feat(sdl): add backend.manifest.zon — manifest-splice codegen (#386)

[apotema]

sdl extraction step (window conformed in #437). Opts the sdl desktop build into the manifest-splice path. Loop-style, desktop-only, no params; link fragment is the single blank the enum .link_sdl emitted (SDL2 linked by the backend's own build.zig). The backend_dep fragment carries the input core-diamond override. Byte-identical to the enum path. zig build test green.

Summary by CodeRabbit

• New Features

  • Added support for an SDL-based desktop backend.
  • Desktop builds now include the necessary setup to run with the SDL backend.

• Bug Fixes

  • Improved backend wiring so the SDL backend connects correctly to core app functionality.

[gemini-code-assist]

Code Review

This pull request introduces the SDL backend manifest and build fragments as part of the pluggable-backends epic. Specifically, it adds backend.manifest.zon to configure the SDL backend, backend_dep.txt to handle SDL-specific module dependencies and override the labelle_core import, and an empty link.txt build fragment. There are no review comments, and I have no feedback to provide.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: eb545e58-e441-4681-88b9-9e5f090cf288

📥 Commits

Reviewing files that changed from the base of the PR and between e68d3c4 and bcead22.

📒 Files selected for processing (3)

• backends/sdl/backend.manifest.zon
• backends/sdl/build_fragments/backend_dep.txt
• backends/sdl/build_fragments/link.txt

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📝 Walkthrough

Walkthrough

This PR adds a new SDL backend manifest file specifying directory/dependency naming, loop style, and template references. It also adds a build dependency fragment that overrides the "labelle_core" import for the input module, and populates the previously empty link fragment file.

Changes

SDL Backend Setup

Layer / File(s)	Summary
Backend manifest definition backends/sdl/backend.manifest.zon	Defines the SDL backend manifest with directory name, dependency name, desktop loop style/template, and references to build_fragments for backend_dep and link.
Build fragments wiring backends/sdl/build_fragments/backend_dep.txt, backends/sdl/build_fragments/link.txt	Adds dependency module bindings and an overrideImport remapping the input module's "labelle_core" import to core_mod, and adds content to the previously empty link fragment.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related PRs

• labelle-toolkit/labelle-assembler#396: Similar bgfx backend dependency fragment also performs labelle_core import overriding.

Poem

A rabbit hops with manifest in paw,
Wiring SDL through a build-time law.
Core module bound, the import made true,
Link.txt now holds a line or two.
🐇✨ Hop, build, and run anew!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding SDL manifest-splice code generation via backend.manifest.zon.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/386-sdl-manifest

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