* fix(web): refill attachments when editing a queued or undone message
Queued prompts that carry images/video are no longer remove-only: clicking one loads its text and attachments back into the composer. Undo ("edit & resend") now restores the message's attachments too, not just its text. useAttachmentUpload gains loadAttachments, which reuses the existing fileIds (no re-upload) and fetches authenticated blob URLs for protected getFileUrl previews so the refilled thumbnails don't 401.
* fix(web): forward attachment refills through ChatDock
When the normal chat dock is mounted (non-empty conversation), bindChatDock receives the ChatDock instance, but ChatDock only exposed loadForEdit/focus — so the new loadAttachmentsForEdit fell back to a no-op and editing a queued media prompt or undoing a media message still dropped the attachments. ChatDock now forwards loadAttachmentsForEdit to the underlying Composer.
* fix(web): replace composer attachments when refilling edits
loadForEdit(text) overwrites the composer text, but loadAttachments appended to any unsent draft attachments, so a later submit sent the stale draft files together with the edited message's files. Make loadAttachments replace the current session's attachments (revoking their object URLs) so an edit/undo replaces the whole composer, mirroring loadForEdit.
* fix(web): clear stale attachments on text-only edits
When the composer already has attachments loaded (for example after editing a queued media prompt) and the user then edits a text-only queued prompt or undoes a text-only message, loadComposerForEdit skipped loadAttachmentsForEdit (the only path that clears the strip) because the new attachment list was empty/undefined, so the next submit would send the stale media with the new text. Always call loadAttachmentsForEdit(attachments ?? []) so text-only edits replace the strip with an empty set.
* fix(web): make fileId-less refilled media resendable
When editing a user turn whose media was base64-inlined by the server (no fileId), loadAttachments used to add a non-uploading chip with no fileId, which handleSubmit silently drops on resend (and an image-only edit would not submit at all). Re-upload the data URL to obtain a fileId so the attachment is actually resendable; when re-upload is unavailable, skip the chip instead of showing a misleading ready attachment. Also factor a patchAttachment helper.
* chore: prefix web changeset entry
The gen-changesets rules require web-app changelog entries to start with 'web: ' so the synced release notes classify web UI changes correctly.
* fix(web): don't dequeue a prompt when the composer is hidden
When a queued media item is clicked while the dock is showing a pending question or approval, ChatDock has no nested Composer (only rendered in its v-else), so loadComposerForEdit no-ops — but handleEditQueued still dequeued the item, losing it. Make ChatDock.loadForEdit report whether the nested composer is present, have loadComposerForEdit return success, and only dequeue when the load actually succeeds.
* fix(web): preserve URL-backed media when refilling composer
When an undone turn contains media with source.kind === 'url' (a URL but no fileId), loadAttachments used to fall through and drop it. Re-upload the URL (data: or http(s):) to obtain a fileId so URL-backed media is preserved on edit/resend; if the URL can't be fetched (CORS / non-2xx) the chip is dropped instead of shown as a misleading ready attachment.
* feat(web): preserve open side panel across session switches
* feat(web): scope composer input history to current session
* fix(web): suppress side panel open animation on session switch
* fix(web): preserve per-session scroll position on session switch
* chore: add changeset for per-session scroll position
* fix(web): preserve follow-bottom state per session
* fix(web): scope composer attachments to their session
* fix(web): restore saved scroll position on session switch
Move the image/video attachment state, the file-picker / paste / drag-drop
handlers, the upload machinery, the preview lightbox, and the paste-listener
+ object-URL cleanup lifecycle out of Composer into useAttachmentUpload.
The composer keeps handleSubmit / handleSteer (which read the attachments to
build the payload) and the hasUpload toolbar flag; it consumes the returned
refs and handlers directly. The destructured names match the originals so the
template bindings are unchanged. handleSubmit / handleSteer now call the
composable's clearAfterSubmit() to revoke object URLs and drop the list.
Composer.vue: 1937 -> 1787 lines. Adds unit tests for useAttachmentUpload. No
behavior change.
