fix(router): toolCallId must only match when tool message is the last turn

[AlemTuzlak]

Summary

match.toolCallId was matching against the most recent tool role message anywhere in history, not the last message in the request. Once a conversation contained any prior tool result, every subsequent request still had a "last tool message" buried in history, and a stale toolCallId fixture could win before any userMessage matcher was even evaluated.

Reproduction (CopilotKit beautiful-chat showcase)

1. Click suggestion 1 (pie chart) → fixture userMessage: "revenue distribution by category" matches → returns tool call `call_fp_pie_chart_001` → frontend renders chart → tool result returns → fixture `toolCallId: "call_fp_pie_chart_001"` matches → content `"Pie chart rendered above — Electronics is the largest slice…"`. ✅
2. Click suggestion 2 (bar chart). Conversation is now:
   ```
   [user1, asst(tool_call), tool(call_fp_pie_chart_001), asst("Pie chart rendered above…"), user2]
   ```
   • aimock iterates fixtures top-down. `toolCallId` fixtures sit at the top of `feature-parity.json`.
   • `getLastMessageByRole(messages, "tool")` returns the stale tool result from suggestion 1.
   • `toolCallId: "call_fp_pie_chart_001"` matches and returns `"Pie chart rendered above — Electronics…"` again — the bar-chart `userMessage` matcher is never reached, no new tool call is made. ❌

Fix

A `toolCallId` fixture answers the model's response to a tool result, which by API contract only happens when the conversation's LAST message is a tool result. Tighten the matcher to require exactly that:

```ts
// before
const msg = getLastMessageByRole(effective.messages, "tool");
if (!msg || msg.tool_call_id !== match.toolCallId) continue;

// after
const last = effective.messages[effective.messages.length - 1];
if (!last || last.role !== "tool" || last.tool_call_id !== match.toolCallId) continue;
```

When the last message is `user` (or anything other than a fresh `tool` result), `toolCallId` matchers are now correctly skipped so `userMessage` matchers can run.

Test plan

• New regression test `does not match when a new user turn follows the tool message` — fails on `main`, passes with the fix
• All 73 `router.test.ts` cases pass
• Full suite: 2610 passed (the one unrelated failure on Windows is the pre-existing `defaultCacheRoot honors XDG_CACHE_HOME` path-separator test in `fixtures-remote.test.ts`)
• `pnpm lint` clean
• `pnpm format:check` clean

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@copilotkit/aimock@148

commit: 56955bc