Follow-up builds (#23)

A build definition may declare afterSuccessOf, running whenever the named build of the same branch turns green — the deployment path chosen over a deployCommand or a separate deploy section. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Co-authored-by: mhoennig <michael@hoennig.de> Reviewed-on: #23
2026-09-05 20:02:32 +02:00
parent 0f9f119687
commit 4db294e1bc
18 changed files with 1015 additions and 34 deletions
@@ -40,9 +40,9 @@ All production code lives under `de.hoennig.werkator`, with sub-packages `comman
 - Everything repository-scoped (results, artifacts, worktrees, git and config access) goes through a `RepoContext`, never through an implicit current directory: the executor serializes per (context, branch) under one global `maxConcurrent`, the watcher polls every context in its own guard. `RepoRegistry` opens one context per entry of the instance configuration `~/.werkator.yml` (ADR 0009), or the current directory without one; the instance-level keys (`server`, `executor`, `watcher.pollInterval`) and the `defaults` block are folded into every repository's effective config by `ConfigLoader` itself, so no consumer reads the home file directly. Server routes carry the repository as `/repos/<name>/…` and `/api/repos/<name>/…`, with the unscoped form permanently meaning the served repository; the pages stay per repository and a drop-down in the page title switches between them.
 - When config keys change, three places must stay in sync: the `WerkatorConfig` data classes, the `InitCommand` templates, and `docs/configuration.md`.
 - Every config file may declare `werkator.version.since`/`below` (the Werkator it is written for, never a format version — no API is involved). `since` is enforced in both directions, using `ConfigVersions.FORMAT_BROKE_IN` for "file predates a breaking change"; `below` only warns. A violation aborts the start for the machine and project config, but fails only that branch's builds for a branch config.
- A branch describes its own CI: its committed `.werkator.yml` is the branch layer (`ConfigLoader.loadWithBranchLayer`, used by the watcher per origin branch and by `loadForWorktree` at build time) and takes precedence over `.git`/project — including the whole `builds` section, so a new configuration can be tried out on a branch without affecting other branches. Only the pinned set is stripped from that layer: secrets (`git`), host/repository sections (`server`, `gitea`, `executor`, `watcher`), the docker (`docker.enabled`, `docker.network`) and werkdock (`werkdock.enabled`, `werkdock.rootfs`, `werkdock.binary`) sandbox policies, and the trust gate (`requirePullRequest`). A branch must never reach credentials, disable its container or sandbox, change its network, substitute a foreign rootfs, raise global concurrency, or bypass its own pull-request gate; a branch's definitions apply to that branch alone.
- A build definition carries the complete description of its build, split in two: the `trigger` block (`onPush`, `atTimes`, `branches`, `activeWithin`) says when and for which branches it runs, everything else what it does. `builds.default` is the base every other definition inherits its settings — never its `trigger` — from. The split is structural so that a selector added to `TriggerConfig` later is non-inheritable by construction; writing a trigger key flat is refused, never ignored, because ignoring it leaves a build that silently stops running. A `!` prefix in `trigger.branches` excludes and always wins.
- The inheritance is applied after all layers are merged: that order is what makes a build a branch invents inherit the host's sandbox policy instead of the data-class default, so the pinning also holds for a build the host has never heard of. Pinned are `requirePullRequest`, `statusContext`, `docker.enabled`, `docker.network`, `werkdock.enabled`, `werkdock.rootfs`, and `werkdock.binary`. Docker and werkdock are mutually exclusive per branch — enabling both is rejected at start. The section was called `bwrap` until v1.2.0 and is still read under that name, with a warning; the hard refusal waits for the release that sets `ConfigVersions.FORMAT_BROKE_IN`.
+- A branch describes its own CI: its committed `.werkator.yml` is the branch layer (`ConfigLoader.loadWithBranchLayer`, used by the watcher per origin branch and by `loadForWorktree` at build time) and takes precedence over `.git`/project — including the whole `builds` section, so a new configuration can be tried out on a branch without affecting other branches. Only the pinned set is stripped from that layer: secrets (`git`), host/repository sections (`server`, `gitea`, `executor`, `watcher`), the docker (`docker.enabled`, `docker.network`) and werkdock (`werkdock.enabled`, `werkdock.rootfs`, `werkdock.binary`) sandbox policies, the trust gate (`requirePullRequest`), and the trigger of a follow-up build (`trigger.afterSuccessOf` everywhere, and the whole `trigger` block of a definition the host defines as a follow-up). A branch must never reach credentials, disable its container or sandbox, change its network, substitute a foreign rootfs, raise global concurrency, bypass its own pull-request gate, or deploy itself; a branch's definitions apply to that branch alone.
+- A build definition carries the complete description of its build, split in two: the `trigger` block (`onPush`, `atTimes`, `afterSuccessOf`, `branches`, `activeWithin`) says when and for which branches it runs, everything else what it does. `afterSuccessOf` makes a definition the follow-up of another one — a deployment is a build that follows a green build (PR#23): it runs at the predecessor's commit after every green run of it, whoever started that run, and the `FollowUpTrigger` that enqueues it is armed only by `Watcher.start()`. `builds.default` is the base every other definition inherits its settings — never its `trigger` — from. The split is structural so that a selector added to `TriggerConfig` later is non-inheritable by construction; writing a trigger key flat is refused, never ignored, because ignoring it leaves a build that silently stops running. A `!` prefix in `trigger.branches` excludes and always wins.
+- The inheritance is applied after all layers are merged: that order is what makes a build a branch invents inherit the host's sandbox policy instead of the data-class default, so the pinning also holds for a build the host has never heard of. Pinned are `requirePullRequest`, `statusContext`, `docker.enabled`, `docker.network`, `werkdock.enabled`, `werkdock.rootfs`, `werkdock.binary`, and the trigger of a follow-up build. Docker and werkdock are mutually exclusive per branch — enabling both is rejected at start. The section was called `bwrap` until v1.2.0 and is still read under that name, with a warning; the hard refusal waits for the release that sets `ConfigVersions.FORMAT_BROKE_IN`.
 - `builds` or the legacy `branches`, never both: `branches` is read only while the merged config defines no build at all (`builds.maxConcurrent` is not one), and ignored with a warning as soon as one exists. The section is deprecated and goes away once the repositories have migrated; then `ConfigVersions.FORMAT_BROKE_IN` gets set and a leftover `branches:` key must be rejected by name — the version check alone cannot catch a file that declares no version.
 - Web UI: server-rendered Thymeleaf plus one hand-written `static/werkator.js` — no SPA framework, no frontend build pipeline; every fetch has a timeout and an explicit error badge; `UiFormats` and `werkator.js` must produce identical display formats.
 - Git and Docker access shells out to the CLIs (`GitCommandRunner`, `docker`) — no JGit, no Docker SDK.
@@ -101,7 +101,9 @@ single branch may decide it:
 - the container sandbox policy: `docker.enabled`/`docker.network` and
  `werkdock.enabled`/`werkdock.rootfs`/`werkdock.binary` — host-pinned as
  long as only the host's configuration sets them, master-pinned once the committed
-  configuration does.
+  configuration does;
+- the trigger of a [follow-up build](#follow-up-builds): `trigger.afterSuccessOf` in every definition, and the whole `trigger` block of a definition the host defines as a follow-up.
+  A branch may say what its deployment does, never that — or for which branches — it happens.

 The distinction is documentary.
 Werkator applies one rule: every pinned key is stripped from the branch layer, and the
@@ -110,7 +112,7 @@ The names say where a key is meant to live, not how it is enforced.

 This keeps a branch from reaching credentials, reporting statuses to another repository,
 raising the global concurrency, disabling its own build container, changing its network
-mode, or bypassing its own pull-request gate. Everything else is the branch's to decide —
+mode, bypassing its own pull-request gate, or deploying itself. Everything else is the branch's to decide —
 it can already run any command through `buildCommand`.
 The pinned settings are stripped wherever they appear, in a build definition as well as in
 a legacy `branches` entry. The deprecated `branches` section itself is read from the repo
@@ -252,6 +254,7 @@ builds:
      # branches: ["*", "!master"]   # names or globs; a "!" pattern excludes; default: all
      # atTimes: ["01:00"]           # daily UTC times HH:MM ("??:05" = every hour at :05)
      # activeWithin: 24h            # only branches with commits in the last 24h
+      # afterSuccessOf: test         # run after every green run of that build, at its commit (pinned)
    # run before each build
    cleanCommand: rm -rf build
    # shell command for each build
@@ -397,9 +400,50 @@ Writing any of its keys outside the block is refused with a message naming the d
 Triggers: `onPush: true` builds every new commit of the selected branches; `atTimes: ["HH:MM", …]` rebuilds their heads once per day and slot (UTC).
 A slot may also be written as `??:MM` — that minute of every hour, expanded to its 24 slots, so the build runs hourly.
 Only the latest due slot of a day triggers, so slots missed while the server was down are skipped instead of piling up, and a slot whose pool is still building is retried on the next poll cycle until it succeeds.
-A definition may have both; one with neither never triggers automatically — which is how `builds.default` is written when it is meant as a settings base only.
+A definition may combine them; one with none of the three triggers (`onPush`, `atTimes`, `afterSuccessOf`) never runs automatically — which is how `builds.default` is written when it is meant as a settings base only.
 Werkator logs a warning once when no definition has a trigger at all, because such an instance never builds anything on its own.

