Configuration

One file, committed to the repo: .linebreak/gate.yml. A boundary whose strictness depends on individual machines is not a boundary; here, a threshold change is itself a PR: visible, reviewable, attributable.

The full file

# .linebreak/gate.yml (all keys optional)
fail_on: critical            # blocking floor: critical (default) | high | medium | low
exclude_paths:               # paths the scanners skip
  - fixtures
  - "sandbox/*"
code_scan: auto              # AI code review: auto (default) | on | off
criteria:
  enforce: true              # acceptance-criteria checking
                             # (default: true when a spec bundle exists)
approvals:                   # signed-approval verification (Pro)
  public_keys:
    - kid: "2026-01"
      public_key: "<base64 Ed25519 verifying key>"

Key by key

Key	Default	Effect
`fail_on`	`critical`	Severity floor that blocks the merge. A finding at or above the floor fails the check.
`exclude_paths`	none	Glob patterns the scanners skip (fixtures, sandboxes, vendored test data).
`code_scan`	`auto`	The AI code review pass. `auto` runs it when a key is available (`ANTHROPIC_API_KEY` takes precedence over `LINEBREAK_LICENSE_KEY`); `off` also makes `report` ignore a committed code verdict, so scan and report can never disagree.
`criteria.enforce`	`true`*	Acceptance-criteria checking. *Default is on whenever an approved spec bundle exists; turning it off is an explicit (and visible) edit to this file.
`approvals.public_keys`	empty	Ed25519 verifying keys (`kid` + base64 key). See below: presence of a non-empty list is what makes signatures required.

Precedence

Explicit CLI flag / Action input → .linebreak/gate.yml → built-in default (critical). An invalid config exits 2: fail closed, never a silent fallback to defaults.

Signature verification keys

The presence of a non-empty approvals.public_keys list is the only switch that flips the gate from “unsigned OK” to “signature required.” It deliberately keys off this config, never off whether the spec manifest happens to carry a signature. Otherwise an attacker could strip the signature to downgrade to honest-unsigned. Multiple keys (distinct kids) let old and new approvals both verify across a key rotation. A malformed key is a config error (exit 2), not a silent verification miss.

GitHub Action inputs

Input	Effect
`fail-on`	Blocking floor for this workflow; overrides `gate.yml`.
`license-key`	`LINEBREAK_LICENSE_KEY`: enables the hosted AI code review and signed approvals (Pro).
`anthropic-api-key`	`ANTHROPIC_API_KEY`: runs the AI code review on your own model key (takes precedence; never billed as credits).
`story`	Scope of the acceptance-criteria check: `all` (default), `auto` (this branch’s story, inferred from `feat/<id>` or `story/<id>`, else started stories only), or a story id. Recommended: `auto` on pull requests, `all` at release.
`manual`	`warn` lists `manual` criteria without a sign-off as pending without blocking; `block` fails the check. Empty means `warn` on `pull_request` and `block` on every other event.
`stage`	`release` (default) evaluates every criterion; `pr` skips criteria marked `check.when: release` in the spec and lists them as release-only, so a shared-staging regression does not block every PR.