Stamp UTC on naive API timestamps before serializing (B-35)

SQLite/aiosqlite returns DateTime columns as naive even though every
value is written in UTC, so a bare .isoformat() dropped the offset and
the frontend's new Date() parsed it as local time. Add a shared
isoformat_utc() helper and use it at every call site that was missing
the fix already applied ad hoc in rounds.py.

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

BUGS.md

@@ -1,11 +1,11 @@
 # Known bugs
 
 A second full-codebase audit on 2026-07-27 found **25 further issues** (4 critical, 6 high,
-7 medium, 8 low), listed below as B-33 … B-49. B-25 through B-34 are fixed (see "Previously
-fixed" below) — no Critical-severity finding remains open; the other 15 are High/Medium/Low.
+7 medium, 8 low), listed below as B-33 … B-49. B-25 through B-35 are fixed (see "Previously
+fixed" below) — no Critical-severity finding remains open; the other 14 are High/Medium/Low.
 The 139-test suite was green at the time of the audit, so none of these were caught by existing
-coverage — every fix lands with a regression test (the ten fixes so far brought the suite
-from 139 to 194).
+coverage — every fix lands with a regression test (the eleven fixes so far brought the suite
+from 139 to 198).
 
 The recurring pattern across the open findings is worth stating once: the code is rigorous
 about the failure modes that have actually been hit, and silent about the ones that have not.
@@ -20,21 +20,6 @@ single-process assumptions, no user-facing history, etc.), see "Known gaps / TOD
 
 ## Medium
 
-### B-35 — Every API timestamp is naive, so the frontend renders it in the wrong timezone
-
-Verified empirically: the `DateTime` columns carry no timezone, so SQLite returns naive
-datetimes and `.isoformat()` produces `2026-07-27T06:56:47.489110` — **no `Z`**. JavaScript's
-`new Date()` parses that as **local time**, so every date in `/admin` (rounds, pending
-transactions, audit log, via `fmtDate` in `app/static/admin.js:50`) and `created_at` in
-`/users/me` display two hours off in Italy.
-
-The codebase knows about this — `api/routes/rounds.py` calls `.replace(tzinfo=timezone.utc)`
-on `opened_at` explicitly — but the fix was never applied systematically.
-
-**Proposed fix.** Make the columns `DateTime(timezone=True)` (Alembic migration) so the value
-round-trips as aware, rather than patching each call site. Until then, at minimum a shared
-serialization helper that stamps UTC, used by every `.isoformat()` in the API layer.
-
 ### B-36 — `_wait_for_next_block` waits forever, with no timeout and no visibility
 
 `rounds/scheduler.py:158-161` loops until a higher block arrives. No timeout, no log, no audit
@@ -195,12 +180,13 @@ already does.
 - **B-29** — a UTXO absent from one server's `listunspent` was marked spent immediately, irreversibly, on a single unauthenticated reply
 - **B-30** — a lost scripthash subscription meant a user's deposits were never credited, with no periodic safety net
 - **B-31** — resubscribing on reconnect ran serially before anything else started, freezing the chain tip (and so an in-flight draw) for the whole sweep
-- **B-32** — an RBF bump's fee delta could fall below BIP125's relay-mandated minimum, so the node rejected it and the same tick retried identically forever; also had no ceiling on how high the fee rate could climb
-- **B-33** — `POST /auth/login` had no rate limiting on a custodial wallet, so a patient distributed attack could brute-force a password against an enumerable username list; fixed with per-username *and* per-IP exponential backoff (`app/auth/rate_limit.py`), registration throttled per-IP too (also bounds B-31's attacker-controlled user count)
-- **B-34** — neither self-service password change nor the admin reset invalidated already-issued JWTs, so a stolen token (or an attacker's own session) survived a password change meant to lock it out; fixed with a `User.token_version` column embedded in every JWT (`"tv"` claim) and checked on every request in `get_current_user`/`get_optional_user`, bumped on both endpoints — change-password hands back a fresh token so the caller's own session keeps working, the admin reset does not
+- **B-32** — an RBF bump could retry forever below BIP125's relay-mandated minimum fee delta, with no ceiling on the fee rate either
+- **B-33** — `POST /auth/login` had no rate limiting, so a password could be brute-forced against an enumerable username list
+- **B-34** — password change/reset didn't invalidate already-issued JWTs, so a stolen token survived a change meant to lock it out
+- **B-35** — API timestamps round-tripped as naive datetimes, so the frontend parsed them as local time instead of UTC
 
