Harden JSON storage (atomic writes + crash-safe loads) + suggestions lightbulb

- storage.py: atomic save_json (temp+fsync+os.replace) and load_json that
  survives missing/corrupt files (moves corrupt aside). Closes #11/#12.
- route all data modules + app.py helpers through storage (closes #31 core);
  fixes mutable DEFAULT_FUNDS/DEFAULT_CARS return (#23).
- gunicorn --workers 1 --threads 4 to remove the write race (#13); strip
  Dockerfile template scaffolding (#40).
- base.html: 💡 suggestions link in the shared nav (shows on every page).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Dockerfile

@@ -24,16 +24,6 @@ RUN chmod +x /entrypoint.sh
 EXPOSE 8000
 ENTRYPOINT ["/entrypoint.sh"]
 
-# ---- ADJUST THIS LINE to the app's real entry point ----
-# Flask  (app object named `app` in app.py):
-CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "2", "app:app"]
-#
-# FastAPI (app object named `app` in main.py) — swap the CMD for:
-#   RUN pip install "uvicorn[standard]"
-#   CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]
-#
-# Django (project package `mysite`):
-#   CMD ["gunicorn", "--bind", "0.0.0.0:8000", "mysite.wsgi:application"]
-#
-# Streamlit:
-#   CMD ["streamlit", "run", "app.py", "--server.port=8000", "--server.address=0.0.0.0"]
+# Single worker + threads: the app stores state in JSON/SQLite files on the
+# volume, so multiple processes would race. Threads handle light concurrency.
+CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "1", "--threads", "4", "app:app"]

app.py

@@ -5,6 +5,7 @@ import pdfplumber
 import re
 from datetime import datetime, date
 import calendar as cal_module
+from storage import load_json, save_json
 from categories import CATEGORIES, CATEGORY_COLORS
 from bills import load_bills, save_bills, bills_for_month, calendar_grid, get_week_num
 from sinking import (load_funds, save_funds, FUND_COLORS, monthly_needed,
@@ -57,14 +58,10 @@ def money_filter(value):
 TAX_FILE = os.path.join(os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data")), "taxes.json")
 
 def load_taxes():
-    if os.path.exists(TAX_FILE):
-        with open(TAX_FILE) as f:
-            return json.load(f)
-    return {"rates": {"se_tax": 15.3, "federal": 22.0, "wi_state": 5.3}, "set_aside": []}
+    return load_json(TAX_FILE, {"rates": {"se_tax": 15.3, "federal": 22.0, "wi_state": 5.3}, "set_aside": []})
 
 def save_taxes(data):
-    with open(TAX_FILE, "w") as f:
-        json.dump(data, f, indent=2)
+    save_json(TAX_FILE, data)
 
 STANDARD_DEDUCTION_MFJ = 30000  # 2025 married filing jointly
 
@@ -177,27 +174,11 @@ NET_WORTH_FILE = os.path.join(DATA_DIR, "net_worth_accounts.json")
 
 
 def load_nw_accounts():
-    if os.path.exists(NET_WORTH_FILE):
-        with open(NET_WORTH_FILE) as f:
-            return json.load(f)
-    return []
+    return load_json(NET_WORTH_FILE, [])
 
 
 def save_nw_accounts(accounts):
-    with open(NET_WORTH_FILE, "w") as f:
-        json.dump(accounts, f, indent=2)
-
-
-def load_json(path, default):
-    if os.path.exists(path):
-        with open(path) as f:
-            return json.load(f)
-    return default
-
-
-def save_json(path, data):
-    with open(path, "w") as f:
-        json.dump(data, f, indent=2)
+    save_json(NET_WORTH_FILE, accounts)
 
 
 def get_transactions():

assets.py

@@ -1,5 +1,7 @@
+import copy
 import json
 import os
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 ASSETS_FILE = os.path.join(DATA_DIR, "assets.json")
@@ -44,20 +46,19 @@ ASSET_CATEGORIES = ["Investments", "Real Estate", "Equipment", "Other Valuables"
 
 
 def load_assets():
-    if os.path.exists(ASSETS_FILE):
-        with open(ASSETS_FILE) as f:
-            data = json.load(f)
+    data = load_json(ASSETS_FILE, None)
+    if data is None:
+        data = {"personal": copy.deepcopy(DEFAULT_CARS), "flips": [], "other_assets": []}
+        save_assets(data)
+        return data
     # migrate old format if needed
     if "other_assets" not in data:
         data["other_assets"] = []
     return data
-    save_assets({"personal": DEFAULT_CARS, "flips": [], "other_assets": []})
-    return {"personal": DEFAULT_CARS, "flips": [], "other_assets": []}
 
 
 def save_assets(data):
-    with open(ASSETS_FILE, "w") as f:
-        json.dump(data, f, indent=2)
+    save_json(ASSETS_FILE, data)
 
 
 def car_display_name(car):

bills.py

@@ -2,21 +2,18 @@ import json
 import os
 from datetime import date, timedelta
 import calendar
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 BILLS_FILE = os.path.join(DATA_DIR, "bills.json")
 
 
 def load_bills():
-    if os.path.exists(BILLS_FILE):
-        with open(BILLS_FILE) as f:
-            return json.load(f)
-    return []
+    return load_json(BILLS_FILE, [])
 
 
 def save_bills(bills):
-    with open(BILLS_FILE, "w") as f:
-        json.dump(bills, f, indent=2)
+    save_json(BILLS_FILE, bills)
 
 
 def get_week_label(day):

debts.py

@@ -2,6 +2,7 @@ import json
 import os
 from datetime import date
 import math
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 DEBTS_FILE = os.path.join(DATA_DIR, "debts.json")
@@ -116,27 +117,19 @@ OWNER_COLORS = {
 
