feat: support toolRestrictions on POST /api/chat (AI-3600)

[claude]

Requested by Jordan Burger · Slack thread

Before / After

Before: KaiClient.send_message(...) had no way to constrain which tools the assistant could use. Every chat ran with the full tool set — you couldn't ask for a read-only session, an allowlist of safe tools, or block specific write tools from the client.

After: Callers can pass an optional tool_restrictions argument to send_message(...) to scope tool usage for a chat:

from kai_client import KaiClient, ToolRestrictions

async with KaiClient(...) as client:
    chat_id = client.new_chat_id()
    async for event in client.send_message(
        chat_id,
        "Show me my tables, but don't change anything",
        tool_restrictions=ToolRestrictions(
            allowed_tools=["list_tables", "get_table_detail"],
            disallowed_tools=["run_job"],
            read_only_mode=True,
        ),
    ):
        ...

How

• A new public ToolRestrictions Pydantic model with three optional fields — allowed_tools, disallowed_tools, read_only_mode — that serialize to the exact JSON keys the backend expects: allowedTools, disallowedTools, readOnlyMode.
• An optional tool_restrictions field on ChatRequest (src/kai_client/models.py), serializing to toolRestrictions.
• An optional tool_restrictions: ToolRestrictions | None = None parameter on send_message (src/kai_client/client.py), plumbed into the ChatRequest.
• Serialization uses model_dump(by_alias=True, exclude_none=True), so when tool_restrictions is None the toolRestrictions key is omitted entirely, and any unset sub-fields are dropped from the payload.
• ToolRestrictions is exported from the package's public API (kai_client.__init__).

Behavioral note (documented, not enforced client-side): restrictions are first-message-wins — the backend persists them from the first message of a chat and silently ignores toolRestrictions on follow-up messages of the same chat.

Pairs with the already-merged backend PR keboola/ui#6267 and Linear AI-3600.

---

Generated by Claude Code

[linear-code]

AI-3600