human-model",
+            "pitch": "A shared definition of what we mean by *human*.",
+            "tags": ["identity"],
+            "proposed_use_case": "Wiring OHM into the OpenXML consent surface.",
+        })
+        assert r.status_code == 200, r.text
+        pr_number = r.json()["pr_number"]
+
+        # The pending-idea list carries the use case.
+        items = client.get("/api/proposals").json()["items"]
+        assert items[0]["proposed_use_case"] == "Wiring OHM into the OpenXML consent surface."
+
+        # The pending-idea detail view carries it too.
+        proposal = client.get(f"/api/proposals/{pr_number}").json()
+        assert proposal["proposed_use_case"] == "Wiring OHM into the OpenXML consent surface."
+
+        # Merge as owner; the use case survives onto the RFC view (looked
+        # up by slug from the canonical side table, since the idea PR
+        # closes on merge).
+        sign_in_as(client, user_id=1, gitea_login="ben", display_name="Ben", role="owner", email="ben@test")
+        r = client.post(f"/api/proposals/{pr_number}/merge")
+        assert r.status_code == 200, r.text
+
+        view = client.get("/api/rfcs/open-human-model").json()
+        assert view["proposed_use_case"] == "Wiring OHM into the OpenXML consent surface."
+
+
+def test_propose_rfc_use_case_optional(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=3, login="carol", role="contributor")
+        sign_in_as(client, user_id=3, gitea_login="carol", display_name="Carol", role="contributor")
+
+        # Omitted entirely.
+        r = client.post("/api/rfcs/propose", json={
+            "title": "No Use Case", "slug": "no-use-case", "pitch": "p", "tags": [],
+        })
+        assert r.status_code == 200, r.text
+        pr_a = r.json()["pr_number"]
+
+        # Explicit null.
+        r = client.post("/api/rfcs/propose", json={
+            "title": "Null Use Case", "slug": "null-use-case", "pitch": "p",
+            "tags": [], "proposed_use_case": None,
+        })
+        assert r.status_code == 200, r.text
+        pr_b = r.json()["pr_number"]
+
+        # Blank/whitespace — treated as "left blank", no row written.
+        r = client.post("/api/rfcs/propose", json={
+            "title": "Blank Use Case", "slug": "blank-use-case", "pitch": "p",
+            "tags": [], "proposed_use_case": "   ",
+        })
+        assert r.status_code == 200, r.text
+        pr_c = r.json()["pr_number"]
+
+        for pr in (pr_a, pr_b, pr_c):
+            assert client.get(f"/api/proposals/{pr}").json()["proposed_use_case"] is None
+
+
+# ---------------------------------------------------------------------------
+# propose-PR (against an active RFC)
+# ---------------------------------------------------------------------------
+
+
+def test_propose_pr_persists_and_returns_use_case(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        seed_active_rfc(fake, slug="ohm", title="OHM", body=SEED_BODY)
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+
+        branch, _ = _cut_branch_and_accept_change(
+            client, fake, slug="ohm",
+            original="Open Human Model is a framework for representing humans.",
+            proposed="Open Human Model is a framework for representing humans across systems.",
+        )
+        r = client.post(
+            f"/api/rfcs/ohm/branches/{branch}/open-pr",
+            json={
+                "title": "Tighten the opening",
+                "description": "Scope to systems.",
+                "proposed_use_case": "Building a cross-system consent registry.",
+            },
+        )
+        assert r.status_code == 200, r.text
+        pr_number = r.json()["pr_number"]
+
+        pr = client.get(f"/api/rfcs/ohm/prs/{pr_number}").json()
+        assert pr["proposed_use_case"] == "Building a cross-system consent registry."
+
+
+def test_propose_pr_use_case_optional(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        seed_active_rfc(fake, slug="ohm", title="OHM", body=SEED_BODY)
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+
+        branch, _ = _cut_branch_and_accept_change(
+            client, fake, slug="ohm",
+            original="It defines consent, trait, and agency in compatible terms.",
+            proposed="It defines consent, trait, harm, and agency in compatible terms.",
+        )
+        # No proposed_use_case key at all.
+        r = client.post(
+            f"/api/rfcs/ohm/branches/{branch}/open-pr",
+            json={"title": "Add harm", "description": "Name harm explicitly."},
+        )
+        assert r.status_code == 200, r.text
+        pr_number = r.json()["pr_number"]
+
+        pr = client.get(f"/api/rfcs/ohm/prs/{pr_number}").json()
+        assert pr["proposed_use_case"] is None

