acp: session/new and session/prompt hang indefinitely — no timeout on MCP registration or tool calls

Description

ACP session/new blocks until every transferred MCP server finishes registering (registerMcpServers in service.ts:196), but there is no timeout — request() (service.ts:710) wraps only Effect.tryPromise. Likewise, session/prompt waits on MCP tool invocations without a deadline.

[Root cause]
Effect.timeout is never applied to the MCP registration path or tool-call path in the ACP service.

• registerMcpServers → request(() => sdk.mcp.add(...)) → no deadline (service.ts:710–722)
• session/prompt → request(() => input.sdk.session.prompt(...)) → no deadline (service.ts:507–526)
• Individual MCP registration failures are silently swallowed (Effect.ignore, ~line 1002), so a hung bunx process is never surfaced as an error — it just waits forever.

[Environment]

• Windows, opencode v1.18.15, Zed 1.14.2+stable, bun 1.3.4
• Affects macOS / Linux as well (same code path)

Plugins

No response

OpenCode version

1.18.15

Steps to reproduce

1. Register one or more slow MCP servers in Zed's context_servers (e.g., bunx shadcn-vue@latest mcp, bunx figma-developer-mcp).
2. Open a Zed thread with opencode as the external agent.
3. session/new blocks for 48–66+ seconds while bunx resolves dependencies and handshakes (measured with acp-driver-*.js test scripts).
4. Re-registration happens per session (registeredMcp is keyed by sessionId, line 966), so every new thread blocks again.
5. Mid-conversation, when the LLM invokes one of those MCP tools and the server is slow/unresponsive, session/prompt hangs silently — no error, no timeout.

[first] session/new sent t=1.2s → session created t=47.8s
[second] session/new sent t=47.8s → session created t=70.6s

Screenshot and/or share link

No response

Operating System

Windows 11

Terminal

Bash