research(mcp): identity propagation, adaptive tool budgeting, structured error semantics — missing MCP primitives (arXiv:2603.13417)

[bug-ops]

Source

arXiv:2603.13417 — Bridging Protocol and Production: Design Patterns for Deploying AI Agents with Model Context Protocol

Finding

Identifies three production gaps in MCP: (1) identity propagation — tool calls don't carry caller identity for access control; (2) adaptive tool budgeting — no per-session token/call budget for tool use; (3) structured error semantics — errors are free-text strings with no machine-readable code. Proposes Context-Aware Broker Protocol and Adaptive Timeout Budget Allocation.

Zeph applicability

• (1) Identity: zeph-mcp has trust levels per server but no per-call caller identity propagation to tools — relevant to ACP multi-session isolation (feat(acp): expose current model in SessionInfoUpdate and session/list response #2435)
• (2) Budgeting: [tools] max_parallel_tools exists but no per-session tool call quota; adaptive budgeting could tie into cost tracking
• (3) Structured errors: current MCP errors are strings; typed error codes would enable retry classification in AdversarialPolicyGateExecutor
• Implementation sketch: add caller_id field to MCP tool call context; extend McpError with a code: u32 field