Update session metrics on createTurn and terminal writes

[bhaveshpatel640]

Summary

Update session.metrics in the same transactions as turn writes: turn count on create, cost and duration on a winning terminal transition.

Linear: AGE-2010

Changes

• createTurn increments total_turns on the session tip update (same tx)
• running → terminal (updateTurnState, or freeze when cancel applies) adds total_cost_in_usd and completed_at − created_at
• Postgres, SQLite, and InMemory; store contract tests for increment, cost/duration, two-turn sums, freeze once.

How was this tested?

• Store contract (InMemory) plus pnpm test:store:sqlite and scripts/test-store-local.sh

Checklist

• I have read the contributing guidelines
• pnpm build, pnpm test, pnpm typecheck, pnpm lint:ci, and pnpm format:check pass locally
• Tests added/updated where it makes sense
• No hand-edits to generated code (packages/trueforge-sdk, .github/fern/openapi/openapi.json, docs/openapi.json) — fork PRs omit SDK regen; maintainers regenerate after merge
• Docs / .env.example updated if configuration or behavior changed

---

Note

Medium Risk
Touches core session-store transactions and billing-adjacent aggregates; incorrect double-folding or missed increments would skew session metrics under concurrency, though first-terminal-wins semantics are tested.

Overview
Session-level aggregates (total_turns, total_cost_in_usd, total_duration_ms) are now updated inside the same store transactions as turn lifecycle writes, with contract docs on ISessionStore describing the behavior.

createTurn increments total_turns on the session tip update (Postgres/SQLite via jsonb_set; in-memory via += 1), rolled back if the rest of the turn insert fails. When a turn first becomes terminal—updateTurnState or freezeAndGetTurn when the running→cancelled update wins—the store adds the turn’s metrics.total_cost_in_usd (default 0) and duration from completed_at − created_at (truncated, floored at 0). Already-terminal freezes and losing second terminal writes do not fold again.

Shared helpers implement this for Postgres, SQLite, and InMemorySessionStore; the contract suite adds coverage for per-create increment, single fold, conflict idempotency, and multi-turn sums.

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