+#### Follow-up builds
+
+`afterSuccessOf: <name>` makes a definition a *follow-up* of another one, its *predecessor*: it runs on the predecessor's branch at the predecessor's commit whenever a run of the predecessor ends green.
+This is how a deployment is configured: a deployment is a build that follows a green build, and it gets everything a build has — its own row in History with log and duration, its own Gitea check under its own `statusContext`, restart, cancel, artifacts, and the per-branch serialization.
+
+Every green run counts, whatever started it — the push watcher, an `atTimes` slot, a UI restart, `werkator retry`, or the startup recovery — and a repeated green run of the same commit triggers the follow-up again.
+The follow-up builds the commit that was tested, not the branch's current origin head.
+A failed, cancelled, or interrupted run triggers nothing.
+The follow-up runs in the branch's worktree, after its predecessor, in the branch's sandbox or container — so a deployment tool like the Docker CLI is provided the way a compiler is.
+It inherits `builds.default` like every definition, so a deployment that wants the predecessor's output has to set `cleanCommand: ""` itself; a deployment command should rather be self-contained and rebuild what it ships, because a restart of the follow-up alone runs without its predecessor.
+The pull-request gate is not consulted for a follow-up: the predecessor passed it for the same commit, and the follow-up's `branches` selector is its own gate.
+
+The trigger of a follow-up is pinned: a branch's committed config can neither add `afterSuccessOf` to a definition nor change the `trigger` block of a definition the host defines as a follow-up, so a branch cannot deploy itself.
+What the deployment *does* comes with the repository, like every build command; where and when it happens, and with which credentials, is the host's.
+The host's part lives in `.git/werkator/.werkator.yml`; credentials reach the sandbox like any build setting, through `werkdock.env`/`docker.env`, and a file such as an SSH key through the werkdock sandbox's persistent toolchain home, `.git/werkator/buildenv/home/` on the host, which the sandbox mounts as `/root`.
+
+```yaml
+# .git/werkator/.werkator.yml — the host's part: when, for which branches, with what
+builds:
+  deploy:
+    trigger:
+      afterSuccessOf: frontend
+      branches: ["main"]
+    statusContext: werkator/deploy
+    werkdock:
+      env:
+        DEPLOY_TARGET: user@host:~/doms/example.org/htdocs-ssl
+```
+
+```yaml
+# .werkator.yml — the repository's part: what
+builds:
+  deploy:
+    cleanCommand: ""
+    buildCommand: scripts/deploy-prod.sh -y "$DEPLOY_TARGET"
+```
+
+A follow-up whose predecessor no definition has, and a cycle of follow-ups, refuse the start with a message naming the definition — a deployment that silently never runs is the failure the flat-key refusal exists to prevent.
+A branch whose committed config drops or renames the predecessor only loses its follow-up, with a warning naming the branch.
+A one-shot `werkator build` runs no follow-ups — its process ends with its build — and says which ones the server would have run.
+
 Selector: `trigger.branches` lists branch names or glob patterns (`*` matches any characters, also across `/`); empty selects all origin branches.
 A pattern prefixed with `!` excludes instead, and an exclusion always wins regardless of order — `["*", "!master"]` is every branch but master.
 That is how a branch gets a build of its own without being built by the default one as well.
@@ -409,6 +453,7 @@ Both parts combine as an intersection.
 Settings: `buildCommand`, `cleanCommand`, `artifactDirs`, `stdoutLog`/`stderrLog`, `requirePullRequest`, `statusContext`, and `docker` and `werkdock` with all their keys.
 A definition carries the complete description of its build; unset keys fall back to `builds.default` and then to Werkator's own defaults.
 `requirePullRequest`, `statusContext`, `docker.enabled`, `docker.network`, `werkdock.enabled`, `werkdock.rootfs`, and `werkdock.binary` are pinned (master-pinned, see [the branch layer](#the-branch-layer-a-branch-describes-its-own-ci)): they are read from the repo install/project config even when a branch sets them in its own committed config.
+So is the trigger of a [follow-up build](#follow-up-builds).
 Inheritance from `builds.default` covers the settings only — the `trigger` block says when and where *this* build runs and is never inherited.
 Definitions are part of the branch layer: a branch may add its own and override those from the project config, for its own builds only.
 Because the inheritance is applied after all layers are merged, a build a branch invents still inherits the host's `builds.default` — its sandbox policy included, which is what keeps the pinning effective for a build the host has never heard of.
@@ -0,0 +1,199 @@
+> **WARNING:** This document describes only the change applied in this PR.
+> It may already be outdated once the next PR is merged.
+> Historic PR-documentation is not maintained along with new PRs — treat it as a snapshot, not as current documentation.
+
+## Related Links
+
+- [ADR 0007 — build definitions](../adrs/0007-2026-08-31.build-definitions.md): the `builds` section and its `trigger` block this PR extends.
+- [configuration.md — build definitions](../configuration.md#build-definitions): the reference this PR updates.
+- Werkbaum's `scripts/deploy-prod.sh`: the first deployment meant to run this way.
+
+## The Problem
+
+Werkator builds and reports, but it cannot deploy.
+Werkbaum's production deployment is still a script run by hand from a developer machine, after looking at the Werkator status.
+The step "if the build is green, run this" is exactly what a CI system is for, and the hand-off between the two is where releases go wrong: the wrong commit gets deployed, or a red commit, or nothing.
+
+Three ways to add deployments were considered:
+
+- A `deployCommand` next to `buildCommand`, run after a green `buildCommand` inside the same run.
+  Simple, but it creates a second command path inside one build — one log, one status, one duration for two different things — and a failed deployment would turn a green build red.
+- A separate `deploy` section with its own executor path, statuses, and cancellation.
+  A second execution path next to `buildCommand`, with everything the first one has to be built again.
+- **A deployment is a build that follows a green build.** Chosen.
+  A build definition may declare that it runs whenever another definition of the same branch turns green.
+  Everything a build has comes for free: its own row in History with log and duration, its own Gitea check under its own `statusContext`, restart without rebuilding, cancel, artifacts, and the per-branch serialization.
+
+## Non-Goals
+
+- A native execution path for deployments.
+  A follow-up build runs where every build of its branch runs — in the werkdock sandbox or the Docker container — so a deployment tool such as the Docker CLI is provided the same way a compiler is.
+- Waiting for *several* builds to be green.
+  `afterSuccessOf` names one build; an `all of` form is a follow-up PR if a repository ever needs it.
+- A separate secrets mechanism.
+  Deployment credentials reach the sandbox the way any build setting does — the host's `werkdock.env`/`docker.env` for the definition, and files placed in the sandbox's persistent toolchain home — and the pinning below keeps them on the branches the host names.
+- Handing the predecessor's artifacts to the follow-up.
+  The follow-up runs in the same worktree, so the predecessor's output is *usually* still there, but a deployment command must not rely on it (see Open Questions).
+- Recovering a follow-up whose enqueueing was lost to a server restart between the two builds.
+  The operator restarts the predecessor, which triggers the follow-up again.
+
+## The Scenarios
+
+### Feature: a build that follows a green build
+
+#### Background
+
+- A *follow-up build* is a build definition whose `trigger` block carries `afterSuccessOf: <name>`, naming another definition of the same configuration — its *predecessor*.
+- The follow-up runs on the predecessor's branch at the predecessor's commit, never at the branch's current origin head, so a deployment always ships the commit that was tested.
+- Like every non-default build it records under its own pool `<branch>@<name>`, and it should carry its own `statusContext` so that Gitea shows the deployment as a check of its own.
+- *Green* is every run of the predecessor that ends with `SUCCESS`, whatever started it: the push watcher, an `atTimes` slot, a UI restart, `werkator retry`, or the startup recovery.
+- The key belongs to the `trigger` block: it says *when* the build runs, so it is never inherited from `builds.default`, and writing it flat is refused like every other trigger key.
+
+#### Scenario#23.01: A green predecessor triggers the follow-up on the same commit
+
+So that a deployment ships exactly the commit that was just tested, with its own log, duration, and Gitea check.
+
+- **Given** a definition `deploy` with `trigger.afterSuccessOf: frontend` and `statusContext: werkator/deploy`
+  - **and** the build `frontend` of branch `main` at commit `c1` is running
+- **When** that build finishes with `SUCCESS`
+- **Then** a build `deploy` of branch `main` at commit `c1` is enqueued
+  - **and** it is recorded under the pool `main@deploy`
+  - **and** its Gitea status is posted under the context `werkator/deploy`
+  - **and** the origin head of `main` having moved on to `c2` meanwhile changes nothing about that
+
+##### Verified by
+
+- [FollowUpTriggerTest — "a green predecessor enqueues the follow-up at the predecessor's commit"](../../src/test/kotlin/de/hoennig/werkator/watcher/FollowUpTriggerTest.kt)
+
+#### Scenario#23.02: Every green run triggers again, including a repeated run of the same commit
+
+So that a deployment can be repeated by rerunning the build — and so that no run of a green build is silently *not* deployed, which would be more confusing than a redundant deployment.
+
+- **Given** the build `frontend` of `main` at `c1` was green and `deploy` ran for it
+- **When** `frontend` at `c1` is restarted from the UI, retried from the CLI, or rebuilt by an `atTimes` slot, and turns green again
+- **Then** `deploy` is enqueued for `c1` again
+
+##### Verified by
+
+- [FollowUpTriggerTest — "every green run of the predecessor triggers the follow-up again"](../../src/test/kotlin/de/hoennig/werkator/watcher/FollowUpTriggerTest.kt)
+
+#### Scenario#23.03: A run that is not green triggers nothing
+
+So that nothing is ever deployed from a failed, cancelled, or interrupted build.
