[witbrock]

Android Gboard can reject a screenshot tile before Von receives a DOM paste event. The main composer now offers More actions (+) → Paste image, with Attach image as recovery when browser clipboard access fails. Both preserve the caption and reuse the existing session-bound upload/preview path. The existing items/files extractor and ordinary text paste remain unchanged.

Reuses the exact initialiseImagePicker helper from #658, whose native Android permission path is now verified. This PR delivers only that bounded recovery; #658's broader layout, upload-cancellation and PWA work remain separate. The original Gboard tile is still browser-limited. Diagnosis and native evidence provenance are recorded in docs/engineering/mobile_screenshot_paste_2026-09-14.md.

Validation:

• 20 targeted frontend tests, 3 existing clipboard-extraction tests and 15 backend image tests passed. Static JavaScript, syntax and whitespace checks passed.
• Native operator evidence: Android 17 / Chrome 145.0.7632.218 / Gboard 17.2, trusted Paste image tap, actual permission prompt and Allow, 109-byte PNG decoded at 24×16, captions preserved. Helper body verified identical to that tested in Complete mobile image picker and recoverable attachment lifecycle #658.
• Production template and initializeChatTab fixture in Chromium 153 at 360/448/1440 pixels: real desktop clipboard upload with window-session header, preview/removal, denied-read recovery through file chooser, preserved captions and multiline text, no page errors or composer overflow. HTTP uploads are stubbed; native evidence is a separate capability trial.
• All six existing composer layout/keyboard profiles passed. Corrected an existing test's ambiguous first-button selector (Retry versus Remove), and completed the request test's API-header mock.

Merge decision: ready for the explicit recovery, at Tier 1. Physical Pixel/Chrome 152, full authenticated Von/PWA and public deployment remain unverified; this PR does not claim the Gboard toast is removed. No deployment requested.

Native task: #V#task_agent_b61e77311c89e38adcf879ff20c995b1. Run evidence retained in .run/mobile-paste/; canonical task updates and requester reporting belong to the controller.