Let the formatter float again, keeping the clean env that actually fixed it

.github/workflows/format-check.yml

@@ -3,20 +3,20 @@ name: Format Check
 # Reusable JuliaFormatter check. The pool follows the CALLER's visibility unless `runner` is
 # passed — private → rosina, public → ubuntu-latest. Canonical note: `autoregister.yml`.
 #
-# TWO things here are load-bearing — do not "simplify" them away:
+# `Pkg.activate(; temp=true)` is load-bearing — do not "simplify" it away. Installing into the
+# runner's shared/default environment lets that depot's existing compat bounds cap the resolve: on
+# rosina a floating spec silently resolved to JuliaFormatter 2.3.2 while a laptop resolved 2.10.1,
+# and a leftover ITensorFormatter there once made the install fail outright. Same code, different
+# verdict, which is the long-standing "format-check flake". It was never a flake, it was the
+# shared env, and that is the half worth defending.
 #
-# 1. `Pkg.activate(; temp=true)` — a CLEAN env. Installing into the runner's shared/default
-#    environment lets that depot's existing compat bounds cap the resolve: on rosina a floating
-#    `version="2"` silently resolved to **JuliaFormatter 2.3.2**, while a laptop resolved 2.10.1.
-#    Same code, different verdict → the long-standing "format-check flake". It was never a flake,
-#    it was version drift.
-# 2. `JF_VERSION` is an EXACT pin, not a range. CI and your laptop must run the *same* formatter
-#    or the check is not reproducible. Bump it here, once, and reformat the fleet with that
-#    version — never let it float.
+# The version floats, deliberately. When a new 2.x reflows files the answer is to adopt it and
+# reformat, not to freeze the old one: a pin here becomes standing debt in every caller and rots
+# while the ecosystem moves. Reproducibility comes from the clean env above, not from the pin.
 #
-# Format locally with exactly this version:
+# Format locally with the same floating spec, in a temp env, so you resolve what CI just did:
 #   julia -e 'using Pkg; Pkg.activate(;temp=true); Pkg.add(PackageSpec(name="JuliaFormatter",
-#             version="2.10.1")); using JuliaFormatter; format(".")'
+#             version="2")); using JuliaFormatter; format(".")'
 on:
   workflow_call:
     inputs:
@@ -26,9 +26,6 @@ on:
         type: string
         default: ''
 
-env:
-  JF_VERSION: '2.10.1'
-
 jobs:
   format-check:
     runs-on: ${{ inputs.runner != '' && fromJSON(inputs.runner) || (github.event.repository.private && fromJSON('["self-hosted","rosina"]') || 'ubuntu-latest') }}
@@ -37,23 +34,27 @@ jobs:
       - uses: julia-actions/setup-julia@v2
         with:
           version: '1'
-      - name: JuliaFormatter ${{ env.JF_VERSION }} check
+      - name: JuliaFormatter check
         shell: julia --color=yes {0}
         run: |
           using Pkg
           Pkg.activate(; temp = true)                       # clean env — no depot compat capping the resolve
-          Pkg.add(PackageSpec(name = "JuliaFormatter", version = ENV["JF_VERSION"]))
+          Pkg.add(PackageSpec(name = "JuliaFormatter", version = "2"))
           using JuliaFormatter
           v = pkgversion(JuliaFormatter)
-          @info "JuliaFormatter $v (pinned $(ENV["JF_VERSION"]))"
-          if string(v) != ENV["JF_VERSION"]
-              println(stderr, "❌ resolved JuliaFormatter $v, expected $(ENV["JF_VERSION"]) — the check would not be reproducible.")
+          # `using` falls back to the depot's default env when the active project does not declare
+          # the package, loading a different version and saying nothing, so ask the project itself.
+          declared = [p.version for (_, p) in Pkg.dependencies() if p.name == "JuliaFormatter"]
+          if declared != [v]
+              println(stderr, "❌ JuliaFormatter $v came from outside the temp project, which holds $declared.")
               exit(1)
           end
+          @info "JuliaFormatter $v"
           ok = format("."; verbose = true, overwrite = false)
           if !ok
-              println(stderr, "❌ Not formatted. Run locally with the SAME version:")
-              println(stderr, "   julia -e 'using Pkg; Pkg.activate(;temp=true); Pkg.add(PackageSpec(name=\"JuliaFormatter\", version=\"$(ENV["JF_VERSION"])\")); using JuliaFormatter; format(\".\")'")
+              println(stderr, "❌ Not formatted, under JuliaFormatter $v. `overwrite=false` above is the check;")
+              println(stderr, "   locally you want `true`, and one pass does not always converge. Run:")
+              println(stderr, "   julia -e 'using Pkg; Pkg.activate(;temp=true); Pkg.add(PackageSpec(name=\"JuliaFormatter\", version=\"2\")); using JuliaFormatter; for _ in 1:5; format(\".\"; overwrite=true) && break end'")
               exit(1)
           end
           println("✅ All files properly formatted.")