fix(acp): default Claude-runtime agents out of inheriting operator claude.ai connectors

[Tr1ckyMag1ca1]

Summary

Extends the per-runtime env-default mechanism introduced in #3420 to the Claude runtime. A Buzz-managed Claude agent currently inherits the operator's claude.ai account connectors (Gmail, Drive, HubSpot, ClickUp, etc.) straight into the agent's tool surface. Those connectors were wired up by the operator for their own use; once the agent is placed in a community and its inbound gate is opened past owner-only, that same connector surface is reachable from a shared agent.

This sets ENABLE_CLAUDEAI_MCP_SERVERS=false as a per-runtime default for the Claude command identities, exactly mirroring how #3420 defaults HERMES_ACP_SKIP_CONFIGURED_MCP=1 for Hermes: the connector surface becomes opt-in rather than inherited-by-default. Nothing else changes.

Why this is the same shape as #3420

default_agent_env() already establishes the pattern: per-runtime env defaults, applied in AcpClient::spawn only when the operator has not set the variable (the std::env::var_os(key).is_none() guard). So an operator or persona that wants the connectors keeps them by setting ENABLE_CLAUDEAI_MCP_SERVERS=true in the parent env or persona extra_env — the default never overrides an explicit choice. This is the identical escape-hatch semantics Hermes gets today.

Scope — deliberately narrow, and honest about it

• ENABLE_CLAUDEAI_MCP_SERVERS is honored by Claude Code from v2.1.63. Older builds ignore the unknown variable (same tolerance the existing GOOSE_SCHEDULER_DISABLED_ENV line relies on), so this is safe across versions — a no-op on old, effective on new.
• It governs the claude.ai connector path only. File-configured MCP servers (.mcp.json, user-scope mcpServers in ~/.claude.json) are a separate inheritance path this PR does not close. Fully isolating those needs --strict-mcp-config + --mcp-config, whose interaction with ACP session-provided MCP servers I have not verified end-to-end, so I've left it out rather than assert behavior I can't stand behind. Happy to follow up in a separate PR if maintainers want it.

Test

Adds default_agent_env_recognizes_claude_identities, mirroring the existing Hermes test. Both env tests pass; cargo fmt -p buzz-acp -- --check is clean.

Sources for the env var

• Claude Code issue #29506 (ENABLE_CLAUDEAI_MCP_SERVERS)
• Claude Code v2.1.63 release notes

Context: I self-hosted Buzz for a community, opened the agent's inbound gate to run a real greeter, and noticed the Claude runtime inherits the operator's connectors with no per-runtime isolation while Hermes now has exactly that. This brings the Claude runtime in line with the precedent #3420 set.