feat(upstream): detect frontend-base landings from the default branch, not legacy-mfe

[blarghmatey]

What

Adds lehrer upstream frontend-base-status, which reports whether each upstream MFE repo OL depends on has landed its frontend-base conversion, plus a daily GitHub Actions job that opens an issue when the answer changes.

Why

Upstream is merging each learner-facing MFE's frontend-base conversion into its repository's default branch (openedx/frontend-base#243, OEP-65 ADR 0004). That merge turns the default branch into an npm module library, so every OL legacy MFE build tracking it stops producing a servable bundle. mitxonline builds seven MFEs from master. The break arrives with no change in this repo and no failing PR, on upstream's schedule rather than ours.

The detection rule changed

Our recorded trigger was "gh api repos/openedx/<repo>/branches/legacy-mfe returns 200". Polling upstream on 2026-09-01 shows that is wrong in both directions:

• False positive. ADR 0004 cuts the branch and then merges. frontend-app-catalog's branch was cut 2026-08-27T19:48:18Z, frontend-app-authn's 2026-08-28T19:12:31Z, frontend-app-learner-dashboard's 2026-08-28T20:31:36Z, frontend-template-application's 2026-08-17T12:50:58Z. A poll inside that window reports a landing that has not happened.
• False negative. The branch is only cut when a supported release still ships the micro-frontend; the ADR 0004 checklist says set openedx.org/release to null "if none does". frontend-app-notifications landed 2026-08-27 with openedx.org/release: null and no branch at all.

The check reads the default branch's package.json instead. After the merge it describes an npm module library: exports is set, and scripts.build no longer names webpack or fedx-scripts. Converted repos use make build, whose target is tsc --project tsconfig.build.json plus a copy of SCSS and assets into dist/ (checked on authn, catalog, notifications and instructor-dashboard). Both conditions are required — a micro-frontend can declare exports for its own consumers, and a repo can wrap webpack in a Makefile.

legacy-mfe is still read, but as a second-order fact answering "which branch does a legacy build move to", not "did it land". Its absence on a landed repo is the load-bearing case: there is nothing to repoint at, so the build has to be retired rather than pinned.

What it finds today

openedx/frontend-app-admin-console         legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-authoring             legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-communications        legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-discussions           legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-gradebook             legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-learning              legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-ora-grading           legacy      no action — default branch still builds the micro-frontend
openedx/frontend-app-instructor-dashboard  LANDED      landed with no legacy-mfe branch — the micro-frontend is gone; drop the legacy build and consume the npm module instead (builds from the default branch: mitxonline, mitx, mitx-staging)
openedx/frontend-app-learner-dashboard     LANDED      landed — pin to legacy-mfe or absorb into the Site Project (no OL deployment builds this from its default branch)

Wave 1 of frontend-base#243 (template-application, notifications, catalog, learner-dashboard, authn) is complete — every sub-issue closed, none open — and broke nothing: none of it is built by an OL deployment from its default branch.

It does surface one live exposure. frontend-app-instructor-dashboard is a module library on main (version: 0.0.0-dev, scripts.build: make build, exports: {".": "./dist/index.js"}, files: ["/dist"], openedx.org/release: null) with no legacy-mfe branch, while ol-infrastructure version_matrix.py (@ 92ad0bdbd) still declares an instructor MFE build against main at lines 535/609/689 for mitxonline, mitx and mitx-staging.

Those three jobs do not fail. They succeed and ship a useless artifact. Removing the rows is a separate ol-infrastructure change, but the silence is a lehrer bug, so this PR also fixes that.

The silent-failure fix

build_legacy ends at container.directory("/app/mfe/dist"). A landed repo's npm run build is tsc plus an SCSS copy, so dist/ exists and holds index.js — non-empty, exports cleanly, pipeline green, and the deployment serves a directory no browser can load. Nothing downstream inspects the artifact's shape, so the build now refuses it.

index.html is the discriminator:

• frontend-build's prod config templates public/index.html through HtmlWebpackPlugin (config/webpack.prod.config.js:205), so every legacy MFE emits one. All seven repos mitxonline builds from master have public/index.html.
• A frontend-base App Repository never does — its build does not touch public/. instructor-dashboard has public/index.html on main and still emits only dist/index.js.

The failure message names the cause and the next command, because where it fires is a Concourse log nobody is reading closely:

no index.html in /app/mfe/dist: this built an npm module library, not a
servable MFE bundle. The upstream default branch has most likely landed its
frontend-base conversion. Run 'lehrer upstream frontend-base-status', then
repoint this build at the legacy-mfe branch or retire it.

