Context remaining shows 0% on 1M context models (hardcoded MAX_CONTEXT_SIZE = 190000)

[a60708090xun]

Problem

The context remaining percentage in the session input bar always shows 0% when using Claude Opus 4.6 with 1M context window. The actual context usage is only ~20%, but the UI clamps it to 0%.

Root Cause

MAX_CONTEXT_SIZE is hardcoded to 190000 in AgentInput.tsx, which is appropriate for 200K context models (Sonnet) but not for 1M context models (Opus 4.6 [1m]).

Code pointers

1. packages/happy-app/sources/sync/reducer/reducer.ts:1115 — contextSize is calculated correctly:

   contextSize: (usage.cache_creation_input_tokens || 0)
              + (usage.cache_read_input_tokens || 0)
              + usage.input_tokens

2. packages/happy-app/sources/components/AgentInput.tsx:78, 286-287 — percentage uses hardcoded limit:

   const MAX_CONTEXT_SIZE = 190000;
   const percentageUsed = (contextSize / MAX_CONTEXT_SIZE) * 100;
   const percentageRemaining = Math.max(0, Math.min(100, 100 - percentageUsed));

Example

With Opus 4.6 (1M context), a session at ~205K context:

• percentageUsed = 205000 / 190000 * 100 = 107.8%
• percentageRemaining = Math.max(0, 100 - 107.8) = 0%
• Actual remaining: ~79.5% (205K / 1M)

Suggested Fix

Make MAX_CONTEXT_SIZE dynamic based on the model in use. The CLI's usage-report doesn't currently include model info, so the model name may need to be passed through or inferred.

Known context window sizes:

• Claude Sonnet / Haiku: 200K → ~190K effective
• Claude Opus 4.6 [1m]: 1M → ~950K effective

Impact

• UI-only: does not affect functionality or billing
• Users on 1M context models see 0% for entire session, losing visibility into actual context usage