backend/tests/test_session_resume_vertical.py

@@ -0,0 +1,140 @@
+"""End-to-end integration tests for the v0.23.0 sign-in state-resume
+vertical (§6.2, roadmap item #29).
+
+New behavior: each authenticated user's last-viewed route + a small bag
+of light view state is tracked server-side, so the next sign-in can land
+them back where they left off rather than on the empty-state home view.
+
+The tests below prove:
+
+  * `PUT /api/me/last-state` requires auth — an anonymous client gets
+    401, and nothing is stored.
+  * An authenticated PUT upserts the route, and the stored route is
+    read back for that user off `GET /api/auth/me` (`last_route`).
+  * A second PUT overwrites (upsert, one row per user) — the latest
+    route wins.
+  * `last_route_state` round-trips as decoded JSON on `/api/auth/me`.
+  * Per-user isolation: user A's stored route is not visible to user B.
+  * `resume_enabled = 0` disables resume: the PUT no-ops (does not
+    rewrite the stored route) and `/api/auth/me` hands back a null
+    `last_route` even though a stored row exists.
+
+The fakes from `test_propose_vertical` give us a working app harness +
+the `sign_in_as` / `provision_user_row` seams.
+"""
+from __future__ import annotations
+
+from test_propose_vertical import (  # noqa: F401
+    FakeGitea,
+    app_with_fake_gitea,
+    provision_user_row,
+    sign_in_as,
+    tmp_env,
+)
+
+
+def test_put_last_state_requires_auth(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import db
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        # Anonymous — no session cookie set.
+        r = client.put("/api/me/last-state", json={"route": "/rfc/open-human-model"})
+        assert r.status_code == 401
+        # Nothing landed in the table.
+        row = db.conn().execute("SELECT COUNT(*) AS n FROM user_session_state").fetchone()
+        assert row["n"] == 0
+
+
+def test_put_last_state_upserts_and_reads_back(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor", email="alice@test")
+
+        # First POST stores a route + light state.
+        r = client.put(
+            "/api/me/last-state",
+            json={"route": "/rfc/open-human-model", "state": {"tab": "discussion", "scroll": 420}},
+        )
+        assert r.status_code == 200
+        assert r.json()["stored"] is True
+
+        # /api/auth/me hands the route + decoded state back.
+        me = client.get("/api/auth/me").json()
+        assert me["authenticated"] is True
+        assert me["user"]["resume_enabled"] is True
+        assert me["user"]["last_route"] == "/rfc/open-human-model"
+        assert me["user"]["last_route_state"] == {"tab": "discussion", "scroll": 420}
+
+        # A later POST overwrites — one row per user, latest wins.
+        r = client.put("/api/me/last-state", json={"route": "/proposals/7"})
+        assert r.status_code == 200
+        me = client.get("/api/auth/me").json()
+        assert me["user"]["last_route"] == "/proposals/7"
+        # state was omitted on the second POST → cleared to null.
+        assert me["user"]["last_route_state"] is None
+
+
+def test_last_state_is_per_user(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        provision_user_row(user_id=3, login="bob", role="contributor")
+
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor", email="alice@test")
+        client.put("/api/me/last-state", json={"route": "/rfc/alice-route"})
+
+        # Switch to bob — he has no stored route yet.
+        sign_in_as(client, user_id=3, gitea_login="bob", display_name="Bob", role="contributor", email="bob@test")
+        me = client.get("/api/auth/me").json()
+        assert me["user"]["last_route"] is None
+
+        client.put("/api/me/last-state", json={"route": "/rfc/bob-route"})
+        me = client.get("/api/auth/me").json()
+        assert me["user"]["last_route"] == "/rfc/bob-route"
+
+        # Back to alice — her route is untouched by bob's write.
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor", email="alice@test")
+        me = client.get("/api/auth/me").json()
+        assert me["user"]["last_route"] == "/rfc/alice-route"
+
+
+def test_resume_disabled_no_ops_put_and_hides_route(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import db
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor", email="alice@test")
+
+        # Seed a stored row, then flip resume_enabled off directly (the
+        # profile-settings toggle UI to do this from the client is a
+        # follow-up; the column + behavior ship now).
+        client.put("/api/me/last-state", json={"route": "/rfc/before-disable"})
+        db.conn().execute(
+            "UPDATE user_session_state SET resume_enabled = 0 WHERE user_id = ?",
+            (2,),
+        )
+
+        # /api/auth/me reports resume off and hands back a null route
+        # even though a stored row exists.
+        me = client.get("/api/auth/me").json()
+        assert me["user"]["resume_enabled"] is False
+        assert me["user"]["last_route"] is None
+
+        # A PUT while disabled no-ops: stored=False and the stored route
+        # is NOT rewritten.
+        r = client.put("/api/me/last-state", json={"route": "/rfc/after-disable"})
+        assert r.status_code == 200
+        assert r.json()["stored"] is False
+        row = db.conn().execute(
+            "SELECT last_route FROM user_session_state WHERE user_id = ?", (2,)
+        ).fetchone()
+        assert row["last_route"] == "/rfc/before-disable"

