Sync mail into a flat per-account message list

[Hohnik]

Parent

Spec: MailChat MVP — email-as-chat

What to build

As a user, once I've connected an account, MailChat periodically polls it in the background and I can see the messages it fetched, per account, without manually refreshing. This ticket proves the ingestion pipeline (fetch → parse → persist → display) end-to-end; conversation grouping is not yet applied — messages are shown as a flat, ungrouped list per account.

Acceptance criteria

• A parser converts raw RFC822/MIME message bytes into a structured representation: headers (From/To/Cc/Subject/Message-ID/In-Reply-To/References/Date) and a safely-renderable body (HTML converted/sanitized for display, no remote content execution).
• A normalizer persists that parsed representation as a Message row tied to the account it was fetched from.
• A background worker runs one polling task per connected account, fetching recent messages via the existing IMAP client and routing each through parser → normalizer; one account's failure/slowness does not block others from syncing.
• A minimal htmx view lists synced messages per account (flat, ungrouped), and updates via polling as new mail arrives without a manual page reload.
• Tests: sync-pipeline tests mocking only the IMAP connection boundary (same pattern as the existing imap_client tests), feeding real captured raw-message fixtures through the real parser → normalizer against a real temporary/in-memory SQLite database, asserting persisted Message rows are correct; an htmx route test asserting the flat message list renders correctly for a seeded account.

Blocked by

• Connect and store a mail account

[Hohnik]

Already implemented and merged — commit 171f17d shipped the parser (RFC822/MIME → structured message, nh3-sanitized body), the normalizer (Message rows deduplicated by Message-ID), and the per-account background worker (asyncio.to_thread-offloaded IMAP calls, failure-isolated across accounts), plus a flat htmx message list. Live-verified against the real T-Online mailbox. Closing to match reality.

Filed under a new wayfinder map for the remaining pipeline: Conversation grouping & reply: pre-build decisions — see that map's note on why #10 and #11 needed it but #9 didn't.