+
+- **Given** the same definitions
+- **When** the build `frontend` ends as `FAILED`, `CANCELLED`, or `INTERRUPTED`
+  - **or** a build other than `frontend` ends as `SUCCESS`
+- **Then** no `deploy` build is enqueued
+
+##### Verified by
+
+- [FollowUpTriggerTest — "only a SUCCESS of the named predecessor triggers"](../../src/test/kotlin/de/hoennig/werkator/watcher/FollowUpTriggerTest.kt)
+
+#### Scenario#23.04: The trigger of a follow-up is host-pinned
+
+So that a branch can never deploy itself: a follow-up build is the host's way to hand real-world effects — targets, credentials — to a commit, and the host alone decides *when* and *for which branches* that happens.
+
+- **Given** the host configuration defines `deploy` with `trigger: {afterSuccessOf: frontend, branches: [main]}`
+- **When** a branch's committed `.werkator.yml` sets `builds.deploy.trigger.branches: ["*"]`
+  - **or** adds `afterSuccessOf` to any definition's trigger
+- **Then** the host's trigger block of `deploy` is used unchanged, and the branch's `afterSuccessOf` is dropped with a warning naming the branch
+  - **and** a branch the host's selector does not name never runs `deploy`, however green its own builds are
+
+##### Verified by
+
+- [ConfigLoaderTest — "a follow-up trigger is pinned to the host, a branch cannot add or widen one"](../../src/test/kotlin/de/hoennig/werkator/config/ConfigLoaderTest.kt)
+
+#### Scenario#23.05: What the follow-up does comes with the repository
+
+So that the deployment command is versioned with the code it deploys, like every other build command — while the host keeps the targets and credentials.
+
+- **Given** the host defines `deploy` with its trigger and `werkdock.env: {DEPLOY_TARGET: …}`
+  - **and** the committed `.werkator.yml` of `main` defines `deploy` with `cleanCommand: ""` and `buildCommand: scripts/deploy-prod.sh -y "$DEPLOY_TARGET"`
+- **When** `deploy` runs for `main`
+- **Then** it runs the committed command with the host's environment, in the branch's sandbox, in the branch's worktree, after its predecessor and serialized with the branch's other builds
+
+##### Verified by
+
+- [BuildExecutorTest — "a follow-up build runs in its branch's worktree after its predecessor"](../../src/test/kotlin/de/hoennig/werkator/build/BuildExecutorTest.kt)
+- [ConfigLoaderTest — "a branch supplies the command of a host-triggered follow-up"](../../src/test/kotlin/de/hoennig/werkator/config/ConfigLoaderTest.kt)
+
+#### Scenario#23.06: A follow-up that could never fire is refused at start
+
+So that a deployment that silently never runs cannot exist — the same reasoning that refuses a flat trigger key.
+
+- **Given** a configuration whose `afterSuccessOf` names a definition that does not exist
+  - **or** whose follow-ups form a cycle (`a` after `b`, `b` after `a`)
+  - **or** which writes `afterSuccessOf` outside the `trigger` block
+- **When** the configuration is loaded
+- **Then** loading fails with a message naming the definition and the reason
+  - **and** a definition with only `afterSuccessOf` counts as triggered, so the "no build triggered" warning is not raised for it
+
+##### Verified by
+
+- [ConfigLoaderTest — "afterSuccessOf must name an existing definition and must not form a cycle"](../../src/test/kotlin/de/hoennig/werkator/config/ConfigLoaderTest.kt)
+- [ConfigLoaderTest — "afterSuccessOf written flat is refused like every trigger key"](../../src/test/kotlin/de/hoennig/werkator/config/ConfigLoaderTest.kt)
+
+#### Scenario#23.07: Follow-ups fire in server mode only
+
+So that the invariant "nothing is scheduled during CLI runs or tests" holds: a CLI `build` ends when its build ends, and a follow-up enqueued into a process that is about to exit would only ever be recorded as interrupted.
+
+- **Given** `werkator build main` runs from the CLI and turns green
+- **When** the command finishes
+- **Then** no follow-up was enqueued, and the CLI says which follow-up the server would have run
+
+##### Verified by
+
+- [FollowUpTriggerTest — "the trigger listens only while the watcher runs"](../../src/test/kotlin/de/hoennig/werkator/watcher/FollowUpTriggerTest.kt)
+- [WatcherTest — "start arms the follow-up trigger before the recovery, stop disarms it"](../../src/test/kotlin/de/hoennig/werkator/watcher/WatcherTest.kt)
+- [BuildCommandTest — "a green CLI build names the follow-up builds the server would run, and runs none"](../../src/test/kotlin/de/hoennig/werkator/commands/BuildCommandTest.kt)
+
+## The Solution
+
+`TriggerConfig` gets a fourth key, `afterSuccessOf: String` (empty: none).
+It sits inside the `trigger` block on purpose, next to `onPush` and `atTimes`: it answers "when does this build run", so the structural rule of ADR 0007 makes it non-inheritable without touching any list, and `checkTriggerBlocks` refuses it written flat by adding it to `FLAT_TRIGGER_KEYS`.
+`isTriggered` counts it, so a definition with nothing but a predecessor is not reported as never triggering.
+A definition may itself be followed; `ConfigLoader` refuses an unknown predecessor and a cycle when it validates the merged configuration.
+
+A new `FollowUpTrigger` in the `watcher` package listens to `BuildStatusChangedEvent`.
+On a `SUCCESS` it resolves the definitions of the result's branch at the result's commit — the same `definitionsFor` the watcher uses for the branch layer — and enqueues, through `BuildExecutor.startBuild(repo, branch, commit, name)`, every definition whose `afterSuccessOf` names the finished build and whose selector selects the branch.
+Passing the commit explicitly is what makes Scenario#23.01's last line true; the executor's duplicate guard folds a follow-up that is already queued for the same commit.
+The listener is armed by the watcher's `start()` and disarmed by `stop()`, which is how it stays silent in CLI runs and tests (Scenario#23.07).
+
+The pinning extends `stripPinned`: `afterSuccessOf` is removed from every trigger of the branch layer, and for every definition whose host trigger carries `afterSuccessOf` the branch layer's whole `trigger` block is dropped.
+That is the smallest rule that makes Scenario#23.04 hold: a branch keeps the right to describe what its deployment does, and loses only the right to decide that — or where — it happens.
+The pull-request gate is not consulted for a follow-up: the predecessor passed it already for the same commit, and the host's selector is the follow-up's own gate.
+
+The follow-up runs like any other build of its branch — same worktree, same sandbox, serialized behind its predecessor.
+It inherits `builds.default`, so a deployment that wants the predecessor's output has to set `cleanCommand: ""` itself.
+
+Three places stay in sync with the new key, as the invariant demands: the data classes, the `init` templates (a commented `afterSuccessOf` line under the `trigger` block), and `docs/configuration.md`, which gets a "Follow-up builds" paragraph under build definitions and the new pinning in the branch-layer section.
+`AGENTS.md` names the key in the trigger and pinning invariants.
+
+## Open Questions
+
+- **Credentials inside the sandbox.**
+  Werkdock clears the environment and mounts the repository's persistent toolchain home as `/root`, so an SSH key placed under `.git/werkator/buildenv/home/.ssh/` on the host is `/root/.ssh/` inside the sandbox, and `werkdock.env` carries the target.
+  For Docker there is no equivalent mount today; a key passed through `docker.env` works but is visible in `docker inspect`.
+  Implemented: nothing new — the PR documents the werkdock path in `configuration.md` and leaves a Docker mount to a follow-up if vm4006 ever deploys.
+- **Restarting the follow-up alone.**
+  Restart re-runs `deploy` without its predecessor, in a worktree that may have been cleaned by a later build of the branch.
+  Implemented: allowed, and the reference recommends a self-contained deployment command that rebuilds what it ships (Werkbaum's `deploy-prod.sh` does).
+- **A predecessor that exists only on a branch.**
+  The host's `afterSuccessOf: frontend` refers to a name the branch layer may rename.
+  Implemented: refused at start for the primary configuration; for a branch whose layer lacks the name, a warning once per branch and commit, and no follow-up
+  (verified by [ConfigLoaderTest — "a branch whose layer lacks the predecessor loses only its follow-up"](../../src/test/kotlin/de/hoennig/werkator/config/ConfigLoaderTest.kt)).
+  An instance fragment checked by `init --apply` is not checked for its predecessor at all: the build it names may well live in the project config it is merged with, and the merged configuration is checked on every load anyway.
+
+## Additional Changes
+
+- `BuildStatusChangedEvent` now carries the `RepoContext` the result belongs to: a `BuildResult` does not know its repository, and the listener has to enqueue into the right one.
+- `ConfigLoader.loadWithBranchLayer` and `loadForWorktree` take an optional branch name, used only to name the branch in the pinning warnings; the watcher passes it.
+- The follow-up check distinguishes three loads: the primary configuration refuses a missing predecessor, a branch layer warns, and an instance fragment (`init --apply`) skips the check — its predecessor may live in the project config it is merged with.
+- The "no build triggered" warning now names `afterSuccessOf` as the third trigger.
+
+## Follow-up PRs
+
+- Werkbaum: commit the `deploy` definition to its `.werkator.yml`, add the host part on mih09, and retire the manual `deploy-prod.sh` invocation from the README.
+- `afterSuccessOf` as a list (all green), if a repository ever needs a deployment gated on more than one build.
+- A Docker bind mount for credential files, if a Docker host deploys.
@@ -119,7 +119,7 @@ class BuildExecutor(
                artifactKey = runningBuild.artifactKey,
            )
        repo.results.append(pending)
-        eventPublisher.publishEvent(BuildStatusChangedEvent(pending))
+        eventPublisher.publishEvent(BuildStatusChangedEvent(pending, repo))
        val activeBuild = ActiveBuild(runningBuild, repo)
        builds[runningBuild.artifactKey] = activeBuild
        publishGiteaStatus(activeBuild, BuildStatus.PENDING, duration = null)
@@ -384,7 +384,7 @@ class BuildExecutor(
                duration = duration,
                artifactKey = runningBuild.artifactKey,
            ).also { build.repo.results.append(it) }
-        eventPublisher.publishEvent(BuildStatusChangedEvent(updated))
+        eventPublisher.publishEvent(BuildStatusChangedEvent(updated, build.repo))
        publishGiteaStatus(build, status, duration)
        return updated
    }
@@ -35,7 +35,12 @@ data class RunningBuild(
    var runningSince: Instant? = null
 }

