diff --git a/fs_data/README.md b/fs_data/README.md
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+# fs_data (PlatformIO data_dir)
+
+This folder is used as a minimal PlatformIO filesystem payload (`data_dir`) for builds that use `buildfs/uploadfs`.
+
+## Why it exists
+In some setups (e.g. ESP32 4MB flash with smaller FS partitions), building a filesystem image from the default `wled00/data` content can exceed the available FS size and fail with errors like:
+- `SPIFFS_write error: File system is full`
+
+To avoid that, `fs_data` contains only small config placeholders (e.g. `cfg.json`, `presets.json`) so filesystem builds remain reproducible on limited partitions.
+
+## What to put here
+- `cfg.json` (optional, can be `{}`)
+- `presets.json` (optional, can be `{}`)
+- `wsec.json` (optional) — **do not commit secrets** (WiFi credentials). Keep it empty (`{}`) or manage locally.
+
+## How it is used
+Typically enabled via `platformio_override.ini`, e.g.:
+- `data_dir = ${PROJECT_DIR}/fs_data`
+
+This keeps upstream files untouched while allowing local/CI builds to succeed.
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diff --git a/fs_data/cfg.json b/fs_data/cfg.json
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+{}
diff --git a/fs_data/presets.json b/fs_data/presets.json
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+++ b/fs_data/presets.json
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+{}
diff --git a/fs_data/wsec.json b/fs_data/wsec.json
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+++ b/fs_data/wsec.json
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+{}
diff --git a/platformio_override.ini.olaf.example b/platformio_override.ini.olaf.example
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+; copy to platformio_override.ini (local override, ignored by git)
+
+[platformio]
+default_envs = esp32_4MB_V4_M
+
+[env]
+build_flags =
+  -D WLED_RELEASE_NAME=\"WLEDMM-OLAF\"
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