[iamnbutler]

Closes #91. Pasting an image into a chat composer now attaches it through the same path as drag-and-drop and the file picker (useAttachments().add). Plain-text, URL-link and multiline paste behave as in canary 0.0.11.

• RichText takes an optional onFiles. When the clipboard holds files and no text/plain, the editor consumes the paste and passes any image/* files to onFiles.
• ChatComposer passes onFiles={attachable ? addFiles : undefined}, the gate drop already uses. canAttach={false} and edit mode therefore attach nothing.
• Text wins when present. WebKit exposes a Numbers or spreadsheet copy as Files + text/plain + text/html, where the file is a rendered image of the cells. These pastes keep the text. Screenshots, Finder copies and Safari "Copy Image" carry no text/plain, so they attach.
• Fixes raw image insertion. On 0.0.11, pasting an image-only clipboard into a composer without attachments (the dashboard) made WebKit put a raw <img> into the editor DOM, outside the schema. That paste is now consumed and ignored.

Validation

Checks ran in Ace-dev built from this branch: WKWebView shell, a disposable source host, and a real macOS pasteboard.

• Channel composer, attachments allowed:
  • A PNG-only (screenshot) clipboard attached image.png.
  • A Finder-style file-URL clipboard attached a.png.
  • A non-image file was ignored.
  • Plain text was inserted.
  • A pasted URL became a link.
  • Multiline text kept its hard breaks, including the blank line.
  • A text + HTML + PNG clipboard pasted the text and attached nothing.
• Sending a pasted image end to end: claude-opus-5-5 received the image and described the screenshot.
• Dashboard (canAttach={false}): a PNG paste and a Finder-style paste inserted nothing and showed no image. Text and mixed pastes still worked.
• WebKit clipboard exposure was confirmed with real copies in a standalone WKWebView probe: screenshot, Finder multi-select, Numbers cells, Safari "Copy Image".
• Edit mode was checked statically only, because apps/app doesn't pass editing yet. It uses the same attachable gate.
• bun types and bun run ci pass.

Known limits:

• A Finder copy of several files exposes only the first file to WebKit, so only one image attaches. Tracked in Attach every image from a multi-file Finder paste #105.
• A text + inline image copy (Notes, Pages) pastes only the text, as before.
• Pasting a non-image file with attachments on does nothing and gives no feedback. Drop accepts any file and fails later.

Built in Ace

Ace agents in Ace channels made all repository edits and ran all builds, checks and GitHub operations for this PR. The review was a separate Ace channel, and dev-paste-validation owned the Ace-dev and host environment. Codex supervised the work by driving the Ace Canary UI with computer use. That was the dogfooding workflow the user asked for; Codex didn't edit the repository, run builds or checks, or use GitHub for this PR.

Gaps that forced workarounds:

• Dev app: reload action and reporting an open launch that exits early #97: a lane's Ace-dev build hit an old installed Ace-dev helper. The validation channel ran an isolated source host instead.
• #106 (tested failures): Ace's desktop tools couldn't focus or paste into the Electrobun WebKit composer.
  • Point clicks were refused as occluded, element clicks didn't move focus, and background Cmd+V didn't paste.
  • Small Swift helpers set the pasteboard, set AX focus and pressed Edit > Paste. One CGEvent keystroke typed a stray character into the disposable draft.
• Avoid macOS Automation prompts when agents drive other apps #103 (prompts and guidance): clipboard cases were set up with osascript (Finder, Numbers, Safari), which raised macOS Automation prompts. Whether desktop_key can copy in Finder is untested; the agent skipped the tool's hint.

Other dogfooding issues found along the way:

• Keep literal braces in timeline message text #94: braces dropped from the timeline.
• Exclude trailing punctuation from linkified URLs in the timeline #95: a trailing colon was included in linkified URLs.
• Start lanes from origin's default branch and measure their diff against it #96: the lane base and Diff tab use the project checkout's HEAD instead of origin/main.