[yohamta0]

Summary

First step toward showing a run's model usage in tokens and cost, per step and per run. llm.Usage carried only prompt, completion and total counts, and providers filled those inconsistently. This PR makes every provider report the same, fuller picture. Nothing records or displays it yet; that comes in the next PRs.

llm.Usage gains:

• CachedPromptTokens: the part of the prompt read from the prompt cache.
• CacheWritePromptTokens: the part written to the cache (Anthropic).
• ReasoningTokens: the part of the completion spent on reasoning.
• Cost *float64: what the provider reported the call cost in US dollars. nil means not reported; zero is a reported free call. Today only OpenRouter reports one, and so do gateways that relay its answers and charge exactly that.

Every provider now reports PromptTokens with cached tokens included and CompletionTokens with reasoning tokens included, naming both parts.

Changes

• providers/chatusage (new): one decoder for the usage object of OpenAI's chat completions API and of APIs compatible with it (prompt_tokens_details.cached_tokens, completion_tokens_details.reasoning_tokens, cost), plus the Responses API's (input_tokens_details, output_tokens_details).
  • openai, openrouter, zai and local share the chat completions decoder, replacing four copies of the same three-field struct.
  • The OpenAI computer-use session and Codex share the Responses API decoder.
• Anthropic:
  • The prompt count now includes cache_read_input_tokens and cache_creation_input_tokens, which the API reports apart from input_tokens.
  • Fixes a streaming bug. message_delta's usage, which carries only output tokens, replaced message_start's, so every streamed message reported 0 prompt tokens. Each event's usage is now merged.
  • The computer-use session reads usage the same way as chat.
• Gemini: chat usage now counts thinking tokens in the completion, as Gemini computer use already did, and names cached content.
• Codex: stops subtracting cached tokens from the prompt, matching every other provider.

Behaviour change to note

The agent loop's observation aging compares the latest prompt size with max_context_tokens. For Anthropic with prompt caching, and for Codex, that size now includes cached tokens. They still occupy the context window, so aging starts when the context is actually that large rather than later.

Test plan

• chatusage: details and cost decoded, cost unknown when absent, a reported zero kept, Responses API counts.
• TestChatCountsCachedInput: Anthropic chat prompt includes cache reads and writes.
• TestStreamResponse_MergesUsage: a streamed Anthropic message keeps message_start's input when message_delta reports only output. It fails without the fix.
• TestStreamUsageCost: OpenRouter's streamed final chunk keeps its cost, cached and reasoning tokens.
• TestStreamResponse_Usage: Gemini completion includes thinking tokens, and cached content is named.
• The Codex stream test now expects the input with cached tokens included.
• The existing computer-use and stream tests for Anthropic, Gemini, OpenAI, OpenRouter and Codex pass. golangci-lint v2.13.2 is clean for darwin, linux and windows.

Summary by CodeRabbit

• Improvements
  • Token usage totals now include cached input and reasoning tokens where reported, with cached reads and cache writes shown separately.
  • Usage summaries from supported AI providers now include reported request costs, distinguishing free calls from costs that were not reported.
  • Streaming responses provide more complete usage details by combining token counts across events and including available usage in completed responses.
  • Token usage details are now reported consistently across supported providers, including cached input, reasoning, and request cost where available.

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Commits

Reviewing files that changed from the base of the PR and between 6271f2c and 554d92f.

Files selected for processing: 2

• internal/llm/providers/chatusage/chatusage.go
• internal/llm/providers/chatusage/chatusage_test.go

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Walkthrough

The change adds cache, reasoning, and reported-cost fields to normalized LLM usage. It adds shared usage conversions and updates Anthropic, Gemini, and several chat providers to use expanded usage data in complete and streaming responses.

Changes: LLM usage accounting

Layer / File(s)	Summary
Usage fields and shared conversions internal/llm/types.go, internal/llm/providers/chatusage/*	llm.Usage adds cached-prompt, cache-write, reasoning, and optional cost fields. Shared types convert chat-completion and Responses API usage details into llm.Usage.
Anthropic cache usage internal/llm/providers/anthropic/anthropic.go, internal/llm/providers/anthropic/computer.go, internal/llm/providers/anthropic/*_test.go	Anthropic includes cache creation and cache read counts in prompt and total tokens. Streaming usage merges cumulative counts and includes converted usage in completion events. Tests cover chat and streaming counts.
Gemini usage conversion internal/llm/providers/gemini/computer.go, internal/llm/providers/gemini/gemini.go, internal/llm/providers/gemini/gemini_test.go	Gemini converts usage metadata for complete and streaming responses. The conversion includes cached prompt and reasoning tokens, with completion tokens combining candidate and thought counts.
Shared usage across chat providers internal/llm/providers/local/local.go, internal/llm/providers/openai/*, internal/llm/providers/openaicodex/*, internal/llm/providers/openrouter/*, internal/llm/providers/zai/zai.go	These providers use shared usage types and conversions in complete and streaming responses. Tests check cached tokens, reasoning tokens, and reported cost.

Priority: Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: Minimal · up to 554d9

No actionable merge-blocking risk remains in the reviewed change.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 78.57% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 18 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: reporting cached tokens, reasoning tokens, and cost in model usage.
Description check		The description provides a detailed summary, change list, behavior change, and test plan. It omits the template's Related Issues and Checklist sections, but it otherwise documents the scope and valida…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description provides a detailed summary, change list, behavior change, and test plan. It omits the template's Related Issues and Checklist sections, but it otherwise documents the scope and validation clearly.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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Inline comments:
Review comments at @internal/llm/providers/chatusage/chatusage.go:
- Around line 23-25: Add a cache-write token field to promptTokensDetails with
the matching JSON key, then update Usage.LLM() to assign it to
llm.Usage.CacheWritePromptTokens so OpenRouter cache-write usage is preserved.

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• Source mode: Auto
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Commits

Reviewing files that changed from the base of the PR and between ec01562 and 6271f2c.

Files selected for processing: 18

• internal/llm/providers/anthropic/anthropic.go
• internal/llm/providers/anthropic/anthropic_test.go
• internal/llm/providers/anthropic/chat_test.go
• internal/llm/providers/anthropic/computer.go
• internal/llm/providers/chatusage/chatusage.go
• internal/llm/providers/chatusage/chatusage_test.go
• internal/llm/providers/gemini/computer.go
• internal/llm/providers/gemini/gemini.go
• internal/llm/providers/gemini/gemini_test.go
• internal/llm/providers/local/local.go
• internal/llm/providers/openai/computer.go
• internal/llm/providers/openai/openai.go
• internal/llm/providers/openaicodex/codex.go
• internal/llm/providers/openaicodex/codex_test.go
• internal/llm/providers/openrouter/openrouter.go
• internal/llm/providers/openrouter/openrouter_test.go
• internal/llm/providers/zai/zai.go
• internal/llm/types.go

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