fix: harden layout push bounds

tests/layout-css.spec.ts

@@ -16,7 +16,14 @@ describe('layout.css conversation column', () => {
 
   it('allows the center column to shrink and wrap long tokens', () => {
     expect(css).toMatch(/min-height:\s*0/)
-    expect(css).toMatch(/overflow:\s*hidden/)
     expect(css).toMatch(/overflow-wrap:\s*anywhere/)
   })
+
+  it('leaves overflow ownership to the host conversation descendants', () => {
+    const conversationRule = css.match(
+      /#root \[data-dsh-frame\][\s\S]*?\{([\s\S]*?)\n\}/,
+    )?.[1]
+    expect(conversationRule).toBeDefined()
+    expect(conversationRule).not.toMatch(/(?:^|[;\s])overflow\s*:/)
+  })
 })

tests/layout-push.spec.ts

@@ -72,4 +72,28 @@ describe('layoutPushSize', () => {
       viewportHeight: 800,
     })).toEqual({ width: 400, height: 220 })
   })
+
+  it('never pushes beyond a viewport smaller than the normal panel minima', () => {
+    expect(layoutPushSize({
+      narrow: false,
+      panelOpen: true,
+      bottomOpen: true,
+      width: 400,
+      bottomHeight: 220,
+      viewportWidth: 200,
+      viewportHeight: 200,
+    })).toEqual({ width: 200, height: 0 })
+  })
+
+  it('turns non-finite geometry into a safe zero push', () => {
+    expect(layoutPushSize({
+      narrow: false,
+      panelOpen: true,
+      bottomOpen: true,
+      width: Number.NaN,
+      bottomHeight: Number.POSITIVE_INFINITY,
+      viewportWidth: Number.NaN,
+      viewportHeight: Number.POSITIVE_INFINITY,
+    })).toEqual({ width: 0, height: 0 })
+  })
 })