Slice 2: the §8 active-RFC view in full

Per the §19.1 brief: the three-column shape (§8.1) opens on main
in discuss mode (§8.2), supports the §8.3 discuss-vs-contribute
flip on non-main branches, hosts §8.4's per-branch chat with AI
participation (§18's <change> protocol → §8.14 changes rows), the
§8.8 change-card panel with §8.9 accept/decline/edit-before-accept,
the §8.10 tracked-change markup + DiffView toggle, the §8.11
manual-edit flushes with the stale-change mechanic, the §8.12
range and paragraph sub-threads, the §8.13 flag affordance, and
the §8.14 discuss-mode buffer.

Backend: bot.py grew per-RFC-repo write ops (cut_branch_from_main,
commit_accepted_change with the structured original/proposed/reason
body and Change-Id + Source-Message-Id + On-behalf-of trailers,
commit_manual_flush, ensure_rfc_repo_seed). cache.py grew
refresh_rfc_repo and the webhook dispatches on repository.full_name.
providers.py and chat.py port the §18 carryovers — multi-provider
LLM abstraction and SSE-streaming chat against the §5 threads /
thread_messages / changes schema. api_branches.py mounts the §17
branches/<branch>/* and threads/<thread_id>/* routes with the §6
/ §11 permission checks inline.

Frontend: RFCView.jsx rebuilt as the §8 surface; Editor.jsx,
ChatPanel.jsx, ChangePanel.jsx, PromptBar.jsx, SelectionTooltip.jsx,
DiffView.jsx, ModelPicker.jsx, modelStyles.js lifted from the
prototype and adapted to the canonical schema.

Covered by `backend/tests/test_rfc_view_vertical.py` — eleven new
integration tests against an extended FakeGitea (PUT contents,
POST orgs/{org}/repos, seed_rfc_repo): main-view read,
promote-to-branch, accept (with and without edit-before-accept),
decline, manual flush + system message, flag creation, visibility
flip, anonymous read-but-no-contribute, stale-change refusal, and
the chat-streaming path with a fake provider injected. The 5
Slice 1 tests continue to pass alongside.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api.py

@@ -17,10 +17,11 @@ from typing import Any
 from fastapi import APIRouter, HTTPException, Request
 from pydantic import BaseModel, Field
 
-from . import auth, db, entry as entry_mod, cache
+from . import api_branches, auth, db, entry as entry_mod, cache
 from .bot import Bot
 from .config import Config
 from .gitea import Gitea, GiteaError
+from .providers import BaseProvider
 
 
 class ProposeBody(BaseModel):
@@ -34,8 +35,22 @@ class DeclineBody(BaseModel):
     comment: str = Field(min_length=1, max_length=4000)
 
 
-def make_router(config: Config, gitea: Gitea, bot: Bot) -> APIRouter:
+def make_router(
+    config: Config,
+    gitea: Gitea,
+    bot: Bot,
+    providers: dict[str, BaseProvider] | None = None,
+) -> APIRouter:
+    # Use `is None` rather than `providers or {}` — an empty dict is
+    # falsy, and the test harness mutates the dict the closure holds to
+    # inject a fake provider; substituting a fresh `{}` here would
+    # silently drop those mutations.
+    if providers is None:
+        providers = {}
     router = APIRouter()
+    # Slice 2: the §8 active-RFC view's endpoints live in api_branches.
+    # Mounting them on the same router keeps the §17 layout flat.
+    router.include_router(api_branches.make_router(config, gitea, bot, providers))
 
     # ---------------------------------------------------------------
     # Auth surface — extends the prototype's pattern but reads role