feat(ai): add tool namespaces

[rekram1-node]

Summary

• add recursive provider-neutral ToolEntry definitions with ToolDefinition leaves and ToolNamespace groups
• normalize, sanitize, deduplicate, and budget recursive tool trees without collapsing sibling namespace identities
• lower outer namespaces natively for OpenAI Responses and recursively flatten them for protocols without native namespace support
• preserve OpenAI namespace identity through streaming events, local dispatch, history normalization, and replay
• keep Core tool registration flat for now while updating its AI definitions and legacy AI SDK adapter for the widened AI surface

Shape

LLM.request({
  model,
  tools: [
    ToolNamespace.make({
      name: "acme",
      description: "Acme tools",
      tools: [
        ToolDefinition.make({
          name: "billing",
          description: "Look up billing details",
          inputSchema: { type: "object" },
        }),
        ToolDefinition.make({
          name: "users",
          description: "Look up users",
          inputSchema: { type: "object" },
        }),
      ],
    }),
  ],
})

OpenAI Responses lowers this to its native { type: "namespace", ... } wire shape. Generic Open Responses and protocols without native namespace support lower the leaves as acme_billing and acme_users, including matching historical calls. OpenAI only accepts one native namespace level, so deeper semantic levels are flattened within the outer native namespace.

Validation

• bun typecheck, full suite (939 passed, 25 skipped), and bun run build in packages/ai
• forced Core typecheck
• 53 focused Core tool/schema/session tests
• changed files pass Prettier and git diff --check