ci(#462): add durable next publish pipeline (#687)

Durable @next integration-line publish: on next pushes, compute <patch+1>-next.<pipeline#> prerelease versions (in-CI, uncommitted) and publish @mosaicstack/* under the next dist-tag; gateway image sha-only on next. Strict guardrails: next-only, never writes latest, never tags from next; main path unchanged. PR-event CI 1631 fully green + review-of-record APPROVE (head b1a887a2). Guardrails independently verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/scratchpads/B1-next-durable-publish-design.md

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+# B1 / @next Durable Publish Pipeline — Design
+
+## Objective
+
+Make `next` a durable integration line that publishes the artifacts required by downstream federation boot tests without manual builds.
+
+Every merge to `next` publishes:
+
+1. **npm prerelease packages** to the Gitea npm registry with dist-tag `next`.
+2. **Gateway container image** tagged only as `gateway:sha-<short>`.
+
+The existing stable release behavior remains isolated to `main` / tags.
+
+## Registry verification
+
+Target registry: `https://git.mosaicstack.dev/api/packages/mosaicstack/npm/`.
+
+Pre-implementation checks:
+
+- `npm view @mosaicstack/mosaic dist-tags --registry https://git.mosaicstack.dev/api/packages/mosaicstack/npm/ --json` returned a dist-tags object (`latest: 0.0.48`).
+- `npm view @mosaicstack/mosaic@latest version --registry https://git.mosaicstack.dev/api/packages/mosaicstack/npm/` resolved `0.0.48`.
+- `@next` currently returns 404 because no `next` dist-tag exists yet; this is expected before the first next prerelease publish.
+
+Pipeline design includes a post-publish verification that `npm view @mosaicstack/mosaic@next version` resolves to the exact CI-computed prerelease version. If Gitea fails to honor the `next` dist-tag, the pipeline fails closed.
+
+## Version scheme
+
+The prerelease version is computed at publish time only; no `package.json` version changes are committed.
+
+For each non-private `@mosaicstack/*` package:
+
+```text
+<target-stable>-next.<CI_PIPELINE_NUMBER>
+```
+
+Where:
+
+- `CI_PIPELINE_NUMBER` is Woodpecker's monotonic pipeline number.
+- `target-stable` is the package's current committed stable version with the patch component incremented.
+  - Example: `@mosaicstack/mosaic` `0.0.48` publishes as `0.0.49-next.1626`.
+  - Example: `@mosaicstack/gateway` `0.0.6` publishes as `0.0.7-next.1626`.
+
+Rationale:
+
+- npm semver sorts `0.0.49-next.1627` above `0.0.49-next.1626`.
+- The prerelease does not overtake the future stable `0.0.49`.
+- The monotonic pipeline number avoids conflicts across repeated `next` merges.
+
+## Branch and tag guardrails
+
+| Pipeline path         | Branch/event                   | Publishes                                               | Forbidden              |
+| --------------------- | ------------------------------ | ------------------------------------------------------- | ---------------------- |
+| stable npm publish    | `main` push/manual or tag      | package versions already committed in package manifests | `@next` dist-tag       |
+| next npm publish      | `next` push/manual only        | CI-computed prereleases with `--tag next`               | `latest` dist-tag      |
+| gateway image         | `main` push/manual or tag      | `sha-<short>` + `latest` on main + tag on tag events    | next prerelease npm    |
+| gateway image         | `next` push/manual only        | `sha-<short>` only                                      | `latest`               |
+| appservice/web images | `main` push/manual or tag only | existing stable image behavior                          | next image publication |
+
+The pipeline has explicit branch checks inside the publish commands as a second fail-closed layer beyond Woodpecker `when` clauses.
+
+## Implementation plan
+
+1. Widen `.woodpecker/publish.yml` top-level `when` to include `next` so the publish pipeline runs on next merges.
+2. Keep existing `publish-npm` on `main` / tags only.
+3. Add `publish-next-npm` for `next` push/manual only:
+   - configure Gitea npm auth from existing `gitea_token` secret as `NPM_TOKEN`;
+   - preflight registry dist-tag metadata;
+   - compute prerelease versions in CI by temporarily editing package manifests in the workspace;
+   - run `pnpm publish ... --tag next` against non-private `@mosaicstack/*` packages;
+   - verify `@mosaicstack/mosaic@next` resolves to the computed version.
+4. Split image `when` anchors:
+   - `image_build_when` includes `next` and is used by `build-gateway`;
+   - `main_image_build_when` keeps appservice/web on main/tags only.
+5. Keep gateway next image destinations to `sha-<short>` only; no `latest` on next.
+
+## Risk controls
+
+- Auth/registry failures are fatal.
+- No manual image build/push path is introduced.
+- No production `latest` tags are touched from `next`.
+- No `@latest` npm dist-tags are touched from `next`.
+- All changes live in CI config and docs; no runtime source behavior changes.