The /codex-runtime slash command short-circuits with "openai_runtime
already set" when invoked with the same value as the current config,
and crucially skips the entire migration block below. The check
conflates two things: (a) "the config value is correct" and (b) "the
world state (managed block in ~/.codex/config.toml, hermes-tools MCP
callback, plugin discovery) is converged".
Common footgun this exposes: a user who pre-sets
`model.openai_runtime: codex_app_server` directly in config.yaml
(reasonable thing to do) and then runs /codex-runtime codex_app_server
to trigger migration sees "already set" and silently gets no migration.
~/.codex/config.toml never receives the managed block, the hermes-tools
MCP callback never registers, and codex falls through to its default
runtime instead of the app-server one — visibly successful but
functionally partial setup.
The migration is idempotent by design (it replaces its own managed
block in place between MIGRATION_MARKER and MIGRATION_END_MARKER), so
re-running it is safe and cheap. Fix the short-circuit to fall through
to migration when re-applying codex_app_server while skipping the
config persist (no value-level change needed). The disable case
(re-applying "auto") still short-circuits because disabling doesn't
touch ~/.codex/config.toml at all.
The user-visible message changes to "openai_runtime already set to
codex_app_server — re-applying migration" so re-runs surface what
happened.
Regression test (test_reapply_codex_app_server_runs_migration) asserts:
- migrate() was called when re-applying
- persist_callback was NOT called (no config write on no-op transitions)
- migration output (MCP servers, sandbox default) surfaces in the
user-visible message
- requires_new_session is True so callers know to /reset
Verified RED→GREEN: the test fails on origin/main with
"migration must run on reapply, not just first enable" and passes with
this fix. Full test_codex_runtime_switch.py suite: 31 passed.
