When we publish a broken extension, we have no fast recovery path. Our changeset-based release process requires reverting PRs, code reviews, and manual version coordination—all while users are experiencing issues in production.

**The pain:** Emergency rollbacks require:
1. Reverting multiple PRs
2. Creating changeset PRs
3. Manual version number calculations
4. Code reviews during an emergency

Added **one-click automatic rollback** to the marketplace publish workflow. Just provide the git tag of a working version, and the system handles everything else.

**Normal publish (unchanged):**
```
Actions → Publish Extension → Run workflow
→ Leave rollback field empty
```

**Emergency rollback:**
```
Actions → Publish Extension → Run workflow
→ rollback_source_version: v4.115.0
```

**That's it!** The system automatically:
1. Calculates next version (e.g., `4.116.2-fix`)
2. Updates `package.json`
3. Checks out old code from tag
4. Builds and publishes

```bash
$ node scripts/set-rollback-version.js v4.115.0

Current version on main: 4.116.1
Rolling back from source: v4.115.0
Calculated rollback version: 4.116.2-fix

SemVer ordering:
  4.116.1 < 4.116.2-fix < 4.116.2

✅ Updated src/package.json to version 4.116.2-fix
```

**Modified:** `.github/workflows/marketplace-publish.yml` (+13 lines)
- Added single optional input: `rollback_source_version`
- Modified `GIT_REF` to use rollback source when provided
- Added simple one-line step: `node scripts/set-rollback-version.js`
- Applied to both extension and JetBrains jobs
- Zero code duplication, fully backward compatible

**Added:** `scripts/set-rollback-version.js` (~105 lines)
- Calculates appropriate rollback version automatically
- Updates `src/package.json` with new version
- Handles edge cases (existing `-fix` versions, etc.)
- All logic consolidated in one place

**Added:** `scripts/__tests__/set-rollback-version.test.js`
- Unit tests for version calculation logic

- ⚡ **Instant**: One input, everything else automatic
- 🧠 **Smart**: Calculates correct SemVer version
- 🎯 **Simple**: No mental math, no version errors
- 🔒 **Safe**: Uses proven code from git history
- ♻️ **Maintainable**: Minimal YAML, logic in JS
- 📦 **SemVer compatible**: Proper ordering guaranteed

```
User Input: v4.115.0
           ↓
Script calculates: 4.116.2-fix
           ↓
Updates package.json
           ↓
Workflow builds & publishes
```

**Version calculation:**
- Checks current version on main: `4.116.1`
- Increments patch: `4.116.2`
- Adds `-fix` suffix: `4.116.2-fix`
- Handles multiple rollbacks: `fix`, `fix2`, `fix3`...

**SemVer ordering ensures users auto-update:**
```
4.116.1 < 4.116.2-fix < 4.116.2
```

**Local test:**
```bash
$ node scripts/set-rollback-version.js v4.115.0
✅ Updated src/package.json to version 4.116.2-fix
```

Script successfully:
- ✅ Reads current version from main branch
- ✅ Calculates next rollback version
- ✅ Updates package.json
- ✅ Provides clear output

**Key insight:** During emergencies, minimize decisions. The system should figure out versions automatically.

**Design principles:**
1. **Single input**: Only ask for what we need (old tag)
2. **Automatic calculation**: System determines version
3. **Minimal YAML**: All logic in JavaScript
4. **Clear output**: Script provides full context

---

**Quick summary:**
> Emergency rollback in one input! Just provide an old git tag (e.g., `v4.115.0`), and the system automatically calculates the version, updates files, and publishes. Recovery in ~15 minutes.

**Copy-paste for Discord/Slack:**
> 🚨 One-click rollback is ready! If we ship a broken version, just provide the old git tag and click run. The system auto-calculates the version, checks out old code, and republishes. Emergency recovery in ~15 minutes with zero manual version calculations. 🎯

Removed duplication where both set-rollback-version.js and the workflow
were calculating the rollback version separately.

Now create-rollback-pr.js imports calculateRollbackVersion() from
set-rollback-version.js - single source of truth for version logic.

Workflow simplified:
- Removed unnecessary get_rollback_version step
- Removed ROLLBACK_VERSION env var passing
- create-rollback-pr.js calculates version itself by reading from main

This keeps version calculation logic in one place and makes the
workflow cleaner.

Prevents failures from invalid tag references:

1. Auto-fixes missing 'v' prefix (accepts v4.115.0 or 4.115.0)
2. Validates tag exists before checkout
3. Shows recent tags if validation fails
4. Uses VALIDATED_TAG for consistent checkout

This makes the rollback workflow more robust and user-friendly.