[alfirus]

Summary

mailbox_entries_with_counts (src/mail.rs) ran a linear scan over the per-account badge rows for every sidebar entry, on every metadata refresh — O(entries × accounts) each time. This builds the account index once (HashMap with entry().or_insert, so the first row wins exactly like the previous linear search) and turns each lookup into O(1).

Change

• One function, mailbox_entries_with_counts; no signature, type, or behaviour change.
• No new dependencies, no new files.

User-visible effects

None intended — identical sidebar counts, computed with fewer steps. Slightly cheaper sidebar refreshes on metadata updates, most noticeable with several accounts.

Tests

• Existing coverage for this projection (mailbox_entries_preserve_unicode_hierarchy_and_stable_ids and the src/mail.rs suite) exercises the changed function; relying on CI (cargo fmt --check, clippy, cargo test) as the gate.
• Could not run the Rust gate locally: this contribution was prepared on a host without the Rust toolchain (no cargo/rustc), against a byte-verified copy of main (src/mail.rs blob 09cd40f, matched via git hash-object before patching).

Notes

• Independent of the folder-sort-keys / unified-totals PRs (separate one-issue branches); P0 and the unified-totals PR touch adjacent regions of src/mail.rs, so a trivial rebase may be needed at merge time — happy to do it on request.
• Disclosure: prepared with AI assistance (Hermes agent). I reviewed every line of the diff and confirm it is my own contribution, submitted under AGPL-3.0-only, with no credentials, mailbox data, or third-party material included.