Removing 900+ lines of config while doubling static checks sounds backwards, but it came from giving AI coding agents fewer places to get confused. The redesign centers on deterministic repository feedback: one canonical gate, executable guardrails, and isolated test state.

• One gate: mise run all now drives local workflows, git hooks, CI, and agent instructions, removing duplicated command lists that had silently drifted.
• Fast isolation: copying a pre-migrated SQLite template cut MLflow test overhead by about 60% after migrations had pushed runtime from 34 to 339 seconds.
• Executable rules: AGENTS.md guides behavior, while tests, linters, and dependency checks verify that commands, paths, and security overrides still hold.

The core lesson is that agents work best when repository rules produce one clear, repeatable source of truth.

A $12,500 transfer missing one approval field can either trigger an opaque failure or a precise, repairable error before the ledger is touched. JSON Schema 2020-12 gives MCP tools a stronger way to encode those rules directly into the contract rather than leaving them in descriptions.

• Conditional validation: if/then, oneOf, and $defs can enforce state-dependent requirements and prevent incompatible argument combinations.
• Clearer recovery: schema failures can return field-specific invalid-params errors that an orchestrator repairs within a bounded retry loop.
• Layered enforcement: validation happens before business logic, while the underlying service still keeps final authority over business rules.

The key design shift is treating tool schemas as executable API contracts that tell agents what can be fixed and what should stop.

A2A v1.0 changed enough on the wire that a 0.3 parser can break even when the task flow looks familiar. The migration also introduces important changes around bindings, durable tasks, agent-card verification, and authorization.

• Breaking changes: kind discriminators are gone, enums changed, and ProtoJSON is now the canonical serialization.
• Durability: ListTasks, database-backed stores, and persistent webhooks help work survive lost IDs, disconnects, and restarts.
• Security: signed agent cards protect endpoint integrity, while AUTH_REQUIRED supports controlled approval and credential escalation.

The practical takeaway is how to migrate A2A systems while preserving compatibility, security boundaries, and durable task behavior.