## What changed
Add `exchange_ema_auth_token` to discover and validate the MCP resource's authorization server before resolving enterprise identity credentials and performing the ID-JAG token exchange. Keep the lower-level exchange primitive private.
- Probe `server/discover` with the enterprise-managed authorization extension, support recognized legacy discovery rejections, and follow protected-resource metadata challenges or well-known fallbacks.
- Match configured resource and issuer constraints, require advertised public-client JWT bearer support, and validate token endpoint metadata without requiring an authorization endpoint.
- Bound discovery with a shared timeout, redirect and authorization-server limits, reject cross-origin metadata redirects, and restrict private authorization-server destinations while allowing local loopback discovery.
## Testing
Add tests covering resource and issuer mismatches before identity access, metadata capability validation, query preservation, modern challenges, JSON and SSE legacy fallback behavior, cross-origin redirect rejection, and private or malformed issuer destinations.
GitOrigin-RevId: 9a55233a20ff42c293f9bd8175e01141ac2d8576
## Why
MCP requests pass through background transport queues, so HTTP requests need the caller's trace context carried explicitly to preserve trace ancestry.
## What changed
- Capture W3C trace context in request metadata for tool and resource operations, custom requests, and event streams.
- Restore that context in an `mcp.http.request` span around HTTP POSTs, linking outgoing HTTP traces to the originating request.
- Preserve application metadata while replacing trace fields with the current caller's context and removing stale `tracestate`. Read the SDK's merged metadata so extension fields retain precedence over parameter metadata.
## Testing
Add a unit test for metadata merge precedence and an integration test covering concurrent paginated requests, tool calls, custom requests, and tool-call continuations across legacy and `2026-07-28` protocol modes. Verify HTTP trace ancestry, metadata preservation, and removal of stale `tracestate`.
GitOrigin-RevId: 0b22cd75f31f9fcb855b27fa8d34ecdffd6e3549
## Why
When silent OAuth refresh cannot recover a rejected MCP tool call, the caller
needs the server's authentication challenge to initiate interactive login. The
rejected call must not be replayed automatically after refresh has failed.
## What changed
- Convert `401 Unauthorized` responses with `WWW-Authenticate` headers into an
MCP tool error containing `mcp/www_authenticate` metadata.
- Preserve multiple authentication challenges by combining all
`WWW-Authenticate` header values.
- Keep successful silent refresh behavior while avoiding replay when refresh
fails.
## Testing
Added coverage for successful and failed refresh, multiple authentication
headers, propagation through agent tool-call events, and no-replay behavior.
GitOrigin-RevId: c560cff6286d7ab09b1f5c6cf3618d4650cde47d
## Why
Rust falls back to `fork` when a macOS command combines a relative executable
path with a working directory, due to a historical `posix_spawnp` issue. This
can make local MCP server startup less reliable.
## What changed
- Spawn relative macOS MCP executables directly with `posix_spawn`, preserving
the configured path, `argv[0]`, working directory, environment, stdio, and
process group.
- Keep the existing launcher for `PATH` lookup and executable text files without
a shebang.
- Use one local child wrapper for legacy and 2026-07-28 protocol framing, with
cancellation-safe waiting and cleanup that kills and reaps dropped children.
## Testing
Add macOS regression coverage for relative scripts, argument and descriptor
preservation, launch errors, cancelled waits, and cleanup after runtime shutdown.
GitOrigin-RevId: 1cbc6b90aed6f67e0a38f551964d80496ebc4471
## What changed
- Re-run the HTTP headers helper after a same-origin `POST` receives a `401` or `403`, and retry the request once when the effective headers changed.
- Share refreshes across concurrent rejected requests, retain the previous headers when refresh fails, and keep the retry within the original timeout.
- Allow helpers to supply `Authorization` while preserving explicit OAuth or bearer credentials, OAuth insufficient-scope challenges, and redirect safety checks.
## Testing
- Cover rotating helper headers for MCP tool calls and same-origin OAuth token refreshes.
- Cover concurrent rejections, failed and unchanged refreshes, retry limits, timeouts, and redirects.
