Universal Agent Hook Scaffold

Scaffold or migrate agent lifecycle hooks so every selected harness points at repo-owned hook scaffolding. This is the single hooks scaffolder: the former scaffold-cc-hooks, scaffold-codex-hooks, scaffold-github-copilot-hooks, scaffold-devin-hooks, and scaffold-opencode-hooks skills are retired and live here as internal harness components under harnesses/<name>/.

Decision Tree

1. If the user says /scaffold-hooks, hooks, lifecycle hooks, hook migration, or names any of Claude Code, Codex, GitHub Copilot, Devin CLI, or OpenCode hooks, use this skill.
2. If the user names harnesses, pass exactly those harnesses with --harnesses <list>. A single-harness request is just --harnesses <name>.
3. If the user gives no target path, use the current workspace or repository root as the target project.
4. If the user gives no harness preference, inspect the target project. When any supported hook surface or managed scaffold state exists, run the universal script without --harnesses so it refreshes exactly the detected harnesses. Do not add new harnesses unless the user explicitly asks.
5. If no supported hook surface exists, ask which harnesses to scaffold. Default to all supported harnesses (claude, codex, copilot, devin, opencode) for a new scaffold.
6. If existing configs point at .claude/hooks/generated, .codex/hooks/generated, or .devin/hooks/generated, treat the work as a migration: strip those managed command entries, scaffold hooks/, and remove only legacy managed folders that contain a manifest.
7. If the project has custom hooks outside managed roots, preserve them unless the user explicitly asks for removal.

Harness Selection

Selection order is deterministic:

1. Explicit --harnesses from the user.
2. A custom universal plan's harnesses list, when present.
3. Detected existing hook surfaces or managed scaffold state in the target repo.
4. The default all-supported set only when none of the above exists.

Detected surfaces include current managed manifests, legacy generated manifests, shared adapters under hooks/, and harness config files that already contain hook entries. If any harness is detected, do not expand to other harnesses without explicit user direction.

• claude — Claude Code, .claude/settings.json
• codex — Codex CLI, .codex/hooks.json (requires the hooks feature flag; see harnesses/codex/references/feature-flag.md)
• copilot — GitHub Copilot (cloud agent + CLI), .github/hooks/copilot-hooks.json with generated events under .github/copilot/hooks/generated/
• devin — Devin CLI, .devin/hooks.v1.json
• opencode — OpenCode, opencode.json plus .opencode/hook/hooks.md through opencode-froggy

Pass explicit additions as --harnesses claude,codex,copilot,devin,opencode (or a subset). A bare run on a repo that already has hooks is a refresh, not an expansion.

Quick Reference

Task	Command
Refresh detected existing harnesses, or scaffold all in a clean repo	scripts/scaffold_all_hooks.sh --project /path/to/project
Preview without writes	scripts/scaffold_all_hooks.sh --project /path/to/project --dry-run
Use a project-specific universal plan	scripts/scaffold_all_hooks.sh --project /path/to/project --plan /path/to/scaffold-hooks.json
Scaffold only selected harnesses	scripts/scaffold_all_hooks.sh --project /path/to/project --harnesses claude,codex
Refresh harness adapters while preserving shared event scripts	scripts/scaffold_all_hooks.sh --project /path/to/project --mode overhaul
Audit a target repo for one harness	harnesses/<name>/scripts/audit_project.sh /path/to/project
Validate a harness component	python3 harnesses/<name>/scripts/validate.py harnesses/<name>
Run a harness test suite	python3 harnesses/<name>/scripts/test_skill.py harnesses/<name>

