JSON output gives no signal when a model has no price; cost silently reads as 0 #1736

Summary

When a model has no known price, its usage is charged at 0. Table output prints a stderr warning ("Missing pricing for X; cost excludes this model"), but --json output carries no signal at all: the row shows "totalCost": 0 and the model breakdown looks identical to a free model. Scripts, dashboards, and the statusline JSON cache cannot tell "free" from "unknown", and the number silently understates spend until the pricing snapshot catches up.

This is the recurring shape behind most pricing issues here (new model lands, users see $0 for days, nobody notices in JSON). The detection already exists: ModelBreakdown.missing_pricing is computed for every entry, but it is #[serde(skip_serializing)] and only the table path reads it.

Reproduce

Any transcript with a model absent from the pricing map. On my machine a pi session logged openrouter/auto-beta:

ccusage pi monthly            # stderr: WARN  Missing pricing for [pi] openrouter/auto-beta ...
ccusage pi monthly --json     # no warning, no field, cost 0

Reproduced on main ef300c9 and on the published 20.0.20.

Proposal

Additive JSON fields, present only when relevant, so existing consumers and the 14 snapshot files that contain totals do not change for priced reports:

• totals.unpricedModels: sorted, deduplicated model names, key omitted when empty. Scripts use .totals.unpricedModels // [].
• modelBreakdowns[].missingPricing: true, omitted when false. Focused codex reports set the same flag on the affected entries of each period's models map.
• --no-cost keeps both, since they describe availability rather than amounts.
• Detection follows the cost mode: display mode and auto mode with stored costs look nothing up and report nothing. Docs state that an absent key means "no unpriced usage detected under this mode", not "every price is current".

Covers daily, weekly, monthly, and session reports for every agent, including --instances, --sections, and --by-agent. Two paths have no totals object and are left for a follow-up if wanted: blocks and session --id.

Two design questions for you

1. Placement. The list lives inside totals next to the numeric aggregates. A consumer that iterates and sums every totals value would break only on a report with an unpriced model. Alternative: a top-level unpricedModels next to totals, or a pricing object. I went with totals because that is where scripts already look, and omit-when-empty keeps priced reports byte-identical. Happy to move it.
2. Name. unpricedModels reads naturally with .totals; missingPricingModels would match the missingPricing flag exactly. Your call.

I have this implemented with tests (core, unified, codex, cost-mode suppression, zero-rate vs unknown, --no-cost survival) and a docs section, and will open the PR right after triage.