[WIP] Add terminal streaming functionality from previous PR

[Copilot]

Terminal Streaming Implementation Plan

Based on analysis of PR #278888, I need to bring terminal streaming functionality to the current main branch. The PR adds real-time streaming of terminal command output in chat.

Analysis Complete:

• Analyzed PR add streaming for the terminal inlined in chat #278888 changes (7 files modified)
• Identified current main branch structure differs slightly from PR branch
• Confirmed key files exist but lack streaming functionality
• Confirmed getRangeAsVT API already exists in terminal.ts

Core Changes Needed:

1. Terminal Command Mirror Streaming (chatTerminalCommandMirror.ts)

• Replace static snapshot rendering with streaming implementation
• Add onDidUpdate event emitter for real-time updates
• Implement cursor tracking and dirty range flushing
• Add streaming lifecycle management (start/stop)
• Handle incremental VT sequence updates

2. Chat Terminal Tool Progress Part (chatTerminalToolProgressPart.ts)

• Remove HTML sanitization and static output rendering
• Integrate streaming mirror for terminal output
• Add prepareMirrorForStreaming to initialize streaming early
• Update command execution listeners to trigger streaming
• Implement dynamic height calculation based on line count
• Add empty state messages and terminal host management

3. Terminal Command Artifact Collector (terminalCommandArtifactCollector.ts)

• Remove fallbackOutput parameter from capture method
• Remove HTML serialization logic
• Simplify to only store command metadata (not output)
• Remove _tryGetSerializedCommandOutput method

4. Run In Terminal Tool (runInTerminalTool.ts)

• Update capture calls to remove fallback output parameter

5. CSS Updates (chatTerminalToolProgressPart.css)

• Add focus-visible styling for output container
• Update layout for terminal host element
• Add no-output state styling
• Hide decoration overview ruler

6. Xterm Terminal (xtermTerminal.ts)

• Verify getRangeAsVT implementation (appears already complete)

Testing Strategy:

• Build and compile TypeScript changes
• Test terminal command execution with streaming output
• Verify output updates in real-time
• Test edge cases (no output, long output, command completion)

Original prompt

This PR brings the terminal streaming functionality originally developed in #278888 ("add streaming for the terminal inlined in chat") onto the current main branch. The original PR cannot be merged directly due to extensive merge conflicts.

Tasks:

• Analyze all code changes from PR add streaming for the terminal inlined in chat #278888 related to terminal streaming in chat and identify the affected files.
• Apply only the streaming-related changes to the current main branch, resolving any and all merge conflicts or incompatibilities, and ensuring the logic aligns with the main branch's current codebase.
• Do not include unrelated refactors or features from the original PR unless necessary for terminal streaming.
• Test and verify that streaming works correctly for terminal inlined in chat against main branch integrations.

This pull request was created from Copilot chat.

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