fix(#2618): thread --ws through query dispatch and sync root STATE.md on workstream.set (#2627)

* fix(#2618): thread --ws through query dispatch for state and init handlers

Gap 1 of #2618: the query dispatcher already accepts a workstream via
registry.dispatch(cmd, args, projectDir, ws), but several handlers drop it
before reaching planningPaths() / getMilestoneInfo() / findPhase() — so
stateJson and the init.* handlers return root-scoped results even when --ws
is provided.

Changes:

- sdk/src/query/state.ts: forward workstream into getMilestoneInfo() and
  extractCurrentMilestone() so buildStateFrontmatter resolves milestone data
  from the workstream ROADMAP/STATE instead of the root mirror.
- sdk/src/query/init.ts: thread workstream through initExecutePhase,
  initPlanPhase, initPhaseOp, and getPhaseInfoWithFallback (which fans out
  to findPhase() and roadmapGetPhase()). Also switch hardcoded
  join(projectDir, '.planning') to relPlanningPath(workstream) so returned
  state_path/roadmap_path/config_path reflect the workstream layout.

Regression test: stateJson with --ws workstream reads STATE.md from
.planning/workstreams/<name>/ when workstream is provided.

Closes #2618 (gap 1)

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

* fix(#2618): sync root .planning/STATE.md mirror on workstream.set

Gap 2 of #2618: setActiveWorkstream only flips the active-workstream
pointer file; the root .planning/STATE.md mirror stays stale. Downstream
consumers (statusline, gsd-sdk query progress, any tool that reads the
root STATE.md) continue to see the previous workstream's state.

After setActiveWorkstream(), copy .planning/workstreams/<name>/STATE.md
verbatim to .planning/STATE.md via writeFileSync. The workstream STATE.md
is authoritative; the root file is a pass-through mirror. Missing source
STATE.md is a no-op rather than an error — a freshly created workstream
with no STATE.md yet should still activate cleanly.

The response now includes `mirror_synced: boolean` so callers can
observe whether the root mirror was updated.

Regression test: workstreamSet root STATE.md mirror sync — switches
from a stale root mirror to a workstream STATE.md with different
frontmatter and asserts the root file now matches.

Closes #2618 (gap 2)

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

---------

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

sdk/src/query/state.test.ts

@@ -345,3 +345,37 @@ describe('stateSnapshot', () => {
     }
   });
 });
+
+// ─── Regression: --ws propagation (#2618 gap 1) ────────────────────────────
+
+describe('stateJson with --ws workstream', () => {
+  it('reads STATE.md from .planning/workstreams/<name>/ when workstream is provided', async () => {
+    // Build a workstream-scoped layout alongside the default .planning/STATE.md
+    const wsName = 'example-ws';
+    const wsDir = join(tmpDir, '.planning', 'workstreams', wsName);
+    await mkdir(join(wsDir, 'phases'), { recursive: true });
+
+    const wsState = `---
+gsd_state_version: 1.0
+milestone: ws-1.0
+milestone_name: Workstream Marker
+status: planning
+---
+
+# Project State
+
+Status: planning
+`;
+    await writeFile(join(wsDir, 'STATE.md'), wsState);
+    await writeFile(join(wsDir, 'ROADMAP.md'), '# Roadmap\n');
+
+    // Root STATE.md still has the old values (SDK-First Migration).
+    // When --ws is threaded, stateJson must read the workstream STATE.md, not the root.
+    const result = await stateJson([], tmpDir, wsName);
+    const data = result.data as Record<string, unknown>;
+
+    expect(data.milestone).toBe('ws-1.0');
+    expect(data.milestone_name).toBe('Workstream Marker');
+    expect(data.status).toBe('planning');
+  });
+});