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codex/codex-rs/codex-mcp
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jif 6d2168f06a Reuse MCP runtimes when selected availability changes nothing (#30148)
## Why

MCP runtime reuse was keyed by every ready selected-capability
environment, even when an environment contributed no MCP servers or
connectors.

For example:

1. a global stdio MCP is running;
2. a selected remote environment contains only a skill;
3. that environment becomes ready;
4. the MCP and connector projection stays exactly the same;
5. Codex nevertheless rebuilds the MCP manager and restarts the global
stdio process.

That restart can interrupt active calls and discard process-local state
even though nothing about MCP changed.

## What changes

When selected-environment availability changes, Codex now resolves the
candidate MCP and connector projection before deciding whether to
replace the runtime:

- if the winning MCP servers or their ownership change, rebuild as
before;
- if the selected connector snapshot changes, rebuild as before;
- if an enabled MCP is explicitly bound to an environment whose
availability changed, rebuild as before;
- otherwise, keep the exact live manager and processes, and update only
the availability input remembered by the snapshot.

```text
ready selected environments:  [] -> [skills-env]
resolved MCP servers:          {global_probe} -> {global_probe}
resolved connectors:           {} -> {}
result:                         reuse manager; keep the same process
```

The comparison uses the resolved winning servers and their sources, so
plugin/config ownership remains part of the runtime identity.

## Existing stack coverage

The integration PR directly below this one already covers both rebuild
boundaries: a selected MCP becomes callable and a selected connector
tool becomes model-visible when their environment becomes available. It
also verifies that an unchanged selected MCP runtime keeps its process.

This PR does not add another remote-attachment integration scenario for
the no-change optimization. `environment/add` returns before readiness,
and app-server does not currently expose a deterministic readiness
signal for an environment that contributes only skills. Keeping a
fixed-delay test would add flake risk; adding a new readiness API would
be outside this fix.

## Scope and assumptions

- This does not change skill discovery, World State rendering, or plugin
metadata caching.
- This does not add file watching or hot reload behavior.
- This does not change disconnect/reconnect handling.
- Selected environment IDs and their capability contents retain the
stack's existing stability assumption.
- Delayed `required = true` executor MCP behavior remains out of scope.
6d2168f06a ยท 2026-06-26 09:27:41 +01:00
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