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Danielle Maywood
5480299cef
## Summary
Fixed a bug where MCP tools with an empty `properties` schema had their
tool definitions sent to OpenAI with `"properties": null`, causing
OpenAI to reject the request.
## Problem
When an MCP server reports a tool with an empty input schema, e.g.:
```json
{
"type": "object",
"properties": {},
"required": []
}
```
Coder was forwarding the tool definition to OpenAI as:
```json
{
"type": "object",
"properties": null
}
```
OpenAI's function-calling API rejects `properties: null`, making these
tools unusable with OpenAI models.
## Root cause
The empty `properties` object collapsed to Go `nil` at two layers:
1. `agent/x/agentmcp/manager.go` `toolInputSchemaMap` stripped the
present-but-empty `"properties": {}` (guarded by `len(properties) > 0`),
so the wire copy lost it entirely.
2. `coderd/x/chatd/chatloop/chatloop.go` `buildToolDefinitions` embedded
`info.Parameters` directly into the input schema. When nil,
`encoding/json` marshals it as `null`.
## Fix
- `buildToolDefinitions` now substitutes an empty object when
`Parameters` is nil, mirroring the existing `required` guard (the sink,
protects all tool sources).
- `toolInputSchemaMap` now preserves an empty `properties` object
instead of dropping it (the upstream producer).
## Tests
Added regression tests (failing before, passing after) covering both
layers and asserting the schema serializes to
`{"type":"object","properties":{}}`:
- `TestBuildToolDefinitionsNilPropertiesBecomesEmptyObject`
- `TestToolInputSchemaMapPreservesEmptyProperties`
-
`TestWorkspaceMCPToolInfosFromResources/EmptyPropertiesYieldsEmptySchema`
---
*This PR was generated by Coder Agents.*