Verify every edit automatically

Goal: stop relying on the agent to remember to check its work. Push the compiler's verdict into the session after every edit, and block a turn that would end with a broken build.

Do It

fuse mcp install --client claude --with-hooks

This writes two Claude Code hooks into your project's .claude/settings.json:

• a PostToolUse hook (on Edit and Write) that runs fuse check --delta --fast, so after every file change the transcript shows exactly the diagnostics that change introduced or resolved, and
• a Stop hook that runs fuse gate, which blocks the turn from ending while the session has introduced compiler errors it has not resolved.

The merge preserves any hooks and settings you already have, and re-running is idempotent. Remove the two fuse entries from the hooks section of that file to uninstall.

What The Agent Sees

After an edit that breaks a call, the hook adds a line like:

fuse: 1 diagnostic(s) introduced, 0 resolved by your change.
  introduced Error CS1061 src/Orders/OrderService.cs:42: 'Order' does not contain a definition for 'Total'

An edit that changes nothing the compiler cares about prints nothing: the hook is silent on an empty delta, so it never spams the transcript. When the turn tries to end while an introduced error remains, fuse gate exits nonzero and names the error, so the harness holds the turn open until the agent fixes or reverts it.

Baseline Discipline

"Red" means only the diagnostics the session itself introduced, never the errors that were already in the repository when the session started. An agent working a repository that does not currently build is not walled in by pre-existing errors; the gate blocks only on what this session broke.

How It Stays Fast

The hooks talk to the already-running Fuse host (the same process your editor and MCP client use) over its local pipe and ask it for the delta; they never run a build. When no host is serving the workspace, the commands exit immediately and silently, so a hook is never a drag on editing. This is why ambient verification needs a resident host: the delta is read from the live compilation the host holds, with no rebuild.

Other Harnesses

The commands are not Claude-specific. Any harness that can run a command after an edit and on turn end can wire the same two commands: fuse check --delta --fast for the per-edit delta and fuse gate for the turn gate. fuse mcp install --with-hooks only automates the Claude Code wiring.

Verify the Hooks

Make a reversible edit that introduces a compiler error. Confirm the post-edit hook reports that new diagnostic and the stop hook blocks while it remains. Revert the edit and confirm the resolved diagnostic clears the gate.