Phase 12A: add foundations pillar README

Author: Builder Weekly

pillars/foundations/README.md

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+# Foundations
+
+What every production agent needs underneath it. Observability, budget enforcement, retry logic, error handling, the stack you would otherwise reinvent for every project.
+
+## Entries
+
+_No entries yet. The first foundations tutorial is in the queue._
+
+## The pattern
+
+Every foundations tutorial teaches one piece of infrastructure that cuts across all agent types. The before-state is always "the agent works until it doesn't and you have no idea why." The after-state is always "the agent works, and when it breaks, you know exactly what happened."
+
+- **Before-state:** "The agent runs in production and you're flying blind."
+- **After-state:** "The agent runs in production and you see everything."
+
+## Cluster tags in this pillar
+
+- `logging` — structured event logging for agent pipelines
+- `tracing` — distributed tracing across agent steps
+- `metrics` — per-step latency and cost tracking
+- `budgets` — spend-based throttling and circuit breakers
+- `rate-limiting` — controlling agent API call velocity
+- `cost-control` — keeping agent operations within budget
+- `orchestration` — multi-step workflow management
+- `human-in-the-loop` — approval gates in automated pipelines
+- `state-machines` — explicit state transitions for complex flows