-/** Published via Spring's `ApplicationEventPublisher` on every persisted status transition. */
+/**
+ * Published via Spring's `ApplicationEventPublisher` on every persisted status transition.
+ * Carries the repository because a [BuildResult] does not: a listener that reacts to the
+ * transition — the follow-up trigger — has to act on that repository.
+ */
 data class BuildStatusChangedEvent(
    val result: BuildResult,
+    val repo: RepoContext,
 )
@@ -1,9 +1,11 @@
 package de.hoennig.werkator.commands

 import de.hoennig.werkator.build.BuildStatus
+import de.hoennig.werkator.config.BuildDefinition
 import de.hoennig.werkator.git.GitService
 import de.hoennig.werkator.repo.RepoContext
 import de.hoennig.werkator.repo.RepoRegistry
+import de.hoennig.werkator.watcher.FollowUpTrigger
 import org.springframework.stereotype.Component
 import picocli.CommandLine.Command
 import picocli.CommandLine.ExitCode
@@ -27,6 +29,7 @@ class BuildCommand(
    private val gitService: GitService,
    private val consoleBuildRunner: ConsoleBuildRunner,
    private val registry: RepoRegistry,
+    private val followUpTrigger: FollowUpTrigger,
 ) : Callable<Int> {
    @Mixin
    var repoOption = RepoOption()
@@ -58,9 +61,33 @@ class BuildCommand(
        }
        println("building branch $branch at commit ${commit.take(12)}")
        val status = consoleBuildRunner.buildAndStream(repo, branch, commit)
+        if (status == BuildStatus.SUCCESS) {
+            reportSkippedFollowUps(branch, commit)
+        }
        return if (status == BuildStatus.SUCCESS) ExitCode.OK else ExitCode.SOFTWARE
    }

+    /**
+     * A one-shot build ends with its process, so it never runs the follow-up builds the
+     * server would enqueue after a green run (PR#23) — it says which ones instead of
+     * leaving the operator to wonder why nothing was deployed.
+     */
+    private fun reportSkippedFollowUps(
+        branch: String,
+        commit: String,
+    ) {
+        val followUps =
+            try {
+                followUpTrigger.followUpsOf(repo, branch, commit, BuildDefinition.DEFAULT)
+            } catch (e: Exception) {
+                System.err.println("warning: could not determine the follow-up builds (${e.message})")
+                return
+            }
+        if (followUps.isNotEmpty()) {
+            println("note: the server would now run the follow-up build(s) ${followUps.joinToString(", ")}; a CLI build does not")
+        }
+    }
+
    /** A one-shot build should still work offline, from the last fetched origin state. */
    private fun fetchBestEffort() {
        try {
@@ -223,6 +223,7 @@ class InitCommand(
                  # branches: ["*", "!master"]   # names or globs; "!" excludes; default: all
                  # atTimes: ["01:00"]           # daily UTC times HH:MM ("??:05" = every hour at :05)
                  # activeWithin: 24h            # only branches with recent commits
+                  # afterSuccessOf: test         # run after every green run of that build, at its commit (pinned)
                # run before each build
                cleanCommand: rm -rf build
                # shell command for each build
@@ -89,8 +89,9 @@ data class BuildDefinition(
 * When a build runs and for which branches — the `trigger` block of a build definition,
 * and the one part of it that is never inherited from `builds.default`.
 *
- * A definition with neither [onPush] nor [atTimes] never triggers automatically; that is
- * how `builds.default` is written when it is meant as a settings base only.
+ * A definition with neither [onPush] nor [atTimes] nor [afterSuccessOf] never triggers
+ * automatically; that is how `builds.default` is written when it is meant as a settings
+ * base only.
 */
 data class TriggerConfig(
    /** Build every new commit of the selected branches. */
@@ -112,7 +113,19 @@ data class TriggerConfig(
     * empty applies no age filter. Combines with [branches] as an intersection.
     */
    val activeWithin: String = "",
+    /**
+     * Name of another definition of this configuration — the *predecessor*: this build
+     * runs on the predecessor's branch at the predecessor's commit whenever a run of it
+     * ends with `SUCCESS`, whatever started that run (PR#23). Empty means none. Sits in
+     * the trigger block because it says *when* this build runs, so it is never inherited;
+     * and it is host-pinned, because a follow-up build is the host's way to hand
+     * real-world effects — deployment targets, credentials — to a green commit.
+     */
+    val afterSuccessOf: String = "",
 ) {
+    /** True when this build follows another one, see [afterSuccessOf]. */
+    fun isFollowUp(): Boolean = afterSuccessOf.isNotBlank()
+
    /** True when [branch] matches the [branches] patterns (or none are configured) and none excludes it. */
    fun selectsByName(branch: String): Boolean {
        val (excluding, including) = branches.partition { it.startsWith(EXCLUDE_PREFIX) }
@@ -90,7 +90,8 @@ class ConfigLoader(
    fun loadForWorktree(
        workingDir: Path,
        worktreeDir: Path,
-    ): WerkatorConfig = withBranchLayer(workingDir, loadFile(worktreeDir.resolve(ConfigFiles.firstExisting(worktreeDir)).toFile()))
+        branch: String? = null,
+    ): WerkatorConfig = withBranchLayer(workingDir, loadFile(worktreeDir.resolve(ConfigFiles.firstExisting(worktreeDir)).toFile()), branch)

    /**
     * The primary/`.git` config with the committed `.werkator.yml` of one branch
@@ -107,30 +108,53 @@ class ConfigLoader(
     * (`requirePullRequest`, which decides whether the branch is built at all).
     * They are stripped from the branch layer before merging, so a branch can neither
     * escape its container, nor bypass its own pull-request gate, nor raise the global
-     * concurrency, nor reach the credentials.
+     * concurrency, nor reach the credentials. The trigger of a follow-up build is pinned
+     * the same way (PR#23): a branch may say what its deployment does, never that — or
+     * where — it happens. [branch] only names the branch in the warnings.
     */
    fun loadWithBranchLayer(
        workingDir: Path,
        branchConfigYaml: String?,
-    ): WerkatorConfig = withBranchLayer(workingDir, parseYaml(branchConfigYaml))
+        branch: String? = null,
+    ): WerkatorConfig = withBranchLayer(workingDir, parseYaml(branchConfigYaml), branch)

    private fun withBranchLayer(
        workingDir: Path,
        branchLayer: Map<String, Any?>,
+        branch: String?,
    ): WerkatorConfig {
        // scoped to this branch: an incompatible branch config fails its own builds and
        // must never stop the server or hold up the branches that are fine
        checkVersion(branchLayer, "the committed .werkator.yml of this branch", BRANCH_HINT)
        checkTriggerBlocks(branchLayer, "the committed .werkator.yml of this branch", BRANCH_HINT)
-        return toConfig(deepMerge(loadRaw(workingDir), stripPinned(branchLayer)))
+        val primary = loadRaw(workingDir)
+        return toConfig(deepMerge(primary, stripPinned(branchLayer, primary, branch)), MissingPredecessor.WARN)
    }

-    private fun toConfig(raw: Map<String, Any?>): WerkatorConfig {
+    /**
+     * What a follow-up whose predecessor no definition has means for this load, see
+     * [checkFollowUps].
+     */
+    private enum class MissingPredecessor {
+        /** The primary configuration: a deployment that could never fire refuses the start. */
+        REFUSE,
+
+        /** A branch layer on top: the branch renamed or dropped the build the host's trigger names, and only loses its follow-up. */
+        WARN,
+
+        /** A fragment checked on its own: the predecessor may well live in the project config it is merged with later. */
+        SKIP,
+    }
+
+    private fun toConfig(
+        raw: Map<String, Any?>,
+        missingPredecessor: MissingPredecessor = MissingPredecessor.REFUSE,
+    ): WerkatorConfig {
        val config =
            if (raw.isEmpty()) {
                WerkatorConfig()
            } else {
-                yaml.convertValue(resolveBuildSections(dropNonDefinitionBuilds(raw)), WerkatorConfig::class.java)
+                yaml.convertValue(resolveBuildSections(dropNonDefinitionBuilds(raw), missingPredecessor), WerkatorConfig::class.java)
            }
        return defaultPublicBaseUrl(config)
    }
@@ -178,7 +202,11 @@ class ConfigLoader(
     * second as soon as the committed configuration carries them.
     */
    @Suppress("UNCHECKED_CAST")
-    private fun stripPinned(branchLayer: Map<String, Any?>): Map<String, Any?> {
+    private fun stripPinned(
+        branchLayer: Map<String, Any?>,
+        primary: Map<String, Any?>,
+        branch: String?,
+    ): Map<String, Any?> {
        if (branchLayer.isEmpty()) {
            return branchLayer
        }
@@ -188,9 +216,55 @@ class ConfigLoader(
            val entries = result[section] as? Map<String, Any?> ?: continue
            result[section] = entries.mapValues { (_, value) -> stripPinnedSettings(value) }
        }
+        (result["builds"] as? Map<String, Any?>)?.let { builds ->
+            val hostBuilds = primary["builds"] as? Map<String, Any?> ?: emptyMap()
+            result["builds"] = builds.mapValues { (name, value) -> stripPinnedTrigger(name, value, hostBuilds[name], branch) }
+        }
        return result
    }

