diff --git a/src/main.ts b/src/main.ts
index 6715fee..310ca7b 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,16 +1,28 @@
 import './style.css'
 import { load, newGame, save } from './state'
 import { tick } from './engine'
-import { render } from './ui'
+import { render, refresh } from './ui'
 import { toggleHelp } from './help'
 
 const app = document.querySelector<HTMLDivElement>('#app')!
 const state = load() ?? newGame()
 
+// User actions (deploy/uninstall/buy/fix/prestige) change the DOM's shape,
+// so they get a full rebuild for instant feedback.
 function scheduleRender() {
   render(app, state, scheduleRender)
 }
 
+// The passive per-tick refresh only patches values that drift on their own
+// (points/rate, background crashes, new log lines) - it never recreates
+// the deploy form or any button, so it can't step on an in-flight click or
+// reset a select the player is mid-choice on.
+function scheduleRefresh() {
+  if (!refresh(app, state, scheduleRender)) scheduleRender()
+}
+
+scheduleRender()
+
 let last = performance.now()
 // Passive UI refresh - user actions call scheduleRender() directly for
 // instant feedback, so this only needs to be fast enough to reflect the
@@ -25,12 +37,7 @@ function loop(now: number) {
 }
 
 function renderLoop() {
-  // Skip the rebuild while a <select> is focused - recreating it mid-render
-  // forces any open native dropdown to close immediately.
-  const active = document.activeElement
-  if (!(active instanceof HTMLSelectElement)) {
-    scheduleRender()
-  }
+  scheduleRefresh()
   setTimeout(renderLoop, RENDER_MS)
 }
 
diff --git a/src/ui.ts b/src/ui.ts
index 659ec10..faa741f 100644
--- a/src/ui.ts
+++ b/src/ui.ts
@@ -69,11 +69,12 @@ function hostLabel(state: GameState, hardwareId: string): string {
   return `${hw.nickname} (${def.name})`
 }
 
+// Full structural rebuild - used for the initial mount and after any user
+// action (deploy/uninstall/buy/fix/prestige), since those already change
+// the shape of the DOM (new rows, new buttons) and are driven by a click
+// that has already completed, so there's nothing left mid-interaction to
+// wipe out.
 export function render(root: HTMLElement, state: GameState, onChange: () => void) {
-  const cap = capacity(state)
-  const rate = totalRate(state)
-  const inOutage = Date.now() < state.outageUntil
-
   if (!selectedHardwareId || !state.hardware.find((h) => h.id === selectedHardwareId)) {
     selectedHardwareId = state.hardware[0]?.id ?? null
   }
@@ -81,12 +82,12 @@ export function render(root: HTMLElement, state: GameState, onChange: () => void
   const prevLogScroll = root.querySelector('.log-list')?.scrollTop
 
   root.innerHTML = ''
-  root.appendChild(buildHeader(state, rate, inOutage))
+  root.appendChild(buildHeader(state))
   root.appendChild(buildRackArt(state))
 
   const grid = document.createElement('div')
   grid.className = 'grid'
-  grid.appendChild(buildLeftColumn(state, cap, onChange))
+  grid.appendChild(buildLeftColumn(state, onChange))
   grid.appendChild(buildRightColumn(state, onChange))
   root.appendChild(grid)
 
@@ -102,22 +103,82 @@ export function render(root: HTMLElement, state: GameState, onChange: () => void
   save(state)
 }
 
