Cost is always displayed as zero ($0.00) for custom models that extend built-in ones

[updbqn]

Description

When extending a built-in model the session cost does not update.

e.g. Using the example from the docs:

https://opencode.ai/docs/models/#configure-models

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "opencode": {
      "models": {
        "gpt-5-high": {
          "id": "gpt-5",
          "options": {
            "reasoningEffort": "high",
            "textVerbosity": "low",
            "reasoningSummary": "auto",
          },
        },
        "gpt-5-low": {
          "id": "gpt-5",
          "options": {
            "reasoningEffort": "low",
            "textVerbosity": "low",
            "reasoningSummary": "auto",
          },
        },
      },
    },
  },
}

Using gpt-5-high the cost is always 0.
Using gpt-5 the cost updates as expected.

[github-actions]

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

• Cost in storage/session is always 0 #2891: Similar cost tracking issue where cost is always displayed as 0 in sessions, though that one specifically mentions Copilot provider

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

[rekram1-node]

Ah prolly a merging issue will fix