Publishing:
- Only send alt text for images (isImage guards on LinkedIn, X, Discord, Mastodon); never inject altText into video/document payloads.
- X sets alt via a best-effort media/metadata call so a metadata failure no longer blocks the tweet.
Validation:
- Validate media alt_text with a closure on media.*.meta so width/height/duration/slide_* survive a post update (Laravel's excludeUnvalidatedArrayKeys was stripping them).
- Add ALT_TEXT_MAX_LENGTH constant, a proper string-type error, and a localized attribute name.
Media attach (REST + MCP):
- Support per-image alt on attach-media-from-url via structured urls: [{url, alt?}] and on the MCP upload tool via an optional alt; alt is stored only for images.
- Carry submitted meta onto hosted external-URL media so alt is no longer dropped.
Composer:
- Alt-text dialog disables Save and reddens the counter over the limit, counting code points of the trimmed value to match the backend.
- Autosave shows 'Saved' only on a successful response; the lightbox alt overlay renders for images only.
Adds unit, feature, MCP, and browser tests covering every path above.
Centralize the per-platform mb_substr truncation that every publisher was
repeating into MediaItem::altTextFor(Platform), delete each publisher's
private altFor() helper, and clarify the Platform::altTextMaxLength()
docblock so it doesn't imply Instagram's documented 1000-char cap is a
guess. Add the assertions review flagged as missing: LinkedInPage/
InstagramFacebook alt-text caps, non-string and literal-"0" alt_text
normalization, altTextFor() truncation/unsupported-platform behavior,
Mastodon's no-description-part case, and the public API's accept/reject
path for media.*.meta.alt_text.
