## Why
A temporary exec-server transport loss could emit a thread environment disconnect notification while the session was still recovering.
## What changed
- Add `EnvironmentConnectionState::Recovering` for interrupted transports and pending session recovery.
- Suppress thread lifecycle notifications during recovery, emit a connected notification after successful recovery, and report disconnection when recovery fails.
- Ignore recovery callbacks from retired clients so they cannot overwrite the connection state during refresh.
## Testing
Add coverage for fast and near-deadline recovery, recovery timeout, rejected session resume, and retired-client callbacks. Extend app-server coverage to verify one lifecycle notification per selected thread and usable `environment/info` after recovery.
GitOrigin-RevId: d6dce5cc5264af29b6f993daa209b93102122e40
## What changed
- Route remote-control enrollment, pairing, client management, and WebSocket connections through the authenticated HTTP client factory. Keep policy denials distinct from authentication failures and wait for policy changes before reconnecting.
- Preserve policy denials through exec-server connection failures so later connection attempts and capability discovery can recover. Keep direct executors running through temporary policy outages while rejecting permanent policy failures.
- Build cached HTTP transports on blocking workers, serialize construction, and retain successful builds after callers time out so request deadlines cover queued construction.
## Testing
Add regression coverage for policy recovery during remote startup, direct registration, accepted WebSocket reconnection, and capability discovery; queued transport construction timeouts; and remote-control WebSocket fallback with invalid custom CA files.
GitOrigin-RevId: c81db18e83de957175bb213d165281ac701089dd
## Why
An executor can renew its registration while retaining its Noise identity. Connection refresh must distinguish registrations even when their keys match, and a stale registry lookup must not retire a session that recovery has already renewed.
## What changed
- Track the installed session's registration and expose it through `Environment::cached_executor_registration_id()` without connecting. Publish registration changes only when the new connection is installed.
- Require both registration and executor key to match before refresh reuses a session. Retry stale lookups and prevent recovery from installing a connection after retirement.
- Pin session recovery to the original Noise key while allowing registration renewal to preserve the session and running processes.
- Expose `CodexThread::active_turn_environment_selections()` so hosts can authorize steering against the active turn's selections, including starting and failed environments, independently of later settings updates.
## Testing
Add regression coverage for registration replacement, renewal with a running process, stale refresh lookups, missing sessions, and rejection of changed Noise keys. Extend active-turn tests to check selection snapshots across settings updates, deferred startup, and turn completion.
GitOrigin-RevId: 4395bc6c57f137691887e6585f52dcc5b958101c
## Why
A remote process can finish while a network policy review is still pending. Normal process cleanup should withdraw that review without turning the completed command into a review failure or losing its output.
## What changed
- Record whether a network policy request was withdrawn because the process finished, was cancelled, lost its executor connection, or timed out.
- Treat normal process completion as cleanup while retaining fail-closed behavior for other cancellation causes.
- Preserve explicit network denials before policy persistence so cleanup cannot replace the reported call outcome.
## Testing
Add an integration test that completes a remote process during a pending network review and verifies that the command reports its successful exit and output without approving the withdrawn request.
GitOrigin-RevId: 7f42d75631ee29eba43bf04cc953eea490f553fc
## What changed
- Wait for the authenticated Noise handshake before sending the JSON-RPC
`initialize` request.
- Share the configured initialization timeout across the handshake and RPC,
while preserving the configured duration in timeout diagnostics.
- Record the handshake and initialization RPC as child spans of the existing
initialization span, and terminate transport tasks when handshake readiness
fails.
## Testing
- Cover stalled handshake timeouts and cleanup of the underlying WebSocket.
- Cover timeout reporting after the handshake has consumed part of the budget.
GitOrigin-RevId: c3eb5f7cfedd8d155fde5b7614fc2eb399ce337c
## What changed
- Allow a valid Ready report to replace a deferred environment's provisioning failure while preserving the same environment instance.
- Treat provisioning failures as retryable and reconnect when a completed or concurrently publishing startup attempt contains a stale failure.
