feat(php-src): add a BSD-licensed crate for php-src derived code

The audit in .ken/php-shim-copying.md judged 14 functions in
shirabe-php-shim (plus php_wordwrap in shirabe-external-packages) to be
line-by-line transcriptions or structural imitations of php-src. PHP's
relicensing to 3-clause BSD makes keeping them legal, but the boundary
between BSD-derived and MIT code was invisible in the source tree.

Moving them into their own crate puts the license into the build
metadata (so NOTICE generation follows the binary), makes a reverse
dependency a compile error, and encodes the origin in the module path,
which mirrors php-src's ext tree. Each function records its origin in a
fixed-format doc comment, and a new php_src_derivation_boundary linter
fails if `php-src` appears in any Rust source outside the crate.

Public paths under shirabe_php_shim:: are unchanged: functions that are
themselves derived are re-exported with `pub use`, and the wrappers that
only validate arguments stay on the MIT side.

This also resolves the duplicate wordwrap implementation.
shirabe_php_shim::wordwrap was todo!(), so SymfonyStyle::block panicked,
while shirabe-external-packages carried its own copy. Both now go
through the single port, verified against real PHP on 13 cases covering
multi-character breaks and cut.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/crates/shirabe-php-src/src/lib.rs b/crates/shirabe-php-src/src/lib.rs
new file mode 100644
index 00000000..1e2c2a0f
--- /dev/null
+++ b/crates/shirabe-php-src/src/lib.rs
@@ -0,0 +1,19 @@
+//! Rust port from the original C implementation in php-src.
+//! See `LICENSE.md` at the repository root.
+//!
+//! Rules for this crate:
+//!
+//! * Any code written while looking at php-src belongs here, and nowhere else. `shirabe-php-shim`
+//!   must not contain php-src derived code; it depends on this crate instead.
+//! * The dependency direction is `shirabe-php-shim` -> `shirabe-php-src` only. This crate must not
+//!   depend on any other crate in the workspace, so that BSD-derived code cannot pull in
+//!   MIT-licensed types.
+//! * The module layout mirrors php-src's own tree (`src/standard/string.rs` holds code derived
+//!   from `ext/standard/string.c`), so the origin of a function is visible from its path.
+//! * Every item carries a fixed-format origin comment:
+//!
+//!   ```text
+//!   /// php-src: ext/standard/strnatcmp.c `strnatcmp_ex` (PHP 8.5.2)
+//!   ```
+
+pub mod standard;