diff --git a/sdk/src/query/phase-lifecycle.test.ts b/sdk/src/query/phase-lifecycle.test.ts
index b623cf329..ab1b77c39 100644
--- a/sdk/src/query/phase-lifecycle.test.ts
+++ b/sdk/src/query/phase-lifecycle.test.ts
@@ -150,6 +150,82 @@ describe('replaceInCurrentMilestone', () => {
     expect(before).toContain('3 plans'); // old milestone untouched
     expect(after).toContain('4 plans'); // current milestone updated
   });
+
+  it('replaces only in current milestone when older milestones are wrapped in <details>', async () => {
+    const { replaceInCurrentMilestone } = await import('./phase-lifecycle.js');
+    const content = [
+      '# Roadmap',
+      '',
+      '<details>',
+      '<summary>✅ v1.18 (shipped)</summary>',
+      '',
+      '### Phase 1: Old Phase',
+      '',
+      '- [ ] Phase 1: Old Phase',
+      '',
+      '</details>',
+      '',
+      '<details>',
+      '<summary>✅ v1.19 (shipped)</summary>',
+      '',
+      '### Phase 2: Another Old Phase',
+      '',
+      '</details>',
+      '',
+      '## Current Milestone: v1.20',
+      '',
+      '- [ ] Phase 3: Current work',
+      '',
+      '### Phase 3: Current work',
+      '',
+      '**Plans:** 0/2 plans',
+      '',
+    ].join('\n');
+
+    const pattern = /\*\*Plans:\*\* [^\n]+/;
+    const result = replaceInCurrentMilestone(content, pattern, '**Plans:** 2/2 plans complete');
+
+    // Should update Phase 3's Plans line (current milestone)
+    expect(result).toContain('**Plans:** 2/2 plans complete');
+    // Should NOT touch v1.18 or v1.19 sections
+    expect(result).toContain('✅ v1.18');
+    expect(result).toContain('✅ v1.19');
+  });
+
+  it('replaces inside active milestone when it is wrapped in a <details> block', async () => {
+    const { replaceInCurrentMilestone } = await import('./phase-lifecycle.js');
+    // Scenario: active milestone is collapsed in <details> (e.g. user collapsed it)
+    const content = [
+      '# Roadmap',
+      '',
+      '<details>',
+      '<summary>✅ v1.18 (shipped)</summary>',
+      '',
+      '### Phase 1: Old Phase',
+      '',
+      '**Plans:** 1/1 plans',
+      '',
+      '</details>',
+      '',
+      '<details>',
+      '<summary>🚧 v1.19 in-progress</summary>',
+      '',
+      '### Phase 2: Current Work',
+      '',
+      '**Plans:** 1/2 plans',
+      '',
+      '</details>',
+      '',
+    ].join('\n');
+
+    const pattern = /\*\*Plans:\*\* [^\n]+/g;
+    const result = replaceInCurrentMilestone(content, pattern, '**Plans:** 2/2 plans complete');
+
+    // The replacement should happen somewhere in the content (not silently dropped)
+    expect(result).toContain('**Plans:** 2/2 plans complete');
+    // v1.18 old plans line should remain untouched
+    expect(result).toContain('**Plans:** 1/1 plans');
+  });
 });
 
 // ─── readModifyWriteRoadmapMd ───────────────────────────────────────────
diff --git a/sdk/src/query/phase-lifecycle.ts b/sdk/src/query/phase-lifecycle.ts
index a44e74b32..c42ebe864 100644
--- a/sdk/src/query/phase-lifecycle.ts
+++ b/sdk/src/query/phase-lifecycle.ts
@@ -85,6 +85,12 @@ function generateSlugInternal(text: string): string {
  * If no `</details>` blocks exist, replaces in the entire content.
  * Otherwise, only replaces in content after the last `</details>` close tag.
  *
+ * Edge case: when the active milestone is itself wrapped in a `<details>` block
+ * (e.g. collapsed before it is fully shipped), the last `</details>` belongs to
+ * the active milestone and the `after` slice is empty. In that case the function
+ * falls back to searching the full content with all complete `<details>` blocks
+ * stripped, so archived milestones are never touched.
+ *
  * @param content - Full ROADMAP.md content
  * @param pattern - Regex or string pattern to match
  * @param replacement - Replacement string
@@ -102,7 +108,40 @@ export function replaceInCurrentMilestone(
   const offset = lastDetailsClose + '</details>'.length;
   const before = content.slice(0, offset);
   const after = content.slice(offset);
-  return before + after.replace(pattern, replacement);
+
+  // Fast path: the current milestone is not inside a <details> block — the
+  // pattern lives in the plain text after the last </details>.
+  if (after.trim().length > 0) {
+    return before + after.replace(pattern, replacement);
+  }
+
+  // Slow path: the active milestone is inside the last <details> block.
+  // Strip every complete <details>…</details> block except the last one, then
+  // apply the replacement inside that last block while leaving the stripped
+  // (archived) blocks untouched.
+  //
+  // Strategy:
+  //   1. Collect all complete <details>…</details> spans.
+  //   2. Replace only inside the LAST span; leave earlier spans unchanged.
+  const detailsBlockRe = /<details>[\s\S]*?<\/details>/gi;
+  const spans: { start: number; end: number; text: string }[] = [];
+  let m: RegExpExecArray | null;
+  while ((m = detailsBlockRe.exec(content)) !== null) {
+    spans.push({ start: m.index, end: m.index + m[0].length, text: m[0] });
+  }
+
+  if (spans.length === 0) {
+    // No complete blocks found — fall back to full-content replace.
+    return content.replace(pattern, replacement);
+  }
+
+  const lastSpan = spans[spans.length - 1];
+  const updatedLastBlock = lastSpan.text.replace(pattern, replacement);
+  return (
+    content.slice(0, lastSpan.start) +
+    updatedLastBlock +
+    content.slice(lastSpan.end)
+  );
 }
 
 // ─── readModifyWriteRoadmapMd ───────────────────────────────────────────