Fix SPM consumer build: qualify cross-directory header imports (#215)

[kostub]

Fixes #215.

Problem

Adding iosMath as a Swift Package Manager dependency fails to build:

fatal error: 'MTMathList.h' file not found
... could not build module 'iosMath'

The bundled demo and swift build/swift test all work, so the bug only hits downstream consumers.

Root cause

Public headers in render/ imported sibling headers from lib/ by bare filename:

// render/MTMathUILabel.h
#import "MTMathList.h"   // actually lives in lib/

That basename only resolves via the lib header search path in cSettings, which is target-internal — applied when SPM compiles iosMath's own sources, but not when a downstream consumer builds the iosMath Clang module from module.modulemap. The consumer's module build only has the public-headers root on its include path, so the cross-directory include fails. (Xcode 16's explicit-modules dependency scanning surfaces it as the error above.)

Fix

• Qualify the render -> lib imports as lib/MTMathList.h so they resolve from the package's public-headers root, which is exposed to consumers.
• Add that root to each target's header search paths so internal builds keep resolving the qualified path.

Regression test

New iosMathConsumerTests target imports iosMath purely as a Clang module with no header search paths, reproducing exactly how an external SPM consumer builds it. The existing test targets can't catch this — their cSettings carry the internal lib/render paths, which leak into the implicit module build and mask the bug.

Verified RED/GREEN: reverting one header to the bare import makes the new target fail with the exact #215 error; with the fix it passes. Full suite: 267 tests, 0 failures.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request resolves issue #215 by fixing cross-directory header imports. Specifically, it updates several public headers in the render/ directory to import MTMathList.h using the relative path lib/MTMathList.h instead of a bare filename. Additionally, it updates Package.swift to include appropriate header search paths and introduces a new regression test target, iosMathConsumerTests, to ensure external consumers can build the module without internal search paths. There are no review comments, and I have no feedback to provide.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.