Fix terminal read for blank TUI tails (#5050)

Co-authored-by: Orca <help@stably.ai>

src/main/runtime/orca-runtime.ts

@@ -3825,6 +3825,59 @@ export class OrcaRuntimeService {
     return rendererSnapshot ? { ...rendererSnapshot, source: 'renderer' } : null
   }
 
+  private async withVisibleSnapshotFallback(
+    ptyId: string,
+    read: RuntimeTerminalRead,
+    opts: { cursor?: number; limit?: number } = {}
+  ): Promise<RuntimeTerminalRead> {
+    if (!shouldFallbackToVisibleTerminalSnapshot(read, opts)) {
+      return read
+    }
+    const lines = await this.readRendererVisibleSnapshotLines(ptyId)
+    if (lines.length === 0) {
+      return read
+    }
+    return buildVisibleSnapshotReadFallback(read, lines, opts.limit)
+  }
+
+  private async readRendererVisibleSnapshotLines(ptyId: string): Promise<string[]> {
+    const controller = this.ptyController
+    if (!controller?.serializeBuffer) {
+      return []
+    }
+    if (controller.hasRendererSerializer && !controller.hasRendererSerializer(ptyId)) {
+      return []
+    }
+    try {
+      // Why: raw PTY tails can be whitespace-only while a full-screen TUI is
+      // visibly nonblank in renderer xterm. Ask the renderer for the active
+      // screen instead of reusing the headless transcript path.
+      const snapshot = await controller.serializeBuffer(ptyId, {
+        scrollbackRows: 0,
+        altScreenForcesZeroRows: false
+      })
+      if (!snapshot || snapshot.data.length === 0) {
+        return []
+      }
+      const emulator = new HeadlessEmulator({
+        cols: snapshot.cols,
+        rows: snapshot.rows,
+        scrollback: 0
+      })
+      try {
+        await emulator.write(snapshot.data)
+        return emulator
+          .getVisibleLines()
+          .map((line) => line.trimEnd())
+          .filter((line) => line.trim().length > 0)
+      } finally {
+        emulator.dispose()
+      }
+    } catch {
+      return []
+    }
+  }
+
   private async serializeHeadlessTerminalBuffer(
     ptyId: string,
     opts: { scrollbackRows?: number; includeEmpty?: boolean } = {}
@@ -5930,7 +5983,8 @@ export class OrcaRuntimeService {
   ): Promise<RuntimeTerminalRead> {
     const pty = this.getLivePtyForHandle(handle)
     if (pty) {
-      return this.readPtyTerminal(handle, pty.pty, opts)
+      const read = this.readPtyTerminal(handle, pty.pty, opts)
+      return this.withVisibleSnapshotFallback(pty.pty.ptyId, read, opts)
     }
 
     const { leaf } = this.getLiveLeafForHandle(handle)
@@ -5944,7 +5998,7 @@ export class OrcaRuntimeService {
       cursor: opts.cursor,
       limit: opts.limit
     })
-    return read
+    return leaf.ptyId ? this.withVisibleSnapshotFallback(leaf.ptyId, read, opts) : read
   }
 
   async sendTerminal(
@@ -15388,6 +15442,41 @@ function readTerminalTail(args: {
   }
 }
 
+function shouldFallbackToVisibleTerminalSnapshot(
+  read: RuntimeTerminalRead,
+  opts: { cursor?: number; limit?: number }
+): boolean {
+  if (typeof opts.cursor === 'number') {
+    return false
+  }
+  if (read.tail.length === 0) {
+    return false
+  }
+  const hasSubstantialBlankTail =
+    read.limited === true || read.truncated || read.tail.length >= DEFAULT_TERMINAL_READ_LIMIT
+  return hasSubstantialBlankTail && read.tail.every((line) => line.trim().length === 0)
+}
+
+function buildVisibleSnapshotReadFallback(
+  read: RuntimeTerminalRead,
+  visibleLines: string[],
+  limit: number | undefined
+): RuntimeTerminalRead {
+  const lineLimit = terminalReadLimit(limit, DEFAULT_TERMINAL_READ_LIMIT)
+  const lineBoundedTail = visibleLines.slice(-lineLimit)
+  const charBoundedTail = trimTerminalPreviewToCharacterBudget(
+    lineBoundedTail,
+    MAX_TERMINAL_PREVIEW_CHARS
+  )
+  return {
+    ...read,
+    tail: charBoundedTail.tail,
+    limited:
+      read.limited || lineBoundedTail.length < visibleLines.length || charBoundedTail.limited,
+    returnedLineCount: charBoundedTail.tail.length
+  }
+}
+
 function getTerminalState(leaf: RuntimeLeafRecord): RuntimeTerminalState {
   if (leaf.connected) {
     return 'running'