-function buildHeader(state: GameState, rate: number, inOutage: boolean): HTMLElement {
+// Passive per-tick refresh - patches the values that drift on their own
+// between user actions (points/rate ticking up, background crashes, new
+// log lines) in place, instead of tearing the whole panel down. Never
+// touches the deploy form or recreates any button, so it can't step on an
+// in-flight click or reset a select the player is mid-choice on.
+export function refresh(root: HTMLElement, state: GameState, onChange: () => void): boolean {
+  const header = root.querySelector('.topbar')
+  const grid = root.querySelector('.grid')
+  if (!header || !grid) return false // nothing built yet - caller should do a full render
+
+  updateHeader(root, state)
+  updateRackArt(root, state)
+  updateHardwareList(root, state)
+  updateBuyButtons(root, state)
+  updateUpgradeList(root, state)
+  updateServiceList(root, state, onChange)
+  updateDeployOptions(root, state)
+  updateLog(root, state)
+
+  const hasBanner = !!root.querySelector('.prestige-banner')
+  if (canPrestige(state) && !hasBanner) {
+    root.appendChild(buildPrestigeBanner(state, onChange))
+  } else if (!canPrestige(state) && hasBanner) {
+    root.querySelector('.prestige-banner')!.remove()
+  }
+
+  save(state)
+  return true
+}
+
+function buildHeader(state: GameState): HTMLElement {
   const header = document.createElement('header')
   header.className = 'topbar'
   header.innerHTML = `
     <div class="brand">rack<span class="cursor">_</span></div>
     <div class="stat">
-      <span class="arrow">${inOutage ? '✗' : '▲'}</span>
-      <span class="rate">${inOutage ? 'OUTAGE' : `${fmt(rate)} pts/sec`}</span>
-      <span class="points">${fmt(state.points)} pts</span>
+      <span class="arrow"></span>
+      <span class="rate"></span>
+      <span class="points"></span>
       <button class="help-btn" title="Help & changelog (?)">?</button>
     </div>
   `
   header.querySelector('.help-btn')!.addEventListener('click', () => toggleHelp())
+  updateHeader(header, state)
   return header
 }
 
+function updateHeader(root: HTMLElement, state: GameState) {
+  const rate = totalRate(state)
+  const inOutage = Date.now() < state.outageUntil
+  const arrow = root.querySelector('.arrow')
+  const rateEl = root.querySelector('.rate')
+  const pointsEl = root.querySelector('.points')
+  if (arrow) arrow.textContent = inOutage ? '✗' : '▲'
+  if (rateEl) rateEl.textContent = inOutage ? 'OUTAGE' : `${fmt(rate)} pts/sec`
+  if (pointsEl) pointsEl.textContent = `${fmt(state.points)} pts`
+}
+
+function rackArtLineHtml(state: GameState, hw: GameState['hardware'][number]): string {
+  const hostCap = hostCapacity(state, hw.id)
+  const badges = state.services
+    .filter((s) => s.hardwareId === hw.id)
+    .map((s) => {
+      const abbr = SERVICE_ABBR[s.defId] ?? '??'
+      const quirk = quirkDef(s.quirkId)
+      const cls = s.status === 'running' ? 'slot-running' : 'slot-crashed'
+      return `<span class="${cls}" title="${SERVICES.find((d) => d.id === s.defId)!.name}${quirk ? ` — ${quirk.name}` : ''}">[${abbr}]</span>`
+    })
+    .join('')
+
+  const freeSlots = Math.max(0, hostCap.ram - hostCap.ramUsed)
+  const dots = '·'.repeat(Math.min(freeSlots, 20))
+
+  return `<span class="rack-host-name">${hw.nickname.padEnd(16, ' ')}</span>${badges}<span class="dim">${dots}</span>`
+}
+
 function buildRackArt(state: GameState): HTMLElement {
   const section = document.createElement('section')
   section.className = 'panel rack-art-panel'
@@ -126,45 +187,41 @@ function buildRackArt(state: GameState): HTMLElement {
   pre.className = 'rack-art'
 
   for (const hw of state.hardware) {
-    const hostCap = hostCapacity(state, hw.id)
     const line = document.createElement('div')
     line.className = 'rack-art-line'
-
-    const badges = state.services
-      .filter((s) => s.hardwareId === hw.id)
-      .map((s) => {
-        const abbr = SERVICE_ABBR[s.defId] ?? '??'
-        const quirk = quirkDef(s.quirkId)
-        const cls = s.status === 'running' ? 'slot-running' : 'slot-crashed'
-        return `<span class="${cls}" title="${SERVICES.find((d) => d.id === s.defId)!.name}${quirk ? ` — ${quirk.name}` : ''}">[${abbr}]</span>`
-      })
-      .join('')
-
-    const freeSlots = Math.max(0, hostCap.ram - hostCap.ramUsed)
-    const dots = '·'.repeat(Math.min(freeSlots, 20))
-
-    line.innerHTML = `<span class="rack-host-name">${hw.nickname.padEnd(16, ' ')}</span>${badges}<span class="dim">${dots}</span>`
+    line.dataset.hw = hw.id
+    line.innerHTML = rackArtLineHtml(state, hw)
     pre.appendChild(line)
   }
   section.appendChild(pre)
   return section
 }
 
