type account param as Optional[str] to fix single-account tool failures

[srijanAtGithub]

Problem

All tool functions declare the account parameter as account: str = None.

In Pydantic v2, this generates a JSON schema that marks account as a required
string field — despite the None default. When an LLM-backed MCP client receives
this schema, it treats account as required and passes an empty string "" when
it has no value to supply.

get_client("") then raises: ValueError: Unknown account ''. Available accounts: default

This breaks every tool call in single-account setups, which is the most common
configuration and is documented as supported.

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How to reproduce

Set up the server in single-account mode. Connect any LLM-backed MCP client.
Then try these two prompts back to back:

Prompt 1 — fails:

"What is the last message from my contact named Alice?"

The LLM picks list_contacts or get_contact_ids, passes account="", and gets
a CONTACT-ERR-* error. The tool never executes.

Prompt 2 — works (same intent, split into two steps):

"Is there a contact named Alice in Telegram?"
(after it responds) "Get her last message."

In step one, the LLM picks search_contacts which has a query param to focus
on, so it omits account entirely. get_client(None) auto-selects the only
configured account and succeeds. Step two then uses chat_id directly, also
bypassing the account problem.

Same underlying intent. Same tools available. The only difference is whether
the LLM feels obligated to fill account.

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Root cause

Pydantic v2 no longer infers Optional from field: str = None. The correct
annotation is Optional[str].

# Before — Pydantic v2 emits {"type": "string"} — looks required to the client
async def list_contacts(account: str = None) -> str:

# After — emits {"anyOf": [{"type": "string"}, {"type": "null"}], "default": null}
async def list_contacts(account: Optional[str] = None) -> str:

With the correct annotation, LLM clients see account as optional and omit it.
get_client(None) then auto-selects the single configured account, as intended.
No logic in runtime.py needed to change.

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Change

account: str = None → account: Optional[str] = None across all tool files.
No behavior change. No logic change. Purely a type annotation correction.

Files changed:

• telegram_mcp/tools/contacts.py

• (will change other files in the similar manner after testing and verifying that no new issues are introduced)

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Affected users

Anyone running single-account mode with an LLM-backed MCP client
(Claude Desktop via langchain-mcp-adapters, Cursor, or similar).
Direct programmatic callers are unaffected.