feat(desktop): add mutation review guardrails

Co-Authored-By: Paperclip <noreply@paperclip.ing>

plans/2026-03-31-hac-31-safe-mutation-guardrails.md

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+# HAC-31 Safe Mutation Guardrails
+
+Date: 2026-03-31
+Owner: Senior Frontend Engineer
+Issue: HAC-31
+
+## Goal
+
+Harden current-phase writable operations without expanding product scope beyond existing string save and TTL controls.
+
+## Scope
+
+- add a scoped review step before string save
+- add a scoped review step before TTL set and TTL removal
+- block no-op mutation submits before they reach the desktop bridge or demo fallback
+- preserve draft value and TTL input when a live mutation fails
+
+## Explicit Non-Goals
+
+- Add Key flow changes
+- real delete execution
+- non-string editing
+- command-surface changes
+- visual refresh beyond mutation clarity
+
+## Implementation
+
+- Added `apps/desktop/src/lib/mutation-guardrails.ts` for mutation summaries and no-op detection helpers.
+- Updated `apps/desktop/src/App.tsx` so save and TTL actions open a shared review dialog with scoped current-vs-next details.
+- Disabled string save when no value change is pending.
+- Disabled TTL set when the requested TTL already matches the active TTL state.
+- Kept live failure handling on the shared operator notice layer while preserving draft state for retry.
+
+## Verification
+
+- `pnpm --filter @redis-gui/desktop test`
+- `pnpm run desktop:build`