Section-level preset composition: replace one ## section of a template

[alfredoperez]

The presets README lists "structural merge strategies" as a future consideration ("replace only ## Security"). SpecKit Companion has been doing this in its own renderer, and the rules that worked for us might be a useful starting point:

• Address a section by its heading text.
• Keep the heading line; replace the body up to the next heading of the same or higher level.
• Refuse (don't append) when the heading isn't in the base template, so a renamed section fails loudly.

Example: a preset that replaces only ## User Scenarios & Testing in spec-template.md, leaving every other section stock. Our implementation and tests: apps/speckit-extension/scripts/template_render.py in alfredoperez/speckit-companion.

Would a strategy like replace_section: "<heading>" fit the preset model? If so, I can write it up as a feature request with the rules above.

AI disclosure: drafted with Claude Code (Claude Opus 5.5, default settings); I checked it before posting.

[markuswondrak]

I actually liked that idea. I also encountered some cases where I would like to replace only one chapter.

The problem is that targeting a chapter based solely on its heading could be somewhat ambiguous, I guess.

[mnriem]

I would love to understand what those cases where because that would make it more real to me to see if this change is warranted

[alfredoperez]

Here are the cases from SpecKit Companion where a project wanted one section changed and everything else stock:

1. Spec: replace ## User Scenarios & Testing with observable outcomes (no P1/P2/P3 stories) for small changes, or with EARS-style numbered requirements (WHEN/THEN/SHALL) so tasks can cite stable IDs.
2. Plan: a team's own ## Technical Context block, with their stack's fields, and nothing else changed.
3. Tasks: replace ## Notes to rule out tasks an agent can't do (UAT, deploy, comms), or the format section so every task says how to verify itself.

Today each of these means copying the whole template, and the copy stops picking up upstream changes to every other section.

On @markuswondrak's ambiguity point: our version matches the exact heading text and fails when no heading matches. If two headings match, it takes the first one. For spec-kit I'd make it stricter and refuse unless exactly one heading matches.

AI disclosure: drafted with Claude Code (Claude Opus 5.5); I checked it before posting.

[mnriem]

Feel free to spec it out a bit more and then file a feature request