Anil Pai
d3ffe15311
## Fix incorrect context size limits for GitHub Copilot Chat models Fixes #44909 ### Problem The agent panel was displaying incorrect token limits for GitHub Copilot models. Users reported that: - The agent panel always showed a **128K token limit** for all GitHub Copilot models, regardless of their actual context window size - Claude models (e.g., Claude 3.7 Sonnet, Claude Opus 4.5) were showing ~90K instead of their actual 200K context window - GPT-4o was showing 110K instead of its actual 128K context window - Users could continue using models beyond the displayed limit, which worked but was confusing ### Root Cause The `max_token_count()` method in `copilot_chat.rs` was returning `max_prompt_tokens` instead of `max_context_window_tokens`: ```rust // Before (incorrect) pub fn max_token_count(&self) -> u64 { self.capabilities.limits.max_prompt_tokens } ``` GitHub's API returns three different token-related fields: - `max_context_window_tokens`: The **full context window size** (e.g., 200K for Claude 3.7) - `max_prompt_tokens`: GitHub's limit for prompt input (e.g., 90K for Claude 3.7) - `max_output_tokens`: Maximum output tokens (e.g., 16K) The `max_token_count()` method in the `LanguageModel` trait is expected to return the **full context window size** — this is consistent with all other providers (Anthropic returns 200K for Claude, OpenAI returns 128K for GPT-4o, etc.). ### Solution <img width="583" height="132" alt="Screenshot 2026-01-25 at 1 07 53 AM" src="https://github.com/user-attachments/assets/847e2fdb-635d-44bc-a630-2d4867ba8c32" /> Changed `max_token_count()` to return `max_context_window_tokens`: ```rust // After (correct) pub fn max_token_count(&self) -> u64 { self.capabilities.limits.max_context_window_tokens as u64 } ``` ### Impact | Model | Before | After | |-------|--------|-------| | Claude 3.7 Sonnet | 90,000 | **200,000** | | Claude Opus 4.5 | 90,000 | **200,000** | | GPT-4o | 110,000 | **128,000** | ### Testing Added a new test `test_max_token_count_returns_context_window_not_prompt_tokens` that: 1. Deserializes model JSON with distinct `max_context_window_tokens` and `max_prompt_tokens` values 2. Verifies Claude 3.7 Sonnet returns 200,000 (context window), not 90,000 (prompt tokens) 3. Verifies GPT-4o returns 128,000 (context window), not 110,000 (prompt tokens) All existing tests continue to pass: ``` running 4 tests test tests::test_unknown_vendor_resilience ... ok test tests::test_max_token_count_returns_context_window_not_prompt_tokens ... ok test tests::test_resilient_model_schema_deserialize ... ok test result: ok. 4 passed; 0 failed ``` Release Notes: - copilot: Fixed incorrect context window size displayed for GitHub Copilot Chat models in the agent panel.
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