Stop the sync poll from rebuilding the panel every 5 s

@Published fires even when the assigned value is unchanged, so the poll's
unconditional lastError = nil invalidated PanelView — which observes
SyncService — every 5 seconds, forever, hidden or visible. Over five days
that was ~185 CPU-minutes and ~190 MB, and clicks started to lag.

- Route poll state through setError, which skips equal values.
- Watch SyncService from a tiny SyncDot view instead of the panel body.
- Skip the URL cache on polls and give them timeouts.
- Only reassign the composer placeholder when it changed.

AGENTS.md

@@ -177,6 +177,14 @@ brew upgrade --cask prompt
 
 ## Gotchas
 
+- **`@Published` publishes on every assignment, even when the value is
+  unchanged.** The 5-second sync poll used to assign `lastError = nil`
+  unconditionally; `PanelView` observes `SyncService`, so the entire panel
+  (rows, overlays, composer) rebuilt every 5 seconds, forever. Over five days
+  of uptime that was ~185 CPU-minutes and ~190 MB of footprint, and every
+  click started to lag. Poll state now goes through `setError`, which no-ops
+  when equal, and the header's sync dot is its own view so sync publishes
+  cannot invalidate the list.
 - **Never assign `NSApp.mainMenu`.** SwiftUI installs a menu whose Edit items
   are how AppKit routes Cmd+C/V/X/A/Z; replacing it with a hand-built menu
   silently breaks pasting, copying and select-all in the composer (this shipped

Sources/Prompt/ComposerView.swift

@@ -67,7 +67,9 @@ struct ComposerView: NSViewRepresentable {
             textView.string = text
             updateHeight(textView)
         }
-        textView.placeholderText = placeholder
+        if textView.placeholderText != placeholder {
+            textView.placeholderText = placeholder
+        }
         if isFocused, scrollView.window?.firstResponder != textView {
             scrollView.window?.makeFirstResponder(textView)
         }

Sources/Prompt/PanelView.swift

@@ -5,7 +5,6 @@ import UniformTypeIdentifiers
 struct PanelView: View {
     @ObservedObject var store: Store
     @ObservedObject private var sync = SyncService.shared
-
     @State private var composer = ""
     @State private var composerFocused = false
     @State private var composerHeight: CGFloat = ComposerView.oneLineHeight
@@ -84,8 +83,7 @@ struct PanelView: View {
             Spacer()
 
             Button { withAnimation(.easeInOut(duration: 0.15)) { showSync.toggle() } } label: {
-                Image(systemName: "arrow.triangle.2.circlepath")
-                    .foregroundStyle(sync.code == nil ? Color.secondary : Color.accentColor)
+                SyncDot()
             }
             .buttonStyle(.plain).help("Sync")
             Button { toggleSearch() } label: { Image(systemName: "magnifyingglass") }
@@ -881,3 +879,15 @@ struct PanelView: View {
         return (try? AttributedString(markdown: string, options: options)) ?? AttributedString(string)
     }
 }
+
+/// Sync status lives in its own view so a `SyncService` publish cannot
+/// invalidate the panel's list. Watching it from `PanelView`'s body meant every
+/// sync event — including the 5-second poll — re-rendered every row.
+private struct SyncDot: View {
+    @ObservedObject private var sync = SyncService.shared
+
+    var body: some View {
+        Image(systemName: "arrow.triangle.2.circlepath")
+            .foregroundStyle(sync.code == nil ? Color.secondary : Color.accentColor)
+    }
+}

Sources/Prompt/SyncService.swift

@@ -193,13 +193,20 @@ final class SyncService: ObservableObject {
 
     private func poll() {
         guard !isSyncing, let code, let versionURL = endpoint("/api/sync/\(code)/version") else { return }
+        // A cached /version would keep reporting the version the client already
+        // has, so polls must always hit the network. The responses are a few
+        // bytes; letting CFNetwork write them to the disk cache every 5 s only
+        // adds churn.
+        var versionRequest = URLRequest(url: versionURL)
+        versionRequest.cachePolicy = .reloadIgnoringLocalCacheData
+        versionRequest.timeoutInterval = 15
         Task {
             do {
                 // Cheap poll first: the full payload can be megabytes of
                 // base64 images, so only download it when the version moved.
-                let (versionData, versionResponse) = try await URLSession.shared.data(from: versionURL)
+                let (versionData, versionResponse) = try await URLSession.shared.data(for: versionRequest)
                 if (versionResponse as? HTTPURLResponse)?.statusCode == 404 {
-                    lastError = "Sync group no longer exists on the server"
+                    setError("Sync group no longer exists on the server")
                     return
                 }
                 guard let versionHTTP = versionResponse as? HTTPURLResponse, versionHTTP.statusCode == 200 else {
@@ -208,12 +215,15 @@ final class SyncService: ObservableObject {
                 }
                 let remoteVersion = try JSONDecoder().decode([String: Int64].self, from: versionData)["version"] ?? 0
                 guard remoteVersion > lastVersion else {
-                    lastError = nil
+                    setError(nil)
                     return
                 }
                 syncLog("poll remote v\(remoteVersion) local v\(lastVersion) — fetching payload")
                 guard let payloadURL = endpoint("/api/sync/\(code)") else { return }
-                let (data, response) = try await URLSession.shared.data(from: payloadURL)
+                var payloadRequest = URLRequest(url: payloadURL)
+                payloadRequest.cachePolicy = .reloadIgnoringLocalCacheData
+                payloadRequest.timeoutInterval = 30
+                let (data, response) = try await URLSession.shared.data(for: payloadRequest)
                 guard let http = response as? HTTPURLResponse, http.statusCode == 200 else { return }
                 let remote = try JSONDecoder().decode(SyncGetResponse.self, from: data)
                 if let payload = remote.data {
@@ -221,15 +231,25 @@ final class SyncService: ObservableObject {
                 } else {
                     lastVersion = remote.version
                 }
-                lastError = nil
+                setError(nil)
             } catch {
                 syncLog("poll failed: \(error.localizedDescription)")
                 // Polling errors are transient; stay quiet unless nothing ever worked.
-                if lastSyncedAt == nil { lastError = "Cannot reach sync server" }
+                if lastSyncedAt == nil { setError("Cannot reach sync server") }
             }
         }
     }
 
+    /// `@Published` fires on every assignment, even when the value is
+    /// unchanged. The 5-second poll would otherwise republish `lastError`
+    /// forever, and since `PanelView` observes this object, the whole panel
+    /// (list, rows, overlays) re-rendered every 5 seconds — the app grew to
+    /// ~190 MB and ~90 ms of layout per poll over five days of uptime.
+    private func setError(_ message: String?) {
+        guard lastError != message else { return }
+        lastError = message
+    }
+
     private func restartPolling() {
         pollTimer?.invalidate()
         pollTimer = nil