Bug: compaction.reserved config is ignored for models without explicit 'input' limit

[andrea-tomassi]

Description

In packages/opencode/src/session/compaction.ts, the isOverflow function calculates usable tokens:

const usable = input.model.limit.input
  ? input.model.limit.input - reserved
  : context - ProviderTransform.maxOutputTokens(input.model)

The problem is that many models (like claude-opus-4.6) do not have an explicit input limit defined in their model definition (only context and output). In this case, the code takes the else branch:

: context - ProviderTransform.maxOutputTokens(input.model)

This calculation completely ignores the reserved variable (which respects config.compaction.reserved). As a result, users cannot tune the compaction threshold to avoid context overflow crashes.

Expected Behavior

The reserved buffer (e.g. 60000 tokens) should be subtracted from the total context in the else branch as well.

Proposed Fix

const usable = input.model.limit.input
  ? input.model.limit.input - reserved
  : context - reserved // (assuming reserved includes maxOutput safety buffer)