diff --git a/get-shit-done/bin/lib/state.cjs b/get-shit-done/bin/lib/state.cjs
index 6fe9dfa09..302603368 100644
--- a/get-shit-done/bin/lib/state.cjs
+++ b/get-shit-done/bin/lib/state.cjs
@@ -236,6 +236,12 @@ function stateReplaceFieldWithFallback(content, primary, fallback, value) {
     result = stateReplaceField(content, fallback, value);
     if (result) return result;
   }
+  // Neither pattern matched — field may have been reformatted or removed.
+  // Log diagnostic so template drift is detected early rather than silently swallowed.
+  process.stderr.write(
+    `[gsd-tools] WARNING: STATE.md field "${primary}"${fallback ? ` (fallback: "${fallback}")` : ''} not found — update skipped. ` +
+    `This may indicate STATE.md was externally modified or uses an unexpected format.\n`
+  );
   return content;
 }
 
diff --git a/get-shit-done/bin/lib/verify.cjs b/get-shit-done/bin/lib/verify.cjs
index 8975f9f39..d05b68adf 100644
--- a/get-shit-done/bin/lib/verify.cjs
+++ b/get-shit-done/bin/lib/verify.cjs
@@ -5,7 +5,7 @@
 const fs = require('fs');
 const path = require('path');
 const os = require('os');
-const { safeReadFile, loadConfig, normalizePhaseName, execGit, findPhaseInternal, getMilestoneInfo, stripShippedMilestones, extractCurrentMilestone, planningDir, planningRoot, output, error, checkAgentsInstalled } = require('./core.cjs');
+const { safeReadFile, loadConfig, normalizePhaseName, escapeRegex, execGit, findPhaseInternal, getMilestoneInfo, stripShippedMilestones, extractCurrentMilestone, planningDir, planningRoot, output, error, checkAgentsInstalled } = require('./core.cjs');
 const { extractFrontmatter, parseMustHavesBlock } = require('./frontmatter.cjs');
 const { writeStateMd } = require('./state.cjs');
 
@@ -757,6 +757,71 @@ function cmdValidateHealth(cwd, options, raw) {
     }
   }
 
+  // ─── Check 9: STATE.md / ROADMAP.md cross-validation ─────────────────────
+  if (fs.existsSync(statePath) && fs.existsSync(roadmapPath)) {
+    try {
+      const stateContent = fs.readFileSync(statePath, 'utf-8');
+      const roadmapContentFull = fs.readFileSync(roadmapPath, 'utf-8');
+
+      // Extract current phase from STATE.md
+      const currentPhaseMatch = stateContent.match(/\*\*Current Phase:\*\*\s*(\S+)/i) ||
+                                 stateContent.match(/Current Phase:\s*(\S+)/i);
+      if (currentPhaseMatch) {
+        const statePhase = currentPhaseMatch[1].replace(/^0+/, '');
+        // Check if ROADMAP shows this phase as already complete
+        const phaseCheckboxRe = new RegExp(`-\\s*\\[x\\].*Phase\\s+0*${escapeRegex(statePhase)}[:\\s]`, 'i');
+        if (phaseCheckboxRe.test(roadmapContentFull)) {
+          // STATE says "current" but ROADMAP says "complete" — divergence
+          const stateStatus = stateContent.match(/\*\*Status:\*\*\s*(.+)/i);
+          const statusVal = stateStatus ? stateStatus[1].trim().toLowerCase() : '';
+          if (statusVal !== 'complete' && statusVal !== 'done') {
+            addIssue('warning', 'W011',
+              `STATE.md says current phase is ${statePhase} (status: ${statusVal || 'unknown'}) but ROADMAP.md shows it as [x] complete — state files may be out of sync`,
+              'Run /gsd:progress to re-derive current position, or manually update STATE.md');
+          }
+        }
+      }
+    } catch { /* intentionally empty — cross-validation is advisory */ }
+  }
+
+  // ─── Check 10: Config field validation ────────────────────────────────────
+  if (fs.existsSync(configPath)) {
+    try {
+      const configRaw = fs.readFileSync(configPath, 'utf-8');
+      const configParsed = JSON.parse(configRaw);
+
+      // Validate branching_strategy
+      const validStrategies = ['none', 'phase', 'milestone'];
+      if (configParsed.branching_strategy && !validStrategies.includes(configParsed.branching_strategy)) {
+        addIssue('warning', 'W012',
+          `config.json: invalid branching_strategy "${configParsed.branching_strategy}"`,
+          `Valid values: ${validStrategies.join(', ')}`);
+      }
+
+      // Validate context_window is a positive integer
+      if (configParsed.context_window !== undefined) {
+        const cw = configParsed.context_window;
+        if (typeof cw !== 'number' || cw <= 0 || !Number.isInteger(cw)) {
+          addIssue('warning', 'W013',
+            `config.json: context_window should be a positive integer, got "${cw}"`,
+            'Set to 200000 (default) or 1000000 (for 1M models)');
+        }
+      }
+
+      // Validate branch templates have required placeholders
+      if (configParsed.phase_branch_template && !configParsed.phase_branch_template.includes('{phase}')) {
+        addIssue('warning', 'W014',
+          'config.json: phase_branch_template missing {phase} placeholder',
+          'Template must include {phase} for phase number substitution');
+      }
+      if (configParsed.milestone_branch_template && !configParsed.milestone_branch_template.includes('{milestone}')) {
+        addIssue('warning', 'W015',
+          'config.json: milestone_branch_template missing {milestone} placeholder',
+          'Template must include {milestone} for version substitution');
+      }
+    } catch { /* parse error already caught in Check 5 */ }
+  }
+
   // ─── Perform repairs if requested ─────────────────────────────────────────
   const repairActions = [];
   if (options.repair && repairs.length > 0) {
diff --git a/tests/health-validation.test.cjs b/tests/health-validation.test.cjs
new file mode 100644