Standard Workflow

1. Inspect the target project first:
   • existing .claude/settings*.json
   • .codex/hooks.json and .codex/config.toml
   • .devin/hooks.v1.json and .devin/config*.json
   • opencode.json, .opencode/hook/hooks.md, old .opencode/plugins/.managed/, and any custom .opencode/plugins/
   • .github/hooks/copilot-hooks.json and .github/copilot/hooks/generated/
   • existing hooks/ tree and repo-owned validation scripts under scripts/
2. Confirm the harness set only when creating a new scaffold or adding harnesses. For a bare invocation on a repo with existing hook surfaces, refresh the detected set only.
3. Verify the live official harness docs before making event-surface changes. Each harness component records its verified contract in harnesses/<name>/assets/hook-events.json and its workflow in harnesses/<name>/PLAYBOOK.md.
4. Start from templates/hook-plan.example.json unless the project already has a clearer plan.
5. Run scripts/scaffold_all_hooks.sh with --dry-run, then without --dry-run.
6. Review hooks/README.md, hooks/.state/scaffold-hooks/manifest.json, the harness config files, and the selected adapters.
7. Run the project's normal validation.

Output Shape

The target project should end up with this pattern:

hooks/
  README.md
  lib/
    agent-hook-runtime.sh
    claude.sh
    codex.sh
    devin.sh
  .state/
    scaffold-hooks/
      manifest.json
    claude/
    codex/
    devin/
  stop/
    script.sh
    claude.sh
    claude.json
    codex.sh
    codex.json
    devin.sh
    devin.json
.opencode/
  hook/
    hooks.md
    README.md
    .managed/
      manifest.json
      plan.snapshot.json
opencode.json

Harness config files stay in their documented locations:

• Claude: .claude/settings.json
• Codex: .codex/hooks.json
• Devin: .devin/hooks.v1.json
• OpenCode: opencode.json loads opencode-froggy; Froggy reads .opencode/hook/hooks.md
• GitHub Copilot: .github/hooks/copilot-hooks.json with generated events under .github/copilot/hooks/generated/ (self-contained because the Copilot cloud agent reads everything from the repo)

Plan Shape

Use templates/hook-plan.example.json as the source of truth for the universal plan schema. The top-level plan controls shared behavior:

• mode: additive or overhaul
• hooks_root: normally hooks
• cleanup_legacy: remove old managed generated folders only when they contain a manifest
• harnesses: subset of claude, codex, copilot, devin, opencode; use this only when intentionally choosing or expanding the harness set
• plans: per-harness plan objects passed to the harness components

Read references/plan-format.md before adding project-specific scripts or commands.

Collision Policy

This skill is conservative:

• Strip old managed generated-root commands before appending new hooks/<event>/<harness>.sh commands.
• Preserve non-managed custom hooks in the same config files.
• Preserve existing hooks/<event>/script.sh files so shared project behavior is not rewritten by another harness.
• In overhaul mode, delete only selected harness adapters/state under hooks/, then call the harness components in additive mode for shell harnesses.
• For OpenCode, preserve unmanaged .opencode/plugins/ files but migrate scaffold-owned plugin output to opencode-froggy and .opencode/hook/hooks.md.

Read references/collision-policy.md before changing merge behavior.

Harness Components

Each supported harness is a self-contained component under harnesses/<name>/ with its own PLAYBOOK.md, scaffolding scripts, event manifest, templates, references, validator, and test suite:

• harnesses/claude/ owns Claude Code event semantics and .claude/settings.json merging.
• harnesses/codex/ owns Codex event semantics, feature-flag handling, and .codex/hooks.json merging.
• harnesses/devin/ owns Devin event semantics and .devin/hooks.v1.json merging.
• harnesses/opencode/ owns OpenCode Froggy configuration, opencode.json plugin merging, and cleanup of prior scaffold-owned local plugin artifacts.
• harnesses/copilot/ owns GitHub Copilot event semantics and .github/hooks/copilot-hooks.json merging for the cloud agent and Copilot CLI.

When an event name, matcher, output contract, or feature flag changes, update the harness component first (manifest, references, scripts, tests), then the universal orchestration. Read references/harness-composition.md when changing the composition order or adding a harness.

Protocol Output Hygiene

Treat stdout as part of the harness protocol, not a scratch log. For JSON-output hooks, stdout is reserved for the final protocol JSON payload; successful no-op paths should stay quiet unless the event contract explicitly allows stdout. Send diagnostics, debug text, filenames, and human-readable failure details to stderr unless the harness requires them on stdout.

