Agent Host: Use SDK shell exit metadata for command decorations

[anthonykim1]

Resolves: #322163
Context: github/copilot-sdk#1803

You will now see proper command decoration when using shell tool from SDK:

• Add shell_exit as Agent Host tool result content for SDK shell command exit metadata.
• Preserve SDK tool.execution_complete.result.contents[] shell exit blocks in both live Copilot Agent Host events and replay/history mapping.
• Use shell_exit.exitCode as the terminal command state source when the custom terminal tool is disabled.
• Treat exitCode === 0 as success, non-zero exit codes as failure, and missing shell exit metadata as unknown/compatibility fallback.
• Keep result.content as the displayed text output and avoid rendering shell_exit.outputPreview as duplicate terminal output.
• Do not create fake terminal URI/resource content for SDK shell exit metadata.

---

Inspirations from:

• Terminal command decoration state follows existing chat terminal behavior where exitCode === undefined means unfinished and non-zero exit codes are failures: chatTerminalToolProgressPart.ts.

[Copilot]

Pull request overview

This PR updates the Agent Host ↔ Chat workbench integration so terminal command decorations can reflect the actual shell exit code provided by the Copilot SDK (shell_exit), including in both live event handling and history replay.

Changes:

• Adds a new ToolResultContentType.ShellExit (shell_exit) content block and corresponding ToolResultShellExitContent type.
• Preserves SDK tool.execution_complete.result.contents[] blocks (specifically shell_exit) when mapping both live session events and replay/history.
• Updates the chat-side terminal tool mapping to prefer shell_exit.exitCode over SDK success when computing terminalCommandState.exitCode (with tests covering non-zero exit codes even when success: true).

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/stateToProgressAdapter.ts	Uses shell_exit.exitCode to drive terminalCommandState.exitCode for terminal tool invocations/serialization.
src/vs/workbench/contrib/chat/test/browser/agentSessions/stateToProgressAdapter.test.ts	Adds tests verifying shell_exit exit codes are used for history and finalize behavior.
src/vs/platform/agentHost/node/copilot/mapSessionEvents.ts	Appends SDK shell_exit typed blocks into tool-result content during replay mapping.
src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts	Appends SDK shell_exit typed blocks for live tool.execution_complete handling.
src/vs/platform/agentHost/test/node/mapSessionEvents.test.ts	Adds replay tests ensuring shell_exit is preserved (including non-zero exit codes).
src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts	Adds live-event test ensuring shell_exit is preserved in tool completion results.
src/vs/platform/agentHost/test/node/copilotTestEvents.ts	Extends minimal SDK test event shapes to include result.contents.
src/vs/platform/agentHost/common/state/sessionState.ts	Re-exports ToolResultShellExitContent from the protocol state barrel.
src/vs/platform/agentHost/common/state/protocol/channels-chat/state.ts	Adds ToolResultContentType.ShellExit and ToolResultShellExitContent to the protocol model.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 2
• Review effort level: Low