# Build reuse and delivery contract

## Input fingerprint

Fingerprint every item that can change generated boot behavior:

- selected board profile file;
- HDF/XSA and optional bitstream;
- project config, rootfs config, kernel config fragments, device-tree overlays, U-Boot overlays/BIF, recipes and custom files;
- PetaLinux, Vivado and SDK versions;
- BOOT.BIN composition;
- QSPI geometry/layout and boot parameters that are not machine-local.

Do not fingerprint credentials, transient logs, IP addresses discovered only for deployment, or build timestamps. Store the generated file as `build_inputs.json` in the delivery.

Example:

```powershell
python <skill>\scripts\qspi_cache.py capture `
  --board-profile <skill>\references\hjx9009-profile.json `
  --input HDF=<path-to-system.hdf> `
  --input SYSTEM_USER_DTSI=<path-to-system-user.dtsi> `
  --input ROOTFS_CONFIG=<path-to-rootfs-config> `
  --value PETALINUX_VERSION=2018.1 `
  --value VIVADO_VERSION=2018.1 `
  --value BOOT_COMPOSITION=FSBL+U-Boot `
  --output <work>\build_inputs.json
```

After building, copy that exact `build_inputs.json` into the delivery and generate `SHA256SUMS` for the delivery artifacts. Do not include `SHA256SUMS` itself in that file.

## Reuse check

```powershell
python <skill>\scripts\qspi_cache.py check `
  --current <work>\build_inputs.json `
  --delivery <delivery-directory>
```

Exit 0 and `reusable: true` allow skipping G1-G3. Any other result requires rebuild or repair. Reuse never skips target-board programming/readback/cold-boot gates.

## Required delivery files

- `BOOT.BIN`
- `image.ub.qspi`
- `flash_layout.json`
- `summary.json`
- `build_inputs.json`
- `SHA256SUMS`
- human-readable manifest containing versions, composition, hashes, layout, bootcmd, gate states, known limitations and evidence paths

`flash_layout.json` must describe total/erase/page bytes, non-overlapping partitions, and the image file, offset, byte count, erase length and RAM load address. Image size must fit the named partition; offsets and erase lengths must align to the actual erase size.