[simonbs]

Upgrade Runestone from Tree-sitter 0.20.9 to 0.27.1 using a pinned upstream Git submodule and a local SwiftPM C target. The gitlink records release commit 10eb5ac119eec9cb4267a8e035066473983f5f3a; the target at tree-sitter/lib compiles only src/lib.c and exposes the public API header. Upstream removed Package.swift, so Runestone owns this small build definition.

Migrate language pointers to OpaquePointer, use explicit UTF-16 byte order, and initialize the new input decoder field. Keep generated grammar headers private. Remove obsolete dependency lockfiles, initialize submodules in build/documentation CI jobs, and trigger relevant checks on gitlink changes. Document contributor setup, pinned updates, source archive limitations, and license notices.

This follows Tree-sitter's C integration guidance and Git's pinned submodule workflow. SwiftPM automatically initializes submodules for Git dependencies. Setup and CI use the recorded commit, never a moving branch or submodule update --remote.

Companion language changes have landed in simonbs/TreeSitterLanguages#32. Release those compatible declarations before adopting this Runestone release. The public TreeSitterLanguage initializer and languagePointer property change from UnsafePointer to OpaquePointer. Consumers using the C API should use Runestone's TreeSitter product to avoid linking a second runtime.

Validation:

• All 184 tests pass with the latest main integrated on Xcode 27.2 / iOS 27.2 Simulator, including Unicode byte orders and ranges, streaming, incremental edits, and HTML-to-JavaScript highlighting/injection.
• Example app builds with the submodule target. Launch/editing checks passed with the identical runtime source commit.
• Fresh remote consumers using separate SwiftPM and Xcode checkouts automatically fetched the exact pinned submodule. The C runtime executable ran successfully, and a downstream Runestone library built for both arm64 and x86_64 iOS Simulator with zero errors or warnings.
• All TreeSitterLanguages products built against the migrated API; all 38 grammars and 72 native query checks pass with this same upstream runtime commit.
• Strict SwiftLint passes for changed Swift files. GitHub's Xcode 16.2 test job passed before integrating the latest main.

The unmodified runtime emits three integer-conversion warnings under the main project's Xcode warning settings. Older iOS runtimes and the legacy Chinese/Korean UI suites were not run locally.

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