[smolinari]

Summary

The detection-and-capture half of #12. A Claude subscription with extra usage enabled spills into per-token "usage credits" once the plan allowance runs out; the logs record no cut-over and no per-turn pool attribution, so this changes what Modelog says, never what it computes.

What changed

• Third billing state. detectBilling() now also reads oauthAccount.hasExtraUsageEnabled and yields "subscription-extra", with dashboard and MCP copy stating plainly that the estimated/billed split is not knowable from disk. billingType alone was never stable enough to carry this — switching an account's payment method has been observed to flip it. Precedence: prepaid still wins (per-token billing is already real money). The modelog.billingMode setting stays a binary override; only detection can land on the third state.
• Per-turn capture. Turn gains serviceTier (usage.service_tier — Anthropic's own field, distinct from Codex's OpenAI tier riding in speed) and fallbackCredit (usage.fallback_credit, the slot built for marking credit-billed turns; observed only as null, so a populated value is serialized verbatim for the day its shape is known, displayed nowhere, priced never).
• Fail-closed pricing. serviceTier joins the modifier check: "standard" prices at 1× from a new service_tier table in pricing.json; an unrecognised value — the card's Batch discount is real but its wire value unconfirmed against a log — yields an unavailable cost rather than a wrong one.
• Store schema v6 (two columns, additive migration — no row wipe needed), CAPTURE_VERSION 3 so pre-capture rows report the gap honestly through uncapturedFields.

Validation

• 333 tests green, including new test/billing.test.ts modeled on the real oauthAccount shape of the account that crossed into usage credits.
• Real-capture end-to-end: all 290 deduplicated turns carry "standard" and still price to the cost-state-exact $61.33, zero unpriced — the new fail-closed modifier cannot regress existing data.

Not in this PR

cost-state reconciliation ingestion (#12 item 3) — needs its own design pass; #12 stays open to track it.

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