fix: grepFile global regex lastIndex bug, add 12 tests

Fix grepFile() silently skipping matches when called with /g flag regex.
The global flag makes .test() stateful, causing alternating match/miss
on consecutive matching lines. Strip g flag since per-line testing
doesn't need global state.

Add first-ever tests for evaluate-session.js (5 tests: short session,
long session, missing transcript, malformed stdin, env var fallback)
and suggest-compact.js (5 tests: counter increment, threshold trigger,
periodic suggestions, below-threshold silence, invalid threshold).

scripts/lib/utils.js

@@ -454,7 +454,15 @@ function grepFile(filePath, pattern) {
 
   let regex;
   try {
-    regex = pattern instanceof RegExp ? pattern : new RegExp(pattern);
+    if (pattern instanceof RegExp) {
+      // Always create a new RegExp without the 'g' flag to prevent lastIndex
+      // state issues when using .test() in a loop (g flag makes .test() stateful,
+      // causing alternating match/miss on consecutive matching lines)
+      const flags = pattern.flags.replace('g', '');
+      regex = new RegExp(pattern.source, flags);
+    } else {
+      regex = new RegExp(pattern);
+    }
   } catch {
     return []; // Invalid regex pattern
   }