fidelity: push per-fund manual snapshot instead of gains-offset DEPOSIT

PlanViewer's DisplayValuation.action JSON already gives us current
fund units + unit price; we were parsing it and throwing it away,
emitting only a single 'unrealised-gains-offset' DEPOSIT to make
Wealthfolio's totals match the dashboard. That hack double-counted
the gain as a cash contribution, hiding £35k of pension growth from
every contribution/growth/ROI panel.

New flow:
- FidelityPlanViewerProvider exposes last_holdings + last_total_contribution
  after fetch() drains.
- fidelity-ingest CLI converts to a ManualSnapshotPayload (cost basis
  allocated proportionally by current fund value share) and posts to
  WF /api/v1/snapshots/import. WF auto-creates unknown fund symbols
  with kind=INVESTMENT, quoteMode=MANUAL, quoteCcy=GBP.
- The gains-offset emission is removed entirely. Historical offset
  rows already in WF are corrected at the dashboard layer by the
  dav_corrected view shipped in infra@2841347e.

WealthfolioSink gains push_manual_snapshots() + ManualSnapshotPayload /
SnapshotPosition wire types. 11 sink tests (3 new) + 9 fidelity
provider tests (2 changed, 1 new) all green; mypy + ruff clean.

tests/providers/test_fidelity_planviewer.py

@@ -1,19 +1,19 @@
 from __future__ import annotations
 
 import json
-from datetime import UTC, datetime
+from datetime import UTC, date, datetime
 from decimal import Decimal
 from pathlib import Path
 
 import pytest
 
-from broker_sync.models import Account, AccountType, ActivityType
+from broker_sync.models import Account, AccountType
 from broker_sync.providers.fidelity_planviewer import (
     ACCOUNT_ID,
     FidelityCreds,
     FidelityPlanViewerProvider,
     FidelityProviderConfigError,
-    _gains_offset_activity,
+    fidelity_holdings_to_snapshot,
 )
 from broker_sync.providers.parsers.fidelity import (
     parse_transactions_html,
@@ -96,21 +96,53 @@ def test_parse_valuation_fixture() -> None:
     assert set(h.units_by_source.keys()) >= {"SASC", "ERXS"}
 
 
-def test_gains_offset_emits_deposit_when_pot_exceeds_contributions() -> None:
+def test_holdings_to_snapshot_real_fixture() -> None:
     html = (_FIXTURES / "transactions-full.html").read_text()
     valuation = json.loads((_FIXTURES / "valuation.json").read_text())
-    txs = parse_transactions_html(html)
     holdings = parse_valuation_json(valuation)
-    as_of = datetime(2026, 4, 18, tzinfo=UTC)
-    offset = _gains_offset_activity(holdings, txs, as_of)
-    assert offset is not None
-    assert offset.activity_type in (ActivityType.DEPOSIT, ActivityType.WITHDRAWAL)
-    assert offset.amount is not None and offset.amount > 0
-    assert offset.external_id == "fidelity:gains:2026-04-18"
+    total_contrib = sum((tx.amount for tx in parse_transactions_html(html)),
+                        Decimal(0))
+
+    snapshot = fidelity_holdings_to_snapshot(
+        holdings=holdings,
+        total_real_contribution=total_contrib,
+        as_of=date(2026, 4, 18),
+    )
+    assert snapshot is not None
+    assert snapshot.date == date(2026, 4, 18)
+    assert snapshot.currency == "GBP"
+    # Cost basis sums to the cash contributions (allocated by fund value share)
+    sum_cost = sum((p.total_cost_basis for p in snapshot.positions), Decimal(0))
+    assert abs(sum_cost - total_contrib) < Decimal("1")
+    # Meta scheme had KDOA + LAFC + one other at fixture time; the
+    # dominant fund must be KDOA.
+    symbols = [p.symbol for p in snapshot.positions]
+    assert "KDOA" in symbols
+    kdoa = next(p for p in snapshot.positions if p.symbol == "KDOA")
+    assert kdoa.quantity > 0
+    # Proportional cost-basis allocation: KDOA holds nearly the whole pot
+    # so it should get the lion's share of cost
+    kdoa_share = kdoa.total_cost_basis / sum_cost
+    assert kdoa_share > Decimal("0.9")
+    # cashBalances zero — pension contributions flow straight into funds
+    assert snapshot.cash_balances == {"GBP": Decimal(0)}
 
 
-def test_gains_offset_none_when_no_holdings() -> None:
-    assert _gains_offset_activity(
-        holdings=[], transactions=[],
-        as_of=datetime(2026, 4, 18, tzinfo=UTC),
+def test_holdings_to_snapshot_none_when_no_holdings() -> None:
+    assert fidelity_holdings_to_snapshot(
+        holdings=[], total_real_contribution=Decimal("100"),
+        as_of=date(2026, 4, 18),
     ) is None
+
+
+def test_provider_caches_holdings_for_cli_snapshot_push() -> None:
+    """The CLI reads `last_holdings` after fetch() drains to push the
+    manual snapshot. This guards the contract that fetch() populates the
+    attribute even when no Activity is yielded (e.g., backfill window
+    cut-off)."""
+    prov = FidelityPlanViewerProvider(FidelityCreds(
+        storage_state_path="/tmp/x", plan_id="META",
+    ))
+    # Pre-fetch state: empty
+    assert prov.last_holdings == []
+    assert prov.last_total_contribution == Decimal(0)