Developer Safety

Developer Safety

The operator-control + safety plugin: hooks that let you halt, redirect, and recover an agent session, plus two standing commit conventions. It's the safety half of the developer plugin suite — installable on its own, and it engages with developer-workflows' phase loop when both are present.

Install

claude plugin install developer-safety@crickets

On Antigravity, install by path (see Install crickets plugins). The hooks run observe / side-effect-only on Antigravity — the veto/inject behaviour is Claude-effective (Compatibility).

What it ships

Primitive	Kind	What it does
kill-switch	hook · PreToolUse	halt the next tool call when .harness/STOP exists — emergency operator stop
steer	hook · PreToolUse	inject .harness/STEER.md into context, then archive it — mid-run redirect
commit-on-stop	hook · Stop	save a dirty tree to an auto-save/<ts> branch at session end — crash recovery (never touches your branch, never pushes)
commit-no-coauthor	snippet	never append a Co-Authored-By trailer — the user is the sole author
worktrees-never-auto	snippet	never auto-create git worktrees

Drive the control trio with the trigger files under .harness/ — see Driving the control trio below; the full hook catalog is in Hooks. The snippets emit as Antigravity rules/ and drop on Claude (where the conventions live in CLAUDE.md/AGENTS.md instead — see Customization types).

Driving the control trio

The three hooks are driven by trigger files under .harness/ (all per-repo):

File	Who writes it	Lifecycle
.harness/STOP	you	touch to halt; rm to resume
.harness/STEER.md	you	the hook renames it to STEER.consumed-<ts>.md after reading
auto-save/<ts> (branch)	commit-on-stop	recover (below), then git branch -D auto-save/<ts>

Halt a runaway session — in another terminal at the repo root:

touch .harness/STOP     # next tool call is blocked; rm .harness/STOP to resume

Redirect mid-run — write the correction; the next tool call injects it into context:

cat > .harness/STEER.md <<'EOF'
Use the existing helper at src/utils.py:format_record() instead of writing a new one.
EOF

To halt and redirect, write STEER.md first, then touch .harness/STOP. kill-switch is declared before steer in the plugin's hooks.json, so the halt always wins; when you rm STOP, the next call passes kill-switch and then steer injects the redirect. (Re-audit on every Claude Code release — this relies on declaration-ordered firing; rationale in ADR 0003.)

Recover crashed work — commit-on-stop saved each dirty turn to a branch:

git branch -a | grep auto-save                        # find the safety branches
git checkout main && git cherry-pick auto-save/<ts>    # bring the commit onto main

The hook never modifies your current branch or pushes — recovery is always your call.

On Antigravity the hooks run observe-only (no veto/inject). Approximate them with an always-on rule (.agents/rules/operator-control.md) that, before each step, checks .harness/STOP (halt) and .harness/STEER.md (apply + rename), and saves a dirty tree to an auto-save/<ts> branch at the end — best-effort, since the agent has to remember to check.

Troubleshooting. A hook didn't fire → confirm claude plugin list shows developer-safety (re-sync with claude plugin install developer-safety@crickets; the hooks run from the plugin, not .claude/hooks/). .harness/STOP ignored → it must be a regular file (touch, not mkdir), resolved against the repo root. No auto-save branch → a silent no-op when git is absent, you're not in a work tree, or the tree is already clean.

How it composes

• Standalone — installs and works on its own; depends on nothing.
• Enhances developer-workflows — soft: its hooks engage across the phase loop (/plan · /work · /review · /release) when both are installed.
• Hosts — both; Claude-effective, observe-only on Antigravity (Compatibility).

Why it works

The primitives compose into a safety net: operator-controllable (kill-switch + steer), recoverable (commit-on-stop saves to a side branch, never your own), and convention-enforcing (the commit guards). The agent stays steerable and its mistakes stay recoverable.

Related

• Hooks — the hook catalog + per-host effectiveness.
• ADR 0003 — base operator hooks — the design rationale + re-audit triggers.
• Plugin anatomy — what a crickets plugin is + its structure.
• Install crickets plugins — all three install modes.
• Developer Plugin Suite design — the developer-workflows / safety / code-review split.