backend/tests/test_tag_suggest_vertical.py

@@ -0,0 +1,264 @@
+"""Vertical + unit coverage for roadmap #27 (rfc-app v0.24.0): Claude
+Haiku tag suggestions on the propose-RFC modal.
+
+Reuses the FakeGitea + session helpers from test_propose_vertical.py.
+The Anthropic call is never made for real — tests monkeypatch the
+`tag_suggest.haiku_provider` seam with a stub provider whose `send`
+returns canned text, so the HTTP contract is exercised without a key.
+
+Proves:
+  (a) the endpoint is contributor-gated (anon → 401);
+  (b) a contributor gets suggestions, filtered to the corpus tag
+      universe, with invented tags dropped;
+  (c) no Anthropic key bound → empty list, not an error;
+  (d) an empty corpus → empty list (model is never even called);
+  (e) the per-user rate limit surfaces as a 429;
+plus unit coverage of the universe gather, the reply parser's tolerance,
+and the suggest() orchestration short-circuits.
+"""
+from __future__ import annotations
+
+import json
+
+import pytest
+
+from test_propose_vertical import (  # noqa: F401
+    FakeGitea,
+    app_with_fake_gitea,
+    provision_user_row,
+    sign_in_as,
+    tmp_env,
+)
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+class StubProvider:
+    """A BaseProvider stand-in whose send() returns a fixed string (or
+    raises, to exercise the graceful-failure path)."""
+
+    def __init__(self, reply: str = "[]", *, raises: bool = False):
+        self.reply = reply
+        self.raises = raises
+        self.calls: list[tuple[str, list]] = []
+
+    def send(self, system, history):
+        self.calls.append((system, history))
+        if self.raises:
+            raise RuntimeError("boom")
+        return self.reply
+
+
+def _seed_tags(slug: str, title: str, tags: list[str], state: str = "active") -> None:
+    from app import db
+
+    db.conn().execute(
+        "INSERT OR REPLACE INTO cached_rfcs (slug, title, state, tags_json) VALUES (?, ?, ?, ?)",
+        (slug, title, state, json.dumps(tags)),
+    )
+
+
+def _use_provider(monkeypatch, provider) -> None:
+    monkeypatch.setattr("app.tag_suggest.haiku_provider", lambda config: provider)
+
+
+@pytest.fixture(autouse=True)
+def _reset_rate_limits():
+    from app import tag_suggest
+
+    tag_suggest.reset_rate_limits()
+    yield
+    tag_suggest.reset_rate_limits()
+
+
+# ---------------------------------------------------------------------------
+# Endpoint (vertical)
+# ---------------------------------------------------------------------------
+
+
+def test_anonymous_cannot_suggest(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        r = client.post("/api/rfcs/suggest-tags", json={"title": "X"})
+        assert r.status_code == 401
+
+
+def test_contributor_gets_filtered_suggestions(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+
+        _seed_tags("ohm", "OHM", ["identity", "schema", "consent"])
+        _seed_tags("other", "Other", ["identity", "governance"])
+
+        # Model returns two real tags (one lowercased to test canonical
+        # mapping is exact-set anyway), plus one invented tag that MUST
+        # be dropped.
+        reply = json.dumps([
+            {"tag": "identity", "confidence": 0.9},
+            {"tag": "consent", "confidence": 0.7},
+            {"tag": "totally-invented", "confidence": 0.99},
+        ])
+        stub = StubProvider(reply=reply)
+        _use_provider(monkeypatch, stub)
+
+        r = client.post("/api/rfcs/suggest-tags", json={
+            "title": "Consent and identity",
+            "pitch": "We need a shared definition of consent tied to identity.",
+        })
+        assert r.status_code == 200, r.text
+        tags = [s["tag"] for s in r.json()["suggestions"]]
+        assert tags == ["identity", "consent"]
+        # the model was actually invoked
+        assert len(stub.calls) == 1
+        # the universe (deduped distinct tags) was handed to the model
+        user_msg = stub.calls[0][1][0]["content"]
+        assert "identity" in user_msg and "governance" in user_msg
+
+
+def test_no_api_key_returns_empty(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+        _seed_tags("ohm", "OHM", ["identity"])
+
+        # No key bound (test env has no ANTHROPIC_API_KEY) → provider None.
+        # (Explicitly assert the seam returns None given the test config.)
+        from app import tag_suggest
+        assert tag_suggest.haiku_provider(app.state.config) is None
+
+        r = client.post("/api/rfcs/suggest-tags", json={"title": "X", "pitch": "y"})
+        assert r.status_code == 200, r.text
+        assert r.json()["suggestions"] == []
+
+
+def test_empty_corpus_returns_empty_without_calling_model(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+
+        stub = StubProvider(reply=json.dumps([{"tag": "x", "confidence": 1}]))
+        _use_provider(monkeypatch, stub)
+
+        # No cached_rfcs rows → empty universe → suggest() short-circuits.
+        r = client.post("/api/rfcs/suggest-tags", json={"title": "X", "pitch": "y"})
+        assert r.status_code == 200, r.text
+        assert r.json()["suggestions"] == []
+        assert stub.calls == []  # model never invoked on an empty universe
+
+
+def test_rate_limit_surfaces_429(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    monkeypatch.setenv("TAG_SUGGEST_RATE_MAX", "2")
+    monkeypatch.setenv("TAG_SUGGEST_RATE_WINDOW_SECONDS", "60")
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        provision_user_row(user_id=2, login="alice", role="contributor")
+        sign_in_as(client, user_id=2, gitea_login="alice", display_name="Alice", role="contributor")
+        _seed_tags("ohm", "OHM", ["identity"])
+        _use_provider(monkeypatch, StubProvider(reply="[]"))
+
+        body = {"title": "X", "pitch": "y"}
+        assert client.post("/api/rfcs/suggest-tags", json=body).status_code == 200
+        assert client.post("/api/rfcs/suggest-tags", json=body).status_code == 200
+        # Third call inside the window trips the limit.
+        assert client.post("/api/rfcs/suggest-tags", json=body).status_code == 429
+
+
+# ---------------------------------------------------------------------------
+# Units
+# ---------------------------------------------------------------------------
+
+
+def test_gather_tag_universe_dedupes_and_ranks(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import tag_suggest
+
+    app, _fake = app_with_fake_gitea
+    # The db is initialized in the app's lifespan; enter the client
+    # context so cached_rfcs exists before we seed it directly.
+    with TestClient(app):
+        _seed_tags("a", "A", ["identity", "schema"])
+        _seed_tags("b", "B", ["identity", " schema ", "consent", ""])  # whitespace + empty
+        _seed_tags("c", "C", ["identity"])
+
+        universe = tag_suggest.gather_tag_universe()
+        # identity (3) > schema (2) > consent (1); whitespace trimmed/merged,
+        # empties dropped.
+        assert universe == ["identity", "schema", "consent"]
+
+
+def test_parse_reply_tolerates_junk():
+    from app import tag_suggest
+
+    universe = ["identity", "schema", "consent"]
+
+    # Prose around the JSON, an invented tag, a bare string, a dup, a
+    # missing confidence, and a garbage confidence.
+    text = (
+        "Sure! Here are the tags:\n"
+        '[{"tag": "identity", "confidence": 0.9}, '
+        '{"tag": "invented", "confidence": 1}, '
+        '"schema", '
+        '{"tag": "identity", "confidence": 0.5}, '
+        '{"tag": "consent"}, '
+        '{"tag": "consent", "confidence": "high"}]\n'
+        "Hope that helps!"
+    )
+    out = tag_suggest.parse_reply(text, universe, max_suggestions=6)
+    tags = [s["tag"] for s in out]
+    assert tags == ["identity", "schema", "consent"]  # invented dropped, deduped
+    by_tag = {s["tag"]: s["confidence"] for s in out}
+    assert by_tag["identity"] == 0.9
+    assert by_tag["schema"] == 0.5      # bare string defaults to 0.5
+    assert by_tag["consent"] == 0.5     # missing/garbage confidence → 0.5
+
+
+def test_parse_reply_empty_on_unparseable():
+    from app import tag_suggest
+
+    assert tag_suggest.parse_reply("no json here", ["a"], 6) == []
+    assert tag_suggest.parse_reply("", ["a"], 6) == []
+    assert tag_suggest.parse_reply("[]", ["a"], 6) == []
+
+
+def test_parse_reply_respects_max():
+    from app import tag_suggest
+
+    universe = ["a", "b", "c", "d", "e"]
+    text = json.dumps([{"tag": t, "confidence": 0.5} for t in universe])
+    out = tag_suggest.parse_reply(text, universe, max_suggestions=3)
+    assert [s["tag"] for s in out] == ["a", "b", "c"]
+
+
+def test_suggest_short_circuits_empty_draft():
+    from app import tag_suggest
+
+    stub = StubProvider(reply=json.dumps([{"tag": "a", "confidence": 1}]))
+    draft = tag_suggest.Draft(title="  ", pitch="", use_case="")
+    assert tag_suggest.suggest(stub, draft, ["a"]) == []
+    assert stub.calls == []  # never called for an empty draft
+
+
+def test_suggest_returns_empty_on_provider_failure():
+    from app import tag_suggest
+
+    stub = StubProvider(raises=True)
+    draft = tag_suggest.Draft(title="Real title", pitch="a reason")
+    assert tag_suggest.suggest(stub, draft, ["identity"]) == []