- Report provisioning failures from `status()` without starting a connection, and retain Ready state when a late failure arrives.
## Testing
- Cover recovery after failed and invalid provisioning reports, capability-root resolution after recovery, and the race between Ready and publication of an earlier startup failure.
GitOrigin-RevId: cce419403248168da81bc5a6ab20f919aed81142
## Why
Planned executor replacement needs a fresh session without waiting for the old
session's transient-disconnect recovery to finish.
## What changed
- Add `Environment::refresh_connection` for remote Noise registry-backed
environments. It performs a fresh registry lookup, reuses a healthy session
when the executor identity is unchanged, and connects to a replacement when
it has changed.
- Retire superseded sessions and connection attempts so they cannot publish
stale state, accept late RPC results, or replay outstanding work.
- Preserve the existing environment and filesystem handles while replacing the
underlying client, and require a live status probe before refresh succeeds.
## Testing
Add coverage for replacement and session reuse, recovery and connection races,
lookup and handshake failures, handle preservation, and late RPC responses.
GitOrigin-RevId: f1d11208cbfe8af8feb25f6b6b8100da82169a99
## What changed
- Add `EnvironmentManager::from_accepted_websocket` so embedding hosts can
construct a remote environment from an already accepted and authenticated
Axum WebSocket.
- Add `replace_accepted_websocket` to retire the current transport and resume
the same exec-server session on a host-supplied replacement connection.
- Serialize replacement handoffs, reject overlapping replacements, and release
the handoff claim when a replacement attempt is cancelled or fails.
## Testing
- Cover initial connection validation and immediate environment readiness.
- Verify replacement retry behavior and recovery of a running process and its
output after reconnecting.
GitOrigin-RevId: 1f2ab7bcf7b5abbbece5c101801432dc84a8058d
## What changed
- Retry transient environment-registry failures while opening the initial Noise rendezvous connection, including timeouts, interrupted response bodies, retryable HTTP statuses, and temporarily offline environments.
- Bound registry attempts with per-request and overall timeouts, exponential backoff, and a retry limit while returning permanent registry errors immediately.
- Preserve the existing one-time bundle refresh after an unauthorized WebSocket handshake, with a fresh registry retry window.
- Treat malformed complete JSON responses as terminal rather than retryable transport failures.
## Testing
- Cover transient and permanent registry responses, stalled requests, retry limits and deadlines, interrupted bodies, malformed JSON, unauthorized bundle refresh, and session-resume behavior.
GitOrigin-RevId: 5929274103702ad477e7a638ab489319a43a93fa
## Why
When a local proxy request disconnects before network approval completes, the
owning tool call needs a model-visible explanation instead of remaining tied to
the abandoned request.
## What changed
- Track disconnect timing while plain HTTP and CONNECT requests await policy
decisions.
- Cancel the owning execution and report how long the request waited when it
disconnects before approval completes.
- Preserve an explicit approval outcome when disconnect cleanup runs afterward.
## Testing
Added unit coverage for disconnect tracking and outcome precedence, plus
end-to-end coverage for plain HTTP and CONNECT requests.
GitOrigin-RevId: b354b29bbe86f38e252fcaf529541f177480136b
## What changed
- Start inbound exec-server request spans when messages enter the connection queue and carry them through dispatch and response handling.
- Record request outcomes for client-handled network policy callbacks, including errors and disconnections.
- Add the `exec_server_request_queue_duration_seconds` histogram, labeled by bounded route name, while excluding synchronous route setup time.
## Testing
- Cover span lifetime and trace-parent propagation across server and client queues.
- Verify queue-duration telemetry and outcome recording for completed, rejected, and cancelled requests.
GitOrigin-RevId: ed67fe5305048bdf283a26ec874337d549e3324f
## What changed
- Add a best-effort `network/policyDecision` notification for final domain and non-domain policy decisions made by executor-local proxies.
- Validate notifications against the active process on the controller and emit audit events with controller-trusted session and execution metadata.
