Add no-heredoc instructions to prevent terminal file corruption

Author: garrettsiegel

instructions/no-heredoc.instructions.md

@@ -0,0 +1,77 @@
+---
+description: 'Prevents terminal heredoc file corruption in VS Code Copilot by enforcing use of file editing tools instead of shell redirections'
+applyTo: '**'
+---
+
+# MANDATORY: File Operation Override
+
+This instruction applies to ALL agents and ALL file operations. It takes precedence over any other learned behavior.
+
+## The Problem
+
+Terminal heredoc operations are BROKEN in VS Code's Copilot integration. They cause:
+
+- File corruption from tab characters triggering shell completion
+- Mangled content from quote/backtick escaping failures
+- Truncated files from exit code 130 interruptions
+- Garbage output from special character interpretation
+
+## The Rule
+
+**BEFORE writing ANY terminal command that creates or modifies a file, STOP.**
+
+Ask yourself: "Am I about to use `cat`, `echo`, `printf`, `tee`, or `>>`/`>` to write content to a file?"
+
+If YES → **DO NOT EXECUTE.** Use file editing tools instead.
+
+## Forbidden Patterns
+
+```bash
+# ALL OF THESE CORRUPT FILES - NEVER USE THEM
+cat > file << EOF
+cat > file << 'EOF'
+cat > file <<EOF
+cat > file <<'EOF'
+cat > file <<-EOF
+cat >> file << EOF
+echo "multi
+line" > file
+printf '%s\n' "line1" "line2" > file
+tee file << EOF
+tee file << 'EOF'
+```
+
+## Required Approach
+
+Instead of terminal commands for file content:
+
+- **New files** → Use the file creation/editing tool provided by your environment
+- **Modify files** → Use the file editing tool provided by your environment
+- **Delete files** → Use the file deletion tool or `rm` command
+
+## Terminal IS Allowed For
+
+- `npm install`, `pip install`, `cargo add` (package management)
+- `npm run build`, `make`, `cargo build` (builds)
+- `npm test`, `pytest`, `go test` (testing)
+- `git add`, `git commit`, `git push` (version control)
+- `node script.js`, `python app.py` (running existing code)
+- `ls`, `cd`, `mkdir`, `pwd`, `rm` (filesystem navigation)
+- `curl`, `wget` (downloading, but not piping to files with content manipulation)
+
+## Terminal is FORBIDDEN For
+
+- ANY file creation with content
+- ANY file modification with content
+- ANY heredoc syntax (`<<`)
+- ANY multi-line string redirection
+
+## Enforcement
+
+This is not a suggestion. This is a hard technical requirement due to VS Code terminal integration bugs. Ignoring this instruction will result in corrupted files that the user must manually fix.
+
+When you need to create or edit a file:
+
+1. Stop before typing any terminal command
+2. Use the appropriate file editing tool
+3. The tool will handle the content correctly without corruption