fix(hooks): use 1M context limit for Claude Opus 4.6

[morphaxl]

Summary

• Add isOpus46() check to context-window-monitor and preemptive-compaction hooks so Claude Opus 4.6 uses its actual 1M context limit instead of the hardcoded 200K default
• The ANTHROPIC_1M_CONTEXT env var is preserved as a fallback for other Anthropic models

Problem

Both hooks hardcode 200_000 as the Anthropic context limit, gated behind the ANTHROPIC_1M_CONTEXT env var. This causes premature compaction at 200K for Opus 4.6 sessions, which actually support 1M context. The env var workaround applies a blanket 1M to all Anthropic models, which is incorrect for 200K models like Sonnet 4.5.

Solution

Check the modelID for Opus 4.6 patterns (opus-4-6, opus-4.6) and use 1M for that model specifically. All other Anthropic models continue using the existing 200K default (or env var override).

Changes

• src/hooks/context-window-monitor.ts — added modelID to interface, isOpus46() check
• src/hooks/preemptive-compaction.ts — added isOpus46() check before provider-based fallback
• src/hooks/preemptive-compaction.test.ts — updated tests for Opus 4.6 vs non-Opus behavior

Testing

• bun run typecheck ✅
• bun test src/hooks/preemptive-compaction.test.ts — 5/5 pass ✅

[github-actions]

All contributors have signed the CLA. Thank you! ✅
_{Posted by the CLA Assistant Lite bot.}

[morphaxl]

I have read the CLA Document and I hereby sign the CLA

[morphaxl]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Requires human review: Logic error in preemptive-compaction.ts: isOpus46 check overrides anthropic provider check entirely. If modelID is undefined for non-anthropic provider, it falls through to DEFAULT_ACTUAL_LIMITCorrect}

[andrerfneves]

🔥 🔥 🔥

[cryptobetEU]

gogogo

[cryptobetEU]

It crashed when I told AI to apply the fix, it fixed it by doing this;

● Here are the code blocks for the fix:

---

1. Create new file: src/hooks/model-utils.ts

export const OPUS_4_6_LIMIT = 1_000_000

export function isOpus46(modelID: string | undefined): boolean {
if (!modelID) return false
return modelID.includes("opus-4-6") || modelID.includes("opus-4.6")
}

---

2. Update src/hooks/context-window-monitor.ts

Remove the local declarations:
// DELETE THESE LINES:
const OPUS_4_6_LIMIT = 1_000_000

function isOpus46(modelID: string | undefined): boolean {
if (!modelID) return false
return modelID.includes("opus-4-6") || modelID.includes("opus-4.6")
}

Add this import at the top with the other imports:
import { isOpus46, OPUS_4_6_LIMIT } from "./model-utils"

---

3. Update src/hooks/preemptive-compaction.ts

Remove the local declarations:
// DELETE THESE LINES:
const OPUS_4_6_LIMIT = 1_000_000

function isOpus46(modelID: string | undefined): boolean {
if (!modelID) return false
return modelID.includes("opus-4-6") || modelID.includes("opus-4.6")
}

Add this import at the top with the other imports:
import { isOpus46, OPUS_4_6_LIMIT } from "./model-utils"