diff --git a/tools/observer-transcript-parser.mjs b/tools/observer-transcript-parser.mjs
index b4f4d875..6b03b08d 100644
--- a/tools/observer-transcript-parser.mjs
+++ b/tools/observer-transcript-parser.mjs
@@ -23,15 +23,29 @@ function parseLines(text) {
   const entries = [];
   let broken = 0;
   let total = 0;
+  // quirk #101 root fix: Claude Code's transcript file accumulates duplicated
+  // context-rebuild snapshots — the same entry is re-printed with the SAME
+  // `uuid`. Without dedup, session_turn / task_size / events double-count and
+  // session_turn becomes non-monotonic across episodes parsed at different
+  // file-growth states. Keep the first occurrence per uuid; entries without a
+  // uuid (synthetic test fixtures) pass through unchanged.
+  const seenUuid = new Set();
   for (const line of String(text || '').split('\n')) {
     const trimmed = line.trim();
     if (!trimmed) continue;
     total += 1;
+    let e;
     try {
-      entries.push(JSON.parse(trimmed));
+      e = JSON.parse(trimmed);
     } catch {
       broken += 1; // broken line — counted for parse_gap, never thrown
+      continue;
     }
+    if (e && e.uuid) {
+      if (seenUuid.has(e.uuid)) continue;
+      seenUuid.add(e.uuid);
+    }
+    entries.push(e);
   }
   return { entries, broken, total };
 }
diff --git a/tools/observer-transcript-parser.test.mjs b/tools/observer-transcript-parser.test.mjs
index 05097223..ccd0cfaa 100644
--- a/tools/observer-transcript-parser.test.mjs
+++ b/tools/observer-transcript-parser.test.mjs
@@ -670,6 +670,108 @@ describe('parseTranscript — AskUserQuestion in-turn choice', () => {
   });
 });
 
+describe('parseTranscript — uuid-dedup for duplicated snapshots (quirk #101)', () => {
+  // Claude Code's transcript file accumulates duplicated context-rebuild
+  // snapshots; the same entry is re-printed with the SAME `uuid`. Without
+  // dedup, session_turn / task_size / events double-count and become
+  // non-monotonic across episodes parsed at different file-growth states.
+  // Root fix: dedup by uuid in parseLines.
+
+  it('collapses duplicated-uuid user prompts (session_turn counts once)', () => {
+    const dup = 'aaaa-bbbb-cccc';
+    const lines = [
+      JSON.stringify({
+        uuid: dup,
+        type: 'user',
+        message: { role: 'user', content: 'hi' },
+        timestamp: '2026-05-19T10:00:00Z',
+        sessionId: 's1',
+      }),
+      JSON.stringify({
+        uuid: dup,
+        type: 'user',
+        message: { role: 'user', content: 'hi' },
+        timestamp: '2026-05-19T10:00:00Z',
+        sessionId: 's1',
+      }),
+    ].join('\n');
+    const ep = parseTranscript(lines, 'fallback');
+    expect(ep.environment.session_turn).toBe(1);
+  });
+
+  it('preserves distinct-uuid entries (no over-dedup)', () => {
+    const lines = [
+      JSON.stringify({
+        uuid: 'one',
+        type: 'user',
+        message: { role: 'user', content: 'first' },
+        timestamp: '2026-05-19T09:00:00Z',
+        sessionId: 's1',
+      }),
+      JSON.stringify({
+        uuid: 'two',
+        type: 'user',
+        message: { role: 'user', content: 'second' },
+        timestamp: '2026-05-19T10:00:00Z',
+        sessionId: 's1',
+      }),
+    ].join('\n');
+    const ep = parseTranscript(lines, 'fallback');
+    expect(ep.environment.session_turn).toBe(2);
+  });
+
+  it('entries without uuid pass through unchanged (synthetic fixtures unaffected)', () => {
+    // Existing tests build entries without `uuid` — must still work.
+    const t = jsonl([
+      userPrompt('one', '2026-05-19T09:00:00Z'),
+      userPrompt('two', '2026-05-19T10:00:00Z'),
+    ]);
+    expect(parseTranscript(t).environment.session_turn).toBe(2);
+  });
+
+  it('collapses duplicated-uuid assistant turns (task_size counted once)', () => {
+    const lines = [
+      JSON.stringify({
+        uuid: 'u-prompt',
+        type: 'user',
+        message: { role: 'user', content: 'go' },
+        timestamp: '2026-05-19T10:00:00Z',
+        sessionId: 's1',
+      }),
+      JSON.stringify({
+        uuid: 'u-asst',
+        type: 'assistant',
+        message: {
+          role: 'assistant',
+          content: [
+            { type: 'tool_use', id: 't1', name: 'Read', input: { file_path: '/x.js' } },
+            { type: 'tool_use', id: 't2', name: 'Edit', input: { file_path: '/x.js' } },
+          ],
+        },
+        timestamp: '2026-05-19T10:01:00Z',
+        sessionId: 's1',
+      }),
+      // EXACT duplicate of the assistant entry — snapshot rebuild artifact
+      JSON.stringify({
+        uuid: 'u-asst',
+        type: 'assistant',
+        message: {
+          role: 'assistant',
+          content: [
+            { type: 'tool_use', id: 't1', name: 'Read', input: { file_path: '/x.js' } },
+            { type: 'tool_use', id: 't2', name: 'Edit', input: { file_path: '/x.js' } },
+          ],
+        },
+        timestamp: '2026-05-19T10:01:00Z',
+        sessionId: 's1',
+      }),
+    ].join('\n');
+    const ep = parseTranscript(lines, 'fallback');
+    expect(ep.task_size.tool_calls).toBe(2);
+    expect(ep.task_size.files_touched).toBe(1);
+  });
+});
+
 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