[FEATURE]: Add thinking/reasoning support for GLM-4.7, Kimi K2.5, and MiniMax M2.1 on Zen

[ErdongChen61]

The Zen gateway currently rejects thinking/reasoning config for GLM-4.7 (paid), Kimi K2.5 (paid), and MiniMax M2.1 (paid). All three models support thinking natively in their weights and via their direct provider APIs.

#### Steps to reproduce

  Tested via `opencode.json` model config with three configurations across all four Zen
  models.

  **Config A — Thinking + interleaved:**
  ```json
  {
    "provider": {
      "opencode": {
        "models": {
          "<model>": {
            "options": {
              "thinking": { "type": "enabled", "budgetTokens": 16000 },
              "interleaved": { "field": "reasoning_content" }
            }
          }
        }
      }
    }
  }

  Config B — Thinking only (no interleaved):
  "options": {
    "thinking": { "type": "enabled", "budgetTokens": 16000 }
  }

  Config C — No config (empty model entry):
  "<model>": {}

  Test command:
  timeout 60 opencode run "What is 2+2? Think step by step." -m opencode/<model> --format
  json

  Results:
  ┌───────────────────┬──────────────────────────┬────────────────────┬──────────────────┐
  │       Model       │  Config A (thinking +    │ Config B (thinking │  Config C (no    │
  │                   │       interleaved)       │        only)       │     config)      │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ kimi-k2.5-free    │ Works (reasoning > 0)    │ Works (reasoning > │ Works            │
  │                   │                          │  0)                │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ kimi-k2.5 (paid)  │ Rejected                 │ Rejected           │ Works            │
  │                   │                          │                    │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ glm-4.7 (paid)    │ Rejected                 │ Rejected           │ Works            │
  │                   │                          │                    │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ minimax-m2.1      │ Rejected                 │ Rejected           │ Works            │
  │ (paid)            │                          │                    │ (reasoning: 0)   │
  └───────────────────┴──────────────────────────┴────────────────────┴──────────────────┘
  Error messages:
  - glm-4.7: Extra inputs are not permitted, field: 'thinking' — Zen doesn't recognize the
   field at all
  - kimi-k2.5 (paid) and minimax-m2.1: Input should be 'disabled', field:
  'thinking.ThinkingConfigDisabled.type' — field exists but only accepts disabled

  Only kimi-k2.5-free accepts thinking config (both A and B) and returns reasoning tokens.
   All three paid models reject it.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Add disable_reasoning parameter for GLM/Cerebras thinking toggle #11987: [FEATURE] Add disable_reasoning parameter for GLM/Cerebras thinking toggle
• Add missing NanoGPT models (kimi-k2.5:thinking and others) #11787: Add missing NanoGPT models (kimi-k2.5:thinking and others)
• GLM 4.7 on Zai coding plan puts tool calls inside the thinking/reasoning tag. #6708: GLM 4.7 on Zen coding plan puts tool calls inside the thinking/reasoning tag
• GLM 4.7 thinking process not properly formatted - missing leading tags #7779: GLM 4.7 thinking process not properly formatted - missing leading tags
• Error "reasoning part reasoning-0 not found" from tool calls using GLM 4.5 Air #6486: Error "reasoning part reasoning-0 not found" from tool calls using GLM 4.5
• MiniMax M2 <think> tags #4033: MiniMax M2 tags rendering
• Latest v1.1.48 Version Analysis: Think Tag Issues with Local Model MiniMax2.1 #11709: Latest v1.1.48 Version Analysis: Think Tag Issues with Local Model MiniMax2.1
• [FEATURE]: Please add the new GLM 4.7 and MiniMax M2.1 models to Nvidia. #7953: [FEATURE] Please add the new GLM 4.7 and MiniMax M2.1 models to Nvidia
• Kimi K2.5 can't enable thinking (reasoning_content missing #12090: Kimi K2.5 can't enable thinking (reasoning_content missing) - CLOSED

Feel free to ignore if none of these address your specific case.

[github-actions]

To stay organized issues are automatically closed after 90 days of no activity. If the issue is still relevant please open a new one.