fix(pricing): let custom-pricing.json express a free model

[junhoyeo]

Addresses the one genuinely-open ask in #1021.

Problem

custom-pricing.json is the documented escape hatch for models no upstream dataset publishes. But custom.rs required at least one rate to be positive:

if !input_cost_per_token.is_some_and(|value| value > 0.0)
    && !output_cost_per_token.is_some_and(|value| value > 0.0)
{
    return Err("at least one of input or output pricing must be present and positive".into());
}

So a free tier was unexpressable. The user knows the price is $0, the file refuses to record it, and the usage stays unpriced — excluded from submission with no way to correct it. As @sigco3111 put it: "I can't use the documented escape hatch for free-tier models."

Fix

Reject only absence, not zero.

0.0 is an assertion — "this model is free". None is an absence — "unknown". Reading a rate-less row as free would invent a $0 total for genuinely unknown pricing, so that case still errors.

This is the same free-vs-absent confusion as the Cursor cache-creation gap in #1067, at the user-facing layer instead of the built-in table.

Negative rates still rejected — a negative price is nonsense, not a statement about cost.

The reporter's other two asks need no code

• --prune-unpriced (their open question 2) — fix(submit): exclude unpriced usage without aborting #1053 made unpriced rows exclude-with-warning instead of failing the batch, and made it the default rather than a flag. Shipped in v4.11.0.
• Missing zai/ provider prefix — no longer reproducible. Verified: tokscale pricing zai/glm-4.5-flash → zai/glm-4.5-flash, and bare glm-4.5-flash resolves to the same key.

Their first ask — a subscription-pricing carrier for github-copilot/ — is a larger design question I'd rather not fold in here; Copilot already prices at the underlying model's rates (github_copilot/gpt-4o → gpt-4o), so the gap is narrower than when it was filed.

Tests

• cargo test -p tokscale-core --lib — 1,490 passed, 0 failed
• fmt and clippy --all-targets -- -D warnings clean
• drops_entries_with_zero_prices renamed to keeps_free_models_but_still_drops_negative_prices and its all-zero assertion inverted; it now asserts the row loads with Some(0.0) on both rates, while the negative-price case stays dropped

---

Summary by cubic

Allow custom-pricing.json to declare free models by accepting 0.0 token rates, so free-tier usage is priced at $0 instead of excluded. Updated READMEs to document that an explicit zero is allowed and different from an omitted (unknown) field.

• Bug Fixes
  • Accept 0.0 for input/output rates; only error if both rates are absent.
  • Continue rejecting negative rates.
  • Updated test to assert all-zero rows load with Some(0.0) and negative-rate rows are dropped.
  • Updated README.md, README.ja.md, README.ko.md, README.zh-cn.md to explain that 0 means free while omission means unknown.

^{Written for commit ca39b51. Summary will update on new commits.}

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
tokscale	Ignored	Preview	Aug 8, 2026 12:01am

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}