Helper and predicate functions must be silent by default and return exit status only. Use quiet checks such as grep -q / grep -Eq, or redirect stdout to /dev/null; do not use filename probes like grep ... | head -1 unless the output is captured and cannot leak to hook stdout. Known regression: hook_has_code_changes must remain an exit-status-only predicate.

Validate generated JSON-output hooks for zero stdout on success/no-op paths, parseable JSON with no prefix or suffix on blocking paths, and no filenames/debug/status lines leaking from shared helpers.

Gotchas

1. Do not pass overhaul directly to the shell harness scaffolders from a universal run. They would rewrite shared script.sh files. The universal script performs harness cleanup first, then calls them additively.
2. OpenCode now uses opencode-froggy as the plugin layer. Do not recreate the old generated .opencode/plugins/*.ts lifecycle adapter unless the user explicitly asks for custom plugin code.
3. Legacy generated folders should be deleted only when they contain a managed manifest. Otherwise they may be user-owned files with an unfortunate path name.
4. A clean-looking config can still collide if old generated commands remain. Always scan final configs for .claude/hooks/generated, .codex/hooks/generated, and .devin/hooks/generated.
5. Keep project policy in repo-owned scripts such as ./scripts/agent-stop-checks.sh; hook adapters should translate protocol, not duplicate validation logic. Generated shell Stop adapters default to run_on_code_changes: true and use detected source/config extensions so expensive checks do not run on clean turns.
6. Copilot does not write adapters into the shared hooks/ tree. Its generated events stay under .github/copilot/hooks/generated/ because the Copilot cloud agent only reads files committed to the repository; keep shared policy in repo-owned scripts/ that both layers call.
7. Shared scripts that emit session context should use the Claude/Codex/Devin hookSpecificOutput.additionalContext JSON shape. Devin strictly parses non-empty stdout as Claude-format JSON and silently drops plain text; Claude Code also accepts the shared JSON shape, so do not special-case Claude for SessionStart. See references/harness-composition.md for details.
8. Treat exit codes and output streams as separate contracts. Exit code controls success, failure, or blocking; stderr is for diagnostics and failure reasons, not successful status messages. Successful routine skips should write to stdout only when the harness protocol allows it, or stay quiet.
9. Froggy's isMainSession condition handles main-session filtering for OpenCode hooks; use it on session lifecycle hooks that should skip child/subagent sessions.
10. Managed manifests record scaffold skill provenance, plan/template hashes, selected harnesses, detected harnesses, selection source, and managed file hashes. Re-runs should use those snapshots to refresh unchanged managed adapters while preserving user-modified files.
11. A bare /scaffold-hooks invocation is conservative. If any supported hook surface is detected, refresh only that detected set; do not expand to other harnesses unless the user explicitly asks.

Hook Visibility Matrix

Harness TUIs differ in whether hook activity is visible. Set expectations during scaffolding so users do not mistake silence for failure:

Harness	Renders hook runs in TUI	Verify hooks via
Claude Code	Partially (errors, verbose mode)	/hooks, transcript
Codex CLI	Yes ("Running SessionStart hook", hook context inline)	visible inline
Devin CLI	No (silent even on success; systemMessage not rendered as of v2026.5.26-8)	/hooks, CLI logs, transcript JSON, ask the agent
OpenCode	Plugin-defined	plugin logs
GitHub Copilot	Cloud agent: session logs; CLI: varies	session logs, .github/copilot/hooks/generated/ output

Progressive Maintainer Drift Check

When this skill changes, live-fetch the official hook docs for every affected harness on the day of the edit and compare them with harnesses/<name>/assets/hook-events.json. Update the harness component first (manifest, references, generators, templates, validators, tests), then the universal orchestration. Do not update this skill from memory; the per-harness manifests are the event-contract source of truth. Each harnesses/<name>/PLAYBOOK.md carries the detailed drift checklist for its harness.