diff --git a/get-shit-done/bin/lib/config.cjs b/get-shit-done/bin/lib/config.cjs
index 756233189..541075a26 100644
--- a/get-shit-done/bin/lib/config.cjs
+++ b/get-shit-done/bin/lib/config.cjs
@@ -25,6 +25,9 @@ const VALID_CONFIG_KEYS = new Set([
   'workflow.use_worktrees',
   'workflow.code_review',
   'workflow.code_review_depth',
+  'workflow.plan_bounce',
+  'workflow.plan_bounce_script',
+  'workflow.plan_bounce_passes',
   'git.branching_strategy', 'git.base_branch', 'git.phase_branch_template', 'git.milestone_branch_template', 'git.quick_branch_template',
   'planning.commit_docs', 'planning.search_gitignored',
   'workflow.subagent_timeout',
@@ -155,6 +158,9 @@ function buildNewProjectConfig(userChoices) {
       skip_discuss: false,
       code_review: true,
       code_review_depth: 'standard',
+      plan_bounce: false,
+      plan_bounce_script: null,
+      plan_bounce_passes: 2,
     },
     hooks: {
       context_warnings: true,
diff --git a/get-shit-done/templates/config.json b/get-shit-done/templates/config.json
index 71a1f44fa..5c727cf49 100644
--- a/get-shit-done/templates/config.json
+++ b/get-shit-done/templates/config.json
@@ -11,7 +11,10 @@
     "security_asvs_level": 1,
     "security_block_on": "high",
     "discuss_mode": "discuss",
-    "research_before_questions": false
+    "research_before_questions": false,
+    "plan_bounce": false,
+    "plan_bounce_script": null,
+    "plan_bounce_passes": 2
   },
   "planning": {
     "commit_docs": true,
diff --git a/get-shit-done/workflows/plan-phase.md b/get-shit-done/workflows/plan-phase.md
index 84718b2c2..48247c962 100644
--- a/get-shit-done/workflows/plan-phase.md
+++ b/get-shit-done/workflows/plan-phase.md
@@ -46,7 +46,7 @@ Parse JSON for: `researcher_model`, `planner_model`, `checker_model`, `research_
 
 ## 2. Parse and Normalize Arguments
 
-Extract from $ARGUMENTS: phase number (integer or decimal like `2.1`), flags (`--research`, `--skip-research`, `--gaps`, `--skip-verify`, `--skip-ui`, `--prd <filepath>`, `--reviews`, `--text`).
+Extract from $ARGUMENTS: phase number (integer or decimal like `2.1`), flags (`--research`, `--skip-research`, `--gaps`, `--skip-verify`, `--skip-ui`, `--prd <filepath>`, `--reviews`, `--text`, `--bounce`, `--skip-bounce`).
 
 Set `TEXT_MODE=true` if `--text` is present in $ARGUMENTS OR `text_mode` from init JSON is `true`. When `TEXT_MODE` is active, replace every `AskUserQuestion` call with a plain-text numbered list and ask the user to type their choice number. This is required for Claude Code remote sessions (`/rc` mode) where TUI menus don't work through the Claude App.
 
@@ -930,6 +930,77 @@ Display: `Max iterations reached. {N} issues remain:` + issue list
 
