Question

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Split-Brain: Analyst-Grade Reasoning Without Raw Transactions on the Server

To deliver analyst-grade answers without centralizing the transaction tape, we engineered a deliberate split-brain: the server never needs your raw history to answer “What is my largest position?”—it needs a semantic summary—allocation, scale, and performance—that fits in a few hundred tokens. This post is the technical truth for that claim: memory on the edge, reasoning in the cloud, one bounded string across the boundary.

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The three zones

1. Local edge (browser): normalized Trade[], computed Position map, UI state. This is where thousands of CSV rows (after import) live as structured objects — not as a paste buffer in ChatGPT.
2. Compiler (client): buildPortfolioContext in app/lib/ai/contextBuilder.ts — deterministic reduction to a fixed-schema text block.
3. Stateless API: POST /api/ai/chat — receives context + message (+ optional attachment for paid tier), streams the model output, does not persist the payload as portfolio rows.

Flow: the app builds that summary on the client, then sends it with each question — the API does not pull your full trade history from a server-side portfolio database for this path.

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The literal compiler: buildPortfolioContext

Below is the actual function as implemented today. Read it as a token funnel: many trades in → one small string out.

const TOP_HOLDINGS_COUNT = 10;

export function buildPortfolioContext(
  trades: Trade[],
  positions?: Record<string, Position> | Position[]
): string {
  const positionMap: Record<string, Position> = (() => {
    if (positions !== undefined) {
      if (Array.isArray(positions)) {
        const map: Record<string, Position> = {};
        positions.forEach((p) => {
          map[p.ticker] = p;
        });
        return map;
      }
      return positions;
    }
    const { positions: derived } = calculatePositions(trades);
    return derived;
  })();

  const positionList = Object.values(positionMap).filter((p) => p.shares > 0);
  const totals = calculatePortfolioTotals(positionMap);

  const lines: string[] = [];
  lines.push('Portfolio summary (for personalization only):');
  lines.push(`Total positions: ${totals.totalPositions}`);
  lines.push(`Total trades: ${trades.length}`);
  if (totals.totalInvested > 0 || totals.totalCurrentValue > 0) {
    lines.push(`Total invested (USD equiv): ${totals.totalInvested.toFixed(2)}`);
    lines.push(`Total current value (USD equiv): ${totals.totalCurrentValue.toFixed(2)}`);
    lines.push(
      `Total unrealized P/L: ${totals.totalUnrealizedPL.toFixed(2)} (${totals.totalUnrealizedPLPercent.toFixed(1)}%)`
    );
  }

  if (positionList.length > 0) {
    const byValue = [...positionList].sort((a, b) => b.currentValue - a.currentValue);
    const top = byValue.slice(0, TOP_HOLDINGS_COUNT);
    lines.push('');
    lines.push('Top holdings by current value:');
    top.forEach((p) => {
      const pct =
        totals.totalCurrentValue > 0 ? (p.currentValue / totals.totalCurrentValue) * 100 : 0;
      lines.push(
        `  ${p.ticker}: ${p.shares.toFixed(2)} shares, ${p.currency} ${p.currentValue.toFixed(2)} (${pct.toFixed(1)}%), P/L ${p.unrealizedPLPercent.toFixed(1)}%`
      );
    });
  }

  return lines.join('\n');
}

What this proves

• Thousands of rows in trades collapse to: one count, portfolio totals, and at most ten ticker lines. Typical output is ~1–2 KB of UTF-8 — not a dump of every fill, date, or broker note.
• No CSV, no “Description”, no “Account Number” column appears here — those fields either never made it into Trade, or they are not selected for emission because the function only prints the allowed template.

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Wire format: what the client actually sends

AskAIModal posts JSON:

body: JSON.stringify({
  message: text,
  context: portfolioContext,
  ...(isPaid && attachedContent ? { attachedContent } : {}),
}),

So the only default portfolio signal is portfolioContext — the string from buildPortfolioContext. The server does not pull trades from a database for this path; it trusts the client-built summary (and optional attachment) for that session.

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Attachment boundary (precision matters)

Paid users may send attachedContent. That is full text for one turn — a different privacy contract than the default top-N summary. Be explicit in product copy and UX.

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Takeaway

Analyst-grade does not require server-side row replay. It requires correct aggregation locally plus grounded prompts on the server (system instructions and live quote injection — the topic of Part 6).

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Part 2 of Sovereign Engineering.

Read the full Sovereign Intelligence book or try the app.