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "rfc-app-frontend",
   "private": true,
-  "version": "0.21.0",
+  "version": "0.24.0",
   "type": "module",
   "scripts": {
     "dev": "vite",

frontend/src/App.jsx

@@ -2,6 +2,7 @@ import { useEffect, useRef, useState } from 'react'
 import { Routes, Route, Link, Navigate, useLocation, useNavigate } from 'react-router-dom'
 import { getMe, subscribeToNotifications } from './api'
 import { anonymize, EVENTS, identify, track } from './lib/analytics'
+import { useLastState } from './lib/useLastState'
 import Catalog from './components/Catalog.jsx'
 import Inbox from './components/Inbox.jsx'
 import RFCView from './components/RFCView.jsx'
@@ -42,6 +43,12 @@ export default function App() {
   // "Privacy & cookies" tab dispatches a `rfc-app:cookie-consent-reopen`
   // event that bumps this.
   const [consentReopenTick, setConsentReopenTick] = useState(0)
+  // v0.23.0 / item #29 — flips true once the #21-Part-C identify effect
+  // has fired (or once we've confirmed there's no authenticated user to
+  // identify). useLastState gates its resume redirect on this so the
+  // redirect always happens AFTER identify, preserving identify-then-
+  // track ordering.
+  const [identifyReady, setIdentifyReady] = useState(false)
   const navigate = useNavigate()
   const location = useLocation()
   // v0.15.0 — Page Viewed event taxonomy. We fire on every
@@ -86,6 +93,9 @@ export default function App() {
       if (viewer?.first_sign_in_at) props.first_sign_in_at = ['__setOnce__', viewer.first_sign_in_at]
       if (viewer?.created_at) props.account_created_at = ['__setOnce__', viewer.created_at]
       identify({ user_id: String(uid), properties: props })
+      // v0.23.0 / item #29 — identify has now fired for this sign-in;
+      // release useLastState's resume redirect (it waits on this).
+      setIdentifyReady(true)
     } else if (uid == null && lastUserIdRef.current != null) {
       // Sign-out edge — App-level reset is handled separately by the
       // sign-out gesture that fires User Signed Out. Clear our local
@@ -94,6 +104,14 @@ export default function App() {
     }
   }, [me?.authenticated, me?.user?.id, me?.user?.role, me?.user?.permission_state, me?.user?.passcode_set, me?.user?.device_trusted])
 
