fix(desktop): default session list density to compact

Keeps the sidebar byte-identical for existing users until they opt into
comfortable/detailed themselves — per the no-default-change salvage rule.

apps/desktop/src/store/session-list-density.test.ts

@@ -11,10 +11,10 @@ describe('session list density preference', () => {
     window.localStorage.clear()
   })
 
-  it('defaults to comfortable and persists changes', async () => {
+  it('defaults to compact (pre-density behavior) and persists changes', async () => {
     const first = await loadStore()
 
-    expect(first.$sessionListDensity.get()).toBe('comfortable')
+    expect(first.$sessionListDensity.get()).toBe('compact')
 
     first.setSessionListDensity('detailed')
 
@@ -22,9 +22,9 @@ describe('session list density preference', () => {
     expect((await loadStore()).$sessionListDensity.get()).toBe('detailed')
   })
 
-  it('falls back to comfortable for an unknown stored value', async () => {
+  it('falls back to compact for an unknown stored value', async () => {
     window.localStorage.setItem('hermes.desktop.sessionListDensity', 'tiny')
 
-    expect((await loadStore()).$sessionListDensity.get()).toBe('comfortable')
+    expect((await loadStore()).$sessionListDensity.get()).toBe('compact')
   })
 })

apps/desktop/src/store/session-list-density.ts

@@ -4,12 +4,14 @@ export type SessionListDensity = 'compact' | 'comfortable' | 'detailed'
 
 const STORAGE_KEY = 'hermes.desktop.sessionListDensity'
 
+// Compact is the pre-density row exactly as it shipped, so existing users see
+// no change until they opt into a denser-information mode themselves (#68119).
 const densityCodec: Codec<SessionListDensity> = {
-  decode: raw => (raw === 'compact' || raw === 'detailed' ? raw : 'comfortable'),
+  decode: raw => (raw === 'comfortable' || raw === 'detailed' ? raw : 'compact'),
   encode: value => value
 }
 
-export const $sessionListDensity = persistentAtom<SessionListDensity>(STORAGE_KEY, 'comfortable', densityCodec)
+export const $sessionListDensity = persistentAtom<SessionListDensity>(STORAGE_KEY, 'compact', densityCodec)
 
 export function setSessionListDensity(density: SessionListDensity) {
   $sessionListDensity.set(density)