fix(#2641): recognize <details><summary> as active-milestone anchor

`extractCurrentMilestone` only matched markdown headings (## v0.9, ### v0.9)
to find the active milestone slice. Projects that wrap their active
milestone's phase details inside `<details><summary>vX.Y …</summary>`
(a common GitHub-friendly collapse pattern, e.g. FAMP) fell through to
`stripShippedMilestones`, which strips ALL `<details>` blocks indiscriminately.

Net effect: `roadmapGetPhase` returned `{found:false}` for phases that ARE in
the active ROADMAP. The `init.phase-op` safety guard at `init.ts:133`
('drop archived disk match when phase is in current ROADMAP') depends on
`roadmapPhase.found`, so it didn't fire. `init.phase-op` then returned a
`phase_dir` pointing at an ARCHIVED milestone's same-numbered phase —
silently routing downstream workflows (e.g. /gsd-discuss-phase) into
completed phases.

Fix: when no markdown heading matches the active version, try matching
`<details\b[^>]*><summary>...vX.Y...</summary>`. Returns the inner content
of the matching block. Purely additive — `stripShippedMilestones` behavior
and its tests are unchanged.

The `\b[^>]*>` form tolerates attributes like `<details open>` or
`<details class="...">` (GitHub commonly emits `<details open>` for
default-expanded sections). Lazy `[\s\S]*?` matches up to the first
`</details>`; nested `<details>` inside the active milestone are not
expected and would mis-anchor (acceptable; falls through to the existing
`stripShippedMilestones` path with no regression vs. today's behavior).

Closes #2641. Distinct from the closed #2642 which bundled three orthogonal
changes (parser fix + checkbox-scan fix + STATE.md counting auth) into one
PR; this PR addresses only the parser anchoring bug, leaving
`stripShippedMilestones`, `roadmapAnalyze`, and `initMilestoneOp` untouched.

Tests added (3, all in `roadmap.test.ts`):
- `bug-2641: finds active milestone wrapped in <details><summary>vX.Y …</summary>`
- `bug-2641: finds active milestone in <details open><summary>vX.Y …</summary>`
- `bug-2641: returns found:true for phase inside <details>-wrapped active milestone` (end-to-end via `roadmapGetPhase`)

All existing `roadmap.test.ts` tests pass (39/39). Real-world repro
verified against an FAMP-style ROADMAP: before the fix,
`gsd-sdk query roadmap.get-phase 3` returned `{found:false}` despite the
phase being at line 113 of the active ROADMAP; after the fix, it returns
the correct phase metadata, and `init.phase-op 3` no longer returns the
v0.8 archived `phase_dir`.

sdk/src/query/roadmap.test.ts

@@ -389,6 +389,80 @@ describe('extractCurrentMilestone', () => {
     expect(result).toContain('### Phase 19: Security Audit');
   });
 
