AI Eng Prep — Batch 04: Memory & context

[MHHamdan]

Completes Path 03 of the AI-Engineering-Preparation sub-repo.

Adds:

• six concept notes: state vs. memory; short, long, and external memory; the memory lifecycle; context engineering; context strategies; context rot and failure modes
• a runnable offline lab: checkpointed state-vs-memory agent and context-budget assembler
• lab scaffold and solution notebooks
• a diagram for agent state, memory, and assembled context
• navigation, glossary, references, and counts updates
• Path 03 now complete

Verification:

• checkpoints.py --self-test passes
• context_budget.py --self-test passes
• notebooks are valid JSON
• internal links resolve
• ruff check passes

Applies on top of Batch 03. All content is original; technical claims cite canonical sources.