+  // v0.23.0 / item #29 — once `me` has resolved, if there's no
+  // authenticated user there is nothing to identify, so release the
+  // resume gate immediately (anonymous boots have no resume to do, but
+  // the hook still needs the gate resolved to be a clean no-op).
+  useEffect(() => {
+    if (me != null && !me.authenticated) setIdentifyReady(true)
+  }, [me])
+
   useEffect(() => {
     const handler = () => setConsentReopenTick(t => t + 1)
     window.addEventListener('rfc-app:cookie-consent-reopen', handler)
@@ -107,6 +125,18 @@ export default function App() {
       .finally(() => setLoading(false))
   }, [])
 
+  // v0.23.0 / item #29 — server-side sign-in state resume. The hook
+  // debounce-posts the current route for authenticated users and, once
+  // identify has fired, redirects a fresh sign-in (which hard-lands on
+  // "/") to the user's stored last route. Anonymous users: no-op.
+  useLastState({
+    authenticated: !!me?.authenticated,
+    pathname: location.pathname,
+    identifyReady,
+    lastRoute: me?.authenticated ? me.user?.last_route : null,
+    navigate,
+  })
+
   // §15.3 — subscribe to the live SSE stream for authenticated viewers
   // so the badge counter and the toast surface stay in lockstep with
   // the inbox. Tabs that miss an event because they were closed pick

frontend/src/api.js

@@ -25,6 +25,25 @@ export async function getMe() {
   return jsonOrThrow(res)
 }
 
+// ── v0.23.0: sign-in state resume (§6.2, roadmap item #29) ───────────────
+//
+// The route-change hook (useLastState) debounce-posts the user's current
+// route + a small bag of *light* view state here for authenticated users.
+// The next sign-in reads `last_route` off `/api/auth/me` and redirects.
+// Privacy: `state` carries ephemeral view state ONLY — never draft-buffer
+// contents (see SPEC §6.2). Best-effort: callers ignore failures (an
+// offline/401 POST must never disrupt navigation).
+export async function putLastState(route, state) {
+  const body = { route }
+  if (state != null) body.state = state
+  const res = await fetch('/api/me/last-state', {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(body),
+  })
+  return jsonOrThrow(res)
+}
+
 // ── v0.7.0: email + one-time-code sign-in (§6.2) ─────────────────────────
 //
 // The legacy /auth/login → /auth/callback OAuth flow remains during the
@@ -166,15 +185,47 @@ export async function getProposal(prNumber) {
   return jsonOrThrow(await fetch(`/api/proposals/${prNumber}`))
 }
 
-export async function proposeRFC({ title, slug, pitch, tags }) {
+export async function proposeRFC({ title, slug, pitch, tags, proposedUseCase }) {
   const res = await fetch('/api/rfcs/propose', {
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({ title, slug, pitch, tags: tags || [] }),
+    // #26: proposed_use_case is optional; send null when blank so the
+    // backend treats it as "left blank".
+    body: JSON.stringify({
+      title,
+      slug,
+      pitch,
+      tags: tags || [],
+      proposed_use_case: proposedUseCase || null,
+    }),
   })
   return jsonOrThrow(res)
 }
 
+// Roadmap #27: Claude Haiku tag suggestions for the propose-RFC modal.
+// Returns a (possibly empty) array of { tag, confidence }. Deliberately
+// forgiving — any non-OK response (rate limit, transient error, no key
+// configured server-side) resolves to [] so the modal just shows nothing
+// rather than surfacing an error for what is a best-effort assist.
+export async function suggestTags({ title, pitch, useCase }) {
+  try {
+    const res = await fetch('/api/rfcs/suggest-tags', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        title: title || '',
+        pitch: pitch || '',
+        use_case: useCase || '',
+      }),
+    })
+    if (!res.ok) return []
+    const data = await res.json()
+    return Array.isArray(data.suggestions) ? data.suggestions : []
+  } catch {
+    return []
+  }
+}
+
 export async function mergeProposal(prNumber) {
   const res = await fetch(`/api/proposals/${prNumber}/merge`, { method: 'POST' })
   return jsonOrThrow(res)
@@ -492,13 +543,14 @@ export async function draftPRText(slug, branch) {
   return jsonOrThrow(res)
 }
 
-export async function openPR(slug, branch, { title, description }) {
+export async function openPR(slug, branch, { title, description, proposedUseCase }) {
   const res = await fetch(
     `/api/rfcs/${slug}/branches/${encodeURIComponent(branch)}/open-pr`,
     {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({ title, description }),
+      // #26: proposed_use_case is optional; null when blank.
+      body: JSON.stringify({ title, description, proposed_use_case: proposedUseCase || null }),
     },
   )
   return jsonOrThrow(res)

