agentHost: Remember and reuse CLI processes for ssh

[roblourens]

Co-authored-by: Copilot copilot@github.com

[Copilot]

Pull request overview

This PR adds SSH remote agent-host process reuse by persisting remote CLI agent-host state (PID/port/token) in a state file and attempting to reconnect to an existing process before starting a new one, reducing orphaned code agent-host processes on reconnect.

Changes:

• Add reusable SSH helper utilities to read/write/validate a remote .agent-host-state file and to clean up stale processes.
• Update the SSH connect flow to (1) detect an existing remote agent-host, (2) reuse it when possible, and (3) fall back to cleanup + fresh start when reuse is not connectable.
• Add node tests covering helper behavior and the end-to-end connect/reuse/cleanup flow via in-process mocks.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/sshRemoteAgentHostService.ts	Integrates remote agent-host reuse into the SSH connect flow; refactors to allow test overrides and uses DisposableMap for connection lifecycle.
src/vs/platform/agentHost/node/sshRemoteAgentHostHelpers.ts	New helper module for shell-safe paths, platform detection, token redaction, and state-file based process reuse/cleanup.
src/vs/platform/agentHost/test/node/sshRemoteAgentHostHelpers.test.ts	Unit tests for helper utilities (token validation, state parsing/cleanup, state writing).
src/vs/platform/agentHost/test/node/sshRemoteAgentHostService.test.ts	Connect-flow tests validating caching, reuse via state, stale cleanup, relay-failure fallback, and sanitization behavior.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 3

[Copilot]

Pull request overview

This PR extends the SSH-based remote agent host bootstrap to persist and reuse a previously-started code agent-host process by recording its PID/port/token on the remote machine, reducing orphaned processes and reconnect overhead.

Changes:

• Add remote “agent host state file” helpers to record and detect an existing running agent host via PID/port/token.
• Update SSHRemoteAgentHostMainService.connect() to reuse an existing agent host when possible, and fall back to starting fresh on relay failures.
• Add new unit tests for the helper utilities and the connect/reuse/fallback flow.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/sshRemoteAgentHostService.ts	Implements process reuse via remote state file lookup + relay fallback behavior; refactors native module loading for testability.
src/vs/platform/agentHost/node/sshRemoteAgentHostHelpers.ts	New helper module for shell-safe paths, state file read/write, reuse detection, and cleanup.
src/vs/platform/agentHost/test/node/sshRemoteAgentHostHelpers.test.ts	Adds coverage for state parsing/validation, shell escaping, URL building, and cleanup/write behavior.
src/vs/platform/agentHost/test/node/sshRemoteAgentHostService.test.ts	Adds connect-flow tests for caching, reuse via state file, stale PID behavior, and relay-failure fallback.
src/vs/workbench/contrib/chat/test/common/model/objectMutationLog.perf.test.ts	Adds an opt-in perf benchmark for Chat ObjectMutationLog (appears unrelated to agentHost SSH changes).

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 2