 
 def load_debts():
-    if os.path.exists(DEBTS_FILE):
-        with open(DEBTS_FILE) as f:
-            return json.load(f)
-    return []
+    return load_json(DEBTS_FILE, [])
 
 
 def save_debts(debts):
-    with open(DEBTS_FILE, "w") as f:
-        json.dump(debts, f, indent=2)
+    save_json(DEBTS_FILE, debts)
 
 
 def load_debt_log():
-    if os.path.exists(DEBT_LOG_FILE):
-        with open(DEBT_LOG_FILE) as f:
-            return json.load(f)
-    return {}
+    return load_json(DEBT_LOG_FILE, {})
 
 
 def save_debt_log(log):
-    with open(DEBT_LOG_FILE, "w") as f:
-        json.dump(log, f, indent=2)
+    save_json(DEBT_LOG_FILE, log)
 
 
 def month_key(year, month):

income.py

@@ -1,6 +1,7 @@
 import json
 import os
 from datetime import date
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 INCOME_FILE = os.path.join(DATA_DIR, "income_log.json")
@@ -21,15 +22,11 @@ OWNER_COLORS = {
 
 
 def load_income_log():
-    if os.path.exists(INCOME_FILE):
-        with open(INCOME_FILE) as f:
-            return json.load(f)
-    return []
+    return load_json(INCOME_FILE, [])
 
 
 def save_income_log(log):
-    with open(INCOME_FILE, "w") as f:
-        json.dump(log, f, indent=2)
+    save_json(INCOME_FILE, log)
 
 
 def month_key(year, month):

mortgage.py

@@ -3,21 +3,18 @@ import os
 from datetime import date
 from dateutil.relativedelta import relativedelta
 import math
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 MORTGAGE_FILE = os.path.join(DATA_DIR, "mortgage.json")
 
 
 def load_mortgage():
-    if os.path.exists(MORTGAGE_FILE):
-        with open(MORTGAGE_FILE) as f:
-            return json.load(f)
-    return {}
+    return load_json(MORTGAGE_FILE, {})
 
 
 def save_mortgage(data):
-    with open(MORTGAGE_FILE, "w") as f:
-        json.dump(data, f, indent=2)
+    save_json(MORTGAGE_FILE, data)
 
 
 def monthly_payment(principal, annual_rate, term_years):

sinking.py

@@ -1,6 +1,8 @@
+import copy
 import json
 import os
 from datetime import date
+from storage import load_json, save_json
 
 DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
 SINKING_FILE = os.path.join(DATA_DIR, "sinking_funds.json")
@@ -25,17 +27,17 @@ DEFAULT_FUNDS = [
 
 
 def load_funds():
-    if os.path.exists(SINKING_FILE):
-        with open(SINKING_FILE) as f:
-            return json.load(f)
-    # First run — seed with defaults
-    save_funds(DEFAULT_FUNDS)
-    return DEFAULT_FUNDS
+    funds = load_json(SINKING_FILE, None)
+    if funds is None:
+        # First run — seed with a copy of the defaults (never hand out the
+        # module-level list, which callers mutate in place).
+        funds = copy.deepcopy(DEFAULT_FUNDS)
+        save_funds(funds)
+    return funds
 
 
 def save_funds(funds):
-    with open(SINKING_FILE, "w") as f:
-        json.dump(funds, f, indent=2)
+    save_json(SINKING_FILE, funds)
 
 
 def months_until(target_date_str):

storage.py

@@ -0,0 +1,50 @@
+"""Crash-safe JSON persistence shared across all data modules.
+
+- load_json: returns `default` if the file is missing, empty, or corrupt
+  (e.g. a partial/interrupted write). A corrupt file is moved aside to
+  `<path>.corrupt` so it can be inspected rather than silently overwritten.
+- save_json: atomic write — serialize to a temp file in the same directory,
+  fsync, then os.replace() (atomic on POSIX). An interrupted write can never
+  leave a truncated or empty target file.
+
+This is the durability backbone for the app's JSON storage (issues #11/#12).
+"""
+import json
+import os
+import tempfile
+
+DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
+
+
+def load_json(path, default):
+    if not os.path.exists(path):
+        return default
+    try:
+        with open(path) as f:
+            return json.load(f)
+    except (json.JSONDecodeError, ValueError):
+        # Corrupt/partial file — preserve it for inspection, fall back to default
+        # instead of crashing the request.
+        try:
+            os.replace(path, path + ".corrupt")
+        except OSError:
+            pass
+        return default
+
+
+def save_json(path, data):
+    directory = os.path.dirname(path) or "."
+    os.makedirs(directory, exist_ok=True)
+    fd, tmp = tempfile.mkstemp(dir=directory, prefix=".tmp-", suffix=".json")
+    try:
+        with os.fdopen(fd, "w") as f:
+            json.dump(data, f, indent=2)
+            f.flush()
+            os.fsync(f.fileno())
+        os.replace(tmp, path)
+    except BaseException:
+        try:
+            os.remove(tmp)
+        except OSError:
+            pass
+        raise

templates/base.html

@@ -23,6 +23,7 @@
       <a href="{{ url_for('debts_view') }}">Debt</a>
       <a href="{{ url_for('net_worth_view') }}">Net Worth</a>
       <a href="{{ url_for('summary') }}">Spending Report</a>
+      <a href="{{ url_for('suggestions.suggestions_page') }}" class="nav-suggest" title="Suggestions &amp; feedback" aria-label="Suggestions">💡</a>
     </div>
   </nav>
   <main>