DCG: When You Get Blocked

Core Insight: Blocks are checkpoints, not errors. A safe alternative almost always exists. Find it before mentioning override.

Constraints

• Never request, generate, or run an allow-once bypass because only the human may authorize and execute the exact blocked command.
• Preserve the user's intended outcome with the narrowest reversible alternative because the guard protects state, not merely command spelling.
• Explain the matched rule and surviving risk before asking for judgment; never retry, obfuscate, or route around a DCG block.

Quick Navigation

THE EXACT WORKFLOW

When blocked, follow this sequence every time:

1. Run `dcg explain "cmd"` → Understand why (see trace)
2. Check Safe Alternatives table → Use if exists (DON'T mention override)
3. No alternative? → Explain risk clearly, let human decide
4. Human approves? → THEY run: dcg allow-once CODE

Never: Ask for override first. Never retry silently. Never circumvent.

Risk-tiered approval counts

When no safe alternative exists and the human must decide, the number of distinct human approvals scales with what the command can destroy:

Stop conditions: never present a tier-2 or tier-3 command as tier-1; never convert several pending blocks into one blanket approval. A single "yes" that gets spent across multiple destructive commands is the approval laundering failure mode — each allow-once code is bound to one command in one directory, and the workflow must keep it that way.

Example block output:

BLOCKED: git reset --hard HEAD
Rule: core.git:reset-hard
Reason: Discards uncommitted changes permanently
Allow-once code: ab12
Safer alternative: git stash

Good response:

"I wanted to discard changes but git reset --hard was blocked. Let me use git stash instead—recoverable if needed." [proceeds with stash]

Safe Alternatives

Quick Reference

dcg doctor              # Health check — hook registered?
dcg explain "cmd"       # WHY is it blocked? (with trace)
dcg test "cmd"          # Would this be blocked? (dry-run)
dcg allow-once CODE     # Human approves (THEY run this)
dcg packs               # List available rule packs
dcg scan --staged       # Pre-commit: scan for issues

What Gets Blocked

Context-aware (measured on dcg 0.5.6): the temp carve-out allows rm -rf under /tmp, /private/tmp, /var/tmp, and the literal $TMPDIR form. Everything else — rm -rf ./build and other relative paths (core.filesystem:rm-rf-general), absolute paths like /home/... and / (core.filesystem:rm-rf-root-home), and even /private/var/tmp — is blocked. Unresolved variables other than $TMPDIR are not treated as temp.

dcg explain example (7-step pipeline):

$ dcg explain "git reset --hard HEAD"
BLOCKED by core.git:reset-hard

Evaluation trace:
  1. Config allow overrides: no match
  2. Config block overrides: no match
  3. Heredoc detection: not applicable
  4. Quick reject: triggered (contains "reset")
  5. Context sanitization: no changes
  6. Normalization: git reset --hard HEAD
  7. Pack evaluation:
     - Safe patterns: no match
     - Destructive: MATCH "reset --hard"

Suggestion: Use `git stash` to preserve changes

Anti-Patterns

❌ "Command blocked. Run dcg allow-once ab12"  → Find alternative first!
❌ *Retrying silently or circumventing*         → Always acknowledge blocks
❌ Treating blocks as errors                    → They're checkpoints
❌ Asking user to allow-once without explaining → They need context

Configuration

# .dcg.toml — enable rule packs per-project
[packs]
enabled = ["database.postgresql", "kubernetes.kubectl", "cloud.aws"]

[overrides]
allow_patterns = ["rm -rf ./node_modules"]  # Project-specific safe

Environment variables:

• DCG_PACKS="containers.docker,kubernetes" — Enable packs
• DCG_DISABLE="kubernetes.helm" — Disable specific packs
• DCG_BYPASS=1 — Escape hatch (human-only)

Key Facts

• 49+ rule packs available (database, containers, k8s, cloud, etc.)
• Sub-millisecond latency — won't slow your workflow
• Fail-open on timeout — if DCG hangs, command runs (with warning)
• Heredoc scanning — inline scripts (bash -c, python -c) are analyzed
• Inline-fragment false positives — because scanning matches a destructive token anywhere in the command string, a pattern that appears only as data (a commit message body, a here-doc payload, a probe argument) can trip a block even though nothing destructive would run. Safe pattern: keep the payload off the command line — pass it via a file or stdin (e.g. git commit -F <file>), or run the intended tool directly instead of inlining the text. Never reconstruct a blocked command by splitting or escaping its tokens to slip past the guard — that defeats the safety layer.
• Allow-once codes — 4 hex chars, 24h expiry, bound to exact command+directory

The Incident That Started It All

On December 17, 2025, an AI agent ran git checkout -- on files containing hours of uncommitted work. The files were recovered via git fsck --lost-found, but it proved: instructions don't prevent execution—mechanical enforcement does.

Validation

# Quick health check
dcg doctor | head -20

# Test if a command would be blocked
dcg test "git reset --hard HEAD"

# Should show: WOULD BE BLOCKED

Output Specification

• Path: the response and command output on stdout/stderr; write .dcg.toml or .dcg/allowlist.toml only when configuration was explicitly requested.
• Filename: preserve DCG's project filenames exactly; ordinary block handling creates no persistent file.
• Format: state the blocked command, matched rule, risk, reversible alternative, and the alternative's validation result; quote commands exactly.
• Exit code: run bash skills/dcg/scripts/validate-dcg.sh and require zero for installation/configuration work; a blocked dcg test result is expected evidence, not permission to bypass.
• Downstream handoff: proceed with the validated safe alternative, or hand the exact risk and allow-once choice to the human when no equivalent exists.

Quality Checklist

• The response identifies the exact block and rule without exposing or suggesting an unauthorized bypass path.
• The chosen alternative is narrower, reversible where possible, and demonstrably preserves the user's requested outcome.
• Validation distinguishes an expected destructive-command block from a broken DCG installation or configuration.

Scripts

References

• COMMANDS.md — Full CLI reference with dcg explain, dcg scan
• PACKS.md — 49+ rule pack system (database, k8s, cloud, etc.)
• CONFIG.md — Configuration, agent profiles, heredoc settings
• SCENARIOS.md — Detailed examples with good/bad responses
• PHILOSOPHY.md — Why DCG works this way
• TROUBLESHOOTING.md — Common issues and fixes