ci(proofs): bisect dogfood startup_failure — minimal skeleton

Temporary: reduce to one trivial job to localise the GitHub-parser
rejection (passes yq + actionlint but startup_failures twice). Jobs
restored in the next commit once the skeleton is confirmed to start.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: claude

.github/workflows/dogfood-proofs-ci.yml

@@ -1,10 +1,6 @@
 # SPDX-License-Identifier: MPL-2.0
-# Gates the ECHIDNA dogfood proof corpus: every theorem under proofs/{coq,lean,agda}
-# must type-check. These proofs had no CI coverage before this workflow -- the
-# language-specific path filters on the other proof workflows (agda-meta-checker
-# -> meta-checker/**, idris2-abi-ci -> src/abi/**) never touched proofs/**, so
-# regressions here were invisible. Each job calls a `just` recipe so local and
-# CI run the identical command (RSR-H14).
+# Gates the ECHIDNA dogfood proof corpus (proofs/{coq,lean,agda}) in CI.
+# (Bisecting a startup_failure: minimal skeleton first, then restore jobs.)
 name: Dogfood Proof Corpus
 
 on:
@@ -22,8 +18,6 @@ on:
       - '.github/workflows/dogfood-proofs-ci.yml'
   workflow_dispatch:
 
-# Cause-B mitigation (#77): cancel superseded runs so stacked pushes
-# to the same ref don't pile up identical jobs in the queue.
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
@@ -37,100 +31,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Install Coq
-        run: |
-          set -euo pipefail
-          sudo apt-get update -qq || sudo apt-get update -qq --fix-missing
-          sudo apt-get install -y --fix-missing coq
-          coqc --version
-
-      - name: Install just
-        uses: taiki-e/install-action@e49978b799e49ff429d162b7a30601a569ab6538 # v2.81.1
-        with:
-          tool: just@1.51.0
-
-      - name: Type-check Coq corpus
-        run: just proofs-coq
-
-  lean:
-    name: Lean 4
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Cache elan + Lean toolchain
-        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
-        with:
-          path: ~/.elan
-          key: elan-${{ runner.os }}-${{ hashFiles('proofs/lean/lean-toolchain') }}
-
-      - name: Install elan (Lean toolchain manager)
-        run: |
-          set -euo pipefail
-          # The toolchain version itself is pinned by proofs/lean/lean-toolchain
-          # (lake reads it and fetches that exact Lean on first invocation).
-          if [ ! -x "$HOME/.elan/bin/lake" ]; then
-            curl -fsSL --retry 3 \
-              https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh \
-              -o /tmp/elan-init.sh
-            sh /tmp/elan-init.sh -y --default-toolchain none
-          fi
-          echo "$HOME/.elan/bin" >> "$GITHUB_PATH"
-
-      - name: Install just
-        uses: taiki-e/install-action@e49978b799e49ff429d162b7a30601a569ab6538 # v2.81.1
-        with:
-          tool: just@1.51.0
-
-      - name: Build Lean corpus
-        run: just proofs-lean
-
-  agda:
-    name: Agda
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Setup Haskell
-        uses: haskell-actions/setup@cd0d9bdd65b20557f41bea4dbe43d0b5fbbfe553 # v2
-        with:
-          ghc-version: '9.6'
-          cabal-version: '3.10'
-
-      - name: Cache cabal (Agda build)
-        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
-        with:
-          # Keyed on the Agda version, not the proofs, so the expensive
-          # from-source Agda build is reused across proof-only changes.
-          path: ~/.cabal
-          key: agda-cabal-${{ runner.os }}-Agda-2.7.0.1
-
-      - name: Install Agda
-        run: |
-          set -euo pipefail
-          cabal update
-          # --overwrite-policy=always: a warm ~/.cabal cache already carries
-          # the agda symlink, so a plain install aborts with "path exists".
-          cabal install Agda-2.7.0.1 --overwrite-policy=always
-          echo "$HOME/.cabal/bin" >> "$GITHUB_PATH"
-
-      - name: Install Agda standard library (v2.1)
-        run: |
-          set -euo pipefail
-          mkdir -p ~/.agda
-          cd /tmp
-          wget -q https://github.com/agda/agda-stdlib/archive/refs/tags/v2.1.tar.gz
-          tar xzf v2.1.tar.gz
-          # Fresh registration each run (`>`), then append the corpus library.
-          echo "/tmp/agda-stdlib-2.1/standard-library.agda-lib" > ~/.agda/libraries
-          echo "standard-library" > ~/.agda/defaults
-          echo "${GITHUB_WORKSPACE}/proofs/agda/echidna-proofs.agda-lib" >> ~/.agda/libraries
-
-      - name: Install just
-        uses: taiki-e/install-action@e49978b799e49ff429d162b7a30601a569ab6538 # v2.81.1
-        with:
-          tool: just@1.51.0
-
-      - name: Type-check Agda corpus
-        run: just proofs-agda
+      - name: Smoke
+        run: echo "skeleton OK"