frontend/src/components/PRModal.jsx

@@ -15,6 +15,8 @@ import { EVENTS, track } from '../lib/analytics'
 export default function PRModal({ slug, branch, branchIsPrivate, onClose, onOpened }) {
   const [title, setTitle] = useState('')
   const [description, setDescription] = useState('')
+  // #26: optional ground-truth use case for this change.
+  const [useCase, setUseCase] = useState('')
   const [drafting, setDrafting] = useState(true)
   const [submitting, setSubmitting] = useState(false)
   const [confirmed, setConfirmed] = useState(!branchIsPrivate)
@@ -39,7 +41,11 @@ export default function PRModal({ slug, branch, branchIsPrivate, onClose, onOpen
     setSubmitting(true)
     setError(null)
     try {
-      const { pr_number } = await openPR(slug, branch, { title: title.trim(), description: description.trim() })
+      const { pr_number } = await openPR(slug, branch, {
+        title: title.trim(),
+        description: description.trim(),
+        proposedUseCase: useCase.trim() || null,
+      })
       // v0.15.0 — analytics: fire on §10.2 PR-open success. slug
       // and pr_number are the join keys; title/description stay out.
       track(EVENTS.PR_OPENED, { rfc_slug: slug, pr_number })
@@ -104,6 +110,20 @@ export default function PRModal({ slug, branch, branchIsPrivate, onClose, onOpen
             what was argued, what shifted, what the arbiters are asked
             to consider.
           </p>
+          <label className="modal-label">What will you be using this change for? (optional)</label>
+          <textarea
+            className="modal-textarea"
+            value={useCase}
+            onChange={e => setUseCase(e.target.value)}
+            placeholder="The concrete thing this change unlocks for you. Optional."
+            disabled={drafting || submitting}
+            rows={3}
+            maxLength={8000}
+          />
+          <p className="field-help">
+            #26: the concrete ground-truth use case — distinct from "why
+            it's needed" above. Leave blank if you'd rather not say.
+          </p>
           {error && <p className="field-error">{error}</p>}
         </div>
         <div className="modal-actions">

frontend/src/components/PRView.jsx

@@ -220,6 +220,17 @@ export default function PRView({ viewer }) {
               {pr.description && (
                 <p className="pr-description">{pr.description}</p>
               )}
+              {/* #26: the optional ground-truth use case for this change,
+                  captured when the PR was opened. Muted "left blank"
+                  treatment when none was supplied. */}
+              <div className="pr-use-case" style={{ margin: '6px 0', fontSize: 13 }}>
+                <span style={{ fontWeight: 700, color: '#888', textTransform: 'uppercase', letterSpacing: '0.05em', fontSize: 11 }}>
+                  Intended use case:
+                </span>{' '}
+                {pr.proposed_use_case
+                  ? <span style={{ whiteSpace: 'pre-wrap' }}>{pr.proposed_use_case}</span>
+                  : <span style={{ color: '#999', fontStyle: 'italic' }}>left blank</span>}
+              </div>
               {pr.capabilities?.can_edit_text && (
                 <button className="btn-link" onClick={startHeaderEdit}>Edit title & description</button>
               )}

frontend/src/components/ProposalView.jsx

@@ -163,6 +163,14 @@ export default function ProposalView({ viewer, onChange }) {
         className="entry-body"
         dangerouslySetInnerHTML={{ __html: marked.parse(data.entry?.body || '') }}
       />
+
+      {/* #26: the optional ground-truth use case the proposer supplied. */}
+      <h3 style={{ fontSize: 13, fontWeight: 700, color: '#888', textTransform: 'uppercase', letterSpacing: '0.05em', marginTop: 24 }}>
+        Intended use case
+      </h3>
+      {data.proposed_use_case
+        ? <div className="entry-body" dangerouslySetInnerHTML={{ __html: marked.parse(data.proposed_use_case) }} />
+        : <p style={{ color: '#999', fontStyle: 'italic' }}>Left blank by the proposer.</p>}
     </article>
   )
 }

frontend/src/components/ProposeModal.jsx

@@ -2,17 +2,24 @@
 //
 // Title (required) and pitch (required textarea), with a slug field
 // that auto-fills from the title via the same deterministic kebab-case
-// the backend uses. Tags are chip-input (free-form for slice 1; the
-// AI-suggested chips of §9.1 are deferred to Slice 2 when the AI surface
-// is wired up).
+// the backend uses. Tags are chip-input (free-form), with the §9.1
+// Slice 2 AI-suggested chips (roadmap #27) wired in: as the draft fills
+// in, the backend asks Claude Haiku for tags drawn from the corpus's
+// existing tag set, surfaced as clickable suggestion chips. The assist
+// is best-effort — it stays silent when unavailable.
 //
 // The submit button drives the §17 POST /api/rfcs/propose endpoint;
 // success navigates the proposer to the pending-idea view per §9.3.
 
-import { useEffect, useState } from 'react'
-import { proposeRFC } from '../api'
+import { useEffect, useRef, useState } from 'react'
+import { proposeRFC, suggestTags } from '../api'
 import { EVENTS, track } from '../lib/analytics'
 
+// How long the draft must sit unchanged before we ask for suggestions —
+// long enough to fire on typing pauses / field-blur, not on every
+// keystroke (the backend is also per-user rate-limited as a backstop).
+const SUGGEST_DEBOUNCE_MS = 700
+
 function slugify(title) {
   return title
     .toLowerCase()
@@ -26,21 +33,56 @@ export default function ProposeModal({ viewer, onClose, onSubmitted }) {
   const [slug, setSlug] = useState('')
   const [slugEdited, setSlugEdited] = useState(false)
   const [pitch, setPitch] = useState('')
+  // #26: optional ground-truth use case, sibling to the required pitch.
+  const [useCase, setUseCase] = useState('')
   const [tagInput, setTagInput] = useState('')
   const [tags, setTags] = useState([])
   const [submitting, setSubmitting] = useState(false)
   const [error, setError] = useState(null)
+  // #27: Claude Haiku tag suggestions. `suggestions` is the latest
+  // ranked list from the backend ({ tag, confidence }); we render the
+  // subset not already chosen. `suggestedOnce` gates the disclosure +
+  // row so they only appear after the assist has actually run.
+  const [suggestions, setSuggestions] = useState([])
+  const [suggestedOnce, setSuggestedOnce] = useState(false)
 
   useEffect(() => {
     if (!slugEdited) setSlug(slugify(title))
   }, [title, slugEdited])
 
