Phase 9 Optional Immer

Phase 9: Optional Immer Adoption

Status

• Not started.

Goal

• Improve nested update readability only where structural cleanup did not solve the pain.
• Avoid using Immer as a substitute for better store boundaries.

Scope

• ui/goose2/src/features/chat/stores/chatStore.ts
• Possibly ui/goose2/src/features/chat/stores/chatSessionStore.ts

Out Of Scope

• Do not add Immer before earlier phases are complete.
• Do not use Immer to justify keeping a broad store.
• Do not convert flat stores where object spread is already clear.
• Do not make dependency changes manually in Cargo.toml; for frontend packages follow the repo's package workflow.

Execution Steps

1. Reassess update complexity after Phases 1 through 7.

   • Check whether chatStore nested updates are still hard to read.
   • Check whether store splits or selectors already reduced the pain enough.

2. Decide whether Immer is worth the dependency and pattern change.

   • Adopt only if it materially improves readability.
   • Skip this phase if the remaining updates are acceptable.

3. If adopting, start with one store.

   • Prefer chatStore first.
   • Convert a small group of related nested updates.
   • Keep behavior exactly the same.

4. Add or update focused tests.

   • Messages update correctly.
   • Runtime state updates correctly.
   • Drafts and cleanup still work.
   • No accidental mutation leaks between sessions.

5. Reassess before expanding.

   • Only convert chatSessionStore if there is still meaningful nested update boilerplate.

Validation

• cd ui/goose2 && pnpm test -- chatStore chatSessionStore useChat
• Focused code review for accidental mutation or changed reference behavior.

Success Criteria

• Update logic is easier to read.
• Behavior is unchanged.
• Immer is used selectively and not as an architectural workaround.