 Offer: 1) Force proceed, 2) Provide guidance and retry, 3) Abandon
 
+## 12.5. Plan Bounce (Optional External Refinement)
+
+**Skip if:** `--skip-bounce` flag, `--gaps` flag, or bounce is not activated.
+
+**Activation:** Bounce runs when `--bounce` flag is present OR `workflow.plan_bounce` config is `true`. The `--skip-bounce` flag always wins (disables bounce even if config enables it). The `--gaps` flag also disables bounce (gap-closure mode should not modify plans externally).
+
+**Prerequisites:** `workflow.plan_bounce_script` must be set to a valid script path. If bounce is activated but no script is configured, display warning and skip:
+```
+⚠ Plan bounce activated but no script configured.
+Set workflow.plan_bounce_script to the path of your refinement script.
+Skipping bounce step.
+```
+
+**Read pass count:**
+```bash
+BOUNCE_PASSES=$(node "$HOME/.claude/get-shit-done/bin/gsd-tools.cjs" config-get workflow.plan_bounce_passes --default 2)
+BOUNCE_SCRIPT=$(node "$HOME/.claude/get-shit-done/bin/gsd-tools.cjs" config-get workflow.plan_bounce_script)
+```
+
+Display banner:
+```
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+ GSD ► BOUNCING PLANS (External Refinement)
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+Script: ${BOUNCE_SCRIPT}
+Max passes: ${BOUNCE_PASSES}
+```
+
+**For each PLAN.md file in the phase directory:**
+
+1. **Backup:** Copy `*-PLAN.md` to `*-PLAN.pre-bounce.md`
+```bash
+cp "${PLAN_FILE}" "${PLAN_FILE%.md}.pre-bounce.md"
+```
+
+2. **Invoke bounce script:**
+```bash
+"${BOUNCE_SCRIPT}" "${PLAN_FILE}" "${BOUNCE_PASSES}"
+```
+
+3. **Validate bounced plan — YAML frontmatter integrity:**
+After the script returns, check that the bounced file still has valid YAML frontmatter (opening and closing `---` delimiters with parseable content between them). If the bounced plan breaks YAML frontmatter validation, restore the original from the pre-bounce.md backup and continue to the next plan:
+```
+⚠ Bounced plan ${PLAN_FILE} has broken YAML frontmatter — restoring original from pre-bounce backup.
+```
+
+4. **Handle script failure:** If the bounce script exits non-zero, restore the original plan from the pre-bounce.md backup and continue to the next plan:
+```
+⚠ Bounce script failed for ${PLAN_FILE} (exit code ${EXIT_CODE}) — restoring original from pre-bounce backup.
+```
+
+**After all plans are bounced:**
+
+5. **Re-run plan checker on bounced plans:** Spawn gsd-plan-checker (same as step 10) on all modified plans. If a bounced plan fails the checker, restore original from its pre-bounce.md backup:
+```
+⚠ Bounced plan ${PLAN_FILE} failed checker validation — restoring original from pre-bounce backup.
+```
+
+6. **Commit surviving bounced plans:** If at least one plan survived both the frontmatter validation and the checker re-run, commit the changes:
+```bash
+node "$HOME/.claude/get-shit-done/bin/gsd-tools.cjs" commit "refactor(${padded_phase}): bounce plans through external refinement" --files "${PHASE_DIR}/*-PLAN.md"
+```
+
+Display summary:
+```
+Plan bounce complete: {survived}/{total} plans refined
+```
+
+**Clean up:** Remove all `*-PLAN.pre-bounce.md` backup files after the bounce step completes (whether plans survived or were restored).
+
 ## 13. Requirements Coverage Gate
 
