[BUG] /context uses 200k window for claude-fable-5, which has a 1M context window

Environment

• Claude Code version: 2.1.207
• Platform: macOS (darwin 25.5.0)
• Model: claude-fable-5 (Fable 5)

Description

/context (and the autocompact logic) assumes a 200k token context window when the session runs on claude-fable-5, but Fable 5 has a 1M context window (1M is also the default; 128K max output).

As a result, /context reports usage over 100% and warns that autocompact is imminent, while actual usage is far below the real limit.

Steps to reproduce

1. Start a session with model claude-fable-5.
2. Accumulate ~220k tokens of conversation.
3. Run /context.

Actual behavior

Context Usage
220.7k/200k tokens (110%)
⚠ Context is 110% full
Autocompact will trigger soon, which discards older messages.

Expected behavior

The denominator should be the model's real context window (1M for claude-fable-5), i.e. ~22% usage in the example above, and autocompact thresholds should be computed against it.

The Models API exposes the correct value:
GET /v1/models/claude-fable-5 → max_input_tokens: 1000000

so the limit could be resolved per-model at runtime instead of a hardcoded 200k.

Notes

• Token counting appears correct; only the window size / percentage / autocompact threshold are wrong.
• Possibly affects other 1M-context models if the limit is hardcoded per tier rather than per model.