diff --git a/.github/workflows/release-dryrun.yml b/.github/workflows/release-dryrun.yml
new file mode 100644
index 0000000..a1f59a7
--- /dev/null
+++ b/.github/workflows/release-dryrun.yml
@@ -0,0 +1,64 @@
+name: release-dryrun
+
+# Continuously rehearses the SIDE-EFFECT-FREE portion of the release pipeline — build, pack, and embed the
+# SBOM for the two published projects — on every push to main and every pull request. release.yml itself
+# runs only on a tag or a manual dispatch, so its packaging path is otherwise exercised for the first time
+# in production, on a tag, once; this catches packaging/SBOM regressions in ordinary CI instead.
+#
+# It deliberately stops before every step that has a side effect:
+#   * no provenance attestation  — that writes a permanent public record (Sigstore/Rekor + the attestation
+#                                  store); it is kept to the manual `release.yml` dispatch dry-run and to
+#                                  real releases, where it runs once and on purpose;
+#   * no NuGet login / push      — nuget.org has no "dry-run push", so the actual publish stays release-only;
+#   * no GitHub Release          — no tag or release is ever created here.
+# Least privilege follows from that: this workflow only reads the repository.
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+# Cancel superseded runs on the same branch / PR.
+concurrency:
+  group: release-dryrun-${{ github.ref }}
+  cancel-in-progress: true
+
+# Read-only: no publishing, no OIDC, no attestation — so none of release.yml's write scopes are needed.
+permissions:
+  contents: read
+
+env:
+  DOTNET_NOLOGO: 'true'
+  DOTNET_CLI_TELEMETRY_OPTOUT: 'true'
+  DOTNET_SKIP_FIRST_TIME_EXPERIENCE: 'true'
+  # A throwaway version: nothing is published, so the exact value is irrelevant — it only has to be a valid
+  # SemVer the pack accepts. (release.yml's version comes from the tag and is validated there.)
+  DRYRUN_VERSION: '0.0.0-dryrun'
+
+jobs:
+  pack:
+    name: Dry-run pack (build + SBOM, no publish)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@26b0ec14cb23fa6904739307f278c14f94c95bf1 # v5
+        with:
+          # The release SDK — the same one release.yml packs with, so this rehearses the real pack path.
+          dotnet-version: '10.0.x'
+
+      - name: Build
+        run: dotnet build FirstClassErrors.sln -c Release -p:Version="$DRYRUN_VERSION"
+
+      # The SAME script release.yml packs with — it packs the two published projects with their SBOM and
+      # then asserts the SBOM is actually embedded. Sharing it is the point: this rehearsal cannot drift
+      # from the real release, because there is only one definition of "pack the release artifacts".
+      # (The unit/integration tests run in ci.yml; this job's unique contribution is the packaging.)
+      - name: Pack with SBOM (build artifacts, no publish)
+        run: tools/packaging/pack.sh "$DRYRUN_VERSION"
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index de84e22..d0696fa 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -8,8 +8,20 @@ on:
   workflow_dispatch:
     inputs:
       version:
-        description: 'Package version to publish, without the leading "v" (e.g. 1.2.3)'
+        description: 'Package version, without the leading "v" (e.g. 1.2.3; a dry run can use any SemVer, e.g. 0.0.0-dry.1)'
         required: true
+      # release.yml is the only workflow no CI run exercises before a real tag: version resolution,
+      # pack, SBOM generation, OIDC and the attestation permissions only ever execute in production
+      # conditions. Three defects were found here that were invisible from the repository (the
+      # +metadata regex, the nuget.org re-signing mismatch, the dispatch-tag target). Dry run makes
+      # all of it testable on demand: everything runs up to AND INCLUDING the attestation — which
+      # deliberately stays in, since OIDC/permission failures are exactly what it rehearses — while
+      # NuGet login, the push and the GitHub Release are skipped. Defaults to true so an accidental
+      # dispatch publishes nothing; publishing requires explicitly unticking it.
+      dry_run:
+        description: 'Dry run: stop after pack + attestation; skip NuGet push and the GitHub Release'
+        type: boolean
+        default: true
 
