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Build Log – 2025-12-16

Build Log – 2025-12-16

📅 Daily Log — December 16, 2025

🧠 Context / Focus for Today

Stabilize Garmin export reliability, resolve FIT SDK failures, and realign the platform around a true planned → completed workout lifecycle with Garmin Connect.

✔️ Things I Got Done Today

Garmin FIT Export Debugging & Fixes

  • Identified and resolved the root cause of a critical FIT export failure (TypeError: encoder.write is not a function).
  • Confirmed the issue stemmed from incorrect usage of the @garmin/fitsdk API rather than Garmin permissions or workout data.
  • Replaced invalid SDK calls with the correct patterns:
    • encoder.writeMesg(...) for FIT message writing
    • encoder.close() for finalizing the FIT file
  • Updated FIT export logic across both routes:
    • app/api/workout/export-fit/route.ts
    • app/api/garmin/export/route.ts
  • Refactored workoutToFIT to:
    • Be fully async
    • Use dynamic imports for ES module compatibility
    • Correctly handle Uint8Array and Buffer boundaries
  • Validated that FIT files now complete successfully instead of failing mid-export.

Garmin Sync Architecture Alignment

  • Clarified the intended long-term Garmin integration model:
    • Push planned workouts to Garmin Connect so they appear on the user's watch.
    • Pull completed activities back into Flow State for comparison against the planned workout.
  • Confirmed that manual FIT download/upload is strictly a temporary fallback, not the intended user experience.
  • Updated Cursor context and mental model to ensure future work aligns with this full end-to-end sync loop.

Platform / Cost Awareness

  • Discussed adding backend tracking for per-user AI token usage to better understand cost drivers and inform future pricing decisions.
  • Reviewed current Vercel constraints with the expectation that upgrading tiers will remove several existing limitations.

🚧 In Progress

  • Reconnecting the Garmin Training API push flow now that FIT export is unblocked.
  • Laying groundwork for completed-activity ingestion and planned-vs-actual comparison.
  • Evaluating where token usage tracking should live in the backend architecture.

🎯 Targets for Tomorrow

  1. Resume direct push of planned workouts to Garmin Connect.
  2. Begin implementing completed activity pull and reconciliation logic.
  3. Decide on the first minimal version of per-user AI usage tracking.
  4. Keep focus tightly on Garmin reliability and closing the planned → completed loop.

🤔 Notes / Observations

  • The Garmin export failure was a tooling misuse issue, not a Garmin platform issue — a good sign for long-term stability.
  • Having tests around FIT generation dramatically reduced uncertainty during debugging.
  • Reconfirming the end-state architecture helped avoid drifting into temporary UX decisions becoming permanent.

📈 Momentum Score: 8.4 / 10

Solid reliability win. Not user-facing yet, but a foundational unblock that clears the path for true Garmin sync progress.