-function buildLeftColumn(state: GameState, cap: ReturnType<typeof capacity>, onChange: () => void): HTMLElement {
+// Same set of hosts still shown (hardware count only changes via buyHardware,
+// which triggers a full render) - just patch each line's badges/free-slot
+// dots, since crashes/fixes flip badge state every tick.
+function updateRackArt(root: HTMLElement, state: GameState) {
+  for (const hw of state.hardware) {
+    const line = root.querySelector<HTMLElement>(`.rack-art-line[data-hw="${hw.id}"]`)
+    if (line) line.innerHTML = rackArtLineHtml(state, hw)
+  }
+}
+
+function buildLeftColumn(state: GameState, onChange: () => void): HTMLElement {
   const col = document.createElement('div')
   col.className = 'col left'
 
   const hwSection = document.createElement('section')
   hwSection.className = 'panel'
-  hwSection.innerHTML = `<h2>HARDWARE <span class="dim">Σ ram ${cap.ramUsed}/${cap.ram} · pwr ${cap.powerUsed}/${cap.power}</span></h2>`
+  hwSection.innerHTML = `<h2>HARDWARE <span class="dim cap-summary"></span></h2>`
   const hwList = document.createElement('div')
   hwList.className = 'list'
+  hwList.dataset.role = 'hw-list'
   for (const hw of state.hardware) {
     const def = HARDWARE.find((h) => h.id === hw.defId)!
-    const hostCap = hostCapacity(state, hw.id)
     const item = document.createElement('div')
     item.className = 'item hardware' + (hw.id === selectedHardwareId ? ' selected' : '')
-    item.innerHTML = `<span class="name">${hostLabel(state, hw.id)}</span><span class="dim tiny">ram ${hostCap.ramUsed}/${hostCap.ram} · pwr ${hostCap.powerUsed}/${hostCap.power}</span>`
+    item.dataset.hw = hw.id
     item.title = `${def.flavour} (click to select as the deploy target)`
     item.onclick = () => {
       selectedHardwareId = hw.id
@@ -174,21 +231,19 @@ function buildLeftColumn(state: GameState, cap: ReturnType<typeof capacity>, onC
   }
   hwSection.appendChild(hwList)
 
-  // Highest-tier hardware the player already owns - buying another unit of
-  // it is a horizontal bridge (more capacity now, at a rising price) for
-  // the often-long grind between one tier's cost and the next tier's.
-  const topOwnedHw = [...state.hardware]
-    .map((h) => HARDWARE.find((d) => d.id === h.defId)!)
-    .sort((a, b) => HARDWARE.indexOf(b) - HARDWARE.indexOf(a))[0]
-  if (topOwnedHw && topOwnedHw.cost > 0) {
-    const repeatCost = hardwareCost(state, topOwnedHw.id)
+  // Every tier the player already owns - buying another unit of any of them
+  // is a horizontal bridge (more capacity now, at a rising price) for the
+  // often-long grind between one tier's cost and the next tier's.
+  const ownedTiers = HARDWARE.filter(
+    (def) => def.cost > 0 && state.hardware.some((h) => h.defId === def.id),
+  )
+  for (const tier of ownedTiers) {
     const repeatBtn = document.createElement('button')
     repeatBtn.className = 'buy-btn'
-    repeatBtn.textContent = `+ buy another ${topOwnedHw.name} (${fmt(repeatCost)})`
-    repeatBtn.disabled = state.points < repeatCost
-    repeatBtn.title = `Add a second ${topOwnedHw.name} as its own host, at a rising price per extra unit.`
+    repeatBtn.dataset.tier = tier.id
+    repeatBtn.title = `Add another ${tier.name} as its own host, at a rising price per extra unit.`
     repeatBtn.onclick = () => {
-      if (buyHardware(state, topOwnedHw.id)) onChange()
+      if (buyHardware(state, tier.id)) onChange()
     }
     hwSection.appendChild(repeatBtn)
   }
@@ -197,6 +252,7 @@ function buildLeftColumn(state: GameState, cap: ReturnType<typeof capacity>, onC
   if (nextHw) {
     const buyBtn = document.createElement('button')
     buyBtn.className = 'buy-btn'
+    buyBtn.dataset.tier = 'next'
     buyBtn.textContent = `+ buy ${nextHw.name} (${fmt(nextHw.cost)})`
     buyBtn.disabled = state.points < nextHw.cost
     buyBtn.title = nextHw.flavour
@@ -217,6 +273,7 @@ function buildLeftColumn(state: GameState, cap: ReturnType<typeof capacity>, onC
     const lockedByReq = up.requires ? !state.upgrades.includes(up.requires) : false
     const row = document.createElement('div')
     row.className = 'item upgrade' + (owned ? ' owned' : '') + (lockedByReq ? ' locked' : '')
+    row.dataset.up = up.id
     row.title = up.flavour
     row.innerHTML = `<span class="name">${up.name}</span><span class="upgrade-status">${
       owned ? '✓' : lockedByReq ? '🔒' : fmt(up.cost)
@@ -232,9 +289,144 @@ function buildLeftColumn(state: GameState, cap: ReturnType<typeof capacity>, onC
   upSection.appendChild(upList)
   col.appendChild(upSection)
 