 See git history for the fix-by-fix breakdown (commits `f13f685`, `50a43ae`, `933760e`, and the
-B-28/B-29/B-30/B-31/B-32/B-33/B-34 fixes). Suite grew from 139 to 194 tests over the ten.
+B-28/B-29/B-30/B-31/B-32/B-33/B-34/B-35 fixes). Suite grew from 139 to 198 tests over the eleven.
 
 A full-codebase audit on 2026-07-26 (commit `d4e0974`) found 24 bugs across every Python
 module under `app/`, both static frontends, and the Docker/Caddy deployment — 5 critical,

CLAUDE.md

@@ -12,7 +12,7 @@ All 10 stages of the original build order are code-complete and unit-tested —
 
 Verified on mainnet with real money: registration + address derivation, deposit crediting (1-conf), a real 10 PLM bet (broadcast → confirmed → change credited back), and one full round cycle (close → draw on a real block hash → 70/30 payout with sat math checked against the broadcast tx → confirmation → close → next round auto-opened). **Withdrawal and the RBF bump path have never been exercised against a live broadcast** — unit-tested only.
 
-**Read [BUGS.md](BUGS.md) before trusting any behaviour here.** Two audits: 2026-07-26 found 24 bugs (5 critical), all fixed; 2026-07-27 found 25 more (B-32 … B-49), of which **18 are still open** — no Critical, but High covers an RBF bump that can loop forever on a replacement the node always rejects (B-32), no brute-force protection on login (B-33), and password change/reset not invalidating existing JWTs (B-34). BUGS.md is the live open list with a proposed fix per finding; "Known gaps" at the end of this file is for limitations accepted **by design** instead. Don't fix a BUGS.md item silently as a side effect of other work — each fix lands with its own regression test.
+**Read [BUGS.md](BUGS.md) before trusting any behaviour here.** Two audits: 2026-07-26 found 24 bugs (5 critical), all fixed; 2026-07-27 found 25 more (B-25 … B-49), of which **14 are still open** — no Critical or High remains, only Medium/Low: `_wait_for_next_block` has no timeout or visibility if a round gets stuck in `drawing` (B-36), no WAL/`busy_timeout` under five concurrent SQLite writer tasks (B-39), among others. BUGS.md is the live open list with a proposed fix per finding; "Known gaps" at the end of this file is for limitations accepted **by design** instead. Don't fix a BUGS.md item silently as a side effect of other work — each fix lands with its own regression test.
 
 Before writing code, read the "Architecture" section below in full plus the diagrams in [flowchart/](flowchart/): [platform-overview.mmd](flowchart/platform-overview.mmd) (the 5-phase flow) and [round-lifecycle.mmd](flowchart/round-lifecycle.mmd) (the round/draw lifecycle). Every node **and edge label** (conditions, retries, loops) is a behaviour that must be implemented as described. Regenerate the companion PDFs with `flowchart/render-pdf.sh <file>.mmd` after editing either.
 

app/api/routes/admin.py

@@ -6,6 +6,7 @@ from pydantic import BaseModel, Field, field_validator
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.api.timeutil import isoformat_utc
 from app.audit.log import write_audit_log
 from app.auth.security import hash_password
 from app.config import settings
@@ -163,7 +164,7 @@ async def list_users(session: AsyncSession = Depends(get_session)) -> list[Admin
             username=u.username,
             address=u.address,
             balance_sats=u.cached_balance_sats,
-            created_at=u.created_at.isoformat(),
+            created_at=isoformat_utc(u.created_at),
         )
         for u in users
     ]
@@ -253,8 +254,8 @@ async def list_rounds(session: AsyncSession = Depends(get_session), limit: int =
         AdminRoundResponse(
             id=r.id,
             status=r.status,
-            opened_at=r.opened_at.isoformat(),
-            closed_at=r.closed_at.isoformat() if r.closed_at else None,
+            opened_at=isoformat_utc(r.opened_at),
+            closed_at=isoformat_utc(r.closed_at),
             draw_block_height=r.draw_block_height,
             draw_block_hash=r.draw_block_hash,
             winner_user_id=r.winner_user_id,
@@ -291,7 +292,7 @@ async def list_audit_log(
             payload=json.loads(e.payload_json),
             user_id=e.user_id,
             round_id=e.round_id,
-            created_at=e.created_at.isoformat(),
+            created_at=isoformat_utc(e.created_at),
         )
         for e in entries
     ]
@@ -333,7 +334,7 @@ async def list_pending_transactions(
             current_txid=p.current_txid,
             fee_rate_sat_vb=p.fee_rate_sat_vb,
             attempt_count=p.attempt_count,
-            broadcast_at=p.broadcast_at.isoformat(),
+            broadcast_at=isoformat_utc(p.broadcast_at),
             replaced_by_txid=p.replaced_by_txid,
         )
         for p in entries

