feat(slice-4): VERSION file + versioned /healthz — the flotilla verify contract (§8.1)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/main.py

@@ -11,6 +11,7 @@ from __future__ import annotations
 import logging
 import sys
 from contextlib import asynccontextmanager
+from pathlib import Path
 from typing import Any
 
 import psycopg
@@ -26,6 +27,15 @@ from app.platform.mailer import Mailer
 from app.platform import session as session_mod
 
 
+# The repo-root VERSION file is the single version source: the deploy pin checks out its
+# tag, and /healthz must report it back (flotilla-core's verify gate compares them).
+_REPO_ROOT = Path(__file__).resolve().parents[2]
+try:
+    _APP_VERSION = (_REPO_ROOT / "VERSION").read_text().strip()
+except OSError:
+    _APP_VERSION = "0.0.0"
+
+
 class RequestCodeBody(BaseModel):
     email: str
 
@@ -94,7 +104,7 @@ def create_app(database_url: str | None = None) -> FastAPI:
         finally:
             app.state.pool.close()
 
-    app = FastAPI(title="ecomm", version="0.3", lifespan=lifespan)
+    app = FastAPI(title="ecomm", version=_APP_VERSION, lifespan=lifespan)
 
     @app.get("/healthz")
     def healthz(response: Response, conn: psycopg.Connection = Depends(get_conn)):
@@ -108,7 +118,7 @@ def create_app(database_url: str | None = None) -> FastAPI:
         if pending:
             response.status_code = 503
             return {"status": "unavailable", "reason": "migrations_pending"}
-        return {"status": "ok"}
+        return {"status": "ok", "version": _APP_VERSION}
 
     @app.post("/api/auth/request-code")
     def request_code(