+  updateHardwareList(col, state)
+  updateBuyButtons(col, state)
+  updateUpgradeList(col, state)
+
   return col
 }
 
+function updateHardwareList(root: HTMLElement, state: GameState) {
+  const cap = capacity(state)
+  const summary = root.querySelector('.cap-summary')
+  if (summary) summary.textContent = `Σ ram ${cap.ramUsed}/${cap.ram} · pwr ${cap.powerUsed}/${cap.power}`
+
+  for (const hw of state.hardware) {
+    const item = root.querySelector<HTMLElement>(`[data-role="hw-list"] .item[data-hw="${hw.id}"]`)
+    if (!item) continue
+    const hostCap = hostCapacity(state, hw.id)
+    item.classList.toggle('selected', hw.id === selectedHardwareId)
+    item.innerHTML = `<span class="name">${hostLabel(state, hw.id)}</span><span class="dim tiny">ram ${hostCap.ramUsed}/${hostCap.ram} · pwr ${hostCap.powerUsed}/${hostCap.power}</span>`
+  }
+}
+
+function updateBuyButtons(root: HTMLElement, state: GameState) {
+  for (const tier of HARDWARE) {
+    const btn = root.querySelector<HTMLButtonElement>(`.buy-btn[data-tier="${tier.id}"]`)
+    if (!btn) continue
+    const cost = hardwareCost(state, tier.id)
+    btn.textContent = `+ buy another ${tier.name} (${fmt(cost)})`
+    btn.disabled = state.points < cost
+  }
+  const nextBtn = root.querySelector<HTMLButtonElement>('.buy-btn[data-tier="next"]')
+  if (nextBtn) {
+    const nextHw = HARDWARE.find((h) => !state.hardware.some((owned) => owned.defId === h.id))
+    if (nextHw) nextBtn.disabled = state.points < nextHw.cost
+  }
+}
+
+function updateUpgradeList(root: HTMLElement, state: GameState) {
+  for (const up of UPGRADES) {
+    const row = root.querySelector<HTMLElement>(`.item.upgrade[data-up="${up.id}"]`)
+    if (!row) continue
+    const owned = state.upgrades.includes(up.id)
+    if (!owned) row.classList.toggle('affordable', state.points >= up.cost)
+  }
+}
+
+function serviceRowHtml(state: GameState, svc: GameState['services'][number]): string {
+  const def = SERVICES.find((s) => s.id === svc.defId)!
+  const showRates = state.upgrades.includes('monitoring')
+  const rate = ratePerSec(state, svc)
+  const badge = svc.redundant ? ' <span class="redundant-badge">×2</span>' : ''
+  const quirk = quirkDef(svc.quirkId)
+  const quirkBadge = quirk ? ` <span class="quirk-badge" title="${quirk.flavour}">${quirk.name}</span>` : ''
+  return `
+    <span class="status-icon">${svc.status === 'running' ? '✓' : '✗'}</span>
+    <span class="name">${def.name}${badge}${quirkBadge}</span>
+    <span class="dim tiny">${hostLabel(state, svc.hardwareId)}</span>
+    <span class="dim">${def.category}</span>
+    <span class="value">${svc.status === 'running' ? `${rate.toFixed(1)}/s` : 'CRASHED'}</span>
+    ${showRates && svc.status === 'running' ? `<span class="dim tiny">risk ${(def.baseCrashPerSec * 3600).toFixed(2)}/hr</span>` : ''}
+  `
+}
+
+function buildServiceRow(state: GameState, svc: GameState['services'][number], onChange: () => void): HTMLElement {
+  const row = document.createElement('div')
+  row.dataset.svc = svc.id