- Reserve outbound RPC capacity so audit notifications cannot block control messages, and expose valid `chatgpt-account-id` header values for audit attribution.
## Testing
- Cover notification serialization, proxy decision capture, executor-to-controller delivery, trusted metadata handling, and reserved RPC capacity.
GitOrigin-RevId: a39f96a6b3d9401c03d54eaef5b9a6d3fe0da78b
## Why
Transient executor disconnects could leave capability discovery and skill catalogs
stuck on a cached failure for the rest of a thread, even after the executor
reconnected.
## What changed
- Replay capability discovery after executor recovery and retry transient failures
on later requests while continuing to cache permanent failures.
- Avoid caching skill catalogs produced from failed discovery so a later step can
load the recovered catalog.
- Mark the MCP runtime dirty when recovered manifests change the projected MCP
servers, and allow discovery to be cancelled with the turn.
## Testing
- Cover same-request recovery after a disconnect and recovery on a later request.
- Cover retry classification through connection-attempt errors and skill catalog
caching after discovery recovers.
GitOrigin-RevId: a57f90844351e73ea831931f72a9ddc4e4f3335c
## Why
A retryable failure during the initial remote exec-server connection left the
environment disconnected on subsequent readiness checks.
## What changed
Route retryable startup errors through the existing reconnect path. This lets
later `get()` and `wait_until_ready()` calls establish a replacement client,
while concurrent callers share the same reconnect attempt.
## Testing
Add a WebSocket test that fails the initial handshake, then verifies that later
readiness and client requests share a successful replacement connection.
GitOrigin-RevId: 82d425af0a73331884439b4350a7a1052d4ae865
## What changed
- Add client-side handling for exec-server network policy requests, including request validation, per-process decision routing, and allow, deny, or ask responses.
- Bound concurrent callbacks and fail closed when requests are invalid, exceed capacity, time out, or outlive their process session.
- Replace the callback opt-in flag with a launch-level `policyDecisionTimeoutMs` value and include transport overhead in the executor timeout.
- Preserve callback admission limits across connection recovery and clean up policy state when process startup is abandoned or a session ends.
## Testing
- Cover decision forwarding, invalid and excess requests, cancellation during process cleanup, abandoned starts, timeout propagation, and launch-config serialization.
GitOrigin-RevId: 6ee2a0139e0f8170cf1a5cdd646bd811b7d3c1f6
## Why
Noise environment registry requests need to follow the exec server's effective
outbound proxy policy without exposing registry URLs or response headers in HTTP
diagnostics.
## What changed
- Build the registry client from the supplied `HttpClientFactory` and use a
route-aware API client with redirects and request logging disabled.
- Defer construction of the Noise connection provider until the outbound HTTP
policy is available.
- Map route-aware request failures into registry errors while retaining timeout
detection across response body reads.
## Testing
Add coverage for system-proxy routing, sensitive registry metadata redaction,
stalled response-body timeouts, and prepared Noise configuration validation.
GitOrigin-RevId: d312dfe037f72732085bf38109af44df76ed0b53
## What changed
- Let `exec-server` issue JSON-RPC requests to its client and correlate responses, with bounded concurrency, timeouts, and connection cleanup.
- When `request_policy_decisions` is enabled, forward proxy policy requests with the process ID and network destination, then apply the client's allow, deny, or ask decision.
- Fail closed for invalid inputs, unavailable or malformed responses, timeouts, process shutdown, and disconnects. Keep callbacks active while inherited process streams keep the proxy alive.
## Testing
- Cover response correlation, request limits, timeouts, disconnect cleanup, validation boundaries, decision forwarding, and process lifecycle behavior.
GitOrigin-RevId: 60e658102c50036589ca9de844760a8bffaa53b0
## What changed
- Track connected and disconnected states across initial remote exec-server connections and reconnection attempts.
- Emit experimental `thread/environment/connected` and `thread/environment/disconnected` app-server notifications for each thread selecting the environment. Each payload identifies the thread and environment; current state is not replayed when a thread starts.
