A user asked Fable to schedule "this Friday at 8am" on Wednesday 4/29
2026. The model picked 4/30 (Thursday) and confidently labeled it
"Friday." The TZ pipeline did everything correctly given the model's
date — the bug was upstream: the model was guessing weekdays from ISO
dates without an anchor, and the calendar tools had no way to verify.
Three layered fixes:
1. **System prompts now name the weekday alongside the ISO date.**
Both the journal-conversation prompt and the general chat prompt
used to say "Today is 2026-04-29 (America/New_York)." They now say
"Today is Wednesday, 2026-04-29 (...)." LLMs are unreliable at
deriving weekday names from ISO dates; supplying the name removes
the guess.
2. **`expected_weekday` parameter on create_event / update_event.**
When the model passes `expected_weekday="friday"`, the backend
computes the resolved start_date's weekday in the user's local
timezone and rejects mismatches with a self-correcting error
("Date 2026-04-30 falls on Thursday, not Friday. Recompute..."),
without creating the event. The check is local-aware: a Friday
23:00 event in Tokyo crosses midnight UTC but the local view
stays Friday, and the validator respects that.
3. **Tool descriptions instruct echo-and-confirm.** create_event and
update_event descriptions now tell the model: when the user names
a weekday, state the resolved date in the reply BEFORE calling
the tool, and pass `expected_weekday`. Costs nothing in code,
reinforces the validator.
6 new tests — match success, mismatch rejection (with create/update
not invoked), omitted-param backcompat, invalid weekday name, local-
not-UTC weekday computation, and the update_event variant. All 18
calendar-tool tests + 33 event-related tests pass; ruff clean.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
A user reported "next Friday at 8am" landing on the wrong day. The
current `start` parameter accepts a combined ISO datetime string — when
the model emits something like `"2026-05-01T00:00:00Z"`, the parser
correctly honors the UTC tag and stores `2026-05-01 00:00 UTC`, which
displays as `2026-04-30 19:00` for a UTC-5 user. The bug isn't in our
parser; it's that we let the model TZ-tag the calendar day at all.
The fix moves the foot-gun: `create_event` and `update_event` now
prefer split fields (`start_date` + `start_time`, plus end variants).
A `YYYY-MM-DD` string carries no TZ metadata for a model to mis-tag,
and the backend builds the local datetime explicitly via
`datetime.combine(date, time, tzinfo=user_tz).astimezone(UTC)`. Strict
regex validation rejects anything with a TZ suffix on either field.
The legacy combined `start` / `end` fields are kept as a fallback so
saved tool-call payloads in conversation history still replay; new
calls are steered toward the split shape via the tool description.
7 new regression tests cover Eastern, Pacific, Tokyo (positive offset),
all-day inference, strict-shape rejection on both fields, backcompat
with the legacy `start` field, and the same fix for `update_event`.
27 of the event-related tests pass; ruff clean.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Two related bugs where the server defaulted naive datetimes to UTC instead
of the configured user timezone, causing all-day events to land on the
previous day and briefings to "disappear" at UTC midnight.
- New services/tz.py helpers: get_user_tz, user_today, user_briefing_date
(the briefing day flips at 4am local to align with the compilation slot,
so the 00:00-04:00 local window still shows yesterday's briefing until
the new one is generated).
- calendar create/list/update tools now parse naive datetimes in the
user's TZ before converting to UTC for storage, and tool descriptions
tell the model to pass plain local dates.
- briefing_conversations.get_or_create_today_conversation and the
reset-today route use user_briefing_date so the in-progress briefing
doesn't get replaced at 19:00 NY / UTC midnight.
- _run_profile_closeout targets user-local "yesterday" for consistency.
Regression tests added for the TZ helpers and the calendar tool.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
bvandeusen