tweak (config): make modalities input/output fields optional so that u can specify one without both being required

[robposch]

Fixes #29269

Problem

When configuring a custom model with only modalities.input (the common case — e.g. enabling image support on a local LM Studio model), opencode crashes on startup:

ConfigInvalidError: Missing key
  at ["provider"]["lmstudio"]["models"]["google/gemma-4-e4b"]["modalities"]["output"]

The entire modalities block is Schema.optional, but once provided, both input and output are required fields inside the struct. The error gives no hint that output is required or what values it accepts. Workaround is to add "output": ["text"] — but users have no way to discover this.

Fix

Wrap each field in Schema.optional so users can specify just the fields relevant to them:

"modalities": { "input": ["image"] }  // now valid

Why this is safe

All consuming code in provider.ts already accesses both fields via optional chaining (?.) with explicit fallback defaults.

[github-actions]

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[github-actions]

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[rekram1-node]

The entire modalities block is Schema.optional, but once provided, both input and output are required fields inside the struct. The error gives no hint that output is required or what values it accepts. Workaround is to add "output": ["text"] — but users have no way to discover this.

uh the error says it right here haha:

ConfigInvalidError: Missing key
at ["provider"]["lmstudio"]["models"]["google/gemma-4-e4b"]["modalities"]["output"]

[rekram1-node]

but i think this is reasonable

[github-actions]

Hey! Your PR title tweak (config): make modalities input/output fields optional so that u can specify one without both being required doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.