GitOrigin-RevId: c662edefdb1cd2876d9d02545a72d5bd6739864f
## Why
Executor-owned HTTP MCP servers need to read their bearer credentials from the
selected executor environment instead of the host process.
## What changed
- Preserve `bearer_token_env_var` for executor-owned HTTP MCP configurations and
resolve it when the executor sends each request.
- Extend delegated HTTP headers with executor-local environment references while
rejecting missing, empty, or protected credential variables.
- Keep transport-provided bearer authentication compatible with MCP redirect and
OAuth handling without sending a placeholder authorization value.
## Testing
- Cover authenticated executor-owned MCP requests end to end.
- Cover delegated header resolution and rejection of protected variables.
- Cover parsing executor-owned bearer configuration and transport-provided bearer
behavior.
GitOrigin-RevId: 442bf7382198ffb69eba797eb36d4c74faabda88
## What changed
- Upgrade `rmcp` and `rmcp-macros` from 3.1.2 to 3.1.3.
- Preserve authentication-required and retryable transport classifications when modern MCP discovery falls back to legacy initialization.
- Prevent unrelated discovery errors from triggering legacy fallback while retaining their diagnostics.
## Testing
- Cover authentication challenges and transient initialization failures during legacy fallback.
- Verify that a failed OAuth issuer check does not consume the pending authorization state.
GitOrigin-RevId: 957c0873fec1148883dd163fbaeb77d7593d8c53
## What changed
- Upgrade `rmcp` from 3.0.0 to 3.1.2.
- Use `rmcp`'s native JSON-RPC decoding and remove the local compatibility layer for multi-round-trip tool results.
- Preserve response metadata on `input_required` SSE results.
- Support OAuth protected-resource metadata discovery and include the discovered resource audience when refreshing tokens.
## Testing
- Add coverage for metadata preservation on modern SSE `input_required` responses.
- Add an OAuth startup scenario that discovers protected-resource metadata and verifies the refresh-token resource audience.
GitOrigin-RevId: 689f009b4a33552b640304111b74585b4009eeb8
## Why
MCP requests can contain sensitive headers and tool-call bodies. Following a
cross-origin redirect could disclose them to another server.
## What changed
- Follow redirects only when every hop remains on the configured server's
origin, and require HTTPS for redirects on non-loopback hostnames.
- Preserve standard redirect method and body handling while sharing the
original timeout and enforcing a 10-hop limit.
- Avoid replaying plaintext proxy credentials across redirects, while leaving
OAuth requests that stop at redirects unchanged.
## Testing
Add coverage for same-origin and cross-origin redirects, redirect methods,
headers and bodies, proxy credentials, timeouts, hop limits, and legacy MCP
tool calls.
GitOrigin-RevId: 3e267911a1665ad8c2fc63825099a758770f4d68
## What changed
- Expose hosted Plugin Runtime event definitions through `McpResourceClient::list_events`.
- Add cancellable `events/stream` subscriptions that route lifecycle notifications to the matching request and cancel when the stream is dropped.
- Bound event notification and queue sizes, time out stalled response headers, and close streamable HTTP responses locally on cancellation.
## Testing
- Add streamable HTTP integration coverage for isolated concurrent subscriptions, local cancellation, and stalled response-header timeouts.
GitOrigin-RevId: 98c6fffa8f004eb2638c1b0705f659222cbbdfdb
## Why
A streamable HTTP MCP handshake could time out while its executor-backed HTTP
request continued running, leaving the serial executor blocked for later
requests.
## What changed
- Track the remaining initialization deadline for streamable HTTP transports.
- Apply it to `initialize`, `notifications/initialized`, and discovery HTTP
requests, then clear it when the handshake finishes.
## Testing
- Added a regression test that stalls the remote MCP endpoint, waits for the
handshake timeout, and verifies that a subsequent executor request completes.
GitOrigin-RevId: d4980a332e898309c885cbaa4fdd598924b440e1
## What changed
- Track Agent Plugin manifests through plugin, skill, and MCP loading so their capabilities use format-specific behavior without changing legacy plugins.