+    /**
+     * The follow-up part of the pinning (PR#23): a branch's definition loses its
+     * `afterSuccessOf`, and where the host's definition of the same name is a follow-up,
+     * the branch's whole `trigger` block — otherwise a branch could widen the host's
+     * selector to include itself, and deploy itself with the host's credentials. Said
+     * out loud, because a trigger the branch wrote and does not see in effect is a
+     * question it would otherwise ask the log in vain.
+     */
+    @Suppress("UNCHECKED_CAST")
+    private fun stripPinnedTrigger(
+        name: String,
+        value: Any?,
+        hostDefinition: Any?,
+        branch: String?,
+    ): Any? {
+        val definition = value as? Map<String, Any?> ?: return value
+        val trigger = definition["trigger"] as? Map<String, Any?> ?: return value
+        val where = branch?.let { "branch '$it'" } ?: "this branch"
+        if (predecessorOf(hostDefinition) != null) {
+            log.warn(
+                "ignoring the trigger block of builds.{} in the committed {} of {}: the host defines that build as a follow-up, " +
+                    "and when and where a follow-up runs is the host's decision alone",
+                name,
+                ConfigFiles.COMMITTED,
+                where,
+            )
+            return definition - "trigger"
+        }
+        if (predecessorOf(definition) == null) {
+            return value
+        }
+        log.warn(
+            "ignoring builds.{}.trigger.afterSuccessOf in the committed {} of {}: a branch cannot make a build follow another, " +
+                "only the host can",
+            name,
+            ConfigFiles.COMMITTED,
+            where,
+        )
+        val stripped = trigger - "afterSuccessOf"
+        return if (stripped.isEmpty()) definition - "trigger" else definition + ("trigger" to stripped)
+    }
+
    @Suppress("UNCHECKED_CAST")
    private fun stripPinnedSettings(value: Any?): Any? {
        val entry = value as? Map<String, Any?> ?: return value
@@ -225,12 +299,16 @@ class ConfigLoader(
     * an empty docker policy and run natively on the host, which is exactly the escape
     * the pinned keys exist to prevent.
     */
-    private fun resolveBuildSections(raw: Map<String, Any?>): Map<String, Any?> {
+    private fun resolveBuildSections(
+        raw: Map<String, Any?>,
+        missingPredecessor: MissingPredecessor,
+    ): Map<String, Any?> {
        @Suppress("UNCHECKED_CAST")
        val definitions = raw["builds"] as? Map<String, Any?> ?: emptyMap()
        if (definitions.isEmpty()) {
            return mergeBranchDefaults(raw)
        }
+        checkFollowUps(definitions, missingPredecessor)
        if (raw.containsKey("branches") && warnedSections.add(LEGACY_BRANCHES_WARNING)) {
            log.warn(
                "ignoring the branches section: this configuration defines builds, and a build definition " +
@@ -252,13 +330,59 @@ class ConfigLoader(
            return
        }
        if (warnedSections.add(NO_TRIGGER_WARNING)) {
-            log.warn("no build defines onPush or atTimes; the watcher will never start a build on its own")
+            log.warn("no build defines onPush, atTimes, or afterSuccessOf; the watcher will never start a build on its own")
        }
    }

    private fun isTriggered(definition: Any?): Boolean {
        val trigger = (definition as? Map<*, *>)?.get("trigger") as? Map<*, *> ?: return false
-        return trigger["onPush"] == true || (trigger["atTimes"] as? List<*>)?.isNotEmpty() == true
+        return trigger["onPush"] == true ||
+            (trigger["atTimes"] as? List<*>)?.isNotEmpty() == true ||
+            predecessorOf(definition) != null
+    }
+
+    private fun predecessorOf(definition: Any?): String? {
+        val trigger = (definition as? Map<*, *>)?.get("trigger") as? Map<*, *> ?: return null
+        return (trigger["afterSuccessOf"] as? String)?.takeIf { it.isNotBlank() }
+    }
+
+    /**
+     * A follow-up build that could never fire must not exist, for the same reason a flat
+     * trigger key is refused: a deployment that silently never runs is worse than a
+     * configuration that refuses to load (PR#23). Refused are a predecessor no definition
+     * has, and a cycle of follow-ups (a build following itself included) — a cycle is a
+     * configuration error whoever wrote it, while a missing predecessor depends on what
+     * is being loaded ([MissingPredecessor]).
+     */
+    private fun checkFollowUps(
+        definitions: Map<String, Any?>,
+        missingPredecessor: MissingPredecessor,
+    ) {
+        val predecessors = definitions.mapValues { (_, definition) -> predecessorOf(definition) }
+        val effective = definitions.keys + BuildDefinition.DEFAULT
+        for ((name, predecessor) in predecessors) {
+            if (predecessor == null || predecessor in effective) continue
+            val message = "builds.$name follows '$predecessor' (trigger.afterSuccessOf), but no build of that name is defined"
+            when (missingPredecessor) {
+                MissingPredecessor.REFUSE -> throw ConfigFormatException("$message. Name an existing build, or remove the follow-up.")
+                MissingPredecessor.WARN -> log.warn("$message on this branch; the follow-up will not run for it")
+                MissingPredecessor.SKIP -> {}
+            }
+        }
+        for (start in predecessors.keys) {
+            val path = mutableListOf(start)
+            var current = predecessors[start]
+            while (current != null && current !in path) {
+                path += current
+                current = predecessors[current]
+            }
+            if (current == start) {
+                throw ConfigFormatException(
+                    "builds.$start follows itself through trigger.afterSuccessOf (${path.joinToString(" -> ")} -> $start); " +
+                        "a follow-up build cannot wait for its own success.",
+                )
+            }
+        }
    }

    /**
@@ -426,7 +550,10 @@ class ConfigLoader(
        checkVersion(raw, fragment.toString(), ROLLBACK_HINT)
        checkTriggerBlocks(raw, fragment.toString(), ROLLBACK_HINT)
        try {
-            strictYaml.convertValue(resolveBuildSections(dropNonDefinitionBuilds(raw)), WerkatorConfig::class.java)
+            strictYaml.convertValue(
+                resolveBuildSections(dropNonDefinitionBuilds(raw), MissingPredecessor.SKIP),
+                WerkatorConfig::class.java,
+            )
        } catch (e: IllegalArgumentException) {
            throw IllegalArgumentException(
                "instance fragment $fragment does not match the configuration schema: ${e.message}",
@@ -610,7 +737,7 @@ class ConfigLoader(
        private val TRIGGER_KEYS = setOf("trigger")

        /** The keys that moved into [TRIGGER_KEYS]; still writing them flat is refused, not ignored. */
-        private val FLAT_TRIGGER_KEYS = setOf("onPush", "atTimes", "branches", "activeWithin")
+        private val FLAT_TRIGGER_KEYS = setOf("onPush", "atTimes", "branches", "activeWithin", "afterSuccessOf")