app/api/routes/users.py

@@ -4,6 +4,7 @@ from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.errors import http_error
+from app.api.timeutil import isoformat_utc
 from app.auth.dependencies import get_current_user
 from app.auth.security import MIN_PASSWORD_LENGTH, create_access_token, hash_password, verify_password
 from app.db.models import Round, RoundParticipant, User
@@ -36,7 +37,7 @@ async def me(
         balance_sats=user.cached_balance_sats,
         pending_balance_sats=pending_balance_sats,
         has_pending=has_pending,
-        created_at=user.created_at.isoformat(),
+        created_at=isoformat_utc(user.created_at),
     )
 
 

app/api/timeutil.py

@@ -0,0 +1,17 @@
+from datetime import datetime, timezone
+
+
+def isoformat_utc(dt: datetime | None) -> str | None:
+    """Serialize a datetime for API responses, stamping it UTC first.
+
+    Every DateTime column is written via app.db.models.utcnow() but SQLite/aiosqlite
+    round-trips it as a naive datetime, so a bare .isoformat() drops the "Z"/offset
+    and JavaScript's `new Date()` on the frontend parses the result as local time
+    instead of UTC (B-35). All stored values are UTC in practice, so a naive value
+    can be safely stamped rather than converted.
+    """
+    if dt is None:
+        return None
+    if dt.tzinfo is None:
+        dt = dt.replace(tzinfo=timezone.utc)
+    return dt.isoformat()

tests/unit/test_api_timeutil.py

@@ -0,0 +1,21 @@
+from datetime import datetime, timezone
+
+from app.api.timeutil import isoformat_utc
+
+
+def test_naive_datetime_is_stamped_utc():
+    # SQLite/aiosqlite round-trips DateTime columns as naive even though every
+    # value written is UTC (app.db.models.utcnow) — this is the exact shape
+    # returned by the ORM after a read (B-35).
+    naive = datetime(2026, 7, 27, 6, 56, 47, 489110)
+    result = isoformat_utc(naive)
+    assert result == "2026-07-27T06:56:47.489110+00:00"
+
+
+def test_aware_datetime_is_left_unchanged():
+    aware = datetime(2026, 7, 27, 6, 56, 47, tzinfo=timezone.utc)
+    assert isoformat_utc(aware) == aware.isoformat()
+
+
+def test_none_passes_through():
+    assert isoformat_utc(None) is None

tests/unit/test_users.py

@@ -162,3 +162,17 @@ async def test_register_rejects_weak_credentials(client, payload):
 async def test_register_accepts_valid_credentials(client):
     resp = await client.post("/auth/register", json={"username": "goodname", "password": "longenough1"})
     assert resp.status_code == 201
+
+
+async def test_me_created_at_is_utc_stamped(client):
+    """B-35: SQLite/aiosqlite returns DateTime columns as naive, even though every
+    value written is UTC (app.db.models.utcnow). A bare .isoformat() on that naive
+    value has no "Z"/offset, and JavaScript's `new Date()` then parses it as local
+    time instead of UTC."""
+    token = await _register(client)
+    headers = {"Authorization": f"Bearer {token}"}
+
+    resp = await client.get("/users/me", headers=headers)
+    assert resp.status_code == 200
+    created_at = resp.json()["created_at"]
+    assert created_at.endswith("+00:00") or created_at.endswith("Z")