index 000000000..3f17f9425
--- /dev/null
+++ b/tests/health-validation.test.cjs
@@ -0,0 +1,388 @@
+/**
+ * GSD Tools Tests - Health Validation
+ *
+ * Tests for fix/health-validation-1473c:
+ *   - W011: STATE/ROADMAP cross-validation (phase divergence detection)
+ *   - W012: branching_strategy validation
+ *   - W013: context_window validation
+ *   - W014: phase_branch_template placeholder validation
+ *   - W015: milestone_branch_template placeholder validation
+ *   - stateReplaceFieldWithFallback field-miss warning
+ *   - Boundary conditions and edge cases
+ */
+
+const { test, describe, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert');
+const fs = require('fs');
+const path = require('path');
+const { runGsdTools, createTempProject, cleanup } = require('./helpers.cjs');
+
+// ─── Helpers ────────────────────────────────────────────────────────────────
+
+function writeMinimalRoadmap(tmpDir, phases = ['1']) {
+  const lines = phases.map(n => `### Phase ${n}: Phase ${n} Description`).join('\n');
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'ROADMAP.md'),
+    `# Roadmap\n\n${lines}\n`
+  );
+}
+
+function writeMinimalStateMd(tmpDir, content) {
+  const defaultContent = content || `# Session State\n\n## Current Position\n\nPhase: 1\n`;
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'STATE.md'),
+    defaultContent
+  );
+}
+
+function writeMinimalProjectMd(tmpDir) {
+  const sections = ['## What This Is', '## Core Value', '## Requirements'];
+  const content = sections.map(s => `${s}\n\nContent here.\n`).join('\n');
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'PROJECT.md'),
+    `# Project\n\n${content}`
+  );
+}
+
+function writeValidConfigJson(tmpDir, overrides = {}) {
+  const base = { model_profile: 'balanced', commit_docs: true };
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'config.json'),
+    JSON.stringify({ ...base, ...overrides }, null, 2)
+  );
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// 1. W011: STATE/ROADMAP cross-validation
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('W011: STATE/ROADMAP cross-validation', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('STATE says current phase but ROADMAP shows it as complete -> warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      `# Roadmap\n\n- [x] Phase 3: Database Layer\n\n### Phase 3: Database Layer\n**Goal:** DB setup\n`
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'STATE.md'),
+      `# Session State\n\n**Current Phase:** 03\n**Current Phase Name:** Database Layer\n**Status:** In progress\n`
+    );
+    writeValidConfigJson(tmpDir);
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '03-database-layer'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      output.warnings.some(w => w.code === 'W011'),
+      `Expected W011 in warnings: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('STATE and ROADMAP agree (phase not checked off) -> no W011 warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      `# Roadmap\n\n- [ ] Phase 2: API Layer\n\n### Phase 2: API Layer\n**Goal:** Build API\n`
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'STATE.md'),
+      `# Session State\n\n**Current Phase:** 2\n**Status:** In progress\n`
+    );
+    writeValidConfigJson(tmpDir);
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '02-api-layer'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      !output.warnings.some(w => w.code === 'W011'),
+      `Should not have W011: ${JSON.stringify(output.warnings)}`
+    );
+  });
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// 2. W012-W015: Config field validation
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('config field validation', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('W012: invalid branching_strategy triggers warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { branching_strategy: 'banana' });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      output.warnings.some(w => w.code === 'W012'),
+      `Expected W012 in warnings: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('W013: negative context_window triggers warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { context_window: -500 });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      output.warnings.some(w => w.code === 'W013'),
+      `Expected W013 in warnings: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('W014: phase_branch_template missing {phase} triggers warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { phase_branch_template: 'gsd/no-placeholder-{slug}' });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      output.warnings.some(w => w.code === 'W014'),
+      `Expected W014 in warnings: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('W015: milestone_branch_template missing {milestone} triggers warning', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { milestone_branch_template: 'release/no-placeholder' });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      output.warnings.some(w => w.code === 'W015'),
+      `Expected W015 in warnings: ${JSON.stringify(output.warnings)}`
+    );
+  });
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// 3. Boundary conditions
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('boundary conditions', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('context_window config accepts 500000 (boundary value)', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { context_window: 500000 });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      !output.warnings.some(w => w.code === 'W013'),
