Added offline token cost estimation with hard-isolated execution path

[saksham-jain177]

Implements --estimate-cost to provide an offline, pre-flight estimate of token usage and cost.

• Estimation runs in a fully isolated path before any provider initialization or network activity
• Token counting is approximate and provider-agnostic, as specified in the issue
• Cost lookup is best-effort and defaults to unavailable for unknown models
• Includes unit tests for the estimator

Closes #57

[brammittendorff]

Thanks for the suggestion! litellm is great but it's a pretty heavy dependency just for pricing lookups - it pulls in a lot of LLM client code we don't need.

Found a lighter option: genai-prices from Pydantic. It's specifically built for pricing data only. Covers 1000+ models across 29 providers, handles tiered pricing (Gemini), off-peak rates (DeepSeek), etc. No client bloat.

https://github.com/pydantic/genai-prices

Or we could just vendor their slim JSON directly.

Either way, we should add a disclaimer to the CLI output warning users that cost estimates are approximate and may not reflect current pricing.

What do you think?

[saksham-jain177]

I see, that makes sense. genai-prices looks like a good fit and avoids pulling unnecessary client code
if you’re aligned, I can update the PR to use genai-prices (or the JSON) while adding a clear disclaimer that estimates are approximate

I kept pricing static initially to stay strictly within the original issue scope.

[brammittendorff]

I see, that makes sense. genai-prices looks like a good fit and avoids pulling unnecessary client code if you’re aligned, I can update the PR to use genai-prices (or the JSON) while adding a clear disclaimer that estimates are approximate

I kept pricing static initially to stay strictly within the original issue scope.

Sounds good, I’m aligned.
Let’s use genai-prices directly, it’s small and keeps pricing updates centralized.
A clear disclaimer that prices are estimates is required.

Thanks for the thoughtful work on this.

[saksham-jain177]

Updated the PR to use genai-prices for dynamic pricing and added a clear disclaimer that estimates are approximate
All changes stay strictly within the original scope and CI is clean could you give it a review when you get a chance ?

[brammittendorff]

Updated the PR to use genai-prices for dynamic pricing and added a clear disclaimer that estimates are approximate All changes stay strictly within the original scope and CI is clean could you give it a review when you get a chance ?

A bit late but will do!

[brammittendorff]

from put them in the top of the file "if you can" or else isort has no use in our pipelines.