chore: switch codex adapter to agentclientprotocol

[dutifulbob]

Summary

ACPX still used the Zed Codex ACP adapter as its built-in Codex backend.
This changes the built-in Codex command to the Agent Client Protocol package and updates the matching docs, tests, and local agent guidance.
It also bumps the built-in Claude ACP adapter range to the latest published @agentclientprotocol/claude-agent-acp package.

What Changed

The built-in codex registry entry now resolves to the Agent Client Protocol package.
Codex model selection is documented as normal ACP model selection through advertised model ids and session/set_model.
The built-in claude registry entry now resolves to the current Claude ACP adapter range.

• Switched src/agent-registry.ts to npx -y @agentclientprotocol/codex-acp@^0.0.44.
• Bumped @agentclientprotocol/claude-agent-acp from ^0.31.0 to ^0.36.1.
• Updated registry tests and client tests for the new package names and ranges.
• Limited the old Codex thought_level -> reasoning_effort alias to legacy @zed-industries/codex-acp commands.
• Updated README, agent docs, CLI docs, conformance docs, security routing, changelog, and the acpx skill docs.
• Updated the persisted-key casing lint fixture to use the current built-in command.

Verification

The normal code and docs gates pass, and the published Codex adapter starts successfully through the new default command.
I also ran a real authenticated one-shot Codex message through the published adapter and got the expected response.
The published Claude adapter package at 0.36.1 resolves and starts from its package binary.

• pnpm run check
• pnpm run check:docs
• pnpm run build:test && node --test dist-test/test/agent-registry.test.js
• npm view @agentclientprotocol/claude-agent-acp version time --json
• npx -y --package @agentclientprotocol/codex-acp@0.0.44 codex-acp --version
• timeout 15s npx -y --package @agentclientprotocol/claude-agent-acp@0.36.1 claude-agent-acp --help
• pnpm run conformance:run -- --case acp.v1.initialize.handshake --agent-command "npx -y @agentclientprotocol/codex-acp@0.0.44" --cwd /tmp/acpx-codex-conformance
• HOME=/tmp/acpx-codex-default-home CODEX_HOME=/tmp/acpx-codex-default-home ACPX_HOME=/tmp/acpx-codex-default-acpx timeout 30s node dist/cli.js --cwd /tmp/acpx-codex-default-work --auth-policy fail --format json codex sessions new
• timeout 120s node dist/cli.js --agent "npx -y @agentclientprotocol/codex-acp@0.0.44" --cwd /tmp/acpx-codex-message --approve-all --format quiet exec "Reply with exactly acpx-codex-ok and nothing else."

Behavior addressed: default acpx codex now launches @agentclientprotocol/codex-acp instead of @zed-industries/codex-acp, and default acpx claude now launches @agentclientprotocol/claude-agent-acp@^0.36.1.
Real environment tested: local Linux checkout with the published @agentclientprotocol/codex-acp@0.0.44 package, isolated temp directories for startup/auth smoke, a real authenticated one-shot Codex prompt in /tmp/acpx-codex-message, and the published @agentclientprotocol/claude-agent-acp@0.36.1 package binary.
Exact steps or command run after this patch: pnpm run check, pnpm run check:docs, focused registry test rebuild/run, published package version/binary smokes, ACP conformance initialize handshake, isolated acpx codex sessions new startup/auth-required smoke, and a real Codex exec prompt.
Evidence after fix: conformance reported Cases: 1 Passed: 1 Failed: 0; the default acpx codex sessions new path returned structured AUTH_REQUIRED from the new adapter instead of failing to spawn; the real prompt returned acpx-codex-ok and exit code 0; the Claude package binary resolved and exited 0.
Observed result after fix: the new Codex adapter package is reachable from the built-in command path, ACP initialize/auth negotiation works, a real Codex message turn completes successfully, and the Claude built-in range points at the latest published adapter.
What was not tested: multi-turn persistent Codex session reuse with the new adapter, and a live Claude Code prompt through the bumped Claude adapter.

Risks

The main compatibility risk is users relying on the old Zed adapter's thought_level alias through the built-in codex name.
That alias is kept only for explicit legacy Zed adapter commands, while the new default follows the current adapter's advertised ACP model ids.

[osolmaz]

Landed via temp rebase onto main.

• Gate: pnpm run check and pnpm run check:docs passed locally on the PR branch after rebasing onto current main.
• Land commit: e517ffe
• Merge commit: 30b5ee5

Thanks @dutifulbob!