fixup! fix(imap): detect iMIP when method= is missing or mime is application/ics

Address review feedback from kesselb:
- drop application/ics handling in both detection sites
  (Thunderbird's stance — re-evaluate if a real-world provider that
  only ships application/ics shows up)
- tighten METHOD regex to /^METHOD:([A-Z]+)/mi with === 1 check
  (matches the iCalendar grammar: METHOD value is bare token, no
  whitespace allowed between colon and value per RFC 5545)
- remove the now-obsolete application/ics fixture + test row

NOTE for squash: original commit body still mentions application/ics
support. When squashing, please drop that section so the message only
covers the Proton Bridge / METHOD-from-body fix.

AI-assisted: Claude Code (Claude Opus 4.7)
Signed-off-by: Wolfgang Lubowski <w.lub92@gmail.com>

Author: lubo92

lib/IMAP/ImapMessageFetcher.php

@@ -287,13 +287,11 @@ public function fetchMessage(?Horde_Imap_Client_Data_Fetch $fetch = null): IMAPM
 	 */
 	private function getPart(Horde_Mime_Part $p, string $partNo, bool $isFetched): void {
 		// iMIP messages
-		// Handle text/calendar and application/ics parts first because they
-		// might be attachments at the same time. Otherwise, some of the
-		// following if-conditions might break the handling and treat iMIP
+		// Handle text/calendar parts first because they might be attachments at the same time.
+		// Otherwise, some of the following if-conditions might break the handling and treat iMIP
 		// data like regular attachments.
 		$allContentTypeParameters = $p->getAllContentTypeParameters();
-		if ($p->getType() === 'text/calendar'
-				|| $p->getType() === 'application/ics') {
+		if ($p->getType() === 'text/calendar') {
 			// Handle event data like a regular attachment
 			// Outlook doesn't set a content disposition
 			// We work around this by checking for the name only
@@ -318,7 +316,7 @@ private function getPart(Horde_Mime_Part $p, string $partNo, bool $isFetched): v
 			$contents = null;
 			if ($method === null) {
 				$contents = $this->loadBodyData($p, $partNo, $isFetched);
-				if (preg_match('/^METHOD:\s*(\S+)/mi', $contents, $m)) {
+				if (preg_match('/^METHOD:([A-Z]+)/mi', $contents, $m) === 1) {
 					$method = $m[1];
 				}
 			}

lib/IMAP/MessageMapper.php

@@ -899,16 +899,15 @@ public function getBodyStructureData(Horde_Imap_Client_Socket $client,
 					$hasAttachments = true;
 				}
 
-				// Flag the message as iMIP when we see a text/calendar or
-				// application/ics part. Proton Mail Bridge is known to strip the
-				// `method=` parameter from the Content-Type header while
-				// re-assembling a message after E2E-decryption, so requiring the
-				// parameter here would drop every Bridge-delivered invitation.
-				// The actual method (REQUEST/REPLY/CANCEL) is parsed out of the
-				// ICS body downstream in ImapMessageFetcher::getPart() — see the
+				// Flag the message as iMIP when we see a text/calendar part.
+				// Proton Mail Bridge is known to strip the `method=` parameter
+				// from the Content-Type header while re-assembling a message
+				// after E2E-decryption, so requiring the parameter here would
+				// drop every Bridge-delivered invitation. The actual method
+				// (REQUEST/REPLY/CANCEL) is parsed out of the ICS body
+				// downstream in ImapMessageFetcher::getPart() — see the
 				// matching fallback there.
-				if ($part->getType() === 'text/calendar'
-						|| $part->getType() === 'application/ics') {
+				if ($part->getType() === 'text/calendar') {
 					$isImipMessage = true;
 				}
 			}

tests/Unit/IMAP/MessageMapperTest.php

@@ -755,10 +755,6 @@ public function isImipMessageProvider(): array {
 			// body. Must still be flagged as iMIP so downstream processing
 			// picks it up.
 			'proton bridge request (method= stripped)' => ['request_proton_bridge', true],
-			// Google occasionally attaches the same invitation twice: once as
-			// text/calendar and once as application/ics. We used to ignore the
-			// latter even though it is functionally equivalent.
-			'application/ics request' => ['request_application_ics', true],
 		];
 	}