templates construct has no way to set a project start date (template dates always anchor to construction date)

[jethrojones]

What happens

  The Basecamp web UI prompts for a start date when creating a project from a template and shifts all the template's relative dates accordingly. basecamp templates construct has no equivalent — --name and --description are the only flags — so every constructed project anchors its dates to today.

  What I tried

  Passing starts_on through the raw API at both the top level and inside project:

  basecamp api post templates/<TEMPLATE_ID>/project_constructions.json \
    -d '{"project":{"name":"...","description":"...","starts_on":"2026-09-01"},"starts_on":"2026-09-01"}'

  The request succeeds (construction created, status pending → completed), but starts_on is silently ignored in both positions.

  Observed result

  Template with relative dates spanning day −2 to ~day +68, constructed on 2026-08-25 with starts_on: 2026-09-01:

  ┌───────────────────────┬───────────────────────────┬────────────┐
  │                       │ Expected (start = Sept 1) │   Actual   │
  ├───────────────────────┼───────────────────────────┼────────────┤
  │ Earliest to-do due_on │ 2026-08-30                │ 2026-08-23 │
  ├───────────────────────┼───────────────────────────┼────────────┤
  │ Latest to-do due_on   │ 2026-11-06                │ 2026-10-30 │
  ├───────────────────────┼───────────────────────────┼────────────┤
  │ Schedule entry        │ 2026-09-20                │ 2026-09-13 │
  └───────────────────────┴───────────────────────────┴────────────┘

  Dates anchored to the construction date (day 0 = 2026-08-25), not the requested start date.

  Confirmed against a second project built from the same template on 2026-07-28: earliest to-do 2026-07-26 — same day-0-equals-construction-date behavior.

  Impact

  Any scripted template construction has to construct first, then walk every to-do list plus the schedule and re-PUT each date with a computed offset. That's N+M extra API calls per project and has to reproduce the template's day-0 convention by hand.

  Ask

  Either a --starts-on flag on templates construct if the API supports it via some parameter I haven't found, or a documentation note that this is UI-only so people don't burn time probing for it.

Project Template ID for your review: https://3.basecamp.com/3104101/templates/34442718