diff --git a/src/state.cts b/src/state.cts
index 0e8199266..37b859091 100644
--- a/src/state.cts
+++ b/src/state.cts
@@ -16,7 +16,7 @@ import configLoaderMod = require('./config-loader.cjs');
 const { loadConfig } = configLoaderMod;
 // eslint-disable-next-line @typescript-eslint/no-require-imports
 import phaseIdMod = require('./phase-id.cjs');
-const { escapeRegex, normalizePhaseName, extractPhaseToken } = phaseIdMod;
+const { escapeRegex, normalizePhaseName, extractPhaseToken, parsePhaseFromProse } = phaseIdMod;
 // eslint-disable-next-line @typescript-eslint/no-require-imports
 import roadmapParserMod = require('./roadmap-parser.cjs');
 const { getMilestoneInfo, getMilestonePhaseFilter, extractCurrentMilestone } = roadmapParserMod;
@@ -1116,22 +1116,13 @@ function matchSessionSection(body: string): RegExpMatchArray | null {
 }
 
 function parseProsePhaseField(value: string | null): { phase: string | null; name: string | null } {
-  if (!value) return { phase: null, name: null };
-  const phaseMatch = value.match(/\b(\d+[A-Z]?(?:\.\d+)*)\b/i);
-  // #2124 review: length-bound the name quantifiers so a crafted long
-  // unterminated `(` / `—` run in an untrusted STATE.md field cannot drive
-  // O(n^2) backtracking (CPU DoS). (Phase 2 / #2125 supersedes this function
-  // by delegating to phase-id.cts:parsePhaseFromProse, which is bounded too.)
-  const parenName = value.match(/\(([^)]{1,200})\)/);
-  const dashName = value.match(/—\s*([^(\n]{1,200}?)(?:\s*\(|$)/);
-  const rawName = parenName?.[1] ?? dashName?.[1] ?? null;
-  const name = rawName && !/^(?:complete|executing|not started)$/i.test(rawName.trim())
-    ? rawName.trim()
-    : null;
-  return {
-    phase: phaseMatch ? phaseMatch[1] : null,
-    name,
-  };
+  // #2121 Phase 2 (#2125): delegate to the canonical anchored parser so this
+  // module holds no independent prose phase-id regex. Drives #2111 — the
+  // anchored parser returns { phase: null } for a "Milestone vX.Y complete"
+  // body line (the old unanchored regex mined the minor-version digit, e.g.
+  // v0.5 -> "5"), so syncStateFrontmatter's #905 guard preserves the real
+  // current_phase instead of clobbering it.
+  return parsePhaseFromProse(value);
 }
 
 function parseProseLastActivityField(value: string | null): { date: string | null; description: string | null } {
diff --git a/tests/milestone.test.cjs b/tests/milestone.test.cjs
index 65c0d26b9..dd65626b5 100644
--- a/tests/milestone.test.cjs
+++ b/tests/milestone.test.cjs
@@ -16,7 +16,7 @@ const { test, describe, before, beforeEach, afterEach } = require('node:test');
 const assert = require('node:assert/strict');
 const fs = require('fs');
 const path = require('path');
-const { runGsdTools, createTempProject, cleanup } = require('./helpers.cjs');
+const { runGsdTools, createTempProject, cleanup, parseFrontmatter } = require('./helpers.cjs');
 
 // ─── helpers ─────────────────────────────────────────────────────────────────
 
@@ -54,6 +54,34 @@ describe('milestone complete command', () => {
   beforeEach(() => { tmpDir = createTempProject(); });
   afterEach(() => { cleanup(tmpDir); });
 
+  test('preserves current_phase frontmatter through milestone complete (#2111)', () => {
+    // Seed STATE.md mid-phase-19: the real current_phase lives in frontmatter
+    // and the only body phase source is the `Phase:` prose line (no explicit
+    // `Current Phase:` field — matching what milestoneCompleteCore writes).
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'STATE.md'),
+      `---\ncurrent_phase: "19"\n---\n# State\n\n**Status:** In progress\n` +
+      `**Last Activity:** 2025-01-01\n**Last Activity Description:** Working\n\n` +
+      `## Current Position\n\nPhase: 19 — EXECUTING\nPlan: 1 of 1\n` +
+      `Status: Executing\nLast activity: 2025-01-01 — Running phase\n`,
+    );
+    // No ROADMAP.md — mirrors 'handles missing ROADMAP.md gracefully' so the
+    // milestone-phase-filter guard never fires.
+
+    const result = runGsdTools('milestone complete v0.5 --name Test', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const state = fs.readFileSync(path.join(tmpDir, '.planning', 'STATE.md'), 'utf-8');
+    const fm = parseFrontmatter(state);
+    // Fails pre-migration: the unanchored parser mined "5" from
+    // "Phase: Milestone v0.5 complete" and clobbered current_phase.
+    assert.strictEqual(
+      fm.current_phase, '19',
+      `current_phase must be preserved across milestone complete, not mined from ` +
+      `the version string (#2111); got ${JSON.stringify(fm.current_phase)}`,
+    );
+  });
+
   test('archives roadmap, requirements, creates MILESTONES.md', () => {
     writeRoadmap(tmpDir, `# Roadmap v1.0 MVP\n\n### Phase 1: Foundation\n**Goal:** Setup\n`);
     fs.writeFileSync(