feat(phase-c): resolve PhpMixed-conversion phase-b TODOs

Implement the foundational PhpMixed conversion infrastructure
(From<bool|i64|f64|String>, order-sensitive PartialEq matching PHP ===)
and resolve the category-G phase-b TODOs that depend on it:

- Fix VCS driver cache paths that discarded parsed JSON or diverged on
  null caches (svn/forgejo/gitlab/git-bitbucket/github).
- Wire up real conversions previously stubbed or dropped: suggests
  platform config, audit ignore-severities, composer_repository search
  and ProviderInfo, class_loader prefix/classmap merges, locker lock
  diff comparison, advisory JSON serialization, SPDX license fields.
- Make GenericRule take a typed ReasonData; populate RULE_ROOT_REQUIRE
  with the constraint and convert PhpMixed at the call sites.

1 files changed, 5 insertions, 4 deletions

diff --git a/crates/shirabe/src/command/suggests_command.rs b/crates/shirabe/src/command/suggests_command.rs
index 5c021b2..b93f7ec 100644
--- a/crates/shirabe/src/command/suggests_command.rs
+++ b/crates/shirabe/src/command/suggests_command.rs
@@ -75,10 +75,11 @@ impl SuggestsCommand {
             )?;
             installed_repos.push(locked_repo.into());
         } else {
-            // TODO(phase-b): Config::get returns PhpMixed; need to coerce to IndexMap<String, PhpMixed>
-            let _platform_cfg = composer.get_config().borrow().get("platform");
-            let platform_overrides: IndexMap<String, PhpMixed> =
-                todo!("extract IndexMap<String, PhpMixed> from PhpMixed config value");
+            let platform_cfg = composer.get_config().borrow().get("platform");
+            let platform_overrides: IndexMap<String, PhpMixed> = platform_cfg
+                .as_array()
+                .map(|m| m.iter().map(|(k, v)| (k.clone(), (**v).clone())).collect())
+                .unwrap_or_default();
             installed_repos.push(RepositoryInterfaceHandle::new(PlatformRepository::new(
                 vec![],
                 platform_overrides,