[stefan-ernst]

Summary

• Normalize inbound HTML into Markdown for ticket descriptions and reply comments, preserving paragraphs, lists, emphasis, safe links, code and simple data tables.
• Prefer HTML unless it has no visible text, conversion fails, or normalized HTML text is less than 25% of a plain-text alternative containing at least 100 Unicode characters. Compare before signature/quote cleanup.
• Preserve literal plain-text formatting and line breaks; flatten layout tables and omit images, unsafe links and active HTML. Bound HTML conversion to 1 MiB with a text fallback.
• Protect code samples from existing signature/reply stripping. Leave system-mail detection, threading, mailbox actions and routing unchanged.

Related: WI-2129; #484. No issue comments were posted.

Tests

Regression tests live in the companion core-tests-internal branch fix/wi-2129-email-markdown. The initial persisted-description and persisted-reply tests failed on the old implementation because emphasis/list formatting was lost; both pass with the fix. Fixtures are synthetic reproductions of the formatting loss, not the original reporter MIME message.

Passed:

• ../core-tests/overlay.sh . -- -tags=test -count=1 ./internal/email/... ./internal/emailutil/... ./internal/sanitize/...
• ../core-tests/overlay.sh . -- -tags=test -race -count=1 ./internal/email/... ./internal/emailutil/... ./internal/sanitize/...
• scripts/run-golangci-lint.sh run --timeout=5m ./internal/email/...
• Whole-repository Go lint and SQL/audit/layering/handler-DB/deprecated-API guards in the pre-commit hook.
• go mod tidy -diff and git diff --check.

The first race command exceeded the shell execution limit; the completed race runs passed without changing Go test timeouts. Existing ignored frontend build artifacts were copied into the worktree to satisfy Go embed during whole-repository lint. Full application, PostgreSQL, frontend and browser suites were not run. No frontend source changes or mailbox/plugin changes.