feat: Migrate to Pydantic's @field_validator and implement lifespan handler in FastAPI

changelog.md

@@ -2,6 +2,7 @@
 
 ## 2025-11-13
 
+- Cleared FastAPI and Pydantic deprecation warnings by migrating `scripts/init_db.py` to `@field_validator`, replacing the `main.py` startup hook with a lifespan handler, auditing template response call signatures, confirming HTTP 422 constant usage, and re-running the full pytest suite to ensure a clean warning slate.
 - Delivered the initial capex planner end-to-end: added scaffolded UI in `templates/scenarios/capex.html`, wired GET/POST handlers through `routes/calculations.py`, implemented calculation logic plus snapshot persistence in `services/calculations.py` and `models/capex_snapshot.py`, updated navigation links, and introduced unit tests in `tests/services/test_calculations_capex.py`.
 - Updated UI navigation to surface the processing opex planner by adding the sidebar link in `templates/partials/sidebar_nav.html`, wiring a scenario detail action in `templates/scenarios/detail.html`.
 - Completed manual validation of the Initial Capex Planner UI flows (sidebar entry, scenario deep link, validation errors, successful calculation) with results captured in `manual_tests/initial_capex.md`, documented snapshot verification steps, and noted the optional JSON client check for future follow-up.

main.py

@@ -1,4 +1,5 @@
 import logging
+from contextlib import asynccontextmanager
 from typing import Awaitable, Callable
 
 from fastapi import FastAPI, Request, Response
@@ -22,42 +23,14 @@ from monitoring import router as monitoring_router
 from services.bootstrap import bootstrap_admin, bootstrap_pricing_settings
 from scripts.init_db import init_db as init_db_script
 
-app = FastAPI()
-
-app.add_middleware(AuthSessionMiddleware)
-app.add_middleware(MetricsMiddleware)
-
 logger = logging.getLogger(__name__)
 
 
-@app.middleware("http")
-async def json_validation(
-    request: Request, call_next: Callable[[Request], Awaitable[Response]]
-) -> Response:
-    return await validate_json(request, call_next)
-
-
-@app.get("/health", summary="Container health probe")
-async def health() -> dict[str, str]:
-    return {"status": "ok"}
-
-
-@app.get("/favicon.ico", include_in_schema=False)
-async def favicon() -> Response:
-    static_directory = "static"
-    favicon_img = "favicon.ico"
-    return FileResponse(f"{static_directory}/{favicon_img}")
-
-
-@app.on_event("startup")
-# TODO: use lifespan events for startup/shutdown tasks
-async def ensure_admin_bootstrap() -> None:
+async def _bootstrap_startup() -> None:
     settings = get_settings()
     admin_settings = settings.admin_bootstrap_settings()
     pricing_metadata = settings.pricing_metadata()
     try:
-        # Ensure DB schema/types/seeds required for bootstrapping exist.
-        # The initializer is idempotent and safe to run on every startup.
         try:
             init_db_script()
         except Exception:
@@ -74,9 +47,6 @@ async def ensure_admin_bootstrap() -> None:
             admin_result.password_rotated,
             admin_result.roles_granted,
         )
-        # Avoid accessing ORM-managed attributes that may be detached outside
-        # of the UnitOfWork/session scope. Attempt a safe extraction and
-        # fall back to minimal logging if attributes are unavailable.
         try:
             seed = pricing_result.seed
             slug = getattr(seed.settings, "slug", None) if seed and getattr(
@@ -102,6 +72,37 @@ async def ensure_admin_bootstrap() -> None:
             "Failed to bootstrap administrator or pricing settings")
 
 
+@asynccontextmanager
+async def app_lifespan(_: FastAPI):
+    await _bootstrap_startup()
+    yield
+
+
+app = FastAPI(lifespan=app_lifespan)
+
+app.add_middleware(AuthSessionMiddleware)
+app.add_middleware(MetricsMiddleware)
+
+
+@app.middleware("http")
+async def json_validation(
+    request: Request, call_next: Callable[[Request], Awaitable[Response]]
+) -> Response:
+    return await validate_json(request, call_next)
+
+
+@app.get("/health", summary="Container health probe")
+async def health() -> dict[str, str]:
+    return {"status": "ok"}
+
+
+@app.get("/favicon.ico", include_in_schema=False)
+async def favicon() -> Response:
+    static_directory = "static"
+    favicon_img = "favicon.ico"
+    return FileResponse(f"{static_directory}/{favicon_img}")
+
+
 app.include_router(dashboard_router)
 app.include_router(calculations_router)
 app.include_router(auth_router)

scripts/init_db.py

@@ -22,7 +22,7 @@ import os
 import logging
 from decimal import Decimal
 
-from pydantic import BaseModel, Field, validator
+from pydantic import BaseModel, Field, field_validator
 from sqlalchemy import create_engine, text
 from sqlalchemy.engine import Engine
 from passlib.context import CryptContext
@@ -454,7 +454,7 @@ class UserSeed(BaseModel):
     is_active: bool = True
     is_superuser: bool = False
 
-    @validator("password")
+    @field_validator("password")
     def password_min_len(cls, v: str) -> str:
         if not v or len(v) < 8:
             raise ValueError("password must be at least 8 characters")