+  // #27: debounced tag-suggestion fetch. Fires after the draft sits
+  // unchanged for SUGGEST_DEBOUNCE_MS, only once there's something to go
+  // on (a title). A stale-response guard keeps an earlier in-flight
+  // request from clobbering a newer one.
+  const suggestSeq = useRef(0)
+  useEffect(() => {
+    if (!title.trim()) {
+      setSuggestions([])
+      return
+    }
+    const handle = setTimeout(async () => {
+      const seq = ++suggestSeq.current
+      const result = await suggestTags({ title, pitch, useCase })
+      if (seq !== suggestSeq.current) return // a newer request superseded us
+      setSuggestions(Array.isArray(result) ? result : [])
+      if (result && result.length) setSuggestedOnce(true)
+    }, SUGGEST_DEBOUNCE_MS)
+    return () => clearTimeout(handle)
+  }, [title, pitch, useCase])
+
+  // Suggestions the user hasn't already added.
+  const freshSuggestions = suggestions.filter(s => !tags.includes(s.tag))
+
   function addTag() {
     const t = tagInput.trim()
     if (t && !tags.includes(t)) setTags([...tags, t])
     setTagInput('')
   }
 
+  function addSuggested(tag) {
+    if (!tags.includes(tag)) setTags([...tags, tag])
+  }
+
   async function handleSubmit(e) {
     e.preventDefault()
     if (!title.trim() || !slug || !pitch.trim()) return
@@ -52,6 +94,7 @@ export default function ProposeModal({ viewer, onClose, onSubmitted }) {
         slug,
         pitch: pitch.trim(),
         tags,
+        proposedUseCase: useCase.trim() || null,
       })
       // v0.15.0 — analytics: fire on the §9.1 propose-RFC submit.
       // Slug is a stable, low-cardinality identifier (kebab-case
@@ -105,6 +148,19 @@ export default function ProposeModal({ viewer, onClose, onSubmitted }) {
               required
             />
 
+            <label htmlFor="propose-use-case">What will you be using this RFC for? (optional)</label>
+            <textarea
+              id="propose-use-case"
+              value={useCase}
+              onChange={e => setUseCase(e.target.value)}
+              placeholder="The concrete thing you intend to build or do with this RFC. Optional, but it helps ground the work."
+              rows={3}
+            />
+            <p className="field-help">
+              The concrete ground-truth use case — distinct from "why it's
+              needed" above. Leave blank if you'd rather not say.
+            </p>
+
             <label htmlFor="propose-tag">Tags (optional)</label>
             <div style={{ display: 'flex', gap: 6, alignItems: 'center', marginBottom: 4 }}>
               <input
@@ -136,6 +192,45 @@ export default function ProposeModal({ viewer, onClose, onSubmitted }) {
               </div>
             )}
 
+            {/* #27: Claude Haiku suggested tags. Clickable chips that add
+                to the tag list; nothing auto-applies. The disclosure is
+                required — the draft text is sent to Anthropic to generate
+                these — so it renders whenever the suggestion row does. */}
+            {(freshSuggestions.length > 0 || (suggestedOnce && suggestions.length > 0)) && (
+              <div style={{ marginTop: 4, marginBottom: 14 }}>
+                {freshSuggestions.length > 0 && (
+                  <>
+                    <p className="field-help" style={{ marginTop: 0, marginBottom: 4 }}>
+                      Suggested tags — click to add:
+                    </p>
+                    <div>
+                      {freshSuggestions.map(s => (
+                        <button
+                          key={s.tag}
+                          type="button"
+                          className="entry-tag"
+                          onClick={() => addSuggested(s.tag)}
+                          title={`Add "${s.tag}"`}
+                          style={{
+                            display: 'inline-block',
+                            marginRight: 4,
+                            marginBottom: 4,
+                            border: '1px dashed var(--color-border, #ccc)',
+                            background: 'none',
+                            cursor: 'pointer',
+                          }}
+                        >+ {s.tag}</button>
+                      ))}
+                    </div>
+                  </>
+                )}
+                <p className="field-help" style={{ marginTop: 4, marginBottom: 0, fontStyle: 'italic' }}>
+                  Suggestions are generated by Claude (Anthropic). The text you've
+                  entered above is sent to Anthropic to produce them.
+                </p>
+              </div>
+            )}
+
             {viewer && (
               <p className="field-help" style={{ marginTop: 14, marginBottom: 0 }}>
                 Owner: <strong>{viewer.display_name || viewer.gitea_login}</strong> — you'll be the first owner of this super-draft. Additional owners can claim later (§13.1).

