FIN-23 · Liabilities detail (Chase APR/statement; AMEX-graceful nulls)

[lbedner]

Milestone: Finance M4 · Depends on: FIN-20.

Goal

Liabilities detail for credit accounts — APR, statement balance, min payment, due date (Chase supports it; AMEX does NOT — the absence must be graceful, not an error).

Implementation

1. Adapter: fetch_liabilities(connection) → /liabilities/get (plaid-python). Only call when the institution's supported_products (seeded FIN-10 + refreshed from Plaid item metadata) includes liabilities — capability-gate, don't try/except your way through.
2. Upsert finance_liability_detail on uq_finance_liability_account (account_id) per pull: last_statement_balance/issue_date, minimum_payment_amount, next_payment_due_date, last_payment_amount/date, is_overdue, APRs array → the aprs JSON column (each {apr_type, apr_percentage_bps: int(round(pct*100)), balance_subject_to_apr, interest_charge_amount} — basis points as int, no floats), full payload → raw.
3. Wire into the nightly job after transaction sync (same per-connection error isolation).
4. Surface: accounts API includes liability fields when present; FIN-18 Accounts tab shows "Due Jul 15 · min $35.00" line under credit accounts that have data, and NOTHING (no error/empty widget) for AMEX-style accounts without it.

Validation (sandbox)

Sandbox institution ins_109508 supports liabilities with fixture data (or use Plaid's custom sandbox user config to control values).

Acceptance criteria

• Sandbox credit account → liability row with correct cents + bps values; re-pull updates in place (1 row per account, ever).
• Connection whose institution lacks liabilities → zero API calls to /liabilities/get (assert via mock), zero rows, zero errors.
• Accounts API/UI render both states correctly.
• make check green.

---

Shared context (read this first — identical in every FIN ticket)

What we're building: a Finance Service for aegis-stack — a personal-finance aggregator (Empower/Quicken class: linked bank/credit/brokerage accounts, Quicken/OFX/CSV import, net-worth-over-time, "wasting money" insights). It is a gated template service like payment/insights: a new include_finance copier flag + a SERVICES["finance"] registry entry. Nothing is bolted into any one generated project.

Authoritative design docs (in this repo):

• docs/plans/finance-service/finance-service-plan.md — the full plan.
• docs/plans/finance-service/finance-schema-canonical.md — THE schema: 33 tables, every column/FK/index/unique/check, dedup contract, ER diagram. Schema tickets inline their slice, but this file is the tiebreaker.
• docs/plans/finance-service/finance-research/ — Plaid/OFX/product research briefs.

The two parallel systems (keep them in sync — this is the #1 thing to understand):

1. Copier template — aegis/templates/copier-aegis-project/{{ project_slug }}/…. Gating = literal {% if include_finance %} blocks in .jinja files + questions in copier.yml (repo root).
2. Python registry — aegis/core/services.py → the SERVICES dict. Single source of truth for: post-gen file pruning (aegis/core/post_gen_tasks.py:139-146 removes every path in a spec's FileManifest.primary when its flag is off), aegis add-service, migrations, aegis update disk-detection (marker_path), and aegis init service listing. Copy the payment spec (services.py:677-763) as the reference.

Migrations are GENERATED, not hand-written. Table definitions live as declarative specs in aegis/core/migration_generator.py: TableSpec / ColumnSpec / IndexSpec(name, columns, unique, where=…) (a where= renders BOTH sqlite_where and postgresql_where — partial uniques work on both engines) / ForeignKeySpec(columns, ref_table, ref_columns, ondelete=…, ref_schema=…) / CheckConstraintSpec(name, sqltext) / AlterTableSpec (for circular FKs; runs in one op.batch_alter_table, SQLite-safe). Revision IDs are auto-assigned at generation time (get_next_revision_id, max+1 zero-padded) — NEVER hardcode a revision number. Which migrations generate is decided by get_services_needing_migrations(context) (migration_generator.py:~1771) — finance gets a block there mirroring payment's (:~1839).

Generated-project conventions (non-negotiable, from the schema doc §conventions):

• int autoincrement PKs (id: int | None = Field(default=None, primary_key=True)) — NO UUIDs.
• Money = int minor units (cents) + a currency code column. NO Decimal/Numeric/float. Fractional share quantities = quantity_e8 (int, ×1e8); prices = int + price_scale; FX = rate_e8.
• Timestamps = naive UTC via a utcnow_naive() helper (datetime.now(UTC).replace(tzinfo=None)).
• Enums we own = String column + CheckConstraint (never native PG enum). Provider taxonomies that grow (Plaid account subtype, PFC categories, security_type) = plain TEXT, no check.
• JSON via sa_column=Column("name", JSON); the attr metadata_ maps to DB column "metadata" (SQLModel reserves metadata).
• Every user-scoped row: owner_user_id FK → user.id (CASCADE, indexed) + nullable organization_id (SET NULL, indexed). These FKs target the auth service's tables — finance declares required_services=["auth"]. Cross-schema FK precedent: payment.payment_customer → auth.user uses ForeignKeySpec(..., ref_schema="auth").
• Every FK indexed. ONE documented exception: currency FKs (low-cardinality) stay unindexed, ON DELETE RESTRICT.
• All finance tables are finance_-prefixed; explicit __tablename__; index names ix_…, uniques uq_…, checks ck_….
• Services: class FinanceService: def __init__(self, db: AsyncSession); queries via sqlmodel.select + await self.db.exec(…); writes self.db.add(…) + await self.db.flush() — services NEVER commit (the request-scoped get_async_db dependency commits).
• Dedup = real UNIQUE constraints + dialect-dispatched idempotent UPSERT (sqlite.insert(...).on_conflict_do_update(...) vs postgresql.insert(...) — pick by db.bind.dialect.name).

Dev workflow / how to validate (all from the aegis-stack repo root):

make check                 # repo's own lint + typecheck + tests — must stay green
make test-template         # generate a project from the template + validate it
make test-stacks-quick     # 3 representative stacks: base, everything, insights
make clean-test-projects   # remove generated test projects

# Generate a throwaway project from your UNCOMMITTED working tree:
uv run aegis init fin-smoke --dev --no-interactive -y \
  -o /tmp/aegis-fin-test \
  -c database,scheduler -s auth,finance
# (…and a second one WITHOUT `finance` in -s to prove pruning.)

Generated-project checks (run inside the generated project): make test, make lint, boot the app, hit endpoints with curl.

Postgres matters: the template supports sqlite AND postgres. FK enforcement, partial-unique behavior, and ON CONFLICT semantics must be validated against postgres too (generate with a postgres database answer, or run the migration against a local postgres). SQLite test sessions don't enforce FKs — don't trust green sqlite tests for constraint behavior.

Ticket codes: FIN-01…FIN-27. Dependencies are cited by code. Do not start a ticket whose dependencies aren't merged.