# Adopt bce on an existing repository Turning a conformance gate on a codebase that already drifts is where most such gates die: a first honest run surfaces dozens of pre-existing violations, "fix all of them first" becomes a blocking chore nobody schedules, and the gate is never turned on. bce is designed so you can turn it on **today** — enforcing from this commit forward for anything new, while the debt that predates the gate burns down as normal work. There is deliberately **no `--skip` flag**. Adoption is handled by committed, PR-reviewed configuration files — never by an invisible CI-line override. That is what keeps a green verdict honest. The two config files are `.bce-mode.json` (advisory mode) and `.blueprints/baseline.json` (the shrink-only baseline).

BCE brownfield adoption begins in committed advisory mode with all existing violations visible. A reviewed shrink-only baseline separates known debt from new drift, then enforced mode blocks every new violation while existing debt decreases from 75 to 38 to zero. A downgrade requires visible reviewed rationale.

## The two adoption controls Mode and baseline are independent, committed controls. Mode decides whether a graded violation blocks; an optional baseline decides which already-recorded violations are non-blocking. Graduation changes mode and does not require an empty baseline. ``` mode: advisory ── graduate ──► enforced baseline: absent ◄──────────────► present (existing debt only) ``` ### Advisory mode: turn it on, block graded violations later Author a blueprint (or have an agent draft one — see [`agent-loop.md`](https://blueprint-conformance.github.io/bce/source/docs/agent-loop.md)) and drop it in `.blueprints/`. Then commit an advisory-mode marker so a red verdict is printed loudly but does not fail the build: ```bash # .bce-mode.json — committed, reviewed; NOT a flag on the gate { "mode": "advisory" } ``` Now `bce gate` runs in CI, prints the full verdict with an unmissable advisory banner, stamps the report `mode: "advisory"` — and exits `0` regardless of the verdict. You see exactly how much drift exists without turning the tree red on anyone. This is the first-look rung: it changes the *whole* gate's exit code to 0; it never hides or softens the verdict. ### Baseline overlay: block new drift, show the debt When you are ready to start *failing on new drift* — but not yet ready to fix all the pre-existing violations — record the current violations into a baseline and switch out of advisory: ```bash bce baseline # writes .blueprints/baseline.json with today's violations rm .bce-mode.json # (or graduate — see rung 3) so the gate enforces again ``` With a baseline present the gate stays **fully enforcing** and partitions every run's violations: - **NEW** (not in the baseline) → **fails the build**, exactly as if no baseline existed. - **BASELINED** (in the file) → reported, counted, and stamped `graded fail; all N BASELINED — non-blocking`. Never hidden, never mistakable for a graded green. An existing baseline **cannot grow in place**. A re-run auto-removes violations you have since fixed and refuses to *add* any that were not already in it. To accept a genuinely new violation you must delete the file and re-create it — and that deletion is a line in a pull request. There is no in-place "add this one" affordance, precisely because that affordance would be the bypass. Baselined violations are identified by a content-addressed `(blueprint, constraint, component)` tuple, so reformatting or moving a line does not spuriously re-redden — but moving a violation to a different component is correctly a new identity, and fails. > Why a baseline is not a `# noqa`-for-the-whole-repo — the full mechanics — is in > [`faq.md` §"Why is `baseline` not a bypass?"](https://blueprint-conformance.github.io/bce/source/docs/faq.md#why-is-baseline-not-a-bypass). ### Graduate: the recorded flip to enforced `bce graduate` records the advisory→enforced transition in-repo and flips the config. It is **one-way**: going back to advisory requires an explicit `--rationale`, recorded in the tree, so the posture is always a governed, visible fact rather than a quiet CI edit. ```bash bce graduate # advisory → enforced, recorded ``` ### Enforced mode: new drift blocks Enforced mode can coexist with a nonempty baseline: new violations block while recorded debt remains visible and non-blocking. As that debt is fixed, the baseline shrinks; when empty, delete it and the gate enforces everything. ## The honest brownfield story On a real codebase a first run might surface, say, 75 pre-existing violations. The dishonest options are "fix all 75 before turning it on" (so it never gets turned on) or "add a skip flag" (so the gate means nothing). bce's answer is the ladder: turn it on today in advisory to *see* the 75, baseline them so *new* drift is caught from this commit forward, and burn the 75 down as normal work with the tool guaranteeing the wall only comes down. Enforcing from day one for everything new; shrink-only for the debt that predates the gate. ## What adoption never does - It never adds a `--skip` / `--no-verify` / `--force` flag. None exists; the test suite asserts, by scanning the CLI source and by throwing every skip-shaped flag at a red gate, that none turns it green. - It never lets advisory or a baseline weaken the **grader**. An empty scan, a malformed blueprint, a repo with no blueprints — each is a hard fail-closed refusal regardless of mode or baseline. A baseline can re-classify a *graded* violation as non-blocking; it can never turn a refusal green. Advisory decides only whether a red *blocks the build* — the verdict is always honestly computed and printed. ## Recommended next step - [`agent-loop.md`](https://blueprint-conformance.github.io/bce/source/docs/agent-loop.md) — wire the gate in as your coding agent's done-check. - [`faq.md`](https://blueprint-conformance.github.io/bce/source/docs/faq.md) — the baseline-is-not-a-bypass mechanics, in full.