 After plans pass the checker (or checker is skipped), verify that all phase requirements are covered by at least one plan.
diff --git a/tests/plan-bounce.test.cjs b/tests/plan-bounce.test.cjs
new file mode 100644
index 000000000..10845f62b
--- /dev/null
+++ b/tests/plan-bounce.test.cjs
@@ -0,0 +1,170 @@
+/**
+ * Plan Bounce Tests
+ *
+ * Validates plan bounce hook feature (step 12.5 in plan-phase):
+ * - Config key registration (workflow.plan_bounce, workflow.plan_bounce_script, workflow.plan_bounce_passes)
+ * - Config template defaults
+ * - Workflow step 12.5 content in plan-phase.md
+ * - Flag handling (--bounce, --skip-bounce)
+ * - Backup/restore pattern (pre-bounce.md)
+ * - Frontmatter integrity validation
+ * - Re-runs checker on bounced plans
+ */
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const GSD_ROOT = path.join(__dirname, '..', 'get-shit-done');
+const CONFIG_CJS_PATH = path.join(GSD_ROOT, 'bin', 'lib', 'config.cjs');
+const CONFIG_TEMPLATE_PATH = path.join(GSD_ROOT, 'templates', 'config.json');
+const PLAN_PHASE_PATH = path.join(GSD_ROOT, 'workflows', 'plan-phase.md');
+
+describe('Plan Bounce: config keys', () => {
+  test('workflow.plan_bounce is in VALID_CONFIG_KEYS', () => {
+    const content = fs.readFileSync(CONFIG_CJS_PATH, 'utf-8');
+    assert.ok(
+      content.includes("'workflow.plan_bounce'"),
+      'VALID_CONFIG_KEYS should contain workflow.plan_bounce'
+    );
+  });
+
+  test('workflow.plan_bounce_script is in VALID_CONFIG_KEYS', () => {
+    const content = fs.readFileSync(CONFIG_CJS_PATH, 'utf-8');
+    assert.ok(
+      content.includes("'workflow.plan_bounce_script'"),
+      'VALID_CONFIG_KEYS should contain workflow.plan_bounce_script'
+    );
+  });
+
+  test('workflow.plan_bounce_passes is in VALID_CONFIG_KEYS', () => {
+    const content = fs.readFileSync(CONFIG_CJS_PATH, 'utf-8');
+    assert.ok(
+      content.includes("'workflow.plan_bounce_passes'"),
+      'VALID_CONFIG_KEYS should contain workflow.plan_bounce_passes'
+    );
+  });
+});
+
+describe('Plan Bounce: config template defaults', () => {
+  test('config template has plan_bounce default (false)', () => {
+    const template = JSON.parse(fs.readFileSync(CONFIG_TEMPLATE_PATH, 'utf-8'));
+    assert.strictEqual(
+      template.workflow.plan_bounce,
+      false,
+      'config template workflow.plan_bounce should default to false'
+    );
+  });
+
+  test('config template has plan_bounce_script default (null)', () => {
+    const template = JSON.parse(fs.readFileSync(CONFIG_TEMPLATE_PATH, 'utf-8'));
+    assert.strictEqual(
+      template.workflow.plan_bounce_script,
+      null,
+      'config template workflow.plan_bounce_script should default to null'
+    );
+  });
+
+  test('config template has plan_bounce_passes default (2)', () => {
+    const template = JSON.parse(fs.readFileSync(CONFIG_TEMPLATE_PATH, 'utf-8'));
+    assert.strictEqual(
+      template.workflow.plan_bounce_passes,
+      2,
+      'config template workflow.plan_bounce_passes should default to 2'
+    );
+  });
+});
+
+describe('Plan Bounce: plan-phase.md step 12.5', () => {
+  let content;
+
+  test('plan-phase.md contains step 12.5', () => {
+    content = fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    assert.ok(
+      content.includes('## 12.5'),
+      'plan-phase.md should contain step 12.5'
+    );
+  });
+
+  test('step 12.5 references plan bounce', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    // The step title should mention bounce
+    assert.ok(
+      /## 12\.5.*[Bb]ounce/i.test(content),
+      'step 12.5 should reference plan bounce in its title'
+    );
+  });
+
+  test('plan-phase.md has --bounce flag handling', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    assert.ok(
+      content.includes('--bounce'),
+      'plan-phase.md should handle --bounce flag'
+    );
+  });
+
+  test('plan-phase.md has --skip-bounce flag handling', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    assert.ok(
+      content.includes('--skip-bounce'),
+      'plan-phase.md should handle --skip-bounce flag'
+    );
+  });
+
+  test('plan-phase.md has backup pattern (pre-bounce.md)', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    assert.ok(
+      content.includes('pre-bounce.md'),
+      'plan-phase.md should reference pre-bounce.md backup files'
+    );
+  });
+
+  test('plan-phase.md has frontmatter integrity validation for bounced plans', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    // Should mention YAML frontmatter validation after bounce
+    assert.ok(
+      /frontmatter.*bounced|bounced.*frontmatter|YAML.*bounce|bounce.*YAML/i.test(content),
+      'plan-phase.md should validate frontmatter integrity on bounced plans'
+    );
+  });
+
+  test('plan-phase.md re-runs checker on bounced plans', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    // Should mention re-running plan checker after bounce
+    assert.ok(
+      /[Rr]e-run.*checker.*bounce|bounce.*checker.*re-run|checker.*bounced/i.test(content),
+      'plan-phase.md should re-run plan checker on bounced plans'
+    );
+  });
+
+  test('plan-phase.md references plan_bounce config keys', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    assert.ok(
+      content.includes('plan_bounce_script'),
+      'plan-phase.md should reference plan_bounce_script config'
+    );
+    assert.ok(
+      content.includes('plan_bounce_passes'),
+      'plan-phase.md should reference plan_bounce_passes config'
+    );
+  });
+
+  test('plan-phase.md disables bounce when --gaps flag is present', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    // Should mention that --gaps disables bounce
+    assert.ok(
+      /--gaps.*bounce|bounce.*--gaps/i.test(content),
+      'plan-phase.md should disable bounce when --gaps flag is present'
+    );
+  });
+
+  test('plan-phase.md restores original on script failure', () => {
+    content = content || fs.readFileSync(PLAN_PHASE_PATH, 'utf-8');
+    // Should mention restoring from backup on failure
+    assert.ok(
+      /restore.*original|restore.*pre-bounce|original.*restore/i.test(content),
+      'plan-phase.md should restore original plan on script failure'
+    );
+  });
+});