HITL: "Always allow this tool" via set_tool_approval gateway meta-tool

[pragati-agrawal-glean]

Summary

Port the revised Always Allow flow from glean-plugins-vnext into the shared Glean MCP adapter.

• Keep the initial Accept/Decline prompt scoped to the current call.
• After Accept, show a separate five-second Always Allow follow-up.
• Persist only an explicit follow-up Accept through set_tool_approval with ALWAYS_ALLOWED.
• Execute the already-approved call once regardless of the follow-up result.
• Treat initial approval failures as fail-closed.
• Skip subsequent prompts through the process-local approval fast path until discovery reflects the persisted grant.

The implementation is in shared source and therefore applies to the Claude/Codex local MCP targets. Cursor excludes the local MCP adapter in the pluginpack configuration and remains on its separately connected MCP path.

Validation

• npm run test:bundle — 340 tests passed
• npm run typecheck:bundle
• npm test — build and validation passed for Claude, Cursor, and Codex