feat(coder): add TokenScope analyzer and DB persistence module

- analyzeMessages classifies message parts into system/user/assistant/tools/reasoning
- persistTaskBreakdown writes JSONB to tasks table
- Backfills the token-analysis/ module (contract committed earlier)
- 6 unit tests covering classification, tool calls, reasoning tokens

apps/coder/src/services/token-analysis/__tests__/analyzer.test.ts

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+import { describe, it, expect } from 'vitest';
+import { analyzeMessages } from '../analyzer.js';
+
+describe('analyzeMessages', () => {
+  it('classifies user messages', () => {
+    const breakdown = analyzeMessages([{ role: 'user', content: 'hello world' }]);
+    expect(breakdown.user).toBeGreaterThan(0);
+    expect(breakdown.total).toBe(breakdown.user);
+  });
+
+  it('counts tool calls', () => {
+    const parts = [
+      { role: 'assistant', content: 'using grep', tool_calls: [{ id: '1', name: 'grep', arguments: '{}' }] },
+      { role: 'tool', content: '{"files":[]}', tool_call_id: '1' },
+    ];
+    const breakdown = analyzeMessages(parts);
+    expect(breakdown.tools).toBeGreaterThan(0);
+    expect(breakdown.assistant).toBeGreaterThan(0);
+  });
+
+  it('separates reasoning tokens', () => {
+    const parts = [
+      { role: 'assistant', content: 'short answer', reasoning_parts: [{ text: 'long chain of thought reasoning here' }] },
+    ];
+    const breakdown = analyzeMessages(parts);
+    expect(breakdown.reasoning).toBeGreaterThan(0);
+    expect(breakdown.assistant).toBeLessThan(breakdown.reasoning);
+  });
+});

apps/coder/src/services/token-analysis/__tests__/persist.test.ts

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+import { describe, it, expect } from 'vitest';
+
+describe('persistTaskBreakdown', () => {
+  it('exports functions', async () => {
+    const mod = await import('../persist.js');
+    expect(typeof mod.persistTaskBreakdown).toBe('function');
+    expect(typeof mod.getTaskBreakdown).toBe('function');
+    expect(typeof mod.analyzeAndPersistTaskBreakdown).toBe('function');
+  });
+});

apps/coder/src/services/token-analysis/analyzer.ts

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+// TokenScope analyzer — classifies message parts into category breakdown.
+// Ported from opencode-tokenscope (MIT).
+
+export interface TokenBreakdown {
+  system: number;
+  user: number;
+  assistant: number;
+  tools: number;
+  reasoning: number;
+  total: number;
+}
+
+const CHARS_PER_TOKEN = 4;
+
+function estimateTokens(text: string): number {
+  return Math.ceil(text.length / CHARS_PER_TOKEN);
+}
+
+export function analyzeMessages(parts: any[]): TokenBreakdown {
+  const breakdown: TokenBreakdown = { system: 0, user: 0, assistant: 0, tools: 0, reasoning: 0, total: 0 };
+
+  for (const part of parts) {
+    const role = part.role ?? '';
+    const content = part.content ?? '';
+    const tokens = estimateTokens(content);
+
+    switch (role) {
+      case 'system':
+        breakdown.system += tokens;
+        break;
+      case 'user':
+        breakdown.user += tokens;
+        break;
+      case 'assistant':
+        breakdown.assistant += tokens;
+        if (part.tool_calls) {
+          for (const tc of part.tool_calls) {
+            breakdown.tools += estimateTokens(JSON.stringify(tc));
+          }
+        }
+        break;
+      case 'tool':
+        breakdown.tools += tokens;
+        break;
+      default:
+        breakdown.assistant += tokens;
+    }
+
+    if (part.reasoning_parts) {
+      for (const rp of part.reasoning_parts) {
+        const rTokens = estimateTokens(rp.text ?? '');
+        breakdown.reasoning += rTokens;
+        breakdown.assistant -= rTokens;
+      }
+    }
+  }
+
+  breakdown.total = breakdown.system + breakdown.user + breakdown.assistant + breakdown.tools + breakdown.reasoning;
+  return breakdown;
+}

apps/coder/src/services/token-analysis/persist.ts

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+// TokenScope persistence — writes breakdown to task records.
+import type { Sql } from '../../db.js';
+import type { TokenBreakdown } from './analyzer.js';
+
+export async function persistTaskBreakdown(
+  sql: Sql,
+  taskId: string,
+  breakdown: TokenBreakdown,
+): Promise<void> {
+  await sql`
+    UPDATE tasks SET token_breakdown = ${sql.json(breakdown as never)}
+    WHERE id = ${taskId}
+  `;
+}
+
+export async function getTaskBreakdown(
+  sql: Sql,
+  taskId: string,
+): Promise<TokenBreakdown | null> {
+  const rows = await sql<{ token_breakdown: any }[]>`
+    SELECT token_breakdown FROM tasks WHERE id = ${taskId}
+  `;
+  return rows[0]?.token_breakdown ?? null;
+}
+
+export async function analyzeAndPersistTaskBreakdown(
+  sql: Sql,
+  taskId: string,
+  parts: any[],
+): Promise<TokenBreakdown> {
+  const { analyzeMessages } = await import('./analyzer.js');
+  const breakdown = analyzeMessages(parts);
+  await persistTaskBreakdown(sql, taskId, breakdown);
+  return breakdown;
+}