Add assistant message copy action and harden related test/storage fallbacks

[shivamhwp]

What Changed

Added a copy action for assistant messages in the chat timeline. The control lives in the assistant footer, copies only the assistant response text, stays visible but disabled while the message is still streaming, and becomes clickable once the response is complete.

The shared message copy button was also extended so it can be rendered as a compact muted button for this footer treatment. Tests were updated to cover the assistant copy visibility and streaming-disabled behavior.

Why

The app already supported copying code blocks and user messages, but not full assistant responses.

This approach keeps the behavior predictable by sourcing the copied content directly from the assistant message text already stored in the timeline, so it does not include work-log entries, command metadata, timestamps, or diff UI. Keeping the button disabled during streaming also avoids partial-copy behavior and makes the interaction state explicit.

UI Changes

This adds a small muted copy button next to the assistant message timestamp in the footer. It is disabled while the assistant is streaming and enabled after the response completes.

Before

After

Fixes #1164

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Note

Add copy button to terminal assistant messages in MessagesTimeline

• Adds a copy button to the last assistant message in each turn, visible on hover next to the timestamp in MessagesTimeline.tsx.
• Introduces resolveAssistantMessageCopyState and deriveTerminalAssistantMessageIds in MessagesTimeline.logic.ts to determine which messages show the copy button; active/streaming turns are excluded.
• MessageCopyButton.tsx now shows an anchored toast on copy success or failure and supports size, variant, and className props.
• Hardens useTheme.ts to skip DOM and storage operations during SSR or when window/localStorage are unavailable.
• Improves height estimates in timelineHeight.ts for assistant messages containing inline code by expanding backtick spans before wrapping calculations.

^{Macroscope summarized 90a1b7a.}

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Note

Medium Risk
Moderate risk due to changes in chat timeline rendering/state (new assistant-copy eligibility logic and streaming/turn handling) and useTheme initialization/SSR guards that affect app-wide theming behavior.

Overview
Adds a hover-revealed copy-to-clipboard action for assistant responses in MessagesTimeline, shown only for the terminal assistant message of each turn and suppressed while the turn/message is still streaming.

Extends MessageCopyButton to support compact icon styling with tooltip and anchored success/error toasts, and updates timeline row derivation/tests to track copy eligibility.

Improves virtualized timeline height estimation for assistant/system messages by accounting for inline code width, and hardens useTheme with SSR/non-browser fallbacks (safe localStorage/window access plus useSyncExternalStore server snapshot).

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[shivamhwp]

no need for this

[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature (copy button for assistant messages) with new UI components, state derivation logic, and prop threading, plus SSR hardening changes. While each individual change is straightforward, the aggregate introduces meaningful new capability. The open review comment about an incorrect aria-label also needs addressing.

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Dismissing prior approval to re-evaluate 1d34730

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 90a1b7a. Configure here.}

[cursor]

Incorrect aria-label says "Copy link" instead of message

Medium Severity

The aria-label on the copy button is "Copy link" but the button actually copies message text to the clipboard. The old code correctly used title="Copy message". This mislabels the action for screen reader users and is inconsistent with the tooltip text "Copy to clipboard".

 

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