refactor(console-io): make ensure_valid_utf8 a no-op, drop iconv shim

Rust's &str is always valid UTF-8, so the mbstring/iconv sanitization
chain can never trigger. Reduce it to a no-op with a TODO(phase-c)
marker: once the codebase strictly separates Vec<u8> from String, this
should take &[u8] and convert lossily. This removes the last caller of
the php-shim iconv(), so delete it as well.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2 files changed, 5 insertions, 42 deletions

diff --git a/crates/shirabe-php-shim/src/string.rs b/crates/shirabe-php-shim/src/string.rs
index 28acb3bb..e0c84836 100644
--- a/crates/shirabe-php-shim/src/string.rs
+++ b/crates/shirabe-php-shim/src/string.rs
@@ -421,24 +421,6 @@ pub fn mb_convert_variables(_to: &str, _from: &str, _vars: &mut Vec<String>) ->
     Some(_from.to_string())
 }
 
-pub fn iconv(_in_charset: &str, _out_charset: &str, _string: &str) -> Option<String> {
-    let from = canonical_encoding(_in_charset);
-    // The output charset may carry a "//TRANSLIT" / "//IGNORE" suffix.
-    let to_base = _out_charset.split("//").next().unwrap_or(_out_charset);
-    let to = canonical_encoding(to_base);
-    // ASCII is a subset of UTF-8, so any conversion among ASCII/UTF-8 that targets UTF-8 is a
-    // byte-level no-op.
-    if to == "UTF-8" && matches!(from.as_str(), "UTF-8" | "ASCII") {
-        return Some(_string.to_string());
-    }
-    if to == "ASCII" && from == "ASCII" {
-        return Some(_string.to_string());
-    }
-    // TODO(phase-d): general iconv conversion needs encoding tables and //TRANSLIT///IGNORE handling
-    // for non-UTF-8 targets, which have not been ported yet.
-    todo!("iconv {} -> {}", from, to)
-}
-
 /// Resolve PHP array_slice/substr-style (offset, length) into a `[start, end)`
 /// pair of indices, honouring negative offsets and lengths.
 fn php_slice_bounds(len: i64, offset: i64, length: Option<i64>) -> (usize, usize) {
diff --git a/crates/shirabe/src/io/console_io.rs b/crates/shirabe/src/io/console_io.rs
index de6fdede..cf488855 100644
--- a/crates/shirabe/src/io/console_io.rs
+++ b/crates/shirabe/src/io/console_io.rs
@@ -7,7 +7,6 @@ use crate::io::IOInterfaceImmutable;
 use crate::io::IOInterfaceMutable;
 use crate::io::io_interface;
 use crate::question::StrictConfirmationQuestion;
-use crate::util::Silencer;
 use indexmap::IndexMap;
 use indexmap::indexmap;
 use shirabe_external_packages::composer::pcre::Preg;
@@ -25,8 +24,8 @@ use shirabe_external_packages::symfony::console::question::ChoiceQuestion;
 use shirabe_external_packages::symfony::console::question::Question;
 use shirabe_external_packages::symfony::console::question::QuestionInterface;
 use shirabe_php_shim::{
-    PhpMixed, array_search, function_exists, implode, in_array, is_array, is_string,
-    mb_check_encoding, mb_convert_encoding, microtime, str_repeat, strip_tags, strlen,
+    PhpMixed, array_search, implode, in_array, is_array, is_string, microtime, str_repeat,
+    strip_tags, strlen,
 };
 
 /// The Input/Output helper.
@@ -313,28 +312,10 @@ impl ConsoleIO {
     }
 
     /// Ensures a string is valid UTF-8, replacing invalid byte sequences with '?'
+    // TODO(phase-c): PHP sanitizes invalid byte sequences here, but `&str` is always valid UTF-8
+    // so this is a no-op for now. The codebase does not yet strictly distinguish `Vec<u8>` from
+    // `String`; once it does, this should take `&[u8]` and lossily convert it to `String`.
     fn ensure_valid_utf8(string: &str) -> String {
-        // Quick check: if string is already valid UTF-8, return as-is
-        if function_exists("mb_check_encoding") && mb_check_encoding(string, "UTF-8") {
-            return string.to_string();
-        }
-
-        // Use mb_convert_encoding to replace invalid sequences with '?'
-        // This makes it visible when data quality issues occur
-        if function_exists("mb_convert_encoding") {
-            return mb_convert_encoding(string.as_bytes().to_vec(), "UTF-8", "UTF-8");
-        }
-
-        // Fallback to iconv if mbstring unavailable
-        if function_exists("iconv") {
-            let cleaned =
-                Silencer::call(|| Ok(shirabe_php_shim::iconv("UTF-8", "UTF-8//TRANSLIT", string)));
-            if let Ok(Some(c)) = cleaned {
-                return c;
-            }
-        }
-
-        // Last resort: return as-is (should never happen - Composer requires mbstring OR iconv)
         string.to_string()
     }