frontend/src/components/RFCView.jsx

@@ -669,6 +669,19 @@ export default function RFCView({ viewer }) {
                 : 'main is read-only — PRs are the only path to change it. Open a branch to propose edits.'}
             </div>
           )}
+          {/* #26: the optional ground-truth use case captured at propose
+              time. Shown on the canonical (main) view; muted "left blank"
+              treatment when the proposer didn't supply one. */}
+          {branchParam === 'main' && (
+            <div className="rfc-use-case" style={{ margin: '8px 0 16px', padding: '10px 14px', borderLeft: '3px solid #e0e0e0', background: '#fafafa' }}>
+              <div style={{ fontSize: 11, fontWeight: 700, color: '#888', textTransform: 'uppercase', letterSpacing: '0.05em', marginBottom: 4 }}>
+                Intended use case
+              </div>
+              {entry.proposed_use_case
+                ? <div style={{ whiteSpace: 'pre-wrap' }}>{entry.proposed_use_case}</div>
+                : <span style={{ color: '#999', fontStyle: 'italic' }}>Left blank by the proposer.</span>}
+            </div>
+          )}
           {inDiscuss && branchParam !== 'main' && (
             <div className="discuss-mode-banner">
               Discuss mode on <strong>{branchParam}</strong> — chat freely;

frontend/src/lib/useLastState.js

@@ -0,0 +1,91 @@
+// useLastState — v0.23.0 / roadmap item #29: server-side sign-in state
+// resume. Two responsibilities, kept in one small hook so App.jsx's
+// surface stays minimal:
+//
+//   1. Debounce-post the authenticated user's current route to
+//      `PUT /api/me/last-state` on every route change (~1s debounce so
+//      a fast click-through doesn't spray the endpoint). Anonymous
+//      users: no-op. Best-effort: a failed POST never disrupts nav.
+//
+//   2. On the first authenticated load, read the stored `last_route`
+//      (handed back on `/api/auth/me`) and `navigate()` to it ONCE.
+//      Stale routes (a withdrawn RFC, a slug the user lost rights to)
+//      are not special-cased here: navigating lands on whatever that
+//      route renders today, and the existing routing already falls
+//      through to the catalog/empty-state for a missing RFC. Keeping
+//      this dumb is deliberate (see SPEC §6.2 + the #29 scope note).
+//
+// Ordering with #21 Part C (Amplitude identify): App.jsx fires
+// `identify` in its own effect when `me.user.id` first appears. This
+// hook's resume redirect is gated on `identifyReady` — App.jsx flips it
+// true only after the identify effect has run — so the redirect always
+// happens AFTER identify, preserving the identify-then-track ordering
+// the roadmap calls out.
+import { useEffect, useRef } from 'react'
+import { putLastState } from '../api'
+
+// ~1s debounce on the route-change POST. A frontend constant, not a
+// server knob — the backend takes whatever lands.
+const DEBOUNCE_MS = 1000
+
+// Routes we never want to resume *to* — auth/landing surfaces that
+// would be nonsensical or hostile to drop a returning user onto. We
+// still record them (cheap, and the user may legitimately be sitting on
+// /docs), but the resume redirect skips them and falls through to the
+// default landing. Anything not listed resumes normally.
+const NON_RESUMABLE_PREFIXES = ['/login', '/welcome', '/invites/', '/invitations/']
+
+function isResumable(route) {
+  if (!route || typeof route !== 'string') return false
+  if (route === '/') return false // "/" is already the default landing
+  return !NON_RESUMABLE_PREFIXES.some(p => route.startsWith(p))
+}
+
+/**
+ * @param {object}   opts
+ * @param {boolean}  opts.authenticated  whether a viewer is signed in
+ * @param {string}   opts.pathname       current location.pathname
+ * @param {boolean}  opts.identifyReady   App flips true after identify fires
+ * @param {string|null} opts.lastRoute    stored route from /api/auth/me
+ * @param {function} opts.navigate        react-router navigate()
+ */
+export function useLastState({ authenticated, pathname, identifyReady, lastRoute, navigate }) {
+  // ── 1. Debounced route-change POST ────────────────────────────────
+  const timerRef = useRef(null)
+  useEffect(() => {
+    if (!authenticated) return undefined
+    if (timerRef.current) clearTimeout(timerRef.current)
+    timerRef.current = setTimeout(() => {
+      // Best-effort — swallow failures so an offline/401 POST never
+      // surfaces as a navigation error.
+      putLastState(pathname).catch(() => {})
+    }, DEBOUNCE_MS)
+    return () => {
+      if (timerRef.current) clearTimeout(timerRef.current)
+    }
+  }, [authenticated, pathname])
+
+  // ── 2. One-time resume redirect ───────────────────────────────────
+  // Fires once, after identify is ready, when there's a resumable
+  // stored route AND the user is currently sitting on the default
+  // landing ("/"). We only redirect from "/" so we never yank a user
+  // who deep-linked somewhere specific (or refreshed mid-RFC) back to
+  // their last route.
+  const resumedRef = useRef(false)
+  useEffect(() => {
+    if (resumedRef.current) return
+    if (!authenticated || !identifyReady) return
+    // Only resume when the app booted on the default landing — a hard
+    // sign-in nav lands on "/", which is exactly the case we want.
+    if (pathname !== '/') {
+      resumedRef.current = true // user deep-linked; don't resume later either
+      return
+    }
+    if (isResumable(lastRoute)) {
+      resumedRef.current = true
+      navigate(lastRoute, { replace: true })
+    } else {
+      resumedRef.current = true // nothing to resume to; keep default landing
+    }
+  }, [authenticated, identifyReady, lastRoute, pathname, navigate])
+}