fix: detect flash failure from output even when returncode is 0

program_flash can return exit code 0 while outputting errors like
'uboot failed' or 'cannot open'. Previously only returncode was
checked, so these silent failures caused the workflow to continue
past a failed erase/program step.

Now scans combined stdout+stderr for failure keywords
(uboot, failed, cannot, abort, invalid, unsupported, timeout)
and returns success=False. Also checks returncode != 0 as fallback.

src/flash_programmer.py

@@ -10,6 +10,7 @@ Compatible with Xilinx 2018.3 — 2023.2.
 from __future__ import annotations
 
 import binascii
+import re
 import subprocess
 from dataclasses import dataclass
 from pathlib import Path
@@ -35,6 +36,27 @@ ProgressCallback = Callable[[str, str], None] | None
 
 # ── Helpers ─────────────────────────────────────────────────────────
 
+# Keywords in program_flash output that indicate failure even with rc=0
+_FAIL_KEYWORDS = [
+    "uboot", "u-boot", "failed", "cannot", "abort",
+    "invalid", "unsupported", "timeout",
+]
+
+
+def _output_has_error(output: str) -> str:
+    """Check combined stdout+stderr for known failure keywords.
+
+    Returns the first matching line, or empty string if clean.
+    """
+    lowered = output.lower()
+    for kw in _FAIL_KEYWORDS:
+        if kw in lowered:
+            # Find the actual line
+            for line in output.splitlines():
+                if kw in line.lower():
+                    return line.strip()[:200]
+    return ""
+
 
 def _run_command(
     cmd: list[str],
@@ -167,12 +189,27 @@ def wipe_flash(
                 callback=callback,
             )
 
-        success = result.returncode == 0
+        combined = result.stdout + result.stderr
+        err_line = _output_has_error(combined)
+        if err_line:
+            return FlashResult(
+                step="wipe",
+                success=False,
+                message=f"Flash erase failed: {err_line}",
+                output=combined[:4000],
+            )
+        if result.returncode != 0:
+            return FlashResult(
+                step="wipe",
+                success=False,
+                message=f"Flash erase failed (exit {result.returncode})",
+                output=combined[:4000],
+            )
         return FlashResult(
             step="wipe",
-            success=success,
+            success=True,
-            message="Flash erased successfully" if success else "Flash erase failed",
+            message="Flash erased successfully",
-            output=(result.stdout + result.stderr)[:4000],
+            output=combined[:4000],
         )
     except subprocess.TimeoutExpired:
         return FlashResult(step="wipe", success=False, message="Flash erase timed out")
@@ -252,12 +289,27 @@ def program_flash_bin(
 
     try:
         result = _run_command(cmd, timeout=config.step_timeouts.get("flash_program", 600), callback=callback)
-        success = result.returncode == 0
+        combined = result.stdout + result.stderr
+        err_line = _output_has_error(combined)
+        if err_line:
+            return FlashResult(
+                step="program",
+                success=False,
+                message=f"Flash programming failed: {err_line}",
+                output=combined[:4000],
+            )
+        if result.returncode != 0:
+            return FlashResult(
+                step="program",
+                success=False,
+                message=f"Flash programming failed (exit {result.returncode})",
+                output=combined[:4000],
+            )
         return FlashResult(
             step="program",
-            success=success,
+            success=True,
-            message="Flash programmed successfully" if success else "Flash programming failed",
+            message="Flash programmed successfully",
-            output=(result.stdout + result.stderr)[:4000],
+            output=combined[:4000],
         )
     except subprocess.TimeoutExpired:
         return FlashResult(step="program", success=False, message="Flash programming timed out (600s)")