feat(billing): add microdollar_usage_daily rollup with dual-write

[RSO]

Summary

PR 1 of 2 to eliminate the 3-month scan of the 800M-row microdollar_usage table that powers kiloPass.getAverageMonthlyUsageLast3Months and currently accounts for ~42% of read-replica execution time.

This PR adds the rollup infrastructure but does not switch the read path:

• New microdollar_usage_daily table with a row per (kilo_user_id, organization_id, usage_date) and two partial unique indexes (one for organization_id IS NULL, one for IS NOT NULL). Modeled on exa_monthly_usage.
• Extended insertUsageAndMetadataWithBalanceUpdate (apps/web/src/lib/ai-gateway/processUsage.ts) with a new CTE that upserts the matching daily row, atomic with the existing microdollar_usage insert in the same single SQL statement. Zero-cost rows are skipped via WHERE ${cost} <> 0.
• A test helper insertMicrodollarUsageWithDailyRollup in apps/web/src/tests/helpers/microdollar-usage.helper.ts for tests that bypass the production hot path and write to microdollar_usage directly. (PR 2 tests will use this; existing tests are left alone since they don't read from the rollup yet.)
• New tests for the dual-write covering personal scope, increments on the same day, separate org-scoped rollup, and the zero-cost no-op.

After deploy, every new microdollar_usage row is mirrored into microdollar_usage_daily. The historical backfill and the read-path switch are tracked in the implementation plan and will land in PR 2.

Plan: .kilo/plans/1778835512309-hidden-sailor.md.

Verification

• Applied the migration locally with pnpm drizzle migrate.
• Inserted a personal-scope usage row through the production hot path and confirmed a corresponding microdollar_usage_daily row appeared with the expected total. Inserted a second row on the same day and confirmed the row's total_cost_microdollars incremented (not duplicated). Inserted an org-scoped row and confirmed it created a separate row hitting the org partial unique index, leaving the personal row unchanged. Inserted a zero-cost row and confirmed the rollup was untouched.
• Confirmed a row with created_at set explicitly to a UTC date lands in microdollar_usage_daily.usage_date as the same calendar day.

Visual Changes

N/A — backend / schema only.

Reviewer Notes

• The dual-write CTE picks the matching partial-unique-index ON CONFLICT target with a JS-level branch on whether organization_id is null. PostgreSQL only allows a single ON CONFLICT clause per statement and the two partial indexes have different column lists, so this branch is required.
• microdollar_usage_daily stores both personal and org-scoped rows in one table to mirror exa_monthly_usage. Only the personal partial index is exercised by the immediate consumer in PR 2; the org-scoped rows are written but unused for now.
• The new table contains no PII (only kilo_user_id, organization_id, usage_date, aggregated cost). Per softDeleteUser policy, microdollar_usage itself is retained on soft-delete as a billing record (apps/web/src/lib/user.ts retention list); this derived rollup follows the same retention. No softDeleteUser change required.
• Risk on the hot path: the added CTE is a single INSERT ... ON CONFLICT DO UPDATE against a small, tightly-indexed table. It shares the same transaction as the existing microdollar_usage insert and the user-balance UPDATE, so atomicity is preserved with no extra round-trip.
• The migration was generated via pnpm drizzle generate per repo convention; no hand-written DDL.

[kilo-code-bot]

Code Review Summary

Status: 2 Issues Found | Recommendation: Address before merge

Executive Summary

Two pre-existing issues remain unaddressed: a redundant dead-code condition in the test helper and a missing trailing newline in the migration file. The new commit only reformats apps/web/tsconfig.json (no logic changes).

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	1

Issue Details (click to expand)

WARNING

File	Line	Issue
apps/web/src/tests/helpers/microdollar-usage.helper.ts	153	!row.cost || row.cost === 0 — the || row.cost === 0 clause is dead code; !0 is already true. Use row.cost === 0 alone for clarity and alignment with production's WHERE cost <> 0.

SUGGESTION

File	Line	Issue
packages/db/src/migrations/0131_known_banshee.sql	11	Missing trailing newline at end of file (indicated by \ No newline at end of file in the diff).

Other Observations (not in diff)

microdollar_usage_daily has no created_at column — The table only has updated_at, so there is no record of when a daily rollup row was first created. This is almost certainly intentional (the row is purely a running aggregate), but worth knowing for future observability queries.

$onUpdateFn in schema won't fire for raw SQL CTEs — updated_at's $onUpdateFn(() => sql\now()`)is a Drizzle ORM hook that only fires when Drizzle's.update()builder is used. The CTE explicitly setsupdated_at = NOW()`, which is correct. The hook is effectively a no-op for the hot path here but that's fine.

Files Reviewed (9 files)

• apps/web/src/lib/ai-gateway/processUsage.ts — no issues
• apps/web/src/lib/ai-gateway/processUsage.test.ts — no issues
• apps/web/src/tests/helpers/microdollar-usage.helper.ts — 1 issue (inline comment posted)
• apps/web/tsconfig.json — no issues (reformatting + removal of explicit moduleResolution: node, which is the default for module: commonjs)
• packages/db/src/schema.ts — no issues
• packages/db/src/migrations/0131_known_banshee.sql — 1 issue (inline comment posted)
• packages/db/src/migrations/meta/0131_snapshot.json — (generated, skipped)
• packages/db/src/migrations/meta/_journal.json — (generated, skipped)

Fix these issues in Kilo Cloud

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_{Review guidance: REVIEW.md from base branch main}