+  row.className = 'item service ' + svc.status
+  row.innerHTML = serviceRowHtml(state, svc)
+
+  if (svc.status === 'crashed') {
+    const fixBtn = document.createElement('button')
+    fixBtn.className = 'fix-btn'
+    fixBtn.textContent = canFix(svc) ? 'fix' : '...'
+    fixBtn.disabled = !canFix(svc)
+    fixBtn.onclick = (e) => {
+      e.stopPropagation()
+      fixService(state, svc.id)
+      onChange()
+    }
+    row.appendChild(fixBtn)
+  }
+  const def = SERVICES.find((s) => s.id === svc.defId)!
+  const uninstallBtn = document.createElement('button')
+  uninstallBtn.className = 'uninstall-btn'
+  uninstallBtn.textContent = 'rm'
+  uninstallBtn.title = `Uninstall ${def.name} (salvage ${Math.round(def.deployCost * 0.25) * (svc.redundant ? 2 : 1)} pts)`
+  uninstallBtn.onclick = (e) => {
+    e.stopPropagation()
+    uninstallService(state, svc.id)
+    onChange()
+  }
+  row.appendChild(uninstallBtn)
+  return row
+}
+
+// Services are only added/removed via deploy/uninstall, which already go
+// through a full render - so on a passive tick the set of rows is stable
+// and only their status/rate/fix-button needs patching (crash/fix happen
+// in the background tick loop).
+function updateServiceList(root: HTMLElement, state: GameState, onChange: () => void) {
+  for (const svc of state.services) {
+    const row = root.querySelector<HTMLElement>(`.item.service[data-svc="${svc.id}"]`)
+    if (!row) continue
+    row.className = 'item service ' + svc.status
+    const fixBtn = row.querySelector<HTMLButtonElement>('.fix-btn')
+    const uninstallBtn = row.querySelector('.uninstall-btn')
+    row.innerHTML = serviceRowHtml(state, svc)
+    if (svc.status === 'crashed') {
+      const btn = fixBtn ?? document.createElement('button')
+      btn.className = 'fix-btn'
+      btn.textContent = canFix(svc) ? 'fix' : '...'
+      btn.disabled = !canFix(svc)
+      if (!fixBtn) {
+        btn.onclick = (e) => {
+          e.stopPropagation()
+          fixService(state, svc.id)
+          onChange()
+        }
+      }
+      row.appendChild(btn)
+    }
+    if (uninstallBtn) row.appendChild(uninstallBtn)
+  }
+}
+
+function updateDeployOptions(root: HTMLElement, state: GameState) {
+  const select = root.querySelector<HTMLSelectElement>('.svc-select')
+  if (!select) return
+  const targetCap = selectedHardwareId ? hostCapacity(state, selectedHardwareId) : null
+  for (const opt of Array.from(select.options)) {
+    const def = SERVICES.find((s) => s.id === opt.value)!
+    const noRoom = !!(
+      targetCap &&
+      (targetCap.ramUsed + def.ram > targetCap.ram || targetCap.powerUsed + def.power > targetCap.power)
+    )
+    opt.disabled = noRoom
+  }
+}
+
 function buildRightColumn(state: GameState, onChange: () => void): HTMLElement {
   const col = document.createElement('div')
   col.className = 'col right'
@@ -245,47 +437,8 @@ function buildRightColumn(state: GameState, onChange: () => void): HTMLElement {
   const svcList = document.createElement('div')
   svcList.className = 'list'
 
