Preserve double-digit command placeholders

Command templates replace numbered placeholders with literal string replacement. Replacing in ascending order lets short placeholders such as $1 consume the prefix of $10 before the intended replacement runs, so templates with double-digit placeholders produce corrupted output.

Constraint: Keep existing last-placeholder-captures-rest behavior unchanged

Rejected: Regex replacement rewrite | larger change than needed for the prefix-collision bug

Confidence: high

Scope-risk: narrow

Directive: Preserve descending replacement unless the placeholder parser is replaced with token-aware substitution

Tested: Docker rust:latest cargo test -p cortex-commands test_substitute_two_digit_placeholders_before_prefixes -- --nocapture

Tested: Docker rust:latest cargo test -p cortex-commands substitute -- --nocapture

Tested: Docker rust:latest cargo check -p cortex-commands

Tested: Docker rust:latest cargo fmt --check --package cortex-commands

Tested: git diff --check

Author: dalbee

src/cortex-commands/src/command.rs

@@ -209,8 +209,8 @@ pub fn substitute_placeholders(template: &str, arguments: &str) -> String {
     // Find the highest numbered placeholder
     let max_placeholder = find_max_placeholder(&result);
 
-    // Replace numbered placeholders
-    for i in 1..=max_placeholder {
+    // Replace longer placeholders first so `$1` does not corrupt `$10`.
+    for i in (1..=max_placeholder).rev() {
         let placeholder = format!("${i}");
         let replacement = if i == max_placeholder {
             // Last placeholder captures all remaining arguments
@@ -374,6 +374,17 @@ No closing delimiter"#;
         assert_eq!(result, "A: only_one, B: , C: ");
     }
 
+    #[test]
+    fn test_substitute_two_digit_placeholders_before_prefixes() {
+        let template = "Run $1 and item $10";
+        let result = substitute_placeholders(
+            template,
+            "alpha beta gamma delta epsilon zeta eta theta iota kappa",
+        );
+
+        assert_eq!(result, "Run alpha and item kappa");
+    }
+
     #[test]
     fn test_command_parse() {
         let content = r#"---