## Why
Local stdio MCP servers may start in a different working directory from Codex,
so inherited relative CA bundle paths can otherwise resolve to the wrong file.
## What changed
- Forward the supported custom CA environment variables to local stdio MCP
servers, convert inherited non-empty paths to absolute paths, and let explicit
MCP environment overrides take precedence.
- Match CA variable names and `PATH` case-insensitively where required, avoiding
duplicate environment entries and preserving executable discovery on Windows.
## Testing
- Add an end-to-end stdio MCP test covering relative inherited CA paths, empty
values, explicit overrides, alternate key casing, and a different server
working directory.
- Exercise executable resolution with Windows-style `Path` casing.
GitOrigin-RevId: ea1bc0ae63bc0dc780acb8363b2ed102120f282e
## What changed
- Add an opt-in `mcp_2026_07_28` protocol mode while preserving the legacy
lifecycle by default.
- Negotiate the new protocol over streamable HTTP with `server/discover`,
including bounded responses, redirect protection, and fallback only when a
response establishes that the endpoint is legacy-only.
- Require stdio servers to opt in with
`CODEX_MCP_PROTOCOL_VERSION=2026-07-28`, and add a bounded local stdio
transport for the modern lifecycle.
- Consume paginated tool, resource, and resource-template catalogs in modern
mode, reject repeated cursors, and retain discovered server identity.
- Reconnect reusable MCP clients when their selected protocol mode changes.
## Testing
- Cover HTTP JSON and SSE discovery, legacy fallback and rejection cases,
redirects, retries, response limits, and pagination.
- Cover local and executor stdio discovery, protocol markers, message limits,
and legacy compatibility.
GitOrigin-RevId: f6a78816e127d2a482292d63b91c8384f1595903
Eric Traut