+  // ─── Bug #2641: <details><summary>vX.Y …</summary> not recognized as anchor ───
+  it('bug-2641: finds active milestone wrapped in <details><summary>vX.Y …</summary>', async () => {
+    // Many projects (GitHub-friendly collapse) wrap the active milestone's
+    // phase details inside <details><summary>v0.9 …</summary>. Without the
+    // <details>-aware fallback, extractCurrentMilestone misses the heading
+    // anchor (because <summary> is HTML), falls through to
+    // stripShippedMilestones, and loses all <details> blocks — including
+    // the active one. Result: roadmapGetPhase returns {found:false} for
+    // phases that ARE in the active ROADMAP.
+    const roadmapWithActiveDetails = `# Roadmap
+
+## Milestones
+- ✅ **v0.8 Foundation** — shipped
+- 📋 **v0.9 Local-First Bus** — active
+
+## Phases
+
+<details>
+<summary>✅ v0.8 Foundation — SHIPPED 2026-04-15</summary>
+
+### Phase 1: Old phase
+**Goal:** Old goal.
+</details>
+
+<details>
+<summary>v0.9 Local-First Bus (active) — Phase Details</summary>
+
+### Phase 1: Library
+**Goal:** Build the library.
+
+### Phase 3: Polish
+**Goal:** Add polish.
+</details>
+`;
+    const state = `---\nmilestone: v0.9\n---\n# State\n`;
+    await writeFile(join(tmpDir, '.planning', 'STATE.md'), state);
+    await writeFile(join(tmpDir, '.planning', 'ROADMAP.md'), roadmapWithActiveDetails);
+
+    const result = await extractCurrentMilestone(roadmapWithActiveDetails, tmpDir);
+
+    // Active milestone's phases must survive
+    expect(result).toContain('### Phase 1: Library');
+    expect(result).toContain('### Phase 3: Polish');
+    expect(result).toContain('Add polish.');
+    // Shipped milestone phases must not bleed in
+    expect(result).not.toContain('Old phase');
+  });
+
+  // ─── Bug #2641: tolerate attributes on <details> tag (e.g. <details open>) ───
+  it('bug-2641: finds active milestone in <details open><summary>vX.Y …</summary>', async () => {
+    // GitHub auto-renders <details open> for sections that should default to
+    // expanded. The <details>-aware fallback regex must use <details\b[^>]*>
+    // (not literal <details>) so attribute-bearing tags also anchor correctly.
+    const roadmapWithDetailsOpen = `# Roadmap
+
+## Phases
+
+<details open>
+<summary>v0.9 Local-First Bus (active) — Phase Details</summary>
+
+### Phase 3: Polish
+**Goal:** Add polish.
+</details>
+`;
+    const state = `---\nmilestone: v0.9\n---\n# State\n`;
+    await writeFile(join(tmpDir, '.planning', 'STATE.md'), state);
+    await writeFile(join(tmpDir, '.planning', 'ROADMAP.md'), roadmapWithDetailsOpen);
+
+    const result = await extractCurrentMilestone(roadmapWithDetailsOpen, tmpDir);
+
+    expect(result).toContain('### Phase 3: Polish');
+    expect(result).toContain('Add polish.');
+  });
+
   // ─── Bug #2422: same-version sub-heading truncation ───────────────────
   it('bug-2422: does not truncate at same-version sub-heading (## v2.0 Phase Details)', async () => {
     const roadmapWithDetails = `# ROADMAP
@@ -456,6 +530,41 @@ describe('roadmapGetPhase', () => {
     expect(data.found).toBe(false);
     expect(data.error).toBe('ROADMAP.md not found');
   });
+
+  // ─── Bug #2641 (regression): end-to-end via roadmapGetPhase ───
+  it('bug-2641: returns found:true for phase inside <details>-wrapped active milestone', async () => {
+    // End-to-end coverage: roadmapGetPhase calls extractCurrentMilestone
+    // internally. Without the <details>-aware fallback, the active
+    // milestone's phases were stripped before the phase-heading lookup,
+    // and roadmapGetPhase returned {found:false} for phases that exist.
+    const roadmap = `# Roadmap
+
+## Milestones
+- 📋 **v0.9 Local-First Bus** — active
+
+<details>
+<summary>v0.9 Local-First Bus (active) — Phase Details</summary>
+
+### Phase 3: Polish
+
+**Goal:** Add polish.
+
+**Success Criteria**:
+1. Polish applied
+2. Tests pass
+</details>
+`;
+    const state = `---\nmilestone: v0.9\n---\n# State\n`;
+    await writeFile(join(tmpDir, '.planning', 'STATE.md'), state);
+    await writeFile(join(tmpDir, '.planning', 'ROADMAP.md'), roadmap);
+
+    const result = await roadmapGetPhase(['3'], tmpDir);
+    const data = result.data as Record<string, unknown>;
+    expect(data.found).toBe(true);
+    expect(data.phase_number).toBe('3');
+    expect(data.phase_name).toBe('Polish');
+    expect(data.goal).toBe('Add polish.');
+  });
 });
 
 // ─── roadmapAnalyze ───────────────────────────────────────────────────────