+      `Should not have W013 for context_window=500000: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('context_window config accepts 200000 (default value)', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir, { context_window: 200000 });
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      !output.warnings.some(w => w.code === 'W013'),
+      `Should not have W013 for context_window=200000: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('W013 does NOT fire when context_window is absent from config', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1 in progress.\n');
+    writeValidConfigJson(tmpDir);
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(
+      !output.warnings.some(w => w.code === 'W013'),
+      `Should not have W013 when context_window is absent: ${JSON.stringify(output.warnings)}`
+    );
+  });
+
+  test('health check handles STATE.md with no Current Phase field (no W011 crash)', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1']);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nSome content but no phase reference.\n');
+    writeValidConfigJson(tmpDir);
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command should not crash: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(typeof output.status === 'string', 'should return a status string');
+    assert.ok(Array.isArray(output.errors), 'should return errors array');
+    assert.ok(Array.isArray(output.warnings), 'should return warnings array');
+  });
+
+  test('health check handles empty ROADMAP.md (no crash)', () => {
+    writeMinimalProjectMd(tmpDir);
+    fs.writeFileSync(path.join(tmpDir, '.planning', 'ROADMAP.md'), '');
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1.\n');
+    writeValidConfigJson(tmpDir);
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command should not crash on empty ROADMAP.md: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(typeof output.status === 'string', 'should return a status string');
+    assert.ok(Array.isArray(output.errors), 'should return errors array');
+    assert.ok(Array.isArray(output.warnings), 'should return warnings array');
+  });
+
+  test('config.json with trailing comma -- validate health reports parse error', () => {
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalStateMd(tmpDir, '# Session State\n\nPhase 1.\n');
+    fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-a'), { recursive: true });
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'config.json'),
+      '{"model_profile": "balanced",}'
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      '# Roadmap\n\n### Phase 1: Test Phase\n'
+    );
+
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `validate health should not crash on invalid JSON: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    const hasE005 = output.errors.some(e => e.code === 'E005');
+    assert.ok(hasE005, `Should report E005 for invalid config.json: ${JSON.stringify(output.errors)}`);
+  });
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// 4. stateReplaceFieldWithFallback warning
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('stateReplaceFieldWithFallback field-miss warning', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('advance-plan completes even when fields are missing (non-fatal)', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'STATE.md'),
+      `# Project State\n\n**Current Phase:** 01\n**Current Plan:** 1\n**Total Plans in Phase:** 3\n`
+    );
+
+    const result = runGsdTools('state advance-plan', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(output.advanced === true || output.reason === 'last_plan', 'advance should complete');
+  });
+
+  test('validate health on 50-phase project completes in under 3000ms', () => {
+    // Stress test for the new health checks at scale
+    let roadmapContent = '# Roadmap v1.0\n\n';
+    for (let i = 1; i <= 50; i++) {
+      roadmapContent += `- [${i <= 25 ? 'x' : ' '}] Phase ${i}: Feature ${i}\n`;
+    }
+    roadmapContent += '\n';
+    for (let i = 1; i <= 50; i++) {
+      const pad = String(i).padStart(2, '0');
+      roadmapContent += `### Phase ${i}: Feature ${i}\n\n**Goal:** Build feature ${i}\n**Plans:** 1 plans\n\n`;
+    }
+    fs.writeFileSync(path.join(tmpDir, '.planning', 'ROADMAP.md'), roadmapContent);
+
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalStateMd(tmpDir, '# Session State\n\n**Current Phase:** 26\n**Status:** Planning\n');
+    writeValidConfigJson(tmpDir);
+
+    const phasesDir = path.join(tmpDir, '.planning', 'phases');
+    for (let i = 1; i <= 50; i++) {
+      const pad = String(i).padStart(2, '0');
+      const phaseDir = path.join(phasesDir, `${pad}-feature-${i}`);
+      fs.mkdirSync(phaseDir, { recursive: true });
+      fs.writeFileSync(path.join(phaseDir, `${pad}-01-PLAN.md`), `# Plan ${i}\n`);
+      if (i <= 25) {
+        fs.writeFileSync(path.join(phaseDir, `${pad}-01-SUMMARY.md`), `# Summary ${i}\n`);
+      }
+    }
+
+    const { performance } = require('perf_hooks');
+    const start = performance.now();
+    const result = runGsdTools('validate health', tmpDir);
+    const elapsed = performance.now() - start;
+
+    assert.ok(result.success, `validate health should succeed: ${result.error}`);
+    assert.ok(elapsed < 3000, `Should complete in under 3000ms, took ${elapsed.toFixed(0)}ms`);
+
+    const output = JSON.parse(result.output);
+    assert.ok(typeof output.status === 'string', 'Should return a status string');
+  });
+});