        /**
         * Top-level sections owned by the instance once a home config exists (ADR 0009):
@@ -0,0 +1,134 @@
+package de.hoennig.werkator.watcher
+
+import de.hoennig.werkator.build.BuildExecutor
+import de.hoennig.werkator.build.BuildResult
+import de.hoennig.werkator.build.BuildStatus
+import de.hoennig.werkator.build.BuildStatusChangedEvent
+import de.hoennig.werkator.config.BuildDefinition
+import de.hoennig.werkator.config.ConfigFiles
+import de.hoennig.werkator.config.ConfigLoader
+import de.hoennig.werkator.git.GitService
+import de.hoennig.werkator.repo.RepoContext
+import org.slf4j.LoggerFactory
+import org.springframework.context.event.EventListener
+import org.springframework.stereotype.Component
+import java.time.Clock
+import java.util.concurrent.atomic.AtomicBoolean
+
+/**
+ * Runs the follow-up builds (PR#23): whenever a build ends with `SUCCESS`, every
+ * definition of that branch whose `trigger.afterSuccessOf` names the finished build —
+ * and whose selector selects the branch — is enqueued on the same branch at the *same
+ * commit*, never at the branch's current origin head, so a deployment always ships the
+ * commit that was tested. Every green run counts, whatever started it, and a repeated
+ * green run of the same commit triggers again: a run of a green build that is silently
+ * not deployed would be more confusing than a redundant deployment.
+ *
+ * The definitions are resolved with the branch's committed config at the finished
+ * build's commit — the same layering the watcher applies — so the follow-up's command
+ * comes with the repository while its trigger stays the host's (pinned by
+ * [ConfigLoader]). The pull-request gate is not consulted: the predecessor passed it for
+ * this very commit, and the host's selector is the follow-up's own gate.
+ *
+ * Armed by [Watcher.start] and disarmed by [Watcher.stop], so a CLI `build` — whose
+ * process ends with its build — never enqueues a follow-up into a JVM that is about to
+ * exit; the CLI names the follow-ups the server would have run instead.
+ */
+@Component
+class FollowUpTrigger(
+    private val gitService: GitService,
+    private val configLoader: ConfigLoader,
+    private val buildExecutor: BuildExecutor,
+    private val clock: Clock,
+) {
+    private val log = LoggerFactory.getLogger(FollowUpTrigger::class.java)
+
+    private val armed = AtomicBoolean(false)
+
+    fun arm() {
+        armed.set(true)
+    }
+
+    fun disarm() {
+        armed.set(false)
+    }
+
+    fun isArmed(): Boolean = armed.get()
+
+    @EventListener
+    fun onBuildStatusChanged(event: BuildStatusChangedEvent) {
+        if (!armed.get() || event.result.status != BuildStatus.SUCCESS) {
+            return
+        }
+        val result = event.result
+        try {
+            for (name in followUpsOf(event.repo, result)) {
+                log.info(
+                    "[{}] enqueueing follow-up build {} of branch {} at commit {}, after {}",
+                    event.repo.name,
+                    name,
+                    result.branch,
+                    result.commit,
+                    result.build,
+                )
+                buildExecutor.startBuild(event.repo, result.branch, result.commit, name)
+            }
+        } catch (e: Exception) {
+            log.error("[{}] could not enqueue the follow-ups of {} at {}", event.repo.name, result.name, result.commit, e)
+        }
+    }
+
+    /** The names of the builds that follow a green [result], in the order of their definitions; nothing is enqueued. */
+    fun followUpsOf(
+        repo: RepoContext,
+        result: BuildResult,
+    ): List<String> = followUpsOf(repo, result.branch, result.commit, result.build)
+
+    /** The names of the builds that follow a green run of [build] on [branch] at [commit]; nothing is enqueued. */
+    fun followUpsOf(
+        repo: RepoContext,
+        branch: String,
+        commit: String,
+        build: String,
+    ): List<String> {
+        val workingDir = repo.workingDir
+        val definitions = definitionsAt(repo, branch, commit)
+        val headCommittedAt = lazy { gitService.originBranchCommitTimes(workingDir)[branch] }
+        return definitions
+            .filter { (_, definition) -> definition.trigger.afterSuccessOf == build }
+            .filter { (_, definition) -> definition.trigger.selects(branch, { headCommittedAt.value }, clock.instant()) }
+            .keys
+            .toList()
+    }
+
+    /**
+     * The branch's definitions at [commit] — not at its head, which may have moved on
+     * since the predecessor started. An unreadable branch config falls back to the
+     * primary definitions, like the watcher does.
+     */
+    private fun definitionsAt(
+        repo: RepoContext,
+        branch: String,
+        commit: String,
+    ): Map<String, BuildDefinition> {
+        val workingDir = repo.workingDir
+        return try {
+            configLoader
+                .loadWithBranchLayer(
+                    workingDir,
+                    ConfigFiles.readCommitted { gitService.showFileAtCommit(commit, it, workingDir) },
+                    branch,
+                ).effectiveBuildDefinitions()
+        } catch (e: Exception) {
+            log.warn(
+                "[{}] ignoring the committed {} of branch {} at {} for its follow-ups: {}",
+                repo.name,
+                ConfigFiles.COMMITTED,
+                branch,
+                commit,
+                e.message ?: e.javaClass.simpleName,
+            )
+            configLoader.load(workingDir).effectiveBuildDefinitions()
+        }
+    }
+}
@@ -41,6 +41,7 @@ class Watcher(
    private val buildExecutor: BuildExecutor,
    private val configLoader: ConfigLoader,
    private val clock: Clock,
+    private val followUpTrigger: FollowUpTrigger,
 ) {
    private val log = LoggerFactory.getLogger(Watcher::class.java)

@@ -83,11 +84,14 @@ class Watcher(
     * Runs the startup recovery of every repository and schedules the poll loop with the
     * fixed delay `watcher.pollInterval` — one loop, one delay: the instance's setting,
     * which every repository's effective config carries; the first poll runs immediately.
+     * Arms the [FollowUpTrigger] first, so the recovery's re-enqueued builds get their
+     * follow-ups too.
     */
    @Synchronized
    fun start(repos: List<RepoContext>) {
        check(scheduler == null) { "watcher is already running" }
        require(repos.isNotEmpty()) { "no repository to watch" }
+        followUpTrigger.arm()
        repos.forEach { recoverSafely(it) }
        val interval = DurationParser.parse(configLoader.load(repos.first().workingDir).watcher.pollInterval)
        scheduler =
@@ -111,6 +115,7 @@ class Watcher(

    @Synchronized
    fun stop() {
+        followUpTrigger.disarm()
        scheduler?.shutdownNow()
        scheduler = null
        state = state.copy(running = false)
@@ -324,6 +329,7 @@ class Watcher(
                    .loadWithBranchLayer(
                        workingDir,
                        ConfigFiles.readCommitted { gitService.showFileAtCommit(commit, it, workingDir) },
+                        branch,
                    ).effectiveBuildDefinitions()
            } catch (e: Exception) {
                log.warn(
@@ -292,6 +292,42 @@ class BuildExecutorTest : FunSpec() {
                .build shouldBe "default"
        }

+        test("a follow-up build runs in its branch's worktree after its predecessor") {
+            val h =
+                Harness(
+                    """
+                    executor:
+                      maxConcurrent: 2
+                    builds:
+                      default:
+                        trigger:
+                          onPush: true
+                        cleanCommand: ""
+                        buildCommand: "sleep 1; echo built > output.txt"
+                      deploy:
+                        trigger:
+                          afterSuccessOf: default
+                        buildCommand: "cat output.txt"
+                    """.trimIndent(),
+                )
+
+            h.executor.startBuild(h.repo, "main", "c1", "default")
+            h.executor.startBuild(h.repo, "main", "c1", "deploy")
+
+            awaitStatus(h, "main@deploy", BuildStatus.SUCCESS)
+            awaitIdle(h)
+            // same branch, same commit: the same worktree, and the follow-up saw the predecessor's output
+            h.workspaceCalls shouldContainExactly listOf("main" to "c1", "main" to "c1")
+            val predecessor = h.repository.latestFor("main").shouldNotBeNull()
+            val followUp = h.repository.latestFor("main@deploy").shouldNotBeNull()
+            predecessor.status shouldBe BuildStatus.SUCCESS
+            followUp.runningSince
+                .shouldNotBeNull()
+                .isBefore(predecessor.runningSince.shouldNotBeNull())
+                .shouldBeFalse()
+            Files.readString(h.workingDir.resolve("output.txt")).trim() shouldBe "built"
+        }
+
        test("a build whose definition was removed from the config falls back to the branch's settings") {
            val h = harness(buildCommand = "echo regular-\$branch")

@@ -4,6 +4,7 @@ import de.hoennig.werkator.build.BuildStatus
 import de.hoennig.werkator.git.GitService
 import de.hoennig.werkator.repo.RepoContext
 import de.hoennig.werkator.repo.RepoRegistry
+import de.hoennig.werkator.watcher.FollowUpTrigger
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.shouldBe
 import io.kotest.matchers.string.shouldContain
@@ -22,16 +23,31 @@ class BuildCommandTest : FunSpec() {
    private val dir: Path = Paths.get(".")
    private val repo = RepoContext("test", dir, mockk(), mockk())
    private val registry = mockk<RepoRegistry>().also { every { it.current() } returns repo }
+    private val followUpTrigger = mockk<FollowUpTrigger>()

    private fun command(fragment: String? = null) =
-        BuildCommand(gitService, consoleBuildRunner, registry).apply {
+        BuildCommand(gitService, consoleBuildRunner, registry, followUpTrigger).apply {
            branchFragment = fragment
        }

    init {
        beforeEach {
-            clearMocks(gitService, consoleBuildRunner)
+            clearMocks(gitService, consoleBuildRunner, followUpTrigger)
            justRun { gitService.fetchOrigin(dir) }
+            every { followUpTrigger.followUpsOf(any(), any(), any(), any()) } returns emptyList()
+        }
+
+        test("a green CLI build names the follow-up builds the server would run, and runs none") {
+            every { gitService.currentBranch(dir) } returns "main"
+            every { gitService.localHeadCommit("main", dir) } returns "local-head"
+            every { gitService.hasNewCommits("main", dir) } returns false
+            every { consoleBuildRunner.buildAndStream(repo, "main", "local-head") } returns BuildStatus.SUCCESS
+            every { followUpTrigger.followUpsOf(repo, "main", "local-head", "default") } returns listOf("deploy")
+
+            val console = captureConsole { command().call() }
+
+            console.stdout.shouldContain("follow-up build(s) deploy")
+            verify(exactly = 1) { consoleBuildRunner.buildAndStream(repo, "main", "local-head") }
        }

        test("builds the current branch at its local head when no branch is given") {
@@ -739,6 +739,190 @@ class ConfigLoaderTest : FunSpec() {
                .shouldBeTrue()
        }

