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@@ -10,7 +10,7 @@ The three required Linux worker jobs in [CI](../../../../.github/workflows/ci.ym
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## Decision
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-Each of the three required Linux worker jobs, the independent native Windows job, and the `all checks passed` verdict job — which would otherwise stay queued on the failed pool even after every worker passed — resolves its runner pool through a repository variable, and the switch is split by platform so an outage on one platform does not retarget the other. The three Linux workers and the `all checks passed` verdict (whose `needs` are the required Linux workers and which runs on the `vm-backup` pool) resolve through `DSH_CI_FAILOVER_LINUX`; the native Windows job resolves through `DSH_CI_FAILOVER_WINDOWS`. Unset (normal), they run on the hosted enterprise pools. Set to `selfhosted` by any repository writer, the corresponding jobs retarget onto the in-house self-hosted pool: under `DSH_CI_FAILOVER_LINUX`, the Linux jobs and verdict move onto the `vm-backup` pool, snapshot concurrency drops to the shared-VM bound, and the hosted-path pnpm cache restores are skipped; under `DSH_CI_FAILOVER_WINDOWS`, the native Windows job moves onto the `dsh-win-ci` pool. Each switch is writer-manageable repository state, not a merge, so it works while every check is red. The in-house pools' readiness is continuously re-proven by the `serial / linux (self-hosted standby)` and `serial / windows (self-hosted standby)` lanes, which run the complete unsharded aggregates on every master push.
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+Each of the three required Linux worker jobs, the independent native Windows job, and the `all checks passed` verdict job — which would otherwise stay queued on the failed pool even after every worker passed — resolves its runner pool through a repository variable, and the switch is split by platform so an outage on one platform does not retarget the other. The three Linux workers and the `all checks passed` verdict (whose `needs` are the required Linux workers and which runs on the `vm-backup` pool) resolve through `DSH_CI_FAILOVER_LINUX`; the native Windows job resolves through `DSH_CI_FAILOVER_WINDOWS`. Unset, they default to the hosted pools; selecting `selfhosted` is an explicit operator choice. Set to `selfhosted` by any repository writer, the corresponding jobs retarget onto the in-house self-hosted pool: under `DSH_CI_FAILOVER_LINUX`, the Linux jobs and verdict move onto the `vm-backup` pool, snapshot concurrency drops to the shared-VM bound, and the hosted-path pnpm cache restores are skipped; under `DSH_CI_FAILOVER_WINDOWS`, the native Windows job moves onto the `dsh-win-ci` pool. Each switch is writer-manageable repository state, not a merge, so it works while every check is red. The in-house pools' readiness is continuously re-proven by the `serial / linux (self-hosted standby)` and `serial / windows (self-hosted standby)` lanes, which run the complete unsharded aggregates on every master push.
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`ci-master.yml` exempts exactly one event from `cancel-in-progress` (`${{ github.event_name != 'push' }}`), so one master push does not cancel the drill still running from the previous one. Each drill runs its complete unsharded aggregate with one gate worker, which takes longer than the interval between master merges; under unconditional cancellation a drill is superseded before reaching a verdict and the lane yields no readiness evidence for a responder to check.
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@@ -18,9 +18,13 @@ The exemption is narrower than "a drill always finishes", in two ways. GitHub ke
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The decision belongs at workflow level because cancellation applies to the whole superseded run: a job-level `concurrency` group does not exempt its job. The negated form is load-bearing rather than cosmetic: naming `pull_request` alone would also stop cancelling `workflow_dispatch`, and each runner benchmark fans out to twelve larger runners for up to fifteen minutes inside this same group on master, so a re-dispatch would queue ahead of a drill instead of replacing a stale measurement. What bounds the cost is that a master push in `ci-master.yml` carries only `wine-apt-cache` and these two drills; the pull-request jobs live in the separate `ci.yml` (which does not see `push`), and the benchmarks are `workflow_dispatch`-gated within `ci-master.yml`. `scripts/ci-workflow.spec.ts` pins that push-reachable set — classifying by exact condition, since a negated event test mentions the event it excludes — so a new push-reachable job cannot quietly start accumulating uncancelled runs.
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+### Release rehearsals share the Linux switch
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+
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+`DSH_CI_FAILOVER_LINUX=selfhosted` also routes the credential-free dependency-layout job and both dsh/vendor pack jobs onto `vm-backup` for eligible same-repository PRs and master pushes. Their [release rehearsal decision](2026-09-06-release-rehearsal-selfhosted.md) owns the stricter event eligibility and hosted manual dispatch. This coupling is intentional: keeping the variable set to save release minutes also keeps the eligible main-CI Linux jobs self-hosted. Clearing it returns both workloads to their hosted targets for subsequent runs; publication stays hosted regardless.
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+
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### What the in-house pool is
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-`vm-backup`: one 64-core VM, six always-on systemd-managed runner instances. Its image must preinstall Playwright Chromium's Linux system packages; CI downloads the lockfile-selected browser but never runs `apt` on this persistent shared host. Check the latest `serial / linux (self-hosted standby)` run before switching: its aggregate includes browser replay, so a green standby verifies both ordinary capacity and this browser prerequisite.
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+`vm-backup`: one shared VM with multiple always-on systemd-managed runner instances. Registrations share its CPU, memory, and disk; their count is not a count of independent machines. Its image must preinstall Playwright Chromium's Linux system packages; CI downloads the lockfile-selected browser but never runs `apt` on this persistent shared host. Check the latest `serial / linux (self-hosted standby)` run before switching: its aggregate includes browser replay, so a green standby verifies both ordinary capacity and this browser prerequisite.
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#### Windows pool
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@@ -40,7 +44,7 @@ The two switches are independent: flip only the one whose platform is degraded.
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## Capacity during failover
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-Six always-on instances absorb normal PR traffic (the pool's steady-state load is one serial standby job per master push, so failover capacity is effectively the full pool). If queues still build, register additional instances with an org registration token (org Settings → Actions → Runners → New runner). Clone an existing runner directory **excluding its identity files** — `rsync -a --exclude '.runner*' --exclude '.credentials*' --exclude '_diag' --exclude '_work' <src>/ <dst>/` (the globs also catch `.runner_migrated`/`.credentials_migrated`, which GitHub writes on migrated runners and which equally trigger the already-configured refusal) — then run `config.sh` (copying `.runner`/`.credentials` verbatim makes it refuse with "already configured"), and **start the listener**: `sudo ./svc.sh install ubuntu && sudo ./svc.sh start`. Registration alone leaves the runner offline; only a started service adds capacity. About a minute per instance.
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+Capacity includes the master standby, main-CI jobs, and three release-rehearsal jobs for each eligible PR or master push while the Linux switch is set. The release workflows do not cancel running rehearsals when another run arrives, so overlapping refs can add sustained build, pack, and install load. Check current CPU, memory, disk, and queue pressure before extending self-hosted operation; extra registrations on this VM add scheduling slots, not machine resources. Do not infer spare capacity from the standby alone. When host resources permit extra registrations, use an org registration token (org Settings → Actions → Runners → New runner). Clone an existing runner directory **excluding its identity files** — `rsync -a --exclude '.runner*' --exclude '.credentials*' --exclude '_diag' --exclude '_work' <src>/ <dst>/` (the globs also catch `.runner_migrated`/`.credentials_migrated`, which GitHub writes on migrated runners and which equally trigger the already-configured refusal) — then run `config.sh` (copying `.runner`/`.credentials` verbatim makes it refuse with "already configured"), and **start the listener**: `sudo ./svc.sh install ubuntu && sudo ./svc.sh start`. Registration alone leaves the runner offline; a started service adds a scheduling slot, not CPU or memory.
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### Switch back
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@@ -55,7 +59,7 @@ The variables are writer-manageable repository state; a pull request event itsel
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**Merge a workflow change to switch pools.** Rejected because the outage that motivates the switch is exactly the state in which no PR can merge: the required checks are the ones failing. A repository variable is writer-manageable state that takes effect on re-run without a merge.
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-**Keep the self-hosted pool always in the required path.** Rejected because it trades hosted-pool availability for the in-house VM's, moving a single point of failure rather than adding a fallback. The variables keep the hosted pools primary and the self-hosted pools proven, one-action standbys; splitting them by platform means an outage on one platform does not retarget the other.
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+**Keep the self-hosted pool always in the required path.** Rejected because it trades hosted-pool availability for the in-house VM's, moving a single point of failure rather than adding a fallback. The unset defaults retain hosted targets and the switches provide a reversible, operator-selected self-hosted path; splitting them by platform means an outage on one platform does not retarget the other.
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## Consequences
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Tianyi Cui