Add configurable Copilot runtime version preference

[ZekeAranyLucas]

Summary

Add an optional, version-agnostic Copilot runtime preference so GraphCode can launch a known-good CLI when a newer release regresses. No release is hardcoded: 1.0.84-5 is only an example.

Changes

• Persist copilotPreferredVersion in the settings shared by the app and daemon; missing or blank values preserve normal Copilot version selection.
• Pass --prefer-version <version> through app and daemon launches and resumes, locally and over SSH, plus title and summary requests.
• Add Preferred versions immediately after Permissions, with a matching row for each backend. Copilot offers Default or Specific version, with a shell-quoted, copyable npm install command; Claude Code, Codex, OpenCode, and Pi remain disabled at Default until their version overrides are implemented.
• Keep backend selection unchanged: the version controls do not change the default backend for loops or Quick Chats.
• Document the required manual order: install on each execution host, verify the reported version, then activate the preference.
• Cover settings compatibility, launch/resume parity, other-backend isolation, headless requests, and shell argument handling.

Scope and remaining rollback work

This is version-preference plumbing, not a complete guided runtime rollback operation.

GraphCode does not execute npm, verify installation readiness, or gate activation on a successful installation. Editing the preference takes effect immediately for subsequent launches. Existing sessions are not interrupted.

The intended complete flow is choose a version, explicitly approve installation, install and verify it on the execution host, and only then activate the preference. Global npm installation also changes Copilot outside GraphCode; that effect needs to be clear before approval. The guided install/verify/activate workflow remains outstanding.

Test plan

• Shared library, daemon, and CLI: swift build passed.
• Initial app build and eight focused suites: 84 tests passed (CopilotVersionTests, GraphcodeSettingsTests, CopilotBackendTests, AttachedSessionPermissionTests, LocalSessionResumeTests, RemoteSessionResumeTests, SummaryStoreTests, TitleSuggestionTests). The SwiftPM build and all 84 tests also passed after rebasing onto main.
• After the Preferred versions UX update: the app built and 30 tests passed across CopilotVersionTests, GraphcodeSettingsTests, CopilotBackendTests, and AttachedSessionPermissionTests, including new coverage that version preferences start at Default and do not change backend selection.
• Strict Swift formatting passed for changed Swift files. Targeted SwiftLint passed for the new behavior; existing file/type-length violations in GhosttyTerminalView.swift and SummaryStoreTests.swift also reproduce on the baseline.
• Confirmed copilot --prefer-version 1.0.84-5 --version selects that installed version and npm publishes the matching package.

Checklist

• I have read the Contributing Guidelines
• I have signed off my commits (git commit -s) per the DCO
• Full make test run (focused suites run instead, as listed above)
• Full make check run (targeted checks run; pre-existing length violations noted above)

[scgopi]

Merging this. The two unticked boxes in your checklist are covered: we ran the full make test (1824 tests, 194 suites, all passing) and the full make check (exit 0) on the branch merged with current main, on macOS. The pre-existing length violations you noted in GhosttyTerminalView.swift and SummaryStoreTests.swift do reproduce on the baseline and are not from this change.

We also verified the cross-backend question directly, since it was the main risk: --prefer-version is emitted from exactly one place in production code, behind a supportsVersionPreference guard that is Copilot-only, and argv goldens across five backends and every launch shape are byte-identical with the preference unset and set. Removing the guard makes those goldens fail, so the coverage is real.

One fix we will land separately on main: the README's install command uses @github/copilot@v1.0.84-5, which 404s — no published version is v-prefixed. 1.0.84-5 is correct, as your next line has it.

The guided install/verify/activate flow you describe as outstanding is a good follow-up. Thanks for this.