fix(heartbeat): record cost_cents for subscription_included events

[om952]

Summary

Heartbeat cost events with billing type subscription_included were incorrectly stored with cost_cents = 0 because normalizeBilledCostCents returned 0 for that billing type. This fix removes the early return and adds a historical backfill migration.

Changes

• server/src/services/heartbeat.ts

  • Remove the subscription_included early return in normalizeBilledCostCents.
  • Export normalizeBilledCostCents for focused unit testing.
  • All billing types now compute Math.max(0, Math.round(costUsd * 100)).

• server/src/tests/heartbeat-cost-cents.test.ts

  • Regression tests for non-numeric inputs, metered_api, subscription_included, subscription_overage, negative clamping, and NaN/Infinity.

• packages/db/src/migrations/0087_backfill_subscription_included_cost_cents.sql

  • Backfills cost_events.cost_cents from heartbeat_runs.result_json for rows where billing_type = 'subscription_included' and cost_cents = 0.
  • Handles cost field variants: costUsd, cost_usd, total_cost_usd.
  • Uses ROUND(cost * 100) and clamps to >= 0.

• packages/db/src/migrations/meta/_journal.json

  • Registers migration 0087.

• packages/db/src/backfill-subscription-included-cost-cents.test.ts

  • Embedded-Postgres tests verifying the backfill migration applies correctly and is idempotent.

Verification

• heartbeat-cost-cents.test.ts: 6/6 passed
• costs-service.test.ts: 16/16 passed
• monthly-spend-service.test.ts: 2/2 passed
• backfill-subscription-included-cost-cents.test.ts: 3/3 passed
• packages/db migration numbering check and build: passed

Notes

• agents.spent_monthly_cents and companies.spent_monthly_cents are hydrated from current-month cost_events on read, so correcting historical cost_events automatically corrects displayed spend.

Fixes #27