feat: add extern "C" guards to public headers

[grzanka]

What

Wraps the five installed public headers in extern "C" linkage guards:

• include/dedx.h
• include/dedx_elements.h
• include/dedx_error.h
• include/dedx_tools.h
• include/dedx_wrappers.h

Each now has, after its include-guard #define (and after any #includes):

#ifdef __cplusplus
extern "C" {
#endif

and the matching close before the final #endif.

Why

These headers are installed and exported via the CMake package, so they form the public API. Without extern "C", a C++ consumer that #includes them gets C++-mangled declarations and link errors against the C-compiled library — they have to wrap the include in their own extern "C" block. Adding the guards makes the headers directly usable from C++ with no consumer-side workaround. For C compilers the blocks are #ifdef __cplusplus-gated, so nothing changes.

This addresses item #2 from the header-hygiene review discussion in #127.

Scope decision

Applied uniformly to all five installed headers, including dedx_elements.h and dedx_error.h which currently contain only macros/enums (nothing that mangles, so the guard is a no-op there today). The reasoning: a consistent pattern across the public surface, and any function declaration added to those headers later is covered automatically. Happy to drop the guards from the two macro-only headers if reviewers would rather keep them strictly where they're needed.

Verification

• g++ -std=c++17 -Iinclude -fsyntax-only on a TU including dedx.h + dedx_tools.h + dedx_wrappers.h → passes (previously this is the scenario that would mangle).
• gcc -std=c11 -Iinclude -fsyntax-only on the same headers → passes (no regression for C).
• Pure documentation/guard change — no functional code touched.

https://claude.ai/code/session_01Wt7wjjWawFBS5uhRtkCYXm

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.73%. Comparing base (36990c2) to head (ef43ab5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   72.73%   72.73%           
=======================================
  Files          12       12           
  Lines        1643     1643           
  Branches      300      300           
=======================================
  Hits         1195     1195           
  Misses        448      448           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

This PR improves C++ interoperability for libdedx’s public C API by adding extern "C" linkage guards to all installed headers, ensuring declarations are not C++-mangled when consumed from C++.

Changes:

• Added #ifdef __cplusplus extern "C" { ... } #endif wrappers to include/dedx.h.
• Added the same C++ linkage guards to the remaining installed public headers (dedx_elements.h, dedx_error.h, dedx_tools.h, dedx_wrappers.h) for uniformity and future-proofing.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
include/dedx.h	Wraps public API declarations in extern "C" for C++ consumers.
include/dedx_elements.h	Adds extern "C" guard (no-op today, keeps public surface consistent).
include/dedx_error.h	Adds extern "C" guard (no-op today, keeps public surface consistent).
include/dedx_tools.h	Wraps tool function declarations in extern "C" for C++ consumers.
include/dedx_wrappers.h	Wraps wrapper function declarations in extern "C" for C++ consumers.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.