grim7/26/2026, 3:10:53 AM

Adds a generated spend-trend chart to the digest embed's thumbnail: the last
14 days of billed (blurple) vs actual (yellow) as overlaid sparklines, so a
reader sees at a glance whether today's drift is a blip or a trend.

Built without any image dependency and without our spend figures leaving our
infra:
- sparkline-png.ts (@tripwire/utils): a dependency-free PNG encoder (hand-
  assembled chunks + CRC32, IDAT via node:zlib) and a pixel-plotted sparkline
  renderer. Pure, unit-tested by parsing the PNG back (signature, IHDR dims,
  chunk order).
- guardedPostMultipart (@tripwire/utils): posts multipart/form-data through
  the SAME SSRF guard as guardedPost. Extracted guardedResolve so the guard is
  single-sourced; the existing guard test suite still passes unchanged.
- getRecentDailyCosts (@tripwire/db): the 14-day billed/actual range query.
- economicsDigest attaches the PNG as files[0] and points the embed thumbnail
  at attachment://econ.png; a day with no invoice yet falls back to its billed
  figure so the actual line stays continuous. Under two points, no chart and
  the embed posts as plain JSON. dry-run prints the payload and the attachment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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