fix: add items to extract_facts array schema

[amreshtech]

Problem

extract_facts exported an MCP array parameter without an items schema:

entity_hints: { type: "array", description: "Existing canonical entity slugs..." }

That shape is tolerated by some clients, but stricter OpenAI Codex tool validation rejects it as an invalid function schema:

Invalid schema for function "mcp_gbrain_extract_facts": array schema missing items

In practice this caused a Hermes Kanban worker on the primary Codex path to fail its first model call and fall back to a secondary model.

Reproduction

1. Start GBrain as an MCP server with the pre-fix schema.
2. Expose its tools to a strict OpenAI-compatible tool consumer.
3. Inspect the generated tool definition for extract_facts.entity_hints or run a worker that loads the toolset.

Observed invalid emitted schema:

{
  "type": "array",
  "description": "Existing canonical entity slugs the agent has already resolved. Helps the extractor pick the right slug."
}

Expected shape:

{
  "type": "array",
  "items": { "type": "string" },
  "description": "Existing canonical entity slugs the agent has already resolved. Helps the extractor pick the right slug."
}

Fix

• add items: { type: "string" } to extract_facts.entity_hints in src/core/operations.ts
• add a regression assertion in test/e2e/mcp.test.ts so every exported MCP array property must include items

No runtime behavior change for valid callers beyond making the MCP tool schema compliant for strict clients.

Test Plan

• bun test ./test/e2e/mcp.test.ts
• bun run verify
• post-fix generated MCP tool defs inspected locally: zero exported array properties missing items
• post-fix Hermes Kanban worker smoke test completed without the prior Codex schema error

[garrytan]

Thanks @amreshtech — extract_facts.entity_hints (and the other MCP array-schema items fixes) already ship in master as of v0.35.3.0. The shared mapper is paramDefToSchema in src/mcp/tool-defs.ts (used by stdio MCP, HTTP MCP, and the subagent registry); test/mcp-tool-defs.test.ts walks every array param and fails the suite if any lacks items.type. If your install is still hitting this on next gbrain upgrade, please reopen with the output of gbrain doctor --json.

Closing as already-shipped. Real appreciation for chasing this — the same bug was independently reported by ~12 contributors which is exactly the kind of signal that gets the structural fix prioritized.