diff --git a/docs/modernization/build-inventory.md b/docs/modernization/build-inventory.md
index 22f52e0..c7545df 100644
--- a/docs/modernization/build-inventory.md
+++ b/docs/modernization/build-inventory.md
@@ -144,7 +144,9 @@ Known local toolchain state:
   covered by `pano_cli_save_project_roundtrip_smoke` and
   `pano_cli_save_project_payload_roundtrip_smoke`, which reload generated
   metadata-only and targeted dirty-face-payload projects through
-  `pano_cli load-project`.
+  `pano_cli load-project`, plus
+  `pano_cli_save_project_rejects_non_finite_opacity`, which verifies rejected
+  automation floats do not create output files.
 - `pano_cli create-document` supports `--frames` and `--frame-duration-ms` and
   is covered by `pano_cli_create_animation_document_smoke`.
 - `pano_cli simulate-document-edits` exercises pure document layer/frame edit
diff --git a/docs/modernization/roadmap.md b/docs/modernization/roadmap.md
index 43cd782..32e7aa5 100644
--- a/docs/modernization/roadmap.md
+++ b/docs/modernization/roadmap.md
@@ -354,7 +354,8 @@ payloads are present.
 visibility, opacity, blend mode, alpha lock, per-layer frame durations, and
 dirty-face payloads targeted to layer/frame/face slots. `pano_cli save-project`
 exposes the generated writer for metadata-only and test dirty-face-payload
-round-trips through `load-project`.
+round-trips through `load-project` and rejects non-finite automation float
+inputs before writing files.
 `pp_document::export_ppi_project_document` converts pure documents into PPI
 bytes using that writer, including PNG-encoded layer/frame face payloads.
 `pano_cli simulate-document-export` exercises that pure document export path,
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 4ca4529..f4bd9d4 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -329,6 +329,15 @@ if(TARGET pano_cli)
     set_tests_properties(pano_cli_save_project_payload_roundtrip_smoke PROPERTIES
         LABELS "assets;document;integration;desktop-fast")
 
+    add_test(NAME pano_cli_save_project_rejects_non_finite_opacity
+        COMMAND "${CMAKE_COMMAND}"
+            -DPANO_CLI=$<TARGET_FILE:pano_cli>
+            -DOUTPUT_PATH=${CMAKE_CURRENT_BINARY_DIR}/data/generated/rejected-non-finite-opacity.ppi
+            "-DEXPECTED_OUTPUT=floating-point value must be finite"
+            -P "${CMAKE_CURRENT_SOURCE_DIR}/cmake/expect_pano_cli_save_project_failure.cmake")
+    set_tests_properties(pano_cli_save_project_rejects_non_finite_opacity PROPERTIES
+        LABELS "assets;document;integration;desktop-fast;fuzz")
+
     add_test(NAME pano_cli_save_document_project_roundtrip_smoke
         COMMAND "${CMAKE_COMMAND}"
             -DPANO_CLI=$<TARGET_FILE:pano_cli>
diff --git a/tests/cmake/expect_pano_cli_save_project_failure.cmake b/tests/cmake/expect_pano_cli_save_project_failure.cmake
new file mode 100644
index 0000000..2443d76
--- /dev/null
+++ b/tests/cmake/expect_pano_cli_save_project_failure.cmake
@@ -0,0 +1,36 @@
+if(NOT DEFINED PANO_CLI)
+    message(FATAL_ERROR "PANO_CLI is required")
+endif()
+
+if(NOT DEFINED OUTPUT_PATH)
+    message(FATAL_ERROR "OUTPUT_PATH is required")
+endif()
+
+if(NOT DEFINED EXPECTED_OUTPUT)
+    message(FATAL_ERROR "EXPECTED_OUTPUT is required")
+endif()
+
+file(REMOVE "${OUTPUT_PATH}")
+
+execute_process(
+    COMMAND "${PANO_CLI}" save-project
+        --path "${OUTPUT_PATH}"
+        --width 64
+        --height 32
+        --layer-opacity nan
+    RESULT_VARIABLE save_result
+    OUTPUT_VARIABLE save_output
+    ERROR_VARIABLE save_error)
+
+if(save_result EQUAL 0)
+    message(FATAL_ERROR "save-project unexpectedly succeeded: ${save_output}${save_error}")
+endif()
+
+string(FIND "${save_output}${save_error}" "${EXPECTED_OUTPUT}" expected_index)
+if(expected_index EQUAL -1)
+    message(FATAL_ERROR "save-project failure did not contain expected output: ${save_output}${save_error}")
+endif()
+
+if(EXISTS "${OUTPUT_PATH}")
+    message(FATAL_ERROR "save-project created output despite rejected inputs: ${OUTPUT_PATH}")
+endif()
diff --git a/tools/pano_cli/main.cpp b/tools/pano_cli/main.cpp
index 5b946b0..e9878a1 100644
--- a/tools/pano_cli/main.cpp
+++ b/tools/pano_cli/main.cpp
@@ -220,6 +220,11 @@ pp::foundation::Result<float> parse_float_arg(std::string_view text)
             pp::foundation::Status::invalid_argument("invalid floating-point value"));
     }
 
+    if (!std::isfinite(value)) {
+        return pp::foundation::Result<float>::failure(
+            pp::foundation::Status::invalid_argument("floating-point value must be finite"));
+    }
+
     return pp::foundation::Result<float>::success(value);
 }