[VDR][v0.6.0] Tutorials broken by post-v0.5.0 changes

[anwithk]

Theme issue grouping v0.6.0-cycle VDR findings: Tutorials broken by post-v0.5.0 changes.

Finding	Severity	Summary
TUT-63304da8	🟠 high	Single-step tutorial's own unit test fails: output items now require a type discriminator
TUT-dc0d74c9	🟠 high	Tutorial's app.py replaces a scaffold it no longer resembles, breaking the scaffolded tests

Child issues are linked as sub-issues below.

_{DX review Gym-1-20260821203248 — incremental from v0.5.0 to fa0d25158. Parent tracker #2214.}