fix(provider): handle anyOf/oneOf/const/$ref in Gemini schema sanitization

[nxxxsooo]

Problem

Gemini's generateContent API rejects JSON schemas containing anyOf, oneOf, const, $ref, and $defs — all valid JSON Schema but unsupported by Gemini's function calling format. This causes MCP tools from servers like Notion, Memory, and Obsidian mcp-tools to fail when used with any Gemini model.

Error example:

GenerateContentRequest.tools[0].function_declarations[32].parameters.properties[format].any_of[0].enum: only allowed for STRING type

Root Cause

The sanitizeGemini function in transform.ts handles integer→string enum conversion and a few other edge cases, but does not transform these unsupported JSON Schema patterns:

Pattern	Source	Example
$ref / $defs	Notion MCP	{ "$ref": "#/$defs/richTextRequest" }
anyOf with const	Obsidian mcp-tools	{ "anyOf": [{ "const": "markdown" }, { "const": "json" }] }
oneOf mixed types	Memory MCP	{ "oneOf": [{ "type": "array" }, { "type": "string" }] }
oneOf multiple objects	Notion MCP	{ "oneOf": [{ "type": "object", "properties": { "page_id": ... } }, ...] }

Solution

Two-phase transformation before existing sanitization:

1. $ref resolution: Inline all $ref references from $defs/definitions, with circular reference detection
2. anyOf/oneOf flattening:
   • All const → enum array
   • Multiple objects → merge properties
   • Mixed types → pick first (most specific)
   • Single-item → unwrap

Testing

Tested against real MCP server schemas:

• Notion MCP: 22/22 tools with issues fully fixed (66 anyOf/oneOf patterns resolved)
• Memory MCP: 4 tools with oneOf tags patterns fixed
• Obsidian mcp-tools: anyOf+const patterns fixed
• All existing behavior preserved (enum→string, required filtering, array items)

Changes

• packages/opencode/src/provider/transform.ts: Added resolveRefs helper and anyOf/oneOf flattening to sanitizeGemini

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

I found potential related PRs to PR #12911:

1. PR fix(provider): fix property order bug in Gemini numeric enum stringification #12827: fix(provider): fix property order bug in Gemini numeric enum stringification

   • Related to Gemini schema sanitization and enum handling

2. PR fix: expand $ref references in JSON Schema for Gemini compatibility #12292: fix: expand $ref references in JSON Schema for Gemini compatibility

   • Directly related - addresses $ref resolution for Gemini, which is one of the core issues in PR fix(provider): handle anyOf/oneOf/const/$ref in Gemini schema sanitization #12911

3. PR fix: apply schema transformation to MCP tools for Gemini compatibility #11968: fix: apply schema transformation to MCP tools for Gemini compatibility

   • Related to MCP tool schema transformation for Gemini compatibility

These PRs appear to be working on related or overlapping aspects of Gemini schema compatibility. PRs #12292 and #11968 are particularly relevant as they address similar schema transformation issues for Gemini.