A build definition says when it runs in a trigger block of its own

`onPush`, `atTimes`, `branches`, and `activeWithin` move into a nested
`trigger`. The split is structural on purpose: the inheritance from
`builds.default` now subtracts one key instead of a list of four, so a
selector added to `TriggerConfig` later is non-inheritable by
construction rather than because someone remembered to extend the list.

A definition still writing those keys flat is refused by name, per file
and scoped like the version check — the machine and project config abort
the start, a branch's committed config fails only that branch. Ignoring
them would leave the build with no trigger at all, which is a job that
quietly stops running: the failure this refusal exists to prevent.

Two more things a definition can now say:

- A `!` prefix in `trigger.branches` excludes, and an exclusion wins
  whatever the order. `["*", "!master"]` gives one branch a build of its
  own without the default build running over it as well — until now the
  only way out of that double build was to drop the second definition's
  push trigger.
- `statusContext` overrides the Gitea check this build reports as, empty
  keeping the repository-wide one. Two builds of a commit shared a
  context and overwrote each other's result, so a quick check beside a
  long build was not readable in Gitea. Pinned like `requirePullRequest`:
  a branch that could pick its context could take over the check a branch
  protection rule depends on.

Fixed on the way: a branch whose builds all belong to named definitions
rendered an empty row in the branches view, reading as "never built"
directly beside its real builds. That row was unreachable before the
exclusion patterns made such a branch possible.

AGENTS.md

@@ -40,7 +40,8 @@ All production code lives under `de.hoennig.gittally`, with sub-packages `comman
 - When config keys change, three places must stay in sync: the `GitTallyConfig` data classes, the `InitCommand` templates, and `docs/configuration.md`.
 - Every config file may declare `gitTally.version.since`/`below` (the GitTally 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 `.gittally.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 sandbox policy (`docker.enabled`, `docker.network`), and the trust gate (`requirePullRequest`). A branch must never reach credentials, disable its container, change its network, 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. `builds.default` is the base every other definition inherits its settings — never its trigger (`onPush`, `atTimes`, `branches`, `activeWithin`) — from, and 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.
+- 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`, and `docker.network`.
 - `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/gittally.js` — no SPA framework, no frontend build pipeline; every fetch has a timeout and an explicit error badge; `UiFormats` and `gittally.js` must produce identical display formats.
 - Git and Docker access shells out to the CLIs (`GitCommandRunner`, `docker`) — no JGit, no Docker SDK.