fix(codex): de-duplicate session-start context and surface one-line summary

Codex's TUI flattens newlines when it surfaces SessionStart hook output and
already echoes additionalContext back as its own "hook context" block. Emitting
the full timeline again through systemMessage (shown as a "warning:" block)
duplicated the wall of text into an unreadable single line.

For the Codex platform, replace the full-timeline systemMessage with a compact
one-line summary (obs/work/savings + live URL) that stays legible after Codex
flattens it. The model still receives the full, properly formatted
additionalContext, and the claude-code/gemini colored multi-line paths are
unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Glucksberg

src/cli/handlers/context.ts

@@ -60,22 +60,40 @@ export const contextHandler: EventHandler = {
         : hint;
     }
 
-    let coloredTimeline = '';
+    const platform = input.platform;
+    const isCodex = platform === 'codex';
+
+    let systemMessage: string | undefined;
     if (showTerminalOutput) {
-      const colorResult = await executeWithWorkerFallback<string>(colorApiPath, 'GET');
-      if (!isWorkerFallback(colorResult) && typeof colorResult === 'string') {
-        coloredTimeline = colorResult.trim();
+      if (isCodex) {
+        // Codex's TUI flattens newlines when it surfaces hook output AND already
+        // echoes additionalContext back as its own "hook context" block. Re-sending
+        // the full timeline through systemMessage just duplicates that wall of text
+        // (shown as a "warning:" block) into an unreadable single line. Surface a
+        // compact one-line summary that stays legible even after Codex flattens it;
+        // the model still receives the full, properly formatted additionalContext.
+        if (additionalContext) {
+          const statsLine = additionalContext.match(/^Stats:\s*(.+)$/m)?.[1]?.trim();
+          const summary = statsLine
+            ? `📋 claude-mem: ${statsLine}`
+            : '📋 claude-mem: recent context loaded';
+          systemMessage = `${summary} · http://localhost:${port}`;
+        }
+      } else {
+        const colorResult = await executeWithWorkerFallback<string>(colorApiPath, 'GET');
+        const coloredTimeline =
+          !isWorkerFallback(colorResult) && typeof colorResult === 'string'
+            ? colorResult.trim()
+            : '';
+        const displayContent =
+          coloredTimeline ||
+          (platform === 'gemini-cli' || platform === 'gemini' ? additionalContext : '');
+        systemMessage = displayContent
+          ? `${displayContent}\n\nView Observations Live @ http://localhost:${port}`
+          : undefined;
       }
     }
 
-    const platform = input.platform;
-
-    const displayContent = coloredTimeline || (platform === 'gemini-cli' || platform === 'gemini' ? additionalContext : '');
-
-    const systemMessage = showTerminalOutput && displayContent
-      ? `${displayContent}\n\nView Observations Live @ http://localhost:${port}`
-      : undefined;
-
     return {
       hookSpecificOutput: {
         hookEventName: 'SessionStart',