Describe algorithms and key logic instead of pasting source code

The implementation chapter is not a printout of your repository. FAST's handbook puts it plainly: implementation details mean "not the programming code but the algorithmic and procedural details", especially the backend logic not covered in the design.

Good content for this chapter:

• The core algorithms, in pseudocode or a short, commented snippet.
• How components connect: APIs, message flows, authentication.
• Data processing steps, such as cleaning, feature extraction or training settings.
• Tricky problems you solved and how, such as sync conflicts or performance issues.
• Tools, libraries and versions used, with credit to open source projects.

Put long listings, configuration files and full API references in an appendix or point to the repository. A page of well-explained pseudocode teaches the reader more than twenty pages of source.