Context
-------
Phase 1 needs live FX rates for USD-denominated RSU vestings (Schwab),
EUR-denominated deposits, and any multi-currency dividend. The FxCache
from an earlier commit stores (currency, date) → rate_to_gbp but was
intentionally left empty — this commit wires the ingestion path.
Design decisions
----------------
- ECB publishes EUR→X, not X→GBP. Everything pivots through EUR:
rate(X→GBP) = rate(EUR→GBP) / rate(EUR→X)
GBP goes into the result at 1.0 so callers iterating the dict get
a consistent shape; `populate_fx_cache` then skips GBP because
`convert_to_gbp` has a dedicated passthrough branch.
- `on_date` parameter is accepted for API symmetry with the future
historical fetcher even though the daily endpoint only serves the
most recent publication. The docstring calls this out explicitly.
- XML is parsed with stdlib `xml.etree.ElementTree`. No `lxml` —
the file is 30 lines, no performance concern, and keeping deps
minimal matters for the container image.
- The HTTP layer takes an optional `httpx.AsyncBaseTransport` the same
way WealthfolioSink does — MockTransport drives all tests, the
production caller just leaves it None.
This change
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- broker_sync/fx_ecb.py:
* `fetch_ecb_rates(on_date, *, transport=None)` — GETs the daily
XML, parses, pivots through EUR, returns `{ccy: rate_to_gbp}`.
Raises `RuntimeError` on non-2xx or if GBP is missing (cannot
pivot). No retries — caller handles resilience.
* `populate_fx_cache(cache, rates, on_date)` — writes every
non-GBP rate with `FxRateSource.ECB_LIVE`.
* `fetch_ecb_rates_historical(start, end)` — `NotImplementedError`
stub; filed as beads task code-thw.2.2. Needed for backfilling
years of T212 history (daily endpoint only covers today).
- tests/fixtures/ecb_2026-04-01.xml: realistic 5-currency ECB snapshot.
- tests/test_fx_ecb.py: fixture-driven tests covering the pivot math,
the 503 failure path, the cache-skip-GBP rule, and the NotImplemented
guard on the historical stub.
Test plan
---------
## Automated
- poetry run pytest -q → 52 passed in 0.50s
- poetry run mypy broker_sync tests → Success: no issues found in 26 source files
- poetry run ruff check . → All checks passed!
## Manual Verification
Live daily endpoint hit deferred to the CLI integration commit — the
fetcher is pure + transport-injectable, so the unit tests cover the
parsing and pivot logic, and the CLI wiring will be the place where
the live call is exercised end-to-end.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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