[yeroo]

What and why

SyncCommand::FetchBody always asked Graph for plain text (Prefer: outlook.body-content-type="text"), so a graphical client embedding the engine got every message as text. Now:

• sync::engine::EngineOptions { body_format } (BodyFormat::{Text, Html}, default Text) is chosen at spawn: spawn runs the default (lookxy unchanged), spawn_with_options takes one. Html sends no Prefer, so each body comes back native (html, or text for a plain-text message).
• bodies.fetched_as (additive migration) records the format FetchBody asked for, not the content type that came back, so a native-text answer to an Html ask is not refetched forever.
• Store::get_body_for(id, format) is the embedder's gate: the stored body when it satisfies the format, else None (send one FetchBody). Old rows from the text-only engine read as "asked for text", so an existing store upgrades one message per open. A draft's body with no recorded format (local, createReply, or a legacy compose edit) satisfies both formats, so a refetch is never invited over unsynced edits (draft = is_draft, or filed under Drafts / the local Drafts sentinel, since delta does not select isDraft).
• update_draft_fields now also writes content_type = 'html' and clears fetched_as on conflict (it used to keep a fetched-as-text draft's text type over html content).
• Inline attachments' contentId / isInline were already stored and fetchable (FetchAttachments, FetchInlineImage); a test now pins it under an Html engine. Reply/forward drafts unchanged.

Closes #1901

Testing

• cargo fmt --check, cargo clippy -p mailcore -p lookxy --all-targets -- -D warnings: clean
• cargo test -p mailcore (317 passed), cargo test -p lookxy (333 passed). Only lookxy depends on mailcore.
• New fake-server engine tests: the default engine sends the text Prefer and records text; an Html engine sends none and stores html; a legacy text body is fetched as html exactly once through the gate; a native-text answer is not fetched again; inline attachments store contentId; a plain-text reply draft is not a refetch candidate. Store tests in store::body_format_tests cover the rule, the migration and the draft cases. Mutation checks (by hand): recording the returned content type, or the old draft conflict arm, or dropping the draft rule each fail a test.

Review record

• Plan agreed in one round (four test amendments from the implementer).
• revmux r1: 3 Minor, 0 Major — fixed: legacy edited drafts could read as refetch candidates under Html (data loss), same for plain-text createReply drafts, and the store tests moved to their own module.
• review stopped: round 1 had no Major; all findings fixed
• Follow-up: mailcore: full-text search indexes HTML markup of HTML bodies #1905 (FTS indexes html bodies' markup under an Html store).

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 96.39640% with 20 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
mailcore/src/sync/engine.rs	93.21%	19 Missing ⚠️
mailcore/src/store/mod.rs	99.62%	1 Missing ⚠️

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[yeroo]

Merged automatically (auto-merge is on for this checkout): review stopped: round 1 had no Major; all findings fixed; merge rounds: 1 CI rerun (a timing flake in the untouched set_automatic_replies_patches_and_emits_updated on windows-latest, green on rerun); whole suite green on 1853953 (fmt, clippy, cargo test -p mailcore -p lookxy: 650 tests); merge-check ok.

Follow-ups: #1905 (FTS indexes html bodies' markup under an Html store), its own issue. No leftovers checklist; nothing deferred or disputed from review.