Report the real cause when jrunner fails

--strict means a failure now exits non-zero, so the returncode branch
raises instead of _detect_silent_failure. That branch used raw stderr,
whose first line is always the JVM's "Picked up JAVA_TOOL_OPTIONS: ..."
banner (_subprocess_env sets JAVA_TOOL_OPTIONS to keep jt400 headless).
Every failed run would therefore have recorded that banner in run_log
instead of the actual error — a regression against the old path, which
extracted the exception header.

_error_message strips the banner and prefers the Java exception header:

  org.postgresql.util.PSQLException: ERROR: relation "..." does not exist
  org.postgresql.util.PSQLException: ERROR: syntax error at or near "SELEKT"

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pipekit/jrunner.py

@@ -158,7 +158,7 @@ def query(
         _unlink_quietly(sql_path, pass_path)
 
     if r.returncode != 0:
-        raise JrunnerError(r.stderr.strip() or r.stdout.strip(),
+        raise JrunnerError(_error_message(r.stdout, r.stderr),
                            stdout=r.stdout, stderr=r.stderr)
     silent = _detect_silent_failure(r.stdout, r.stderr)
     if silent:
@@ -250,7 +250,7 @@ def migrate(
         _unlink_quietly(sql_path, pass_path)
 
     if proc.returncode != 0:
-        raise JrunnerError(stderr.strip() or stdout.strip(),
+        raise JrunnerError(_error_message(stdout, stderr),
                            stdout=stdout, stderr=stderr)
     silent = _detect_silent_failure(stdout, stderr)
     if silent:
@@ -317,6 +317,26 @@ def _parse_row_count(text: str) -> int | None:
 # nearly every failure site (see jrunner.java). Detect those by scanning
 # for a Java stack-trace signature so callers don't treat silent failures
 # as success.
+_JVM_NOISE_RE = re.compile(r"^Picked up JAVA_TOOL_OPTIONS:.*$", re.M)
+
+
+def _error_message(stdout: str, stderr: str) -> str:
+    """Best single-line cause for a failed jrunner call.
+
+    The JVM prints "Picked up JAVA_TOOL_OPTIONS: ..." as the first stderr line
+    whenever JAVA_TOOL_OPTIONS is set (which _subprocess_env always does, to
+    keep jt400 headless), so raising raw stderr surfaces that banner instead of
+    the actual error. Prefer the Java exception header, which names the real
+    failure, and fall back to whatever output remains once the banner is gone.
+    """
+    cleaned_err = _JVM_NOISE_RE.sub("", stderr or "").strip()
+    cleaned_out = _JVM_NOISE_RE.sub("", stdout or "").strip()
+    m = _EXCEPTION_HEADER_RE.search(cleaned_err) or _EXCEPTION_HEADER_RE.search(cleaned_out)
+    if m:
+        return m.group(0).strip()
+    return cleaned_err or cleaned_out or "jrunner failed with no output"
+
+
 _STACK_FRAME_RE = re.compile(r"^\s*at [\w.$<>]+\([^)\n]*\.java:\d+\)", re.M)
 _EXCEPTION_HEADER_RE = re.compile(
     r"^(?:[\w.$]+\.)*[\w$]+(?:Exception|Error)(?::[^\n]*)?$", re.M)