fix(observer): narrow parallel_session detector to tool_result evidence (C-2)

extractEnvironment was scanning JSON.stringify(turn) for collision markers
(чужой staged / foreign git index / index.lock / another git process). Prose
mentions in user/assistant text flipped parallel_session=true. Live FP proven
on episodes-2026-05.jsonl line 20: my own analysis turn was non-parallel but
recorded parallel_session: true because the finding text mentioned the markers.

Fix: collectToolResultText(turn) — gather text only from tool_result blocks
(both string content and structured `[{type:text,text}]` arrays). Scan THAT
for collision markers; prose is no longer a signal.

Tests: rewrote `parallel_session narrowed` block — false on user/assistant
prose / no-tool-result turns; true on tool_result strings + structured form.
106/106 parser tests green.

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

tools/observer-transcript-parser.test.mjs

@@ -670,26 +670,83 @@ describe('parseTranscript — AskUserQuestion in-turn choice', () => {
   });
 });
 
-describe('extractEnvironment — parallel_session narrowed', () => {
-  const wrap = (text) => [
-    {
-      message: { role: 'user', content: text },
-      timestamp: '2026-05-19T10:00:00.000Z',
+describe('extractEnvironment — parallel_session narrowed to tool_result evidence', () => {
+  // Collision detection scans ONLY tool_result content (real command output).
+  // Prose mentions in user prompts / assistant text — including analysis text
+  // that references collision phrases — must not trigger.
+  const userMsg = (text) => ({
+    message: { role: 'user', content: text },
+    timestamp: '2026-05-19T10:00:00.000Z',
+  });
+  const assistantText = (text) => ({
+    message: { role: 'assistant', content: [{ type: 'text', text }] },
+    timestamp: '2026-05-19T10:00:01.000Z',
+  });
+  const toolResultText = (text, isError = false) => ({
+    message: {
+      role: 'user',
+      content: [{ type: 'tool_result', tool_use_id: 't1', content: text, is_error: isError }],
     },
-  ];
+    timestamp: '2026-05-19T10:00:02.000Z',
+  });
 
-  it('is false when text only casually mentions parallel sessions', () => {
-    const env = extractEnvironment(wrap('давай обсудим фичу параллельные сессии и parallel session coordination'), 0);
+  it('is false when a USER prompt only mentions a collision marker', () => {
+    const env = extractEnvironment([userMsg('в моём ходе появился чужой staged-файл — что делать?')], 0);
     expect(env.parallel_session).toBe(false);
   });
 
-  it('is true on a real collision marker (foreign git index)', () => {
-    const env = extractEnvironment(wrap('git commit поймал foreign git index'), 0);
+  it('is false when ASSISTANT prose mentions a collision marker (e.g., analysis text)', () => {
+    const env = extractEnvironment(
+      [userMsg('go'), assistantText('я писал про чужой staged и foreign git index в разборе')],
+      0
+    );
+    expect(env.parallel_session).toBe(false);
+  });
+
+  it('is true when a tool_result (Bash output) contains "foreign git index"', () => {
+    const env = extractEnvironment(
+      [
+        userMsg('go'),
+        toolResultText('fatal: another git process is running\nforeign git index detected', true),
+      ],
+      0
+    );
     expect(env.parallel_session).toBe(true);
   });
 
-  it('is true on a real collision marker (чужой staged)', () => {
-    const env = extractEnvironment(wrap('в коммит попал чужой staged-файл'), 0);
+  it('is true when a tool_result contains "чужой staged"', () => {
+    const env = extractEnvironment(
+      [userMsg('go'), toolResultText('error: чужой staged-файл присутствует в индексе')],
+      0
+    );
+    expect(env.parallel_session).toBe(true);
+  });
+
+  it('is false when there are no tool_result entries at all', () => {
+    const env = extractEnvironment([userMsg('говорим о параллельных сессиях вообще')], 0);
+    expect(env.parallel_session).toBe(false);
+  });
+
+  it('handles tool_result with content as a structured array of text blocks', () => {
+    const env = extractEnvironment(
+      [
+        userMsg('go'),
+        {
+          message: {
+            role: 'user',
+            content: [
+              {
+                type: 'tool_result',
+                tool_use_id: 't1',
+                content: [{ type: 'text', text: 'index.lock exists, another process is holding it' }],
+              },
+            ],
+          },
+          timestamp: '2026-05-19T10:00:02.000Z',
+        },
+      ],
+      0
+    );
     expect(env.parallel_session).toBe(true);
   });
 });