- Stop forwarding connection events when an environment selection is removed or replaced.
## Testing
- Cover connection, disconnection, reconnection, shared-environment notifications, and replacement of a selected environment.
GitOrigin-RevId: 5dd767372363c4a2a8319fc16164be117d5bd20c
## Why
A thread can select skill roots that live in an executor environment.
`skills/list` needs a passive snapshot of the roots that are usable now:
it must not start an executor, wait for recovery, or reconnect a failed
environment.
The initial implementation checked the immutable first startup result.
After a successful connection later entered recovery or failed, that
result still looked successful. A read-only catalog request could then
wait for recovery or trigger a new connection while reading the
filesystem.
## What
- inspect readiness from the current exec-server connection state
- return roots only while their environment can serve a request
immediately
- omit environments that have not started, are connecting, or are
recovering
- return warnings for missing environments and terminal connection
failures
- add a fail-fast filesystem view that never starts, waits for, or
reconnects an environment
- expose the passive selected-root snapshot through `CodexThread`
## Behavior
- Local and currently connected environments are ready.
- Starting and recovering environments are omitted without a warning so
callers can retry later.
- Missing and terminally failed environments are omitted with a warning.
- A disconnect between readiness inspection and filesystem access fails
promptly instead of crossing into the normal recovery path.
- Normal model-turn and execution paths keep their existing reconnect
behavior.
## Design
The recovery policy is private to the exec-server client. Callers choose
the explicit fail-fast filesystem method; the existing client and
filesystem APIs remain reconnecting. This keeps the passive contract at
the transport boundary instead of plumbing timeout or retry flags
through the skills stack.
## Coverage
- a lazy stdio environment stays unstarted during passive inspection
- missing and terminally failed environments surface warnings
- a real websocket disconnect proves current readiness drops, a
previously acquired fail-fast filesystem handle returns promptly, and
readiness returns after recovery
## Scope
This PR only provides passive readiness and fail-fast filesystem
primitives. It does not add app-server API fields or notifications.
## Stack
- #31582 uses these primitives for experimental thread-scoped
`skills/list`.
- #30228 adds targeted invalidation notifications.
## Why
A malicious exec-server can send out-of-order process notifications
faster than missing events arrive. The client retained every future
event in a per-session reorder map, so many tiny events or a few large
output chunks could grow orchestrator memory without bound.
## What changed
- cap each session's pending process-event reorder state at 256 events
and 1 MiB
- reject individual process events larger than 1 MiB
- release byte accounting as events publish or a session fails
- fail and detach only the affected process session when a limit is
exceeded
- let the next expected event drain a full buffer, so the limits apply
to retained future state
- apply the same bounded insertion path during reconnect recovery while
safely handling dense tail output, missing exit events, newer live
notifications, and conflicting `Closed` sequences
Sequence distance is intentionally not capped because it does not affect
allocation; the event-count and byte limits are the resource-exhaustion
boundary.
## Tests
Focused exec-server tests cover oversized output, full count/byte
buffers, gap-closing delivery, dense recovery interleaved with newer
notifications, missing exit reconstruction, and conflicting terminal
sequences.
## Scope
This is limited to per-session process-event reorder state. It does not
introduce a scheduler, quota framework, or new public configuration.
## Why
An untrusted exec-server can stop reading requests, never answer them,
or send guessed responses before queued requests are written. Without
client-side admission, the orchestrator can retain unbounded RPC call
futures and request payloads.
We need a hard bound without adding a blanket timeout, because
individual operations already own their timeout and cleanup semantics.
