fix(BUG-4): updateDoc patch on activeDisplay (not setDoc replace)

All 5 storage.setDoc(activeDisplay, {...}, {merge:true}) →
storage.updateDoc(activeDisplay, {...}).

setDoc merge:true worked in prod (firebase honors merge) but ws adapter
+ mock ignore opts arg entirely → clobbers doc. updateDoc uses PATCH
across all adapters (firebase real updateDoc, ws PATCH endpoint, mock
merge). Consistent, no clobber.

Sites fixed:
- hidePlayerHp toggle
- startEncounter (set active ids)
- endEncounter (null active ids)
- deactivate active display
- activate new display

TDD: HideHpToggle.test RED first (assert updateDoc patch, impl still
setDoc → 0 calls found). GREEN after switch.

Char tests updated: Encounter.characterization (2) + Combat.characterization
(2) assert updateDoc on activeDisplay, not setDoc.

BUG-4: prod was already fixed (merge:true), test was RED due to mock
ignoring opts. Now all 3 adapters consistent via updateDoc.

TODO.md

@@ -90,7 +90,7 @@ REWORK_PLAN.md.
 
 ### bug-3 was a halucination has been removed
 
-### BUG-4: hide-player-HP breaks display view (preexisting)
+### BUG-4: hide-player-HP breaks display view (preexisting) --- PROD FIXED, TEST RED (mock bug)
 - **Broader than hide-HP**: ALL 5 `storage.setDoc(getPath.activeDisplay(), ...)` calls
   use `{merge:true}` which is IGNORED (setDoc = replace per contract).
   Each write clobbers other fields on activeDisplay/status doc.
@@ -108,6 +108,13 @@ REWORK_PLAN.md.
   activeEncounterId with null (setDoc replace vs updateDoc patch).
 - Fix: use updateDoc (patch) not setDoc (replace); or include all existing
   fields when writing.
+- Status update (2026-07): all 5 sites now use `{merge:true}`. Real firebase
+  adapter honors merge → production works. BUT jsdom test still RED because
+  `src/__mocks__/firebase/firestore.js` setDoc records call, IGNORES opts
+  (no actual merge). Mock must simulate firebase merge semantics for test
+  to pass. Fix = mock setDoc: if opts.merge, MOCK_DB.merge(path,data) else
+  replace. OR change App.js setDoc(merge) → updateDoc (cleaner, ws adapter
+  uses PATCH). Decide which.
 - Test: render App + DisplayView, toggle hide-HP, assert display still shows
   encounter (not paused).