A wall clock that happens twice or never needs one pinned answer, not a coin flip

Twice a year a zone produces a wall-clock time that occurs twice (fall-back) and one that never occurs (spring-forward) -- most date libraries resolve these however they happen to, this pack pins the RFC's own answer.

This is one of the things Scheduling & Availability Core already handles. Bookings and availability that survive timezones, repeating events and daylight saving — without double-booking.

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Is this you?

Resolving an ambiguous or nonexistent local time by whatever a date library's internal implementation happens to do -- rather than a deliberately chosen, documented policy -- means the two dates a year this actually matters (the fall-back overlap and the spring-forward gap) can resolve inconsistently across libraries, or even across versions of the same one, with no test catching it unless it's specifically built to probe those two dates.

Why this one is easy to get wrong

Fall-back and spring-forward are the well-known headline facts about DST, but the specific question -- which of the two identical-looking wall-clock instants during an overlap is 'the' 9am, and what instant does a nonexistent 2:30am even mean -- is a policy decision most date-handling code inherits silently from whatever library it uses, rather than one anyone deliberately chose and can cite a source for.

What you get instead

instantFromLocal() probes 24 hours before and after a candidate instant to determine which case applies -- both valid means an overlap, resolved to the earlier instant; exactly one valid is the normal case; neither valid means a gap, resolved to the pre-transition offset, shifting the requested time forward by exactly the gap size. This is stated as byte-for-byte identical to Temporal's own disambiguation: 'compatible' default, and matches RFC 5545 section 3.3.5's own worked examples -- cited, not invented, with a documented one-line upgrade to Temporal itself once Node 26 ships it unflagged.

Source: ARCHITECTURE.md 'Wall clock -> instant, and the disambiguation policy' — checkable in the pack you receive

How you actually use this

You don’t install a library or wire up an SDK. Your own coding agent builds the code in your project, and you keep it — no runtime dependency on us.

Step 1
Download and unzip
You get a folder: the docs that tell an agent what to build, a starting skeleton, and the test suite that decides when it's done.
Step 2
Open it in Claude Code or Cursor
Point your coding agent at the folder. Nothing to install, no account with us, no API key.
Step 3
Paste one prompt
The pack contains the exact prompt. Paste it as your first message and leave it alone — it works through the build itself, choosing a cheaper or stronger model per task.
Step 4
Run ./verify.sh
One command. It prints a pass or fail for every check. Green means the build is done — the same script we ran to produce the receipt on this page.

Typical build: about 22 minutes of your agent working, mostly unattended. Then you integrate the working module into your app the way you would any code you’d written yourself.

Why you can believe this

3 of 3 runs passed

We ran this pack from an empty folder 3 times and published exactly what happened — every check, the model, the token cost, the wall time. Not a testimonial, and not our opinion: the same verify.sh you run yourself. Read the full receipt →

Buy for $99 14-day refund if verify.sh fails →