fix: prevent infinite auto-compact loop for unknown 3P models (#635) (#636)

- Raise context window fallback from 8k to 128k for unknown OpenAI-compat models.
  The 8k fallback caused effective context (8k minus output reservation) to go
  negative, making auto-compact fire on every single message.
- Add safety floor in getEffectiveContextWindowSize(): effective context is
  always at least reservedTokensForSummary + 13k buffer, ensuring the
  auto-compact threshold stays positive.
- Add missing MiniMax model entries (M2.5, M2.5-highspeed, M2.1, M2.1-highspeed)
  all at 204,800 context / 131,072 max output per MiniMax docs.
- Add tests for MiniMax variants, 128k fallback, and autoCompact floor.

Fixes #635

Co-authored-by: root <root@vm7508.lumadock.com>

src/services/compact/autoCompact.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  getEffectiveContextWindowSize,
+  getAutoCompactThreshold,
+} from './autoCompact.ts'
+
+describe('getEffectiveContextWindowSize', () => {
+  test('returns positive value for known models with large context windows', () => {
+    // claude-sonnet-4 has 200k context
+    const effective = getEffectiveContextWindowSize('claude-sonnet-4')
+    expect(effective).toBeGreaterThan(0)
+  })
+
+  test('never returns negative even for unknown 3P models (issue #635)', () => {
+    // Previously, unknown 3P models got 8k context → effective context was
+    // 8k minus 20k summary reservation = -12k, causing infinite auto-compact.
+    // Now the fallback is 128k and there's a floor, so effective is always
+    // at least reservedTokensForSummary + buffer.
+    process.env.CLAUDE_CODE_USE_OPENAI = '1'
+    try {
+      const effective = getEffectiveContextWindowSize('some-unknown-3p-model')
+      expect(effective).toBeGreaterThan(0)
+      // Must be at least summary reservation (20k) + buffer (13k) = 33k
+      expect(effective).toBeGreaterThanOrEqual(33_000)
+    } finally {
+      delete process.env.CLAUDE_CODE_USE_OPENAI
+    }
+  })
+})
+
+describe('getAutoCompactThreshold', () => {
+  test('returns positive threshold for known models', () => {
+    const threshold = getAutoCompactThreshold('claude-sonnet-4')
+    expect(threshold).toBeGreaterThan(0)
+  })
+
+  test('never returns negative threshold even for unknown 3P models (issue #635)', () => {
+    process.env.CLAUDE_CODE_USE_OPENAI = '1'
+    try {
+      const threshold = getAutoCompactThreshold('some-unknown-3p-model')
+      expect(threshold).toBeGreaterThan(0)
+    } finally {
+      delete process.env.CLAUDE_CODE_USE_OPENAI
+    }
+  })
+})