add support for compatible custom tools (compatible_with)

[johnrichardrinehart]

Summary

• add support for compatible custom tools via a new compatible_with setting
• preserve the configured custom tool identity instead of rewriting wrapper tools to built-in names during tmux detection
• route Codex compatibility paths through the configured wrapper command so restart, resume, parsing, hooks, and session tracking keep using the custom tool

Example configuration

[tools.my-codex]
command = "my-codex"
compatible_with = "codex"
icon = "💻"

This lets my-codex behave like Codex for agent-deck feature handling while still preserving the custom tool name and command.

Example wrapper script

#!/usr/bin/env bash
set -euo pipefail

export OPENAI_API_KEY="${OPENAI_API_KEY:?missing OPENAI_API_KEY}"
exec codex "$@"

For example, save that as ~/bin/my-codex, make it executable, and then point the tool config at my-codex.

Testing

• go test ./...
• manual validation with a custom wrapper configured as compatible_with = "codex"
• confirmed that restart/resume continues to use the wrapper command rather than falling back to plain codex
• confirmed that the custom tool identity is preserved instead of being rewritten to the built-in tool name

Notes

• this has been tested with compatible_with = "codex" and it is working great
• this branch is currently stacked on top of fix(test): stabilize tmux-backed test suites #551, which contains the test-suite stabilization changes used while validating this work

[johnrichardrinehart]

This branch is now rebased on top of #551. GitHub cannot set a PR base to a fork-only branch, so #550 still targets main, but reviewers should treat #551 as the prerequisite lower PR in the stack.