This is the half that matters when nobody has run the detection command: the daily job tells you a landing happened, the guard stops the pipeline shipping garbage regardless. Happy to split it into its own PR if you would rather review it separately — it is one commit (7cf4cea).

Layout

• src/lehrer/core/upstream.py — classification only, no I/O and no knowledge of OL deployments (the lehrer-core-boundary hook enforces the latter).
• src/lehrer/cli/upstream.py — gh/npm reads, watch-list loading, operator-facing advice.
• deployments/mit-ol/upstream_watch.yaml — which OL deployments build each repo from its default branch. ol-infrastructure version_matrix.py stays the source of truth for what is built; this only records the exposure, verified against 92ad0bdbd.
• .github/workflows/frontend-base-landing.yml — daily poll. Notifies on a digest of (repo, stage), so an unactioned issue does not collect a daily comment repeating itself.

Testing

tests/cli/test_upstream.py, 14 cases built from the shapes actually observed upstream, including both the false-positive and false-negative cases above, plus 3 in tests/core/test_mfe.py running the guard's generated script against a real webpack-shaped and a real module-library-shaped dist/. Full suite 292 passed; mypy and pre-commit clean. The command and the workflow's shell logic were both run against live upstream.

🤖 Generated with Claude Code

https://claude.ai/code/session_014KwW2f9msAkAuR45QQGRj9

[Copilot]

Pull request overview

Adds upstream frontend-base conversion detection and automated daily alerting.

Changes:

• Classifies MFE repositories using default-branch package metadata.
• Adds a CLI status command and deployment watch list.
• Adds tests and a scheduled issue-notification workflow.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/lehrer/core/upstream.py	Implements landing classification.
src/lehrer/cli/upstream.py	Adds upstream polling and reporting CLI.
src/lehrer/cli/__init__.py	Registers the upstream command.
deployments/mit-ol/upstream_watch.yaml	Defines watched repositories and exposures.
.github/workflows/frontend-base-landing.yml	Adds daily polling and issue updates.
tests/cli/test_upstream.py	Tests classification, advice, and configuration loading.

Suppressed comments (7)

deployments/mit-ol/upstream_watch.yaml:22

• The referenced version_matrix.py also tracks authoring at release="master" for mitx and mitx-staging (lines 582–585 and 662–665). These deployments should be included so the alert reports the full exposure.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:24

• The referenced version_matrix.py also tracks communications at release="master" for mitx and mitx-staging (lines 577–580 and 657–660). The current list causes status and advice to omit both exposed deployments.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:26

• The referenced version_matrix.py also tracks discussions at release="master" for mitx and mitx-staging (lines 587–590 and 667–670). Include those deployments so a branch cut or landing reports every affected build.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:28

• The referenced version_matrix.py also tracks gradebook at release="master" for mitx and mitx-staging (lines 604–606 and 684–686). The watch entry currently omits those exposed builds.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:30

• The referenced version_matrix.py also tracks learning at release="master" for mitx and mitx-staging (lines 620–623 and 695–698). Add them so the alert does not understate the landing's impact.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:32

• The referenced version_matrix.py also tracks ora-grading at release="master" for mitx and mitx-staging (lines 629–632 and 709–712). Both deployments are exposed and should appear in this entry.

  exposed_deployments: [mitxonline]

deployments/mit-ol/upstream_watch.yaml:45

• This is not built only from Verawood: the referenced matrix tracks learner-dashboard from master for mitx and mitx-staging (lines 615–618 and 700–703). Since master maps to the upstream default branch, the landed conversion already exposes both deployments, but this entry reports none and prevents --fail-on-landing from flagging them.

# Built only at release="verawood" today, so no deployment is exposed, but the
# Site Projects will consume the module library and mitx/xpro move to Willow
# eventually.  Watched, not urgent.
- repo: openedx/frontend-app-learner-dashboard
  exposed_deployments: []

---

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[blarghmatey]

Updated the body: the open question about Concourse is answered. Those three instructor jobs succeed and ship a useless artifact rather than failing, so the pipeline has never signalled this.

That makes the silence a lehrer bug, not just an ol-infrastructure config drift, so I added 7cf4cea: build_legacy now asserts dist/index.html exists before returning the directory. Evidence that the assertion is safe for every legacy MFE is in the commit message and the code comment — frontend-build templates it via HtmlWebpackPlugin, and all seven of mitxonline's master-tracked repos have public/index.html.

Drop that commit if you would rather it went in on its own; the rest of the PR stands without it.