fix(sync): skip no-op draft rewrites and treat \Deleted as removed

[TDannhauer]

Summary

• Acknowledge draft Modify commands that carry no changes without performing the IMAP append+delete rewrite (breaks Gmail's Modify echo cycle).
• Treat \Deleted per native Exchange semantics in all IMAP change-detection strategies: excluded from initial sync, exported as Remove when a tracked message gains the flag, re-exported as Add when it loses the flag.

Motivation

Issue #94: when a third-party IMAP client (e.g. Thunderbird) updates a draft via append + \Deleted flag, Gmail resurrects the old version. Two server-side defects combine:

1. Gmail echoes a content-identical Modify for every draft Add it receives. The server applied it as a full rewrite: IMAP append+delete, a new UID, and the client's copy materialized over server state.
2. \Deleted messages were synced as live mail, so the old draft version a third-party client flagged for deletion was never removed from the device — the device kept "reconciling" it back.

Native Exchange neither rewrites an unchanged item nor exposes messages flagged for deletion. This PR aligns Horde with both behaviors for all EAS clients and all mail folders — no Gmail-specific special-casing.

Relation to #93 / #77

This branch is stacked on #93 (fix/draft-uid-alias-wire-identity), which keeps the client's ServerId stable across draft UID churn. #93 fixes the identity bookkeeping; this PR removes the churn itself for no-op edits and completes the deletion semantics. Together they close the loop that the ServerId echo from #77 originally opened. The diff shows both commits until #93 merges, after which it reduces to this one.

Changes

• lib/Horde/ActiveSync/Connector/Importer.php — _isNoOpDraftModify(): before a draft rewrite, fetch the current server copy (untruncated, in the body type the client sent) and compare the EAS-visible fields (To/Cc/Bcc, subject, importance, read, follow-up flag, categories, body with normalized line endings). On a no-op, reply success with the same stable stat shape as a real edit and leave the message untouched. Conservative by design: attachment add/remove instructions, fetch failures, or any mismatch fall through to the regular rewrite path. Expected exception type caught: Horde_Exception (from Horde_ActiveSync_Driver_Base::fetch()).
• lib/Horde/ActiveSync/Imap/Strategy/Initial.php — initial sync searches with UNDELETED; covers both the CONDSTORE priming path and non-CONDSTORE servers.
• lib/Horde/ActiveSync/Imap/Strategy/Modseq.php — a tracked message that gained \Deleted is diverted from the change list into the removals (merged with VANISHED UIDs); an untracked one is never exported. A message that loses the flag is untracked by then and exports as a regular Add (genuine undelete).
• lib/Horde/ActiveSync/Imap/Strategy/Plain.php — same semantics for servers without CONDSTORE, applied in the per-poll flag fetch.
• Tests: five new importer tests (no-op skip with line-ending normalization, changed-body rewrite, attachment bypass, fetch-failure fallback, aliased-UID comparison) and a new StrategyDeletedFlagTest (Modseq remove/suppress/merge, Plain remove, Initial UNDELETED search).

Upgrade note

Messages already carrying \Deleted before this change converge on their next flag/MODSEQ event or a folder resync; fresh syncs are correct immediately.

Test plan

• New unit tests for both behaviors (importer no-op detection, strategy \Deleted handling)
• Full package unit suite: no new failures (only the four known pre-existing environment failures)
• Reporter re-test of the issue Gmail undeletes previous versions of draft messages when they are updated by third party over IMAP #94 scenario (Thunderbird draft edit over IMAP → Gmail via EAS)

[github-actions]

🔍 CI Results

Overall: ❌ 12/12 lanes failed

TL;DR: ❌ Quality issues: PHPStan: 243 unique errors in 11 lanes; PHP-CS-Fixer: 30 files.

Summary by PHP Version

PHP	dev	stable
8.0	❌	❌
8.1	❌	❌
8.2	❌	❌
8.3	❌	❌
8.4	❌	❌
8.5	❌	❌

Quality Metrics

• PHPUnit: did not run (11 lanes exited non-zero with no test output) ❌
• PHPStan (advisory): 243 unique errors in 11 lanes ⚠️
• PHP-CS-Fixer: 30 unique files with issues (of 211 checked) ⚠️

❌ Failed Lanes

php8.0-dev

• PHPUnit: 0 failures, 0 errors

php8.0-stable

• PHPUnit: ❌ Setup failed (Composer install failed in /tmp/horde-ci/lanes/php8.0-stable/ActiveSync: Your requirements could not be resolved to an installable set of packages.)
• PHPStan: ❌ Setup failed (Composer install failed in /tmp/horde-ci/lanes/php8.0-stable/ActiveSync: Your requirements could not be resolved to an installable set of packages.)

php8.1-dev

• PHPUnit: 0 failures, 0 errors

php8.1-stable

• PHPUnit: 0 failures, 0 errors

php8.2-dev

• PHPUnit: 0 failures, 0 errors

php8.2-stable

• PHPUnit: 0 failures, 0 errors

php8.3-dev

• PHPUnit: 0 failures, 0 errors

php8.3-stable

• PHPUnit: 0 failures, 0 errors

php8.4-dev

• PHPUnit: 0 failures, 0 errors
• PHP-CS-Fixer: 30 files with issues

php8.4-stable

• PHPUnit: 0 failures, 0 errors

php8.5-dev

• PHPUnit: 0 failures, 0 errors

php8.5-stable

• PHPUnit: 0 failures, 0 errors

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[TDannhauer]

Field testing (issue #94) surfaced two follow-ups, pushed as separate commits so they can be judged independently:

• e0bc7fa — core fix: exclude the read state from the draft no-op comparison. Gmail hardcodes Read 0 in echoed Modifies, so any \Seen draft failed the comparison and was rewritten anyway. Comparison failures are now logged with the mismatching field.
• 8003d81 — one-time convergence: messages flagged \Deleted before this branch (the flag was ignored by all prior releases) never produce another MODSEQ event, so they would linger on clients forever. A once-per-folder SEARCH DELETED sweep removes them; the swept state persists in the folder state. Without this, every upgrading user would need to re-provision their account.