feat(webui): versioned project registry API (Closes #635)

Evolve the MVP project registry (#427) into a versioned, fail-closed
project registry API for the console (Phase 1, read-only).

- Add schema version 2 with project `status`, per-step onboarding
  `state`/`required`, optional redacted `last_seen_health`, and
  `remote_name`. Version 1 files stay loadable and are normalized with
  explicit defaults.
- Serve `/api/v1/projects` and `/api/v1/projects/{project_id}` with API
  provenance (`api_version`, `schema_version`, `source`). `/api/projects`
  is retained as an unversioned Phase 1 alias.
- Replace bare `ValueError` with `RegistryError`, carrying an operator
  `remediation` and `field_path`; invalid registries fail closed as a
  500 JSON payload or a dedicated HTML error page instead of a traceback.
- Reject credential-shaped keys before any DTO is built, reusing
  `registry_safety.is_forbidden_key` as the single source of truth
  shared with the worker registry (#798).
- Render HTML views from `project_to_dict`, so the console and the JSON
  API cannot disagree about status or onboarding progress.
- Document the contract in docs/webui-project-registry-api.md.

Tests: registry load/validate (valid, missing project, schema
validation, credential rejection) and API route coverage.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

webui/app.py

@@ -11,8 +11,20 @@ from starlette.routing import Route
 
 from webui.deployment_boundary import deployment_snapshot
 from webui.layout import render_page
-from webui.project_registry import find_project, load_registry, registry_to_dict
-from webui.project_views import render_project_detail, render_projects_list
+from webui.project_registry import (
+    ProjectRegistry,
+    RegistryError,
+    find_project,
+    known_project_ids,
+    load_registry,
+    project_detail_to_dict,
+    registry_to_dict,
+)
+from webui.project_views import (
+    render_project_detail,
+    render_projects_list,
+    render_registry_error,
+)
 from webui.prompt_library import find_prompt, library_to_dict
 from webui.prompt_views import render_prompt_detail, render_prompts_page
 from final_report_validator import FINAL_REPORT_TASK_KINDS
@@ -81,14 +93,26 @@ async def api_queue(_request: Request) -> JSONResponse:
     return JSONResponse(queue_snapshot_to_dict(load_queue_snapshot()))
 
 
+def _load_project_registry() -> tuple[ProjectRegistry | None, RegistryError | None]:
+    """Load the registry, converting validation failure into a fail-closed pair."""
+    try:
+        return load_registry(), None
+    except RegistryError as exc:
+        return None, exc
+
+
 async def projects(_request: Request) -> HTMLResponse:
-    registry = load_registry()
+    registry, error = _load_project_registry()
+    if error is not None:
+        return HTMLResponse(render_registry_error(error), status_code=500)
     return HTMLResponse(render_projects_list(registry))
 
 
 async def project_detail(request: Request) -> HTMLResponse:
     project_id = request.path_params["project_id"]
-    registry = load_registry()
+    registry, error = _load_project_registry()
+    if error is not None:
+        return HTMLResponse(render_registry_error(error), status_code=500)
     project = find_project(registry, project_id)
     if project is None:
         return HTMLResponse(
@@ -106,10 +130,47 @@ async def project_detail(request: Request) -> HTMLResponse:
 
 
 async def api_projects(_request: Request) -> JSONResponse:
-    registry = load_registry()
+    """Unversioned MVP alias, retained through Phase 1 (#632 section 6)."""
+    registry, error = _load_project_registry()
+    if error is not None:
+        return JSONResponse(error.to_dict(), status_code=500)
     return JSONResponse(registry_to_dict(registry))
 
 
+async def api_v1_projects(_request: Request) -> JSONResponse:
+    registry, error = _load_project_registry()
+    if error is not None:
+        return JSONResponse(error.to_dict(), status_code=500)
+    return JSONResponse(registry_to_dict(registry))
+
+
+async def api_v1_project_detail(request: Request) -> JSONResponse:
+    project_id = request.path_params["project_id"]
+    registry, error = _load_project_registry()
+    if error is not None:
+        return JSONResponse(error.to_dict(), status_code=500)
+    project = find_project(registry, project_id)
+    if project is None:
+        return JSONResponse(
+            {
+                "error": "project_not_found",
+                "project_id": project_id,
+                "known_project_ids": known_project_ids(registry),
+                "remediation": (
+                    "Request one of the known project ids, or add the project to the "
+                    "registry file named in 'source'."
+                ),
+                "source": {
+                    "kind": "file",
+                    "path": str(registry.source_path),
+                    "inventory_complete": True,
+                },
+            },
+            status_code=404,
+        )
+    return JSONResponse(project_detail_to_dict(registry, project))
+
+
 async def prompts(_request: Request) -> HTMLResponse:
     return HTMLResponse(render_prompts_page())
 
@@ -268,6 +329,12 @@ def create_app(*, bind_host: str | None = None) -> Starlette:
             Route("/projects", projects, methods=["GET"]),
             Route("/projects/{project_id}", project_detail, methods=["GET"]),
             Route("/api/projects", api_projects, methods=["GET"]),
+            Route("/api/v1/projects", api_v1_projects, methods=["GET"]),
+            Route(
+                "/api/v1/projects/{project_id}",
+                api_v1_project_detail,
+                methods=["GET"],
+            ),
             Route("/prompts", prompts, methods=["GET"]),
             Route("/prompts/{prompt_id}", prompt_detail, methods=["GET"]),
             Route("/api/prompts", api_prompts, methods=["GET"]),