## What changed
- hold one of 64 shared admission permits for the full lifetime of each
regular RPC call, so an early response cannot free capacity while the
call remains queued
- allow `process/terminate` and `fs/close` to use one additional cleanup
permit
- close the transport and fail pending calls if the cleanup permit is
also stuck, allowing teardown or recovery to release remote resources
- leave the wire format and existing timeout behavior unchanged
## Tests
- `rpc_client_call_has_no_implicit_deadline` verifies that ordinary
calls remain untimed
- `rpc_client_bounds_in_flight_calls_and_preserves_cleanup` covers the
regular-call cap, guessed early responses, cleanup admission, and the
cleanup circuit breaker
## Summary
- complete unified-exec processes from the ordered event stream instead
of issuing a final zero-wait `process/read`
- add optional executor sandbox-denial state to `process/exited`
- retain `process/read` as a retained-output and compatibility fallback
for receiver lag, sequence gaps, and legacy servers
- recover sandbox-denial state across transport reconnection
- cover the real `TestCodex` remote-exec path without adding a public
test-only event constructor
## Why
A successful one-shot tool call currently receives its output and
terminal notifications, then pays another wide-area `process/read` round
trip before returning. Staging traces showed that remote response wait
accounted for more than 99.8% of RPC time; local serialization,
queueing, and deserialization were below 0.6 ms.
## Measured impact
A direct staging A/B used the same build and route and changed only
completion mode. Each arm ran three times with 30 one-shot
`/usr/bin/true` calls per run. The table reports the median of the three
per-run percentiles.
| Metric | Final `process/read` | Pushed events | Change |
| --- | ---: | ---: | ---: |
| End-to-end completion p50 | 159.5 ms | 118.7 ms | -40.8 ms (-25.6%) |
| End-to-end completion p95 | 182.4 ms | 131.7 ms | -50.6 ms (-27.8%) |
| Completion-wait p50 | 80.1 ms | 41.5 ms | -38.5 ms (-48.1%) |
| Final `process/read` RPC p50 | 79.9 ms | eliminated | -79.9 ms |
TCP_NODELAY was enabled in both A/B arms, so its effect cancels out. The
successful, complete, in-order event path issued zero final
`process/read` calls.
## Compatibility and recovery
- new servers send `sandboxDenied` on `process/exited`
- legacy servers omit it, which triggers one compatibility
`process/read`
- broadcast lag or a sequence gap triggers a retained-output read
- recovery remains bounded by the server's existing 1 MiB
retained-output window
- complete, in-order event streams issue no completion read
- sandbox denial is attached to the exit event before consumers can
observe process completion
- server-first and client-first rollouts remain wire-compatible;
server-first realizes the latency win immediately
## Integration coverage
The `TestCodex` suite exercises four distinct remote-exec contracts:
- complete pushed output/exit/close with zero reads
- direct pushed sandbox denial with zero reads
- legacy missing denial metadata with exactly one compatibility read
- count-bounded replay eviction recovered from retained output without
duplication
## Validation
- `just test -p codex-core
exec_command_consumes_pushed_remote_process_events`: 4 passed
- `just test -p codex-core unified_exec::process_tests::`: 4 passed
- `just test -p codex-exec-server`: 294 passed, 2 skipped
- `just test -p codex-exec-server-protocol`: 5 passed
- `just test -p codex-rmcp-client`: 89 passed, 2 skipped
- focused Bazel `//codex-rs/core:core-all-test`: passed across 16 shards
- scoped `just fix` passed for core and exec-server
- `just fmt` passed
The complete workspace suite was not rerun; focused Cargo and Bazel
coverage passed for the changed behavior.
## Summary
- retry ERS `409 environment_offline` responses inside the existing
exec-server recovery loop
- keep all other registry conflicts terminal
- add focused coverage for both cases
## Root cause
When an exec server disconnects and reconnects, the client already
starts recovery and calls ERS `/connect`. During the transient executor
presence gap, ERS can return `409 environment_offline`. The retry
classifier treated every 409 as terminal, so the first response aborted
the existing 25-second recovery window before the executor came back
online. That then caused active processes to be marked lost.
This change classifies only the structured `environment_offline`
conflict as retryable. Recovery continues with the existing bounded
deadline, exponential backoff, and jitter.
