[jhodapp]

Description

Recurring series were expanded in naive UTC, while the .ics anchors the series in the coach's zone (DTSTART;TZID + RRULE). Calendars keep the local wall time across DST, so after a transition every occurrence was stored an hour off the calendar. Single-occurrence reschedules and cancels then named a RECURRENCE-ID no client held, and Google dropped them (production repro: Nov 5 occurrence of series 67d9d4a5).

This expands series on local wall time in the zone the series was published in, exactly as RFC 5545 clients do, and stores that zone on the series so later invites and expansions cannot split apart.

GitHub Issue: Fixes #456

Changes

• expand_recurrence(start_at, rule, zone) steps on local wall time and resolves each slot to UTC per RFC 5545 §3.3.5 (a skipped time uses the offset before the gap, a repeated time its first pass). until is compared against the resolved instant.
• Weekdays and month days are validated in local time, so an evening series (Thu 7 PM Chicago, Friday in UTC) no longer gets a 422.
• New 422s: a monthly series starting after day 28 in the coach's zone (clients disagree on short months), and a start in the second pass of a repeated hour.
• SeriesRule.timezone: the zone actually emitted (UTC when no VTIMEZONE exists), set at create and reschedule. Every invite under the series UID (master, occurrence move and cancel, snapshot resend, series cancel) uses it, even if the coach later changes zone.
• Migration backfills rule.timezone on existing series from the coach's current zone (unknown names become UTC). down removes the key.
• RRULE now carries WKST=MO.
• Manual test plan: new "Series across a DST change" section.

Testing Strategy

• Unit tests for every frequency across fall-back and spring-forward in Chicago, London, Sydney, Kolkata and UTC, plus evening and morning weekday series, biweekly with Sunday, the until boundary, gap, overlap and the new 422s.
• Oracle test: the rrule crate (already in the tree via icalendar, added as a dev-dependency) expands the exact DTSTART + RRULE we emit across 20 cases, and must equal our slots. Mutation-checked: it fails if expansion reverts to UTC or the overlap rule changes.
• Stored-zone tests: a coach who moved from Chicago to New York still gets Chicago RECURRENCE-ID/EXDATE/TZID on occurrence move, occurrence cancel and the snapshot.
• Migration run up, down and up against local Postgres; down restores every rule exactly.
• Live: the new HD/SD cases in docs/test-plans/ics-calendar-invites-manual-test-plan.md, run with a Chicago coach against Google Calendar.

Concerns

• Existing drifted rows are not changed by this PR. A one-time repair (run separately after deploy, with a dry run first) realigns them and resends where a calendar update was dropped. It must run before about Oct 31, when reminders for post-DST sessions start going out.
• Create and reschedule now read the coach's user row once more to resolve the zone.

[greptile-apps]

Confidence Score: 4/5

[Medium impact] The changes affect recurring coaching schedules and their calendar updates.

The PR still needs the stored monthly-series resend fix completed before merging.

Findings

1.  Existing series cannot resend ▶

Summary

Recurring sessions now keep their local start time across daylight-saving changes.

• Recurring sessions keep their local time across daylight-saving changes.
• Series invites keep using the timezone they were first published in.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Create or reschedule] --> B[Resolve coach publication zone]
    B --> C[Validate and expand in local time]
    C --> D[Store rule, zone, and UTC sessions]
    D --> E[Build invites using stored zone]
    F[Resend stored series] --> G[Expand published rule]
    G --> H[Match stored sessions to slots]
    H --> E

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_{Reviews (2) · Last reviewed commit: "fix: expand stored series without the ch..." · Reviewed by Greptile}