+        test("afterSuccessOf must name an existing definition and must not form a cycle") {
+            val dir = Files.createTempDirectory("werkator-test")
+            val project = dir.resolve(".werkator.yml").toFile()
+            project.writeText(
+                """
+                builds:
+                  default:
+                    trigger:
+                      onPush: true
+                  deploy:
+                    trigger:
+                      afterSuccessOf: default
+                      branches: ["main"]
+                    buildCommand: scripts/deploy.sh
+                """.trimIndent(),
+            )
+            // a follow-up with nothing but its predecessor is a triggered build, and it binds
+            val deploy = loader.load(dir).buildDefinitions.getValue("deploy")
+            deploy.trigger.afterSuccessOf shouldBe "default"
+            deploy.trigger.isFollowUp().shouldBeTrue()
+            deploy.trigger.onPush.shouldBeFalse()
+
+            project.writeText(
+                """
+                builds:
+                  deploy:
+                    trigger:
+                      afterSuccessOf: frontend
+                """.trimIndent(),
+            )
+            shouldThrow<ConfigFormatException> { loader.load(dir) }.message.let {
+                it.shouldContain("builds.deploy")
+                it.shouldContain("frontend")
+            }
+
+            project.writeText(
+                """
+                builds:
+                  a:
+                    trigger:
+                      afterSuccessOf: b
+                  b:
+                    trigger:
+                      afterSuccessOf: a
+                """.trimIndent(),
+            )
+            shouldThrow<ConfigFormatException> { loader.load(dir) }.message.shouldContain("a -> b -> a")
+
+            project.writeText(
+                """
+                builds:
+                  a:
+                    trigger:
+                      afterSuccessOf: a
+                """.trimIndent(),
+            )
+            shouldThrow<ConfigFormatException> { loader.load(dir) }.message.shouldContain("builds.a follows itself")
+        }
+
+        test("a branch whose layer lacks the predecessor loses only its follow-up") {
+            val dir = Files.createTempDirectory("werkator-test")
+            dir.resolve(".werkator.yml").toFile().writeText(
+                """
+                builds:
+                  frontend:
+                    trigger:
+                      onPush: true
+                  deploy:
+                    trigger:
+                      afterSuccessOf: frontend
+                """.trimIndent(),
+            )
+            // the branch renamed the predecessor: a warning, not a failed load — the branch's
+            // own builds must keep running, its follow-up simply never fires for it
+            val config =
+                loader.loadWithBranchLayer(
+                    dir,
+                    """
+                    builds:
+                      frontend: null
+                      ui:
+                        trigger:
+                          onPush: true
+                    """.trimIndent(),
+                )
+            config.buildDefinitions
+                .getValue("ui")
+                .trigger.onPush
+                .shouldBeTrue()
+            config.buildDefinitions
+                .getValue("deploy")
+                .trigger.afterSuccessOf shouldBe "frontend"
+        }
+
+        test("afterSuccessOf written flat is refused like every trigger key") {
+            val dir = Files.createTempDirectory("werkator-test")
+            dir.resolve(".werkator.yml").toFile().writeText(
+                """
+                builds:
+                  default:
+                    trigger:
+                      onPush: true
+                  deploy:
+                    afterSuccessOf: default
+                """.trimIndent(),
+            )
+            val thrown = shouldThrow<ConfigFormatException> { loader.load(dir) }
+            thrown.message.shouldContain("builds.deploy: afterSuccessOf")
+            thrown.message.shouldContain("trigger:")
+        }
+
+        test("a follow-up trigger is pinned to the host, a branch cannot add or widen one") {
+            val dir = Files.createTempDirectory("werkator-test")
+            dir.resolve(".werkator.yml").toFile().writeText(
+                """
+                builds:
+                  frontend:
+                    trigger:
+                      onPush: true
+                  deploy:
+                    trigger:
+                      afterSuccessOf: frontend
+                      branches: ["main"]
+                """.trimIndent(),
+            )
+            val config =
+                loader.loadWithBranchLayer(
+                    dir,
+                    """
+                    builds:
+                      deploy:
+                        trigger:
+                          afterSuccessOf: frontend
+                          branches: ["*"]
+                      nightly:
+                        trigger:
+                          atTimes: ["01:00"]
+                          afterSuccessOf: frontend
+                    """.trimIndent(),
+                    "feature/x",
+                )
+            // the host's trigger block of the follow-up is used unchanged
+            val deploy = config.buildDefinitions.getValue("deploy").trigger
+            deploy.afterSuccessOf shouldBe "frontend"
+            deploy.branches shouldBe listOf("main")
+            deploy.selectsByName("feature/x").shouldBeFalse()
+            // and a branch cannot make any build of its own a follow-up
+            val nightly = config.buildDefinitions.getValue("nightly").trigger
+            nightly.afterSuccessOf shouldBe ""
+            nightly.atTimes shouldBe listOf("01:00")
+        }
+
+        test("a branch supplies the command of a host-triggered follow-up") {
+            val dir = Files.createTempDirectory("werkator-test")
+            Files.createDirectories(dir.resolve(".git/werkator"))
+            dir.resolve(".git/werkator/.werkator.yml").toFile().writeText(
+                """
+                builds:
+                  deploy:
+                    trigger:
+                      afterSuccessOf: default
+                      branches: ["main"]
+                    werkdock:
+                      env:
+                        DEPLOY_TARGET: host:/srv/www
+                """.trimIndent(),
+            )
+            val worktree = Files.createTempDirectory("werkator-test-worktree")
+            worktree.resolve(".werkator.yml").toFile().writeText(
+                """
+                builds:
+                  deploy:
+                    cleanCommand: ""
+                    buildCommand: scripts/deploy-prod.sh -y "${'$'}DEPLOY_TARGET"
+                """.trimIndent(),
+            )
+
+            val settings = loader.loadForWorktree(dir, worktree, "main").buildSettings("main", "deploy")
+
+            settings.buildCommand shouldBe "scripts/deploy-prod.sh -y \"${'$'}DEPLOY_TARGET\""
+            settings.cleanCommand shouldBe ""
+            settings.werkdock.env shouldBe mapOf("DEPLOY_TARGET" to "host:/srv/www")
+        }
+
        test("builds.default is the base of every other build, but never its trigger") {
            val dir = Files.createTempDirectory("werkator-test")
            dir.resolve(".werkator.yml").toFile().writeText(
@@ -113,7 +113,7 @@ class PermanentBranchRoutesTest : FunSpec() {
            every { registry.byName(any()) } returns null
            every { registry.byName("test") } returns repo
            every { configLoader.load(any()) } returns WerkatorConfig()
-            every { configLoader.loadWithBranchLayer(any(), anyNullable()) } returns WerkatorConfig()
+            every { configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns WerkatorConfig()
            every { gitService.showFileAtCommit(any(), any(), any()) } returns null
            every { controlTokens.token() } returns "test-token"
            every { branchListing.branches(any()) } returns emptyList()
@@ -142,7 +142,7 @@ class UiControllerTest : FunSpec() {
                    server = ServerConfig(impressumUrl = "https://example.org/imprint"),
                    gitea = GiteaConfig(baseUrl = "https://git.example.org", owner = "acme", repo = "widget"),
                )
-            every { configLoader.loadWithBranchLayer(any(), anyNullable()) } returns WerkatorConfig()
+            every { configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns WerkatorConfig()
            every { gitService.showFileAtCommit(any(), any(), any()) } returns null
            every { controlTokens.token() } returns "test-token"
            every { repository.latestGreenFor(any()) } returns null
@@ -385,7 +385,7 @@ class UiControllerTest : FunSpec() {
                )
            every { repository.history() } returns listOf(pitestResult)
            every { artifactStore.artifactDir("main-pitest-key") } returns null
-            every { configLoader.loadWithBranchLayer(any(), anyNullable()) } returns
+            every { configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns
                WerkatorConfig(
                    branches = mapOf("default" to BranchConfig(buildCommand = "./gradlew quick-check")),
                    buildDefinitions = mapOf("pitest" to BuildDefinition(buildCommand = "./gradlew pitestFull")),
@@ -0,0 +1,173 @@
+package de.hoennig.werkator.watcher
+
+import de.hoennig.werkator.build.ArtifactKeys
+import de.hoennig.werkator.build.BuildExecutor
+import de.hoennig.werkator.build.BuildResult
+import de.hoennig.werkator.build.BuildStatus
+import de.hoennig.werkator.build.BuildStatusChangedEvent
+import de.hoennig.werkator.build.RunningBuild
+import de.hoennig.werkator.config.BuildDefinition
+import de.hoennig.werkator.config.ConfigLoader
+import de.hoennig.werkator.config.TriggerConfig
+import de.hoennig.werkator.config.WerkatorConfig
+import de.hoennig.werkator.git.GitService
+import de.hoennig.werkator.repo.RepoContext
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.collections.shouldBeEmpty
+import io.kotest.matchers.collections.shouldContainExactly
+import io.mockk.every
+import io.mockk.mockk
+import java.nio.file.Files
+import java.time.Clock
+import java.time.Instant
+import java.time.ZoneOffset
+import java.util.concurrent.CopyOnWriteArrayList
+
+class FollowUpTriggerTest : FunSpec() {
+    private val noon = Instant.parse("2026-09-04T12:00:00Z")
+
+    /** Which build was started on which branch at which commit. */
+    private data class Started(
+        val branch: String,
+        val commit: String,
+        val build: String,
+    )
+
+    private inner class Harness(
+        config: WerkatorConfig,
+    ) {
+        val workingDir = Files.createTempDirectory("werkator-followup-test")
+        val gitService = mockk<GitService>()
+        val configLoader = mockk<ConfigLoader>()
+        val buildExecutor = mockk<BuildExecutor>()
+        val repo = RepoContext("test", workingDir, mockk(), mockk())
+        val started = CopyOnWriteArrayList<Started>()
+        val trigger = FollowUpTrigger(gitService, configLoader, buildExecutor, Clock.fixed(noon, ZoneOffset.UTC))
+
+        init {
+            every { configLoader.load(any()) } returns config
+            every { configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns config
+            every { gitService.showFileAtCommit(any(), any(), any()) } returns null
+            // the branch moved on since the predecessor started
+            every { gitService.originHeadCommit(any(), any()) } returns "c2"
+            every { gitService.originBranchCommitTimes(any()) } returns mapOf("main" to noon.minusSeconds(60))
+            every { buildExecutor.startBuild(any(), any(), any(), any()) } answers {
+                val branch = secondArg<String>()
+                val commit = thirdArg<String>()
+                val build = arg<String>(3)
+                started += Started(branch, commit, build)
+                val staging = Files.createTempDirectory("werkator-followup-staging")
+                RunningBuild(
+                    repo = repo,
+                    branch = branch,
+                    build = build,
+                    commit = commit,
+                    artifactKey = ArtifactKeys.buildKey(BuildDefinition.poolName(branch, build), noon),
+                    startedAt = noon,
+                    stagingDir = staging,
+                    liveLogFile = staging.resolve("build.log"),
+                )
+            }
+        }
+
+        fun finished(
+            build: String,
+            status: BuildStatus,
+            branch: String = "main",
+            commit: String = "c1",
+        ) {
+            val result =
+                BuildResult(
+                    branch = branch,
+                    build = build,
+                    commit = commit,
+                    status = status,
+                    startedAt = noon,
+                    artifactKey = ArtifactKeys.buildKey(BuildDefinition.poolName(branch, build), noon),
+                )
+            trigger.onBuildStatusChanged(BuildStatusChangedEvent(result, repo))
+        }
+    }
+
+    private fun deployAfter(
+        predecessor: String,
+        branches: List<String> = emptyList(),
+    ): WerkatorConfig =
+        WerkatorConfig(
+            buildDefinitions =
+                mapOf(
+                    "frontend" to BuildDefinition(trigger = TriggerConfig(onPush = true)),
+                    "backend" to BuildDefinition(trigger = TriggerConfig(onPush = true)),
+                    "deploy" to
+                        BuildDefinition(
+                            trigger = TriggerConfig(afterSuccessOf = predecessor, branches = branches),
+                            buildCommand = "scripts/deploy.sh",
+                        ),
+                ),
+        )
+
+    init {
+        test("a green predecessor enqueues the follow-up at the predecessor's commit") {
+            val h = Harness(deployAfter("frontend", branches = listOf("main")))
+            h.trigger.arm()
+
+            h.finished("frontend", BuildStatus.SUCCESS, commit = "c1")
+
+            // c1, not the origin head c2 the branch has moved on to
+            h.started shouldContainExactly listOf(Started("main", "c1", "deploy"))
+        }
+
+        test("every green run of the predecessor triggers the follow-up again") {
+            val h = Harness(deployAfter("frontend"))
+            h.trigger.arm()
+
+            h.finished("frontend", BuildStatus.SUCCESS, commit = "c1")
+            h.finished("frontend", BuildStatus.SUCCESS, commit = "c1")
+
+            h.started shouldContainExactly
+                listOf(
+                    Started("main", "c1", "deploy"),
+                    Started("main", "c1", "deploy"),
+                )
+        }
+
+        test("only a SUCCESS of the named predecessor triggers") {
+            val h = Harness(deployAfter("frontend", branches = listOf("main")))
+            h.trigger.arm()
+
+            h.finished("frontend", BuildStatus.FAILED)
+            h.finished("frontend", BuildStatus.CANCELLED)
+            h.finished("frontend", BuildStatus.INTERRUPTED)
+            h.finished("frontend", BuildStatus.PENDING)
+            h.finished("frontend", BuildStatus.RUNNING)
+            h.finished("backend", BuildStatus.SUCCESS)
+            // a branch the host's selector does not name never runs the follow-up
+            h.finished("frontend", BuildStatus.SUCCESS, branch = "feature/x")
+
+            h.started.shouldBeEmpty()
+        }
+
+        test("the trigger listens only while the watcher runs") {
+            val h = Harness(deployAfter("frontend"))
+
+            h.finished("frontend", BuildStatus.SUCCESS)
+            h.started.shouldBeEmpty()
+
+            h.trigger.arm()
+            h.finished("frontend", BuildStatus.SUCCESS)
+            h.started shouldContainExactly listOf(Started("main", "c1", "deploy"))
+
+            h.trigger.disarm()
+            h.finished("frontend", BuildStatus.SUCCESS)
+            h.started shouldContainExactly listOf(Started("main", "c1", "deploy"))
+        }
+
+        test("followUpsOf names the follow-ups without enqueueing anything") {
+            val h = Harness(deployAfter("default"))
+
+            h.trigger.followUpsOf(h.repo, "main", "c1", "default") shouldContainExactly listOf("deploy")
+            h.trigger.followUpsOf(h.repo, "main", "c1", "frontend").shouldBeEmpty()
+            h.started.shouldBeEmpty()
+        }
+    }
+}
@@ -63,6 +63,7 @@ class WatcherTest : FunSpec() {
        val artifactStore = mockk<ArtifactStore>()
        val startedBuilds = CopyOnWriteArrayList<Pair<String, String>>()
        val configLoader = mockk<ConfigLoader>()
+        val followUpTrigger = mockk<FollowUpTrigger>(relaxed = true)
        val repo = RepoContext("test", workingDir, repository, artifactStore)
        val watcher =
            Watcher(
@@ -70,6 +71,7 @@ class WatcherTest : FunSpec() {
                buildExecutor = buildExecutor,
                configLoader = configLoader,
                clock = Clock.fixed(noon, ZoneOffset.UTC),
+                followUpTrigger = followUpTrigger,
            )

