Improve Terminal Reliability + Copilot Image Attachments

[hendrikmennen]

Overview

Improves terminal reliability and shell integration, and adds image attachment support to Copilot chat.

Terminal reliability

Output no longer lost in background tabs — ReplayBufferedConnection wraps the pty connection and buffers output produced while no control is subscribed (i.e. while a tab is not selected), replaying it once the tab is shown again. Previously every byte written by a shell in an unselected tab was dropped, leaving holes in the output — or nothing at all for commands the AI ran in a background tab. The buffer is capped at 1 MB and only fills when there is no subscriber, so data is never delivered twice. Covered by ReplayBufferedConnectionTests.

Shell integration — the shell now emits invisible OSC 633 sequences at prompt boundaries so OneWare can detect when a command starts and what exit code it finished with. Hooks are installed via startup files (bash --init-file, zsh ZDOTDIR, PowerShell -Command) so nothing is ever echoed into the user-facing terminal. Scripts live under ~/.oneware/shell-integration rather than the shared temp directory to avoid a TOCTOU swap by another user.

PowerShell is now launched with -ExecutionPolicy Bypass, matching VS Code. Without it, systems with the default Restricted/AllSigned policy failed to dot-source the integration script and greeted the user with a PSSecurityException on every terminal start.

Copilot image attachments

Ctrl+V in the chat input now attaches an image from the clipboard instead of doing nothing useful:

• IChatService.TryAddImageAttachment is a new opt-in member with a default false return, so existing chat services stay source- and binary-compatible.
• CopilotChatService implements it by mapping the bytes onto the SDK's AttachmentBlob (base64 Data + MimeType).
• The attachment chip shows a small decoded thumbnail for images; file/selection chips keep the existing icon.
• If the clipboard holds no image — or the active service doesn't support images — the handler falls back to a normal text paste, so Ctrl+V behaviour is unchanged elsewhere.

Thumbnails are disposed when a chip is removed and after send.

Installer

Fixes a signing issue in the Windows installer build.

Testing

• dotnet build clean on the touched projects (0 errors).
• New unit tests for ReplayBufferedConnection covering buffering, replay, and the byte cap.
• Manually verified the PowerShell terminal starts without a PSSecurityException under a restricted execution policy.