Read-Only Inbox Census With Explicit Alias Mapping

Problem/Feature Description

You need the smallest truthful Node.js workflow for a read-only AgentMail inbox census.

The environment contract is slightly awkward:

• AGENTMAIL_API_KEY is still the default supported credential variable
• a nearby AGENTMAIL_KEY may exist on the machine
• you must not silently auto-alias AGENTMAIL_KEY
• if and only if the task explicitly opts in, it is acceptable to map a proven AGENTMAIL_KEY into the SDK apiKey field while saying that mapping out loud

The goal is to write a script that keeps this boundary honest while doing one bounded live-style read-only operation.

Output Specification

Write a single Node script named inbox_census.js that:

1. Imports the official AgentMail SDK from agentmail
2. Prefers AGENTMAIL_API_KEY as the default credential source
3. Does not silently fall back to AGENTMAIL_KEY
4. Allows explicit alias mapping only when an opt-in flag is present via --allow-agentmail-key-alias
5. Initializes the AgentMail client with the chosen credential
6. Performs exactly one read-only inbox census call using client.inboxes.list()
7. Prints a truthful result that includes the inbox count
8. Handles the empty-account case honestly rather than treating zero inboxes as an error
9. Makes no write/create/send/delete calls

If neither a direct AGENTMAIL_API_KEY nor an explicitly allowed alias path is available, the script should fail clearly and non-optimistically.

Do not write tests or extra files.