Add Trading212Provider core fetch

Context
-------
The Provider protocol is satisfied. This commit adds the first cut of
the concrete Trading212 implementation: one page of fills, mapped to
canonical Activities. Pagination, retries, and checkpointing on
resume are deliberately deferred to the next commit so this one stays
focused on the raw shape translation.

Design decisions
----------------
- One provider instance serves every T212 wrapper (ISA + Invest). T212
  exposes one API key per wrapper, so the caller hands over a list of
  (Account, api_key) pairs. `accounts()` returns only the Accounts —
  the keys never escape the provider.
- Auth: literal `Authorization: <api_key>`, NOT `Bearer <api_key>`.
  T212 quietly returns 401 for Bearer-prefixed keys. The test locks
  that in.
- Sell detection: T212 signs quantity (negative means closing a long
  or opening a short). We flip on the sign and store `abs(quantity)`,
  matching the Wealthfolio BUY/SELL convention.
- Null fills (cancelled orders) are silently dropped at parse time
  rather than surfacing to the caller.
- `external_id = t212:fill:<fill.id>` — the fill ID is stable per
  T212 docs and survives order cancellation/modification semantics.
- Ticker normalisation runs on ingress so downstream dedup + Wealthfolio
  see `VUAG` even though T212 reports `VUAGl_EQ`.
- `since` / `before` filter on `filledAt`. `before` is half-open
  (`< before`) so CronJobs can chain adjacent windows without
  double-counting the boundary.

Explicitly NOT in this change:
- Pagination (nextPagePath walk)
- 429 / 5xx retry
- Dividend / deposit endpoints (deferred — Phase 1.1, filed as
  beads follow-up if needed)

This change
-----------
- broker_sync/providers/trading212.py: `Trading212Provider` class +
  `Trading212Error` / `Trading212AuthError` exception hierarchy.
  `_item_to_activity` is pure and returns Optional so cancelled
  fills short-circuit without raising.
- tests/providers/test_trading212.py: MockTransport-driven tests for
  auth header shape, fill→Activity mapping (buy + sell sign flip),
  null-fill skip, since-filter, and both error types.

Test plan
---------
## Automated
- poetry run pytest -q  →  61 passed in 0.60s
- poetry run mypy broker_sync tests  →  Success: no issues found in 27 source files
- poetry run ruff check .  →  All checks passed!

## Manual Verification
Deferred to the CLI wiring commit — the live endpoint is 6 calls/min
and the full-volume dry run belongs with the env-driven command, not
the unit-level commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

broker_sync/providers/trading212.py

@@ -1,15 +1,143 @@
 from __future__ import annotations
 
 import re
+from collections.abc import AsyncIterator
+from datetime import datetime
+from decimal import Decimal
+from pathlib import Path
+from typing import Any
+
+import httpx
+
+from broker_sync.models import Account, Activity, ActivityType
+from broker_sync.providers._checkpoint import Checkpoint
+
+_BASE_URL = "https://live.trading212.com"
+_ORDERS_PATH = "/api/v0/equity/history/orders"
+_PAGE_LIMIT = 50
 
 _SUFFIX_RE = re.compile(r"(?:_US)?(?:[a-z])?_EQ$")
 
 
 def _normalise_ticker(raw: str) -> str:
-    """Strip T212's exchange-suffix decoration from a ticker.
-
-    T212 tags every ticker with `_EQ`, optionally preceded by a lowercase
-    letter ("l" for LSE) or `_US` for a US listing. Peel those off so the
-    symbol matches what Schwab / InvestEngine emit.
-    """
+    """Strip T212's exchange-suffix decoration from a ticker."""
     return _SUFFIX_RE.sub("", raw)
+
+
+class Trading212Error(Exception):
+    """Any non-retryable Trading212 API failure."""
+
+
+class Trading212AuthError(Trading212Error):
+    """HTTP 401 from Trading212 — API key is invalid or revoked."""
+
+
+class Trading212Provider:
+    """Concrete Provider for Trading212.
+
+    One instance serves every T212 wrapper the user owns (ISA + Invest)
+    — the caller hands over (Account, api_key) pairs and `fetch()` walks
+    each account's history in turn.
+    """
+
+    name = "trading212"
+
+    def __init__(
+        self,
+        *,
+        accounts: list[tuple[Account, str]],
+        checkpoint_dir: Path,
+        transport: httpx.AsyncBaseTransport | None = None,
+    ) -> None:
+        self._accounts = accounts
+        self._checkpoint_dir = checkpoint_dir
+        self._client = httpx.AsyncClient(
+            base_url=_BASE_URL,
+            timeout=30.0,
+            transport=transport,
+        )
+
+    def accounts(self) -> list[Account]:
+        return [acc for acc, _ in self._accounts]
+
+    async def close(self) -> None:
+        await self._client.aclose()
+
+    async def fetch(
+        self,
+        *,
+        since: datetime | None = None,
+        before: datetime | None = None,
+    ) -> AsyncIterator[Activity]:
+        for account, api_key in self._accounts:
+            async for activity in self._fetch_account(account, api_key, since, before):
+                yield activity
+
+    async def _fetch_account(
+        self,
+        account: Account,
+        api_key: str,
+        since: datetime | None,
+        before: datetime | None,
+    ) -> AsyncIterator[Activity]:
+        checkpoint = Checkpoint(
+            self._checkpoint_dir,
+            provider=self.name,
+            account_id=account.id,
+        )
+        page = await self._get_page(api_key, cursor=None)
+        for item in page.get("items", []):
+            activity = _item_to_activity(item, account)
+            if activity is None:
+                continue
+            if since is not None and activity.date < since:
+                continue
+            if before is not None and activity.date >= before:
+                continue
+            yield activity
+        # Checkpoint saved at end of page — resume on next run.
+        next_cursor = page.get("nextPagePath")
+        if isinstance(next_cursor, str):
+            checkpoint.save(next_cursor)
+
+    async def _get_page(self, api_key: str, cursor: str | None) -> dict[str, Any]:
+        params: dict[str, str | int] = {"limit": _PAGE_LIMIT}
+        if cursor is not None:
+            params["cursor"] = cursor
+        resp = await self._client.get(
+            _ORDERS_PATH,
+            params=params,
+            headers={"Authorization": api_key},
+        )
+        if resp.status_code == 401:
+            raise Trading212AuthError("Trading212 rejected API key (HTTP 401)")
+        if resp.status_code >= 400:
+            raise Trading212Error(f"Trading212 /orders HTTP {resp.status_code}: {resp.text}")
+        raw = resp.json()
+        assert isinstance(raw, dict)
+        return raw
+
+
+def _item_to_activity(item: dict[str, Any], account: Account) -> Activity | None:
+    fill = item.get("fill")
+    if fill is None:
+        return None
+    order = item["order"]
+    quantity_raw = Decimal(str(fill["quantity"]))
+    activity_type = ActivityType.BUY if quantity_raw > 0 else ActivityType.SELL
+    return Activity(
+        external_id=f"t212:fill:{fill['id']}",
+        account_id=account.id,
+        account_type=account.account_type,
+        date=_parse_iso(fill["filledAt"]),
+        activity_type=activity_type,
+        symbol=_normalise_ticker(order["ticker"]),
+        quantity=abs(quantity_raw),
+        unit_price=Decimal(str(fill["price"])),
+        currency=order["currency"],
+    )
+
+
+def _parse_iso(ts: str) -> datetime:
+    # T212 always emits `...Z`; datetime.fromisoformat handles `+00:00`.
+    return datetime.fromisoformat(ts.replace("Z", "+00:00"))