Prove durable scheduler-owned Hello Echo execution

[flyingrobots]

Outcome

Run the compiler-produced Hello Echo package as a standalone external application through Echo's supported generic runtime boundary and prove durable, recoverable semantics.

Acceptance criteria

• An Edict-authored Action envelope binds typed application input to the generic runtime invocation.
• Submission acknowledgement follows accepted-submission WAL commit.
• Scheduler-owned bounded evaluation constructs one atomic Tick.
• Decided-Tick WAL commit precedes frontier, outcome, state, and Receipt publication.
• Greeting creation succeeds once.
• Duplicate creation yields typed AlreadyExists obstruction without hidden mutation.
• Restart recovers the Action, Tick, state, outcome, and Receipt.
• Mutated pre-Tick initial state causes recovery refusal.
• The witness contains no runtime fake, native application callback, handwritten package, or host-checkout path.

This is singleton scheduler integration only; it does not claim permanent multi-Action Tick composition.

Dependencies

Blocked by: #1

Blocked by: flyingrobots/echo#690