-  const showRates = state.upgrades.includes('monitoring')
-
   for (const svc of state.services) {
-    const def = SERVICES.find((s) => s.id === svc.defId)!
-    const row = document.createElement('div')
-    row.className = 'item service ' + svc.status
-    const rate = ratePerSec(state, svc)
-    const badge = svc.redundant ? ' <span class="redundant-badge">×2</span>' : ''
-    const quirk = quirkDef(svc.quirkId)
-    const quirkBadge = quirk ? ` <span class="quirk-badge" title="${quirk.flavour}">${quirk.name}</span>` : ''
-    row.innerHTML = `
-      <span class="status-icon">${svc.status === 'running' ? '✓' : '✗'}</span>
-      <span class="name">${def.name}${badge}${quirkBadge}</span>
-      <span class="dim tiny">${hostLabel(state, svc.hardwareId)}</span>
-      <span class="dim">${def.category}</span>
-      <span class="value">${svc.status === 'running' ? `${rate.toFixed(1)}/s` : 'CRASHED'}</span>
-      ${showRates && svc.status === 'running' ? `<span class="dim tiny">risk ${(def.baseCrashPerSec * 3600).toFixed(2)}/hr</span>` : ''}
-    `
-    if (svc.status === 'crashed') {
-      const fixBtn = document.createElement('button')
-      fixBtn.className = 'fix-btn'
-      fixBtn.textContent = canFix(svc) ? 'fix' : '...'
-      fixBtn.disabled = !canFix(svc)
-      fixBtn.onclick = (e) => {
-        e.stopPropagation()
-        fixService(state, svc.id)
-        onChange()
-      }
-      row.appendChild(fixBtn)
-    }
-    const uninstallBtn = document.createElement('button')
-    uninstallBtn.className = 'uninstall-btn'
-    uninstallBtn.textContent = 'rm'
-    uninstallBtn.title = `Uninstall ${def.name} (salvage ${Math.round(def.deployCost * 0.25) * (svc.redundant ? 2 : 1)} pts)`
-    uninstallBtn.onclick = (e) => {
-      e.stopPropagation()
-      uninstallService(state, svc.id)
-      onChange()
-    }
-    row.appendChild(uninstallBtn)
-    svcList.appendChild(row)
+    svcList.appendChild(buildServiceRow(state, svc, onChange))
   }
   svcSection.appendChild(svcList)
 
@@ -323,10 +476,7 @@ function buildRightColumn(state: GameState, onChange: () => void): HTMLElement {
   const logList = document.createElement('div')
   logList.className = 'log-list'
   for (const entry of state.log) {
-    const line = document.createElement('div')
-    line.className = 'log-line'
-    line.innerHTML = `<span class="log-time">${timeAgo(entry.t)}</span> ${entry.text}`
-    logList.appendChild(line)
+    logList.appendChild(buildLogLine(entry))
   }
   logSection.appendChild(logList)
   col.appendChild(logSection)
@@ -334,6 +484,25 @@ function buildRightColumn(state: GameState, onChange: () => void): HTMLElement {
   return col
 }
 
+function buildLogLine(entry: GameState['log'][number]): HTMLElement {
+  const line = document.createElement('div')
+  line.className = 'log-line'
+  line.innerHTML = `<span class="log-time">${timeAgo(entry.t)}</span> ${entry.text}`
+  return line
+}
+
+// The log only ever grows (new entries pushed on crash/fix/purchase/etc) -
+// append what's new rather than rebuilding the whole scrollable list, which
+// would also reset the user's scroll position.
+function updateLog(root: HTMLElement, state: GameState) {
+  const logList = root.querySelector('.log-list')
+  if (!logList) return
+  const rendered = logList.children.length
+  for (let i = rendered; i < state.log.length; i++) {
+    logList.appendChild(buildLogLine(state.log[i]))
+  }
+}
+
 function buildPrestigeBanner(state: GameState, onChange: () => void): HTMLElement {
   const banner = document.createElement('div')
   banner.className = 'prestige-banner'