Lab: the 3-session build

Build lab (Module 11, L11.5): recover by replaying the append-only log and re-verifying against disk. Naive recovery trusts todos.json and scores 2 PASS / 3 FAIL, with phantoms U1 and U2, a chain of 5 events seq 0..4, and work/u2.py missing. Replay then session 3 scores 5/5 on a chain of 7 events seq 0..6. events.jsonl leaves U1 done and U2 pending. Emptying work/u1.py demotes U1 to pending; trusting unit_done leaves U1 done. The agent may only append. Fowler, Event Sourcing, 12 December 2005 (read 2026-11-05), is the published sentence; it does not show a disk re-verify or a todo file. In-memory only; scripted sessions; no threads or provider call.

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