feat(agent-mode): migrate Codex ACP and guide legacy users

[zeroliu]

Summary

User state	App behavior	Recovery path
New / unconfigured	Show only @agentclientprotocol/codex-acp setup	Install the current package, then auto-detect
Legacy or below minimum	Show Update required, block startup, and explain why	Remove the old package, install the supported package, then re-detect
Supported	Start normally and show adapter/effective CLI provenance in settings	Update the adapter when a newer compatibility floor is required

Why: The superseded Zed Codex ACP adapter can fail at startup or hide current models, leaving users to blame Copilot without a clear diagnosis or recovery path.

What: Agent Mode now uses the maintained App Server adapter, classifies the configured installation before launch, blocks legacy/outdated binaries with exact migration guidance, and explains the adapter/bundled CLI/override relationship in settings and docs.

Decisions

• Treat legacy @zed-industries/codex-acp as a blocking migration state, not a retryable generic boot error.
• Enforce release-owned compatibility floors instead of requiring a live registry-latest check at startup.
• Keep CODEX_PATH for advanced users, while identifying it as an unbundled override and surfacing its effective CLI version and warning.
• Explicitly remove the old global package before installing the maintained package.
• Retain a compact adapter/effective-CLI readout in healthy Codex settings for supportability.
• Preserve Windows support with Node/npm and direct dist/index.js launching, without shell-based .cmd spawning.

Changes

• ef5716a8 — Models Codex installation health and provenance with bounded shell-free probes, device-local caching, compatibility floors, Windows/POSIX resolution, and blocking remediation details. Verify legacy, supported bundled, override, invalid, and below-minimum classifications.
• edd984ea — Adopts the replacement adapter runtime contract through CODEX_CONFIG, INITIAL_AGENT_MODE, current mode IDs, health-aware descriptor wiring, and Node-based Windows launch. Verify instructions, auth, model switching, modes, and cross-platform spawn descriptors remain correct.
• 2e522a77 — Surfaces migration and version clarity in chat and settings, prevents stale or blocked installs from starting, adds forced re-detection and accessible copy actions, and keeps healthy chat uncluttered. Verify blocked, invalid, unconfigured, bundled, override, and unrelated-backend UI states.
• 37de5054 — Replaces the legacy Windows installer/setup path and documents bundled versus overridden CLI provenance plus missing-model troubleshooting. Verify all setup commands target @agentclientprotocol/codex-acp and no user-facing path installs or launches the Zed adapter.

Notes / follow-ups

• A current binary still cannot guarantee every model is visible: auth state, account entitlements, provider configuration, staged rollout, duplicate installs, an overridden CLI, and models_cache.json can independently affect the catalog.
• Native PowerShell parser validation was unavailable on the development machine; the installer was reviewed for quoting, idempotency, path resolution, and actionable failures, and its surrounding UI/docs tests and repository gates passed.