diff --git a/apps/api/src/api/tool_instances.py b/apps/api/src/api/tool_instances.py
index 18dd13c..c3c3b74 100644
--- a/apps/api/src/api/tool_instances.py
+++ b/apps/api/src/api/tool_instances.py
@@ -1071,7 +1071,11 @@ async def _prepare_manifest_instance(
         dockerfile = compile_dockerfile(manifest)
         entrypoint = compile_entrypoint(manifest)
 
-        logger.info("Compiled Dockerfile for instance %s (%d chars)", instance.id, len(dockerfile))
+        logger.info(
+            "Compiled Dockerfile for instance %s (%d chars)",
+            instance.id,
+            len(dockerfile),
+        )
         logger.debug("Dockerfile content: %s", dockerfile)
         logger.info("Compiled entrypoint for instance %s", instance.id)
         logger.debug("Entrypoint content: %s", entrypoint)
diff --git a/apps/api/src/services/docker_build.py b/apps/api/src/services/docker_build.py
index 0dad9a9..11f9624 100644
--- a/apps/api/src/services/docker_build.py
+++ b/apps/api/src/services/docker_build.py
@@ -6,7 +6,9 @@ import subprocess
 logger = logging.getLogger(__name__)
 
 
-def build_image(instance_dir: str, dockerfile: str, tag: str, build_context: dict | None = None) -> tuple[int, str, str]:
+def build_image(
+    instance_dir: str, dockerfile: str, tag: str, build_context: dict | None = None
+) -> tuple[int, str, str]:
     """Build a Docker image from a Dockerfile.
 
     Args:
@@ -20,12 +22,23 @@ def build_image(instance_dir: str, dockerfile: str, tag: str, build_context: dic
     """
     from pathlib import Path
 
+    # Defensive: normalise any CRLF that may have crept in from manifest DB
+    # strings — Docker's legacy builder treats \r as a character after the
+    # backslash, breaking RUN continuations and producing
+    # "unknown instruction" errors.
+    dockerfile = dockerfile.replace("\r\n", "\n").replace("\r", "\n")
+
     # Write Dockerfile
     dockerfile_path = Path(instance_dir) / "Dockerfile"
     dockerfile_path.write_text(dockerfile, newline="\n")
     logger.info("Wrote Dockerfile to %s (%d bytes)", dockerfile_path, len(dockerfile))
     logger.debug("Dockerfile content:\n%s", dockerfile)
 
+    # Hex-dump first 8 lines so we can see exactly what bytes Docker receives
+    lines_for_hex = dockerfile.split("\n")[:8]
+    for i, line in enumerate(lines_for_hex, start=1):
+        logger.info("Dockerfile line %d hex: %s", i, line.encode("utf-8").hex())
+
     # Write build context files
     if build_context:
         for file_path, content in build_context.items():
@@ -34,19 +47,27 @@ def build_image(instance_dir: str, dockerfile: str, tag: str, build_context: dic
             try:
                 full_path.resolve().relative_to(Path(instance_dir).resolve())
             except ValueError:
-                logger.error("Build context file path escapes instance directory: %s", file_path)
-                raise ValueError(f"Build context file path '{file_path}' escapes instance directory")
-            
+                logger.error(
+                    "Build context file path escapes instance directory: %s", file_path
+                )
+                raise ValueError(
+                    f"Build context file path '{file_path}' escapes instance directory"
+                )
+
             full_path.parent.mkdir(parents=True, exist_ok=True)
-            full_path.write_text(content, newline="\n")
+            normalized = content.replace("\r\n", "\n").replace("\r", "\n")
+            full_path.write_text(normalized, newline="\n")
             logger.debug("Wrote build context file: %s", full_path)
 
     # Build image
     logger.debug("Building Docker image with tag: %s", tag)
     cmd = [
-        "docker", "build",
-        "-t", tag,
-        "-f", str(dockerfile_path),
+        "docker",
+        "build",
+        "-t",
+        tag,
+        "-f",
+        str(dockerfile_path),
         instance_dir,
     ]