fix(emlx): skip re-ingest when attachment restoration changes nothing

[salmonumbrella]

What changed

• import-emlx now restores cached attachments into the stored raw of an archived partial message first, and skips the message when that changes nothing. Only messages that gain a newly cached attachment are re-ingested.
• Skipped messages still get the current mailbox label and the Message-ID / In-Reply-To repair, same as the ordinary skip path. If the label add fails, the message still goes through ingestion so the label gets retried, as it did before.
• A shrinking Apple Mail cache still never removes attachment bytes that are already archived.
• The summary's restored count now means attachments this run added to the archive, counted once per message after ingestion succeeds. An idle rerun reports 0 instead of every cached attachment it read again.

Why

Since 0.20.0, every rerun rewrote each archived .partial.emlx message whose attachments are still in Apple Mail's Attachments/ cache, whether or not the archive already had them. With a large Mail library, a nightly incremental import went from about an hour to 6–10 hours, logged slow-transaction warnings, and rebuilt the analytics cache from all the rewritten rows while adding only a few hundred new messages.

Usage

No usage change. A rerun over an unchanged Mail tree now reports Updated: 0 and counts those messages under Skipped (dup).

Closes #957

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (1b70533)

Verdict: Changes require fixes for 1 finding.

Medium

• internal/importer/emlx_import.go:414: When stored raw MIME equals the restored MIME, ingestion is skipped entirely. A message first imported with --no-attachments may retain attachment bytes in message_raw without attachment files or rows, and a later normal import silently skips materializing them.

  Fix: Check attachment-storage completeness before skipping, or materialize attachments independently of the message upsert while retaining the no-rewrite optimization. Add a regression test for no-attachments import followed by normal import.

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Reviewers: codex, codex (security) | Synthesis: codex, 5s | Total: 4m59s

[roborev-ci]

roborev: Combined Review (57aeb5f)

Verdict: No findings at or above medium severity.

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Reviewers: codex, codex (security) | Synthesis: codex | Total: 3m37s