[mikemaccana]

The companion program now rejects a Pyth price whose confidence interval is wider than 1% of the price. The check fails with OracleConfidenceTooWide and shipped in quicknode/solana-program-examples#188, which is merged and on main. Following the "fixed there, not described here" rule, this PR makes the chapter describe the defense in place of the gap.

Changes to building-financial-products-in-solana/managed-fund.md:

• Failure Modes: the "a production fund should" sentence is replaced with a description of the check. The new text explains why it matters: deposits are priced from the price feed, and rebalance sets its slippage floor from it. It notes that withdrawal reads no price, so investors can still leave in kind. It names test_wide_confidence_price_rejected.
• The same bullet said that no "deposit, withdrawal, or rebalance" runs on a bad price. Withdrawal never reads a price, so it now says "deposit or rebalance".
• Valuation paragraph: the list of price-load rejections gains the confidence check, as its own sentence to stay under the lint's sentence-length limit.
• Tests paragraph: names the new test.

OracleConfidenceTooWide and test_wide_confidence_price_rejected both exist in the companion repository's main.

npm run lint, node scripts/check-figure-geometry.mjs and npm run build-pdf all pass.

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