IBKR MCP: search_contracts and get_option_parameters fail with generic error while price/history/theme tools work fine

### What happened?

Calling `search_contracts` (by ticker/company name) and `get_option_parameters` consistently fails with a generic error: "Error invoking method: An error occurred. Please try again later." This reproduces across multiple sessions over several days, not a one-off blip.

Notably, other tools on the same connector work fine in the same session: `whats_new`, `get_price_snapshot` and `get_price_history` (when a contract_id is already known, e.g. AAPL=265598), `search_investment_topics`, `get_theme_details`, `get_company_themes`, and `get_company_connections` all return correct data.

Account-tied tools (e.g. `get_account_summary`) also fail with the same generic error, which is expected since no brokerage account is linked. But `search_contracts` and `get_option_parameters` do NOT require account linkage per their tool descriptions, and still fail the same way.

This makes the connector effectively unusable for resolving a new ticker/company name to a contract_id, since `search_contracts` is the documented way to do that (and it's a prerequisite for `search_futures`, `get_option_data`, and `get_combo_identifier`, which I could not test as a result).

### What did you expect to happen?

`search_contracts` should return matching instruments with their `contract_id` for a ticker/company name query (e.g. query="AAPL"), and `get_option_parameters` should return option expirations for a known `underlying_contract_id` — consistent with their tool descriptions, with no account linkage required.

### Steps to reproduce

1. Connect the Interactive Brokers (IBKR) MCP connector on Claude.ai (no brokerage account linked)
2. Call search_contracts with query="AAPL" (or any ticker/company name)
3. Observe: "Error invoking method: An error occurred. Please try again later."
4. Call get_option_parameters with underlying_contract_id=265598 (AAPL)
5. Observe the same generic error
6. For contrast, call get_price_snapshot with contract_id=265598 — this succeeds and returns live price/bid-ask data
7. Also call get_company_themes with contract_id=265598 — this succeeds and returns theme/peer data

### Area

Tool Discovery / Invocation

### MCP Server (if applicable)

Interactive Brokers (IBKR)

### Error messages or logs

```shell
Error invoking method: An error occurred. Please try again later.

(This is the full text surfaced to the client — no status code, request id, or stack trace is exposed.)
```

### Additional context

Reproduced consistently over multiple days/sessions, not a one-off. Possibly related to (though not identical to) these existing reports, which may share a root cause around this connector's session/backend routing:
- #405 "Interactive Brokers (IBKR) MCP - OAuth token expired, no way to reconnect"
- #571 "IBKR MCP connector shows connected but exposes zero tools across new sessions"
- #761 "IBKR connector: get_option_data fails on every call since Aug 3 while all other IBKR tools work" — notably, for that reporter search_contracts, get_option_parameters, and account tools all work fine, and only get_option_data is down. That's effectively the inverse of my case (search_contracts/get_option_parameters/account tools down, price/theme tools fine), which suggests this isn't one specific endpoint being broken but rather per-tool/per-user flakiness in how this connector proxies to IBKR's backend.

My connector shows as "connected" and most tools work fine — only search_contracts, get_option_parameters (and by extension get_option_data, search_futures, get_combo_identifier, which depend on them) plus account-tied tools fail for me. This suggests the failing endpoints may require a live/fresh brokerage session that isn't being maintained for non-account-linked users, while the working endpoints (price snapshot/history, theme/connections data) route through a different backend path that doesn't need it.