        private var seedCounter = 0L
@@ -85,7 +87,7 @@ class WatcherTest : FunSpec() {
            every { gitService.originBranchCommitTimes(any()) } returns emptyMap()
            every { gitService.originBranchHeads(any()) } returns emptyMap()
            every { gitService.showFileAtCommit(any(), any(), any()) } returns null
-            every { configLoader.loadWithBranchLayer(any(), anyNullable()) } returns config
+            every { configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns config
            every { gitService.pullRequestHeads(any()) } returns emptySet()
            every { gitService.worktreePrune(any()) } returns Unit
            every { gitService.fastForwardLocalBranches(any()) } returns emptyList()
@@ -157,6 +159,19 @@ class WatcherTest : FunSpec() {
        )

    init {
+        test("start arms the follow-up trigger before the recovery, stop disarms it") {
+            val harness = Harness()
+
+            harness.watcher.start(listOf(harness.repo))
+            try {
+                verify(exactly = 1) { harness.followUpTrigger.arm() }
+                verify(exactly = 0) { harness.followUpTrigger.disarm() }
+            } finally {
+                harness.watcher.stop()
+            }
+            verify(exactly = 1) { harness.followUpTrigger.disarm() }
+        }
+
        test("a fetch failure is exposed in the state and only retried next cycle") {
            val harness = Harness()
            every { harness.gitService.fetchOrigin(any()) } throws RuntimeException("origin unreachable")
@@ -526,7 +541,7 @@ class WatcherTest : FunSpec() {
            every { harness.gitService.originBranchHeads(any()) } returns
                mapOf("main" to "commit-main", "experiment" to "commit-exp")
            every { harness.gitService.showFileAtCommit("commit-exp", Watcher.CONFIG_FILE, any()) } returns "branch-yaml"
-            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml") } returns branchLayer
+            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml", anyNullable()) } returns branchLayer
            every { harness.gitService.originHeadCommit("experiment", any()) } returns "commit-exp"
            every { harness.gitService.originHeadCommit("main", any()) } returns "commit-main"

@@ -549,7 +564,7 @@ class WatcherTest : FunSpec() {
            every { harness.gitService.originBranches(any()) } returns listOf("experiment")
            every { harness.gitService.originBranchHeads(any()) } returns mapOf("experiment" to "commit-exp")
            every { harness.gitService.showFileAtCommit("commit-exp", ".gittally.yml", any()) } returns "branch-yaml"
-            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml") } returns branchLayer
+            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml", anyNullable()) } returns branchLayer
            every { harness.gitService.originHeadCommit("experiment", any()) } returns "commit-exp"

            harness.watcher.poll(harness.repo)
@@ -568,7 +583,7 @@ class WatcherTest : FunSpec() {
            every { harness.gitService.originBranchHeads(any()) } returns
                mapOf("main" to "commit-main", "experiment" to "commit-exp")
            every { harness.gitService.showFileAtCommit("commit-exp", Watcher.CONFIG_FILE, any()) } returns "branch-yaml"
-            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml") } returns branchLayer
+            every { harness.configLoader.loadWithBranchLayer(any(), "branch-yaml", anyNullable()) } returns branchLayer
            every { harness.gitService.originHeadCommit(any(), any()) } returns "commit-any"

            harness.watcher.poll(harness.repo)
@@ -608,7 +623,7 @@ class WatcherTest : FunSpec() {
                    buildDefinitions = mapOf("nightly" to BuildDefinition(trigger = TriggerConfig(atTimes = listOf("11:00")))),
                )
            every { harness.configLoader.load(any()) } returns edited
-            every { harness.configLoader.loadWithBranchLayer(any(), anyNullable()) } returns edited
+            every { harness.configLoader.loadWithBranchLayer(any(), anyNullable(), anyNullable()) } returns edited

            harness.watcher.poll(harness.repo)

@@ -622,7 +637,7 @@ class WatcherTest : FunSpec() {
            every { harness.gitService.hasNewCommits("main", any()) } returns true
            every { harness.gitService.originBranchHeads(any()) } returns mapOf("main" to "commit-main")
            every { harness.gitService.showFileAtCommit("commit-main", Watcher.CONFIG_FILE, any()) } returns "broken"
-            every { harness.configLoader.loadWithBranchLayer(any(), "broken") } throws
+            every { harness.configLoader.loadWithBranchLayer(any(), "broken", anyNullable()) } throws
                RuntimeException("mapping problem")
            every { harness.gitService.originHeadCommit("main", any()) } returns "commit-main"