- Discover only direct-child skills, exclude app and hook capabilities, isolate MCP data, and reject MCP configuration files that are non-regular or resolve outside the plugin root.
- Bound model-visible skill instructions, plugin instructions, MCP descriptions, schemas, individual tools, and the aggregate Agent Plugin MCP tool set.
- Stop MCP and OAuth redirects when Agent Plugins send configured or authorization headers, while retaining existing redirect behavior for legacy MCP servers.
## Testing
- Add coverage for capability filtering, skill discovery, isolated MCP data and reserved-path expansion, unsafe MCP configuration files, context limits, and redirect handling.
GitOrigin-RevId: c9af66b051269f3226628ca280a58d32c808c38f
## What changed
- Add `parse_agent_plugin_mcp_config` to translate Agent Plugins v1 `mcp.json` files into Codex MCP server configuration.
- Normalize `stdio` and streamable HTTP transports, including `PLUGIN_ROOT` and `PLUGIN_DATA` expansion, contained plugin paths, secure endpoint validation, and filtering of client-owned HTTP headers.
- Keep valid sibling servers when another server is invalid, while returning per-server parse errors.
- Preserve UTF-8 HTTP header values when forwarding streamable HTTP protocol headers.
## Testing
- Cover transport mapping, placeholder expansion, path containment, schema and field validation, per-server errors, platform-specific environment handling, and UTF-8 headers.
GitOrigin-RevId: ed4ab0fcf495afbb381ce48beb93989629444c56
## Why
Some legacy MCP servers reject `server/discover` before creating a session and
return a null-ID JSON-RPC error with a non-JSON content type or without echoing
the rejected protocol version. These responses prevented the client from
falling back to legacy initialization.
## What changed
- Parse HTTP 400 discovery errors without a session ID regardless of their
declared content type.
- Fall back to `initialize` when error code `-32000` reports a missing session
or advertises only known legacy protocol versions, including supported
versions other than `2025-06-18`.
- Continue rejecting unrelated error codes, correlated responses, non-400
statuses, malformed version lists, and lists containing modern or unknown
versions.
## Testing
Added MCP discovery coverage for legacy error variants, server-selected legacy
protocol versions, non-JSON content types, and non-legacy rejection cases.
GitOrigin-RevId: 4d3ee2d7d852ce0d0ab3f486da23cb653a7ff5ca
## What changed
- Require callers to provide an HTTP client for MCP OAuth discovery and login, removing the separate direct `reqwest` path.
- Use the shared `http` and `url` types throughout the MCP client and drop its direct `reqwest` dependency.
- Preserve configured MCP headers when routing OAuth discovery through the provided client.
## Testing
- Add coverage that routed OAuth discovery forwards configured headers.
GitOrigin-RevId: 1345f56bd794626533133447597a5908e57b9b48
## What changed
- Drive multi-round `tools/call` and `resources/read` requests through
`input_required` responses, preserving opaque request state and elicitation
metadata across JSON, SSE, and stdio transports.
- Decode modern discovery and elicitation result shapes while retaining legacy
initialization, elicitation defaults, and discovery fallback behavior.
- Apply the 8 MiB modern-protocol response limit to JSON, SSE events, and stdio
messages, and reject executor stream recovery when output sequence gaps would
corrupt the protocol stream.
## Testing
Added integration coverage for discovery, multi-round requests, legacy
fallbacks, message limits, stdio launchers, SSE responses, session recovery,
and executor output recovery.
GitOrigin-RevId: d26a08883a2825e8ce2408ac498114b33859225e
## 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
## What changed
- Update the `rmcp` model and transport integrations for `3.0.0-beta.3`.
- Preserve legacy `elicitation/create` form requests, schema defaults, metadata, and wire-format compatibility while adopting the new elicitation types.
- Harden OAuth discovery by using GET-first discovery without starting an MCP session, preventing cross-origin header redirects, validating authorization-server and callback issuers, and retaining compatibility with metadata that omits an issuer.