 # Never publish the same ref twice concurrently.
 concurrency:
@@ -89,14 +101,13 @@ jobs:
       # bundled inside the main package, and the CLI / worker / samples are not published.
       # GenerateSBOM activates Microsoft.Sbom.Targets (referenced by both packable projects): each
       # package embeds its SPDX inventory at _manifest/spdx_2.2/manifest.spdx.json. Deliberately
-      # passed only HERE, not hardcoded in the csproj, so local packs and the floor-check job's
-      # throwaway pack stay fast and SBOM-free — only published artifacts carry one.
+      # tools/packaging/pack.sh is the single source of truth for producing the packages (packed projects,
+      # flags, embedded SBOM, and the SBOM-present check). The release-dryrun workflow calls the same script,
+      # so the automatic rehearsal can never drift from the real release.
       - name: Pack
         env:
           VERSION: ${{ steps.version.outputs.version }}
-        run: |
-          dotnet pack FirstClassErrors/FirstClassErrors.csproj -c Release --no-build -p:Version="$VERSION" -p:GenerateSBOM=true -o artifacts
-          dotnet pack FirstClassErrors.Testing/FirstClassErrors.Testing.csproj -c Release --no-build -p:Version="$VERSION" -p:GenerateSBOM=true -o artifacts
+        run: tools/packaging/pack.sh "$VERSION"
 
       - name: Upload packages as build artifacts
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7
@@ -127,13 +138,18 @@ jobs:
       # Requires a trusted publishing policy on nuget.org (owner Reefact / repo first-class-errors /
       # workflow release.yml) for each published package, and the NUGET_USER secret set to the nuget.org
       # account username (profile name, not the email address).
+      # Everything from here on PUBLISHES and is skipped on a dry run. A tag push always publishes
+      # (inputs.* is empty on push events, so the event check short-circuits first); a manual dispatch
+      # publishes only with dry_run explicitly unticked.
       - name: NuGet login (OIDC)
+        if: github.event_name == 'push' || inputs.dry_run == false
         id: nuget-login
         uses: NuGet/login@8d196754b4036150537f80ac539e15c2f1028841 # v1
         with:
           user: ${{ secrets.NUGET_USER }}
 
       - name: Push to NuGet
+        if: github.event_name == 'push' || inputs.dry_run == false
         env:
           NUGET_API_KEY: ${{ steps.nuget-login.outputs.NUGET_API_KEY }}
         run: |
@@ -152,6 +168,7 @@ jobs:
       # even when dispatched from a hotfix branch or an older SHA. The `|| upload --clobber` fallback
       # keeps a re-run idempotent if the release already exists.
       - name: Publish GitHub Release with attested packages
+        if: github.event_name == 'push' || inputs.dry_run == false
         env:
           GH_TOKEN: ${{ github.token }}
           VERSION: ${{ steps.version.outputs.version }}
diff --git a/maintainers/ReleaseDryRun.en.md b/maintainers/ReleaseDryRun.en.md
new file mode 100644
index 0000000..7b77185
--- /dev/null
+++ b/maintainers/ReleaseDryRun.en.md
@@ -0,0 +1,94 @@
+# Release dry run (manual)
+
+> Maintainer / operational documentation. This is **not** part of the library's
+> user documentation under `doc/`.
+
+## What it is
+
+The `release` workflow (`.github/workflows/release.yml`) publishes the NuGet
+packages. It normally runs **only when a version tag is pushed** (`v1.2.3`), so
+its whole pipeline — version parsing, build, test, pack, SBOM generation, OIDC,
+provenance attestation, and the publish steps — otherwise runs *for the first
+time in production, on a tag, once*.
+
+The **manual dry run** lets you run that same pipeline **on demand**, all the way
+through the provenance attestation, **without publishing anything**. It is a
+rehearsal: you confirm the release machinery is healthy before it matters.
+
+## What it does — and does not do
+
+| Step | Real release (tag push) | Dry run |
+| --- | --- | --- |
+| Resolve & validate version | ✅ | ✅ |
+| Restore, build, test | ✅ | ✅ |
+| Pack the two published projects | ✅ | ✅ |
+| Embed the SPDX SBOM | ✅ | ✅ |
+| Upload packages as workflow artifacts | ✅ | ✅ |
+| **Sign the provenance attestation** | ✅ | ✅ (see *Impacts*) |
+| Log in to NuGet (OIDC) | ✅ | ⛔ skipped |
+| **Push to nuget.org** | ✅ | ⛔ skipped |
+| **Create the GitHub Release** | ✅ | ⛔ skipped |
+
+The three publish steps are gated on
+`github.event_name == 'push' || inputs.dry_run == false`, so:
+
+- a **tag push always publishes** — the normal release path is untouched;
+- a **manual run publishes only if you explicitly untick `dry_run`**.
+
+## How to run it
+
+1. On GitHub, open the **Actions** tab.
+2. In the left sidebar, select the **release** workflow.
+3. Click **Run workflow** (top right).
+4. Fill in the inputs:
+   - **version** — any valid SemVer; use an obviously fake one such as
+     `0.0.0-dry.1` (nothing is published, so the value only has to be valid).
+   - **dry run** — **already ticked by default**. Leave it ticked.
+5. Click **Run workflow** and watch the run.
+
+If the run is green through *Attest build provenance*, the release pipeline is
+healthy.
+
+## Impacts
+
+A dry run is *almost* free of side effