diff --git a/openspec/changes/trunk-based-ci-cd/design.md b/openspec/changes/trunk-based-ci-cd/design.md
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+## Context
+
+See `proposal.md` for motivation. Today's model, implemented in `release-train.yml` + `.github/actions/release-train-detect/detect.sh`, treats git tags as the single source of truth for versioning and hardcodes a branch → channel mapping (`develop`→alpha, `staging`→beta, `main`→stable). `docker-release.yml` (called both by `release-train.yml` and by the manual `release.yml` in `legacy` mode) always rebuilds the image from source at release time — there is no existing mechanism to promote an already-built artifact.
+
+No consuming repo has real deploy infrastructure yet, so this design defines the pipeline's shape and the exact point where real deploys will plug in, without implementing those deploys.
+
+## Goals / Non-Goals
+
+**Goals:**
+
+- Decouple git branch topology (single `main`) from release/environment topology (`dev` → `pre` → `prod`).
+- Guarantee "build once, promote the same artifact" for the path from `pre` to `prod`.
+- Ship this as a purely additive change to `sisques-labs/workflows` so no existing consumer breaks or needs to act.
+- Define where real deploy steps will plug in later, without requiring that infra to exist now.
+
+**Non-Goals:**
+
+- Implementing actual deployment logic to real dev/pre/prod infrastructure (no consuming repo has environments provisioned).
+- Migrating any specific consuming repo — beacon-api will pilot this as a separate change in its own repository.
+- Deprecating or modifying `release-train.yml` for repos that keep using it — that is a later, separate decision once the pilot is validated.
+- Auditing which repos have consumers pinned to `:alpha`/`:beta` image tags — required before any given repo migrates, but tracked per-repo, not here.
+
+## Decisions
+
+### D1 — Two-phase versioning: continuous (unversioned) vs. release (versioned)
+
+Every merge to `main` builds and publishes `image:sha-<shortsha>` (+ floating `image:edge`). No `npm version` bump, no git tag, no GitHub Release happens on merge. `package.json` is untouched until a release is explicitly cut.
+
+**Alternatives considered:** computing a semver pre-release (`X.Y.Z-rc.N`) on every merge, mirroring today's alpha/beta channels — rejected because it produces version churn nobody consumes once there is only one branch, and it reintroduces the "which pre-release tag is actually deployed" ambiguity this change is meant to remove.
+
+### D2 — `prod` releases promote an existing image by digest, never rebuild
+
+`docker-release.yml` gains `bump_mode: promote`, which takes the digest of the already-built `sha-*` image (the one validated in `pre`) and runs `docker buildx imagetools create --tag <image>:X.Y.Z --tag <image>:latest <image>@sha256:<digest>`. The existing `legacy` and `release-train` modes (which build-then-push) are untouched — `promote` is a new branch in the existing mode dispatch, not a rewrite.
+
+**Risk to validate during implementation:** `imagetools create` must correctly copy the full multi-arch manifest list (the repo builds `linux/amd64,linux/arm64`), not just a single-platform digest — confirm this before relying on it for a real release.
+
+### D3 — Job graph: `build` → `deploy-dev` → `deploy-pre`, sequential
+
+New reusable workflow `trunk-ci-cd.yml` (`workflow_call`), consumed via a repo's own `push: [main]` trigger:
+
+```
+build-and-publish (lint, test, build, push sha-*/edge tags)
+        │
+        ▼
+   deploy-dev   (needs: build-and-publish; no gate)
+        │
+        ▼
+   deploy-pre   (needs: deploy-dev; gate optional per consumer input)
+```
+
+`prod` is deliberately **not** a job in this workflow — it is only reachable via the manual `release.yml` dispatch (D2), which promotes the artifact that has already gone through `dev` and `pre`.
+
+**Alternatives considered:** deploying `dev` and `pre` in parallel from `build` — rejected per the org's explicit decision to keep DEV as an early-feedback gate before promoting to the QA-facing `pre` environment.
+
+### D4 — `deploy-dev`/`deploy-pre` ship as placeholders
+
+Since no consuming repo has dev/pre/prod infrastructure yet, both jobs are defined with a placeholder step (log-only) in this iteration. The job graph, `needs:` ordering, and environment names are the real deliverable; wiring an actual deploy target is follow-up work once a repo provisions real infrastructure.
+
+### D5 — Environments are configured per-repo, not in this shared repo
+
+`dev`/`pre`/`prod` GitHub Environments (and any required-reviewer gates on them) are Settings-level config owned by each consuming repo. `sisques-labs/workflows` only defines the job names/order that reference environment names by convention.
+
+### D6 — Rollout is additive and opt-in per repo
+
+No file this change touches is edited in place for its existing behavior: `trunk-ci-cd.yml` is a new file nothing currently references, and `docker-release.yml`'s new `bump_mode: promote` branch is unreachable unless a caller explicitly passes it. A repo migrates by changing its *own* workflow files to reference the new pieces — `sisques-labs/workflows` never forces a migration.
+
+### D7 — Changelog/release generation is reused, simplified
+
+`docker-release.yml`'s existing git-cliff + GitHub Release steps apply unchanged when `release_type: stable`. Because there is only one channel once a repo migrates, the alpha/beta/rc tag-ignoring logic in the changelog range computation becomes dead code for that repo's future releases but is not removed here (other repos still exercise it via `legacy`/`release-train` modes).
+
+## Risks / Trade-offs
+
+- **[Risk] Multi-arch digest promotion is unproven** → Validate `imagetools create` against a real multi-platform image before beacon-api's pilot relies on it for an actual prod release.
+- **[Risk] Downstream consumers pinned to `:alpha`/`:beta` tags** → Each repo must audit this before migrating; out of scope for this shared-workflow change.
+- **[Trade-off] `deploy-dev`/`deploy-pre` are placeholders** → The pipeline shape ships now; real deploy logic is deferred until a repo has infrastructure to target.
+- **[Trade-off] Org-wide standardization without a forced cutover** → Slower convergence (repos migrate on their own schedule) in exchange for zero blast radius on this change.
+
+## Migration Plan
+
+1. Merge this proposal/design into `sisques-labs/workflows` as documentation — no consumer is affected by merging it.
+2. Implement `trunk-ci-cd.yml` and `docker-release.yml`'s `promote` mode per `tasks.md`.
+3. Beacon-api pilots the migration in its own repository/change: drop `release-train.yml`, adopt `trunk-ci-cd.yml`, switch `release.yml` to `bump_mode: promote`.
+4. Validate the pilot (including the multi-arch promotion risk in D2) before any other repo migrates.
+5. Other repos opt in individually, on their own schedule.
+6. Deprecating `release-train.yml` org-wide is a separate future decision, made only after enough repos have migrated.
+
+## Open Questions
+
+- Should `deploy-pre` carry a mandatory approval gate by default, or is that left to each repo's own GitHub Environment configuration?
+- What is the audit process for repos with external consumers pinned to `:alpha`/`:beta` image tags before they migrate?
diff --git a/openspec/changes/trunk-based-ci-cd/proposal.md b/openspec/changes/trunk-based-ci-cd/proposal.md
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+## Why
+
+Every consuming repo releases through `release-train.yml`, which maps git branch to release channel (`develop` → alpha, `staging` → beta, `main` → stable) via `release-train-detect/detect.sh`. This couples the org's git topology to its release topology. Today no consuming repo has real environments provisioned, so `develop`/`staging` gate a version channel but not an actual deployment — the three-branch model carries the cost of environment branches (merge overhead, drift risk between branches) without their benefit.
+
+Standardizing on a single long-lived `main` branch (trunk-based development) lets environment promotion be driven by the CI/CD pipeline instead of by branch merges: one artifact is built per merge to `main` and the *same* artifact is promoted through `dev` → `pre` → `prod`, rather than being rebuilt per branch. This removes an entire class of "works in staging, different bytes in prod" risk.
+
+## What Changes
+
+- Add a new reusable workflow `trunk-ci-cd.yml`: triggered by a consumer's `push: [main]`, it builds and publishes an immutable, commit-addressed image (`image:sha-<shortsha>` + floating `image:edge`) with no version bump, then runs `deploy-dev` followed by `deploy-pre` (`needs: deploy-dev`).
+- Add a new `bump_mode: promote` to the existing `docker-release.yml` reusable workflow. When set, the release job skips the build step entirely and promotes an already-published image by digest (`docker buildx imagetools create`) to the release tag(s) instead of rebuilding from source — guaranteeing the exact bytes validated in `pre` are what ships to `prod`.
+- Both changes are strictly additive: `release-train.yml`, `release-train-detect/detect.sh`, and the existing `legacy`/`release-train` bump modes in `docker-release.yml` are untouched. No consuming repo is affected until it edits its own workflow file to reference `trunk-ci-cd.yml` and pass `bump_mode: promote`.
+- **Out of scope for this change**: implementing real deploy steps for `dev`/`pre`/`prod` (no consuming repo has provisioned environments yet — the jobs are defined as the pipeline's shape with a placeholder deploy step); migrating any specific repo (beacon-api will pilot this in its own repo as a follow-up change); deprecating `release-train.yml` for repos that don't migrate (a later decision, once the pilot is validated).
+
+## Capabilities
+
+### New Capabilities
+
+- `trunk-based-ci-cd`: A continuous integration/delivery pipeline that builds an artifact once per merge to `main` and promotes that same artifact through `dev` → `pre` → `prod`, decoupling release/environment topology from git branch topology.
+
+### Modified Capabilities
+
+- `docker-release`: gains a `promote` bump mode that retags an existing image by digest instead of rebuilding, for use when cutting a `prod` release from an already-validated artifact.
+
+## Impact
+
+- **Code**: new file `.github/workflows/trunk-ci-cd.yml`; additive changes to `.github/workflows/docker-release.yml` (new `bump_mode` branch, no existing code path touched). No other file is modified.
+- **Consumers**: zero impact on existing repos using `release-train.yml` — nothing here is wired into any consumer's workflow yet.
+- **Environments**: `dev`/`pre`/`prod` GitHub Environments are configured per-repo (not part of this shared-workflows change) when a repo migrates and provisions real infrastructure.
+- **Rollback**: revert this PR; nothing references the new workflow or bump mode until a consumer opts in.
diff --git a/openspec/changes/trunk-based-ci-cd/tasks.md b/openspec/changes/trunk-based-ci-cd/tasks.md
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+## 1. `trunk-ci-cd.yml` reusable workflow
+
+- [ ] 1.1 Add `.github/workflows/trunk-ci-cd.yml` (`workflow_call`) with a `build-and-publish` job: lint, test, build, push `image:sha-<shortsha>` + floating `image:edge` — no version bump, no git tag
+- [ ] 1.2 Add `deploy-dev` job (`needs: build-and-publish`) with a placeholder deploy step (no real target yet) — verify it runs unconditionally after a successful build
+- [ ] 1.3 Add `deploy-pre` job (`needs: deploy-dev`) with a placeholder deploy step and an optional consumer-provided gate input — verify it never runs before `deploy-dev` succeeds
+
+## 2. `docker-release.yml` promote mode
+
+- [ ] 2.1 Add `bump_mode: promote` as a new accepted value alongside `legacy`/`release-train` — verify existing modes' code paths are untouched
+- [ ] 2.2 When `bump_mode: promote`, accept the source image digest as an input and skip the existing build steps entirely
+- [ ] 2.3 Implement the promotion step with `docker buildx imagetools create` retagging the digest to the computed release tag(s) + `:latest`
+- [ ] 2.4 Verify multi-arch manifest lists (`linux/amd64,linux/arm64`) survive the promotion intact, not just a single-platform digest — this is the flagged risk in `design.md` D2
+- [ ] 2.5 Confirm changelog (git-cliff) and GitHub Release creation steps run unchanged for `promote` mode when `release_type: stable`
+
+## 3. Documentation
+
+- [ ] 3.1 Document the new `trunk-ci-cd.yml` inputs/outputs and the `promote` bump mode in this repo's README, alongside the existing `release-train.yml`/`docker-release.yml` docs
+- [ ] 3.2 Note in the README that `trunk-ci-cd.yml` is opt-in per repo and does not affect existing `release-train.yml` consumers
+
+## 4. Verification
+
+- [ ] 4.1 Dry-run `trunk-ci-cd.yml` against a disposable test repo/branch to confirm the `build-and-publish` → `deploy-dev` → `deploy-pre` ordering holds
+- [ ] 4.2 Dry-run `docker-release.yml` with `bump_mode: promote` against a real multi-arch image and confirm the promoted tag pulls correctly on both architectures
+- [ ] 4.3 Confirm no existing repo's `release-train.yml`-based pipeline changed behavior after this PR merges