fix(observer): exclude synthetic user-role messages from turn detection

Root cause (systematic-debugging): isRealUserPrompt treated skill-content
("Base directory for this skill:"), local-command output
(<local-command-stdout>), and interrupt markers as genuine prompts.
findTurnStart then anchored a turn on the synthetic message — the turn
slice missed the genuine prompt's UserPromptSubmit hook_additional_context
attachment → economy_level: null, wrong prompt_signal/task_classification.
Same cause made extractLastUserPromptText return skill content, so the
Stop-hook routing-gate false-positive-blocked autonomous §12 skill
invocations (detectMethodDirected saw the node name in skill text).

Fix: SYNTHETIC_PROMPT_MARKERS + isSyntheticPrompt — isRealUserPrompt
returns false for synthetic messages. One fix closes both the
economy_level capture gap and the 2nd routing-gate FP class.

160/160 tools tests GREEN (+3 new).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/observer-transcript-parser.mjs

@@ -36,16 +36,40 @@ function parseLines(text) {
   return { entries, broken, total };
 }
 
-// A genuine user prompt (turn boundary) — not a tool_result carrier message.
+// Synthetic user-role messages — NOT genuine prompts, must not be turn boundaries.
+// Skill invocation content, local slash-command output/invocation, interrupt markers
+// are recorded with role:'user' but carry no UserPromptSubmit hook context.
+const SYNTHETIC_PROMPT_MARKERS = [
+  'Base directory for this skill:',
+  '<local-command-stdout>',
+  '<local-command-caveat>',
+  '<command-name>',
+  '[Request interrupted by user]',
+];
+
+function isSyntheticPrompt(text) {
+  const t = String(text || '').trimStart();
+  return SYNTHETIC_PROMPT_MARKERS.some((m) => t.startsWith(m));
+}
+
+// A genuine user prompt (turn boundary) — not a tool_result carrier nor a
+// synthetic skill/command/interrupt message.
 function isRealUserPrompt(entry) {
   const msg = entry && entry.message;
   if (!msg || msg.role !== 'user') return false;
   const c = msg.content;
-  if (typeof c === 'string') return c.trim().length > 0;
+  if (typeof c === 'string') {
+    return c.trim().length > 0 && !isSyntheticPrompt(c);
+  }
   if (Array.isArray(c)) {
     const hasToolResult = c.some((b) => b && b.type === 'tool_result');
     const hasText = c.some((b) => b && b.type === 'text');
-    return hasText && !hasToolResult;
+    if (!hasText || hasToolResult) return false;
+    const text = c
+      .filter((b) => b && b.type === 'text')
+      .map((b) => b.text || '')
+      .join(' ');
+    return !isSyntheticPrompt(text);
   }
   return false;
 }