## Validation
- `just test -p codex-exec-server client::recovery::tests` — 4 passed
- `just fix -p codex-exec-server` — passed
- `just fmt` — passed
- Full `just test -p codex-exec-server` reached unrelated macOS
filesystem-sandbox integration failures because nested
`/usr/bin/sandbox-exec` is denied in this environment (`sandbox_apply:
Operation not permitted`).
## Why
#29113 moved remote sandbox setup and enforcement to the exec server.
That gives the executor ownership of the platform-specific work: a Linux
executor chooses and runs a Linux sandbox even when the Codex
orchestrator is running on macOS or Windows.
It also means the orchestrator no longer knows which concrete sandbox
the executor selected. When that sandbox blocks a remote command, the
orchestrator currently sees only a failed process and can treat the
denial as an ordinary command failure. The existing sandbox approval and
retry path is then skipped.
This PR lets the executor report one portable fact:
> This command probably failed because the executor sandbox blocked it.
The executor keeps its concrete sandbox type private. The protocol sends
only the semantic result.
## Example
Suppose a local macOS Codex session asks a Linux devbox to write outside
the allowed workspace.
Before this PR:
```text
Linux sandbox blocks the write
-> remote process exits with "Permission denied"
-> local orchestrator sees an ordinary command failure
-> the normal sandbox approval and retry path can be skipped
```
With this PR:
```text
Linux sandbox blocks the write
-> executor reports sandboxDenied: true
-> unified exec returns UnifiedExecError::SandboxDenied
-> the existing approval prompt is shown
-> an approved retry runs through the existing unsandboxed retry path
```
## What changes
### The executor remembers its selected sandbox
The prepared remote process now retains the executor-selected
`SandboxType`. This value never crosses the executor boundary.
Commands started without a sandbox retain `SandboxType::None` and are
never reported as sandbox denials.
### The executor uses the existing denial heuristic
The existing local denial heuristic moves from `codex-core` into the
shared `codex-sandboxing` crate.
When a sandboxed remote process exits, the executor:
1. waits the same short output grace period used by local unified exec;
2. reads the output currently available in the existing retained output
buffer;
3. runs the existing heuristic using the exit code and common denial
messages;
4. stores the yes/no result before publishing the process exit.
This deliberately matches the old local unified-exec behavior. It does
not add a new streaming classifier, another output buffer, or stronger
output-retention guarantees.
### The protocol reports a portable boolean
`process/read` gains `sandboxDenied`:
```json
{
"exited": true,
"exitCode": 1,
"closed": false,
"sandboxDenied": true
}
```
The field defaults to `false` when an older executor omits it. The
response does not expose the executor sandbox implementation or
executor-native paths.
### Unified exec uses the existing error path
The exec-server client carries `sandboxDenied` into the unified process
state. If it is true, unified exec returns the existing `SandboxDenied`
error instead of trying to classify remote output using an
orchestrator-side sandbox type.
Remote process exit remains visible as soon as the process exits. This
PR does not wait for stdout or stderr to close and does not change the
existing process lifecycle.
## Scope
This PR is intentionally limited to matching the existing local
unified-exec behavior for the initial command execution path.
It does not add:
- incremental denial tracking across the full output stream;
- new denial handling for commands completed later through
`write_stdin`;
- new guarantees for preserving the semantic flag during the narrow
reconnect-recovery race.
Those can be considered separately if the same behavior is added for
local execution.
## Test coverage
One remote end-to-end integration test covers the complete intended
flow:
```text
remote read-only sandbox
-> denied write
-> executor reports the denial
-> Codex requests approval
-> user approves
-> retry succeeds on the remote executor
```
Existing lifecycle coverage continues to verify that remote process exit
is reported before late output streams close.
## Why
PR #28512 retries a failed session recovery every 100 ms. Every Noise
recovery attempt first asks the environment registry for a fresh
connection bundle, even when the eventual failure comes from the
WebSocket or initialize handshake. During an outage, that could make
each disconnected client call the registry about 250 times during the
25-second recovery window.