- Keep stored OAuth credentials readable and avoid requiring reauthorization after transient refresh failures.
## Testing
- Add coverage for legacy elicitation round trips, OAuth discovery variants, callback issuer validation, credential migration, and refresh failures.
GitOrigin-RevId: 756197d26f3fd347c28c400228f6b3d06ed493b7
## Why
#28522 routes selected-plugin HTTP MCP traffic through the owning
executor, but OAuth bootstrap and refresh still used host-local clients.
Executor-only servers therefore cannot complete discovery or login
through the same network boundary as the MCP connection.
## What changed
- adapt `codex_exec_server::HttpClient` to RMCP 1.8's `OAuthHttpClient`
contract
- let RMCP own discovery, dynamic registration, PKCE, token exchange,
and refresh
- route auth status, persisted-token startup, and app-server login
through the server runtime while preserving the existing local discovery
path
- add optional `threadId` to `mcpServer/oauth/login` and echo it in the
completion notification
- implement RMCP's redirect policy and 1 MiB OAuth response limit over
executor HTTP
- cover selected-thread OAuth discovery and login through an
executor-only route
Depends on #28522.
## Summary
- Retry transient streamable HTTP failures during RMCP startup when the
failure happens while sending the initialize request.
- Retry transient streamable HTTP failures for tools/list, which is
read-only and safe to replay.
- Cover both retryable HTTP statuses and request-layer failures where no
HTTP status is returned.
- Surface retryable HTTP statuses from the streamable HTTP adapter as
typed client errors.
- Add integration coverage for initialize retry, tools/list retry,
no-status request failure retry, and non-retryable initialize status.
## Root cause
The observed codex_apps failures can happen before normal tool
execution: RMCP startup fails while sending initialize, or the first
read-only tools/list fails after startup. Retrying hosted_apps_bridge
tools/call would not cover initialize and would risk replaying
side-effecting tool calls. This change retries the streamable HTTP
handshake itself, recreates the transport between initialize attempts,
and retries only tools/list among post-initialize service operations.
## Validation
- cargo fmt --package codex-rmcp-client
- cargo test -p codex-rmcp-client --test streamable_http_recovery
Adds failure-only logging for MCP streamable HTTP post_message calls and
the underlying reqwest send path, capturing the MCP method/request id,
endpoint shape, auth-header presence, timeout/connect classification,
and sanitized error source chain without logging headers, bodies,
tokens, or full URLs.
WIll make it easier to uprev when the new draft spec is supported.
Also updates reqwest where needed for compatibility but doesn't update
it everywhere since this is already a large diff.
The new version of rmcp handles certain kinds of authentication failures
differently, this patch includes support for identifying the failing scope
in a WWW-Authenticate header.
### Why
The RMCP layer needs a Streamable HTTP client that can talk either
directly over `reqwest` or through the executor HTTP runner without
duplicating MCP session logic higher in the stack. This PR adds that
client-side transport boundary so remote Streamable HTTP MCP can reuse
the same RMCP flow as the local path.
### What
- Add a shared `rmcp-client/src/streamable_http/` module with:
- `transport_client.rs` for the local-or-remote transport enum
- `local_client.rs` for the direct `reqwest` implementation
- `remote_client.rs` for the executor-backed implementation
- `common.rs` for the small shared Streamable HTTP helpers
- Teach `RmcpClient` to build Streamable HTTP transports in either local
or remote mode while keeping the existing OAuth ownership in RMCP.
- Translate remote POST, GET, and DELETE session operations into
executor `http/request` calls.
- Preserve RMCP session expiry handling and reconnect behavior for the
remote transport.
- Add remote transport coverage in
`rmcp-client/tests/streamable_http_remote.rs` and keep the shared test
support in `rmcp-client/tests/streamable_http_test_support.rs`.
### Verification
- `cargo check -p codex-rmcp-client`
- online CI
### Stack
1. #18581 protocol
2. #18582 runner
3. #18583 RMCP client
4. #18584 manager wiring and local/remote coverage
---------
Co-authored-by: Codex <noreply@openai.com>
Nick Steele