When an MCP server restarts or a network connection drops between
tool calls, the existing session throws ClosedResourceError,
BrokenPipeError, ConnectionResetError, etc. Currently these are
caught as generic exceptions and returned as permanent failures
to the LLM, which then tells the user 'my tools are broken.'
This change adds a single automatic retry with a 1-second backoff
for transient connection-class errors in MCPToolWrapper,
MCPResourceWrapper, and MCPPromptWrapper. Non-transient errors
(ValueError, RuntimeError, McpError, etc.) are not retried.
The retry is conservative:
- Only 1 retry (not configurable, to keep the change minimal)
- Only for a specific set of connection-class exceptions
- Matched by exception class name to avoid importing anyio/etc.
- 1s sleep between attempts to allow the server to recover
- Clear logging distinguishes retried vs permanent failures
In production this eliminates most 'MCP tool call failed:
ClosedResourceError' noise when MCP bridge processes restart
(e.g. after config changes or OOM kills).
Tests: 22 new tests covering retry, exhaustion, non-transient
bypass, timeout bypass, and all three wrapper types.
Anthropic does not support assistant-message prefill and returns a 400
error when the conversation ends with an assistant turn. This commonly
happens when heartbeat/system messages accumulate trailing assistant
replies in the session history.
The _merge_consecutive method already handles same-role merging but did
not strip trailing assistant messages. The base provider's
_enforce_role_alternation (used by OpenAI-compat) does strip them, but
AnthropicProvider uses its own _merge_consecutive instead.
Add a trailing-assistant stripping loop to _merge_consecutive, matching
the behavior already present in _enforce_role_alternation.
Includes 7 new tests covering merge + strip behavior.
When a user sends /stop to interrupt an active agent turn, the task is
cancelled via CancelledError. Previously, the cancellation handler just
logged and re-raised, discarding any tool results and assistant messages
accumulated during the interrupted turn.
The runtime checkpoint mechanism already persists partial turn state
(assistant messages, completed tool results, pending tool calls) into
session metadata via _emit_checkpoint. However, this checkpoint was only
materialized into session history on the NEXT incoming message via
_restore_runtime_checkpoint — not at cancellation time.
Now the CancelledError handler in _dispatch calls
_restore_runtime_checkpoint immediately, so the partial context is
preserved in session history. This means the next message the user sends
will see all the work that was done before /stop, rather than starting
from scratch.
Fixes#2966
Includes 3 tests verifying checkpoint restoration on cancellation.
hussein1362andXubin Ren