## What changes
All retryable Noise recovery failures now use a separate backoff
schedule:
```text
base: 500 ms -> 1 s -> 2 s -> 4 s -> 5 s maximum
actual: 500-750 ms, 1-1.5 s, 2-3 s, 4-6 s, 5-7.5 s
```
The extra 0-50% is deterministic per-session jitter so disconnected
clients do not retry together. Direct WebSocket recovery keeps the
existing 100 ms retry because it does not re-enter the registry.
Supersedes #28288 (closed).
## Why
A short WebSocket interruption currently ends every client-side process
handle, even though exec-server keeps the server session and its
processes alive for a short time.
This is especially visible for executor-backed stdio MCP servers: a
temporary connection loss becomes a permanent `Transport closed` error.
The server already has the information needed to resume the session, but
the client opens a fresh session instead of using it.
This change reconnects below the process and MCP layers. Existing
process handles stay valid, missed output is recovered, and the same
server-side processes continue running.
## State machine
One logical `ExecServerClient` stays alive while its underlying RPC
connection changes generations.
```text
transport closes
+------------------------------------------------+
| v
+-------------+ +-------------+
| Connected | | Recovering |
+-------------+ +-------------+
^ |
| session resumed, processes caught up | retryable error
+------------------------------------------------+ loops until deadline
|
| deadline or permanent error
v
+-------------+
| Failed |
+-------------+
```
### `Connected`
- New RPC calls use the current connection.
- Process notifications are published in sequence order.
- A disconnect only starts recovery if it came from the current
connection generation. Late events from older generations cannot replace
the active connection.
### `Recovering`
- New calls wait instead of choosing a half-connected RPC client.
- Existing process handles, wake subscriptions, and event subscriptions
stay open.
- Streaming HTTP response bodies fail immediately because their byte
streams cannot be resumed safely.
- Recovery first waits for process starts that were already in flight. A
start whose result became ambiguous is cleaned up after reconnection
instead of being silently adopted.
- The client reconnects with the learned `session_id`. The server may
briefly report that the old connection is still attached, so that error
is retried until the detach finishes.
- The notification consumer starts before the resume handshake
completes. This prevents a busy process from filling the notification
queue and blocking the initialize response.
- Before installing the new connection, the client catches up every
recoverable process with `process/read`.
### `Failed`
- Recovery stops after 25 seconds or after a permanent error.
- Waiting calls are released with one stable disconnect error.
- Existing process sessions receive a terminal failure instead of
waiting forever.
## Recovering process events
Output, exit, and close events share one sequence. During normal
operation, the client buffers early events until every lower sequence
has been published.
After reconnection, the client reads each process starting after its
last published sequence:
1. Retained output chunks are inserted by sequence number.
2. Exit and close state are reconstructed in their sequence positions.
3. Events already received as live notifications are ignored as
duplicates.
4. Newly contiguous events are published in order.
5. If the server no longer retains enough output to fill a sequence gap,
only that process is terminated and failed. The recovered connection
remains usable for other processes.
The server reports its full next event sequence for unbounded reads,
including exit and close events. Closed processes remain readable for
the same 30-second window used to retain detached sessions.
## Other details
- Detached server sessions are retained for 30 seconds, leaving margin
around the client's 25-second recovery deadline.
- Session attach and detach update the active notification sender under
the same attachment lock, so an old connection cannot clear a newly
attached sender.
- A dedicated error code distinguishes the temporary "session is still
attached" race from permanent initialization errors.
- Process starts are identity-checked on both client and server. Cleanup
from an older start cannot remove a newer process that reused the same
ID.
- Mutating requests that were already in flight when the transport
closed are not replayed, because the client cannot know whether the
server applied them. Requests started after recovery is known wait for
the replacement connection.
- We assume the server/client version stays in sync (on the before/after
this PR)
## User impact
Long-running commands and stdio MCP servers can survive a temporary
exec-server WebSocket interruption without changing process IDs or
losing output produced during the outage.
richardopenai