## Summary
Clarify the `js_repl` prompt guidance around persistent bindings and
redeclaration recovery.
This updates the generated `js_repl` instructions in
`core/src/project_doc.rs` to prefer this order when a name is already
bound:
1. Reuse the existing binding
2. Reassign a previously declared `let`
3. Pick a new descriptive name
4. Use `{ ... }` only for short-lived scratch scope
5. Reset the kernel only when a clean state is actually needed
The prompt now also explicitly warns against wrapping an entire cell in
block scope when the goal is to reuse names across later cells.
## Why
The previous wording still left too much room for low-value workarounds
like whole-cell block wrapping. In downstream browser rollouts, that
pattern was adding tokens and preventing useful state reuse across
`js_repl` cells.
This change makes the preferred behavior more explicit without changing
runtime semantics.
## Scope
- Prompt/documentation change only
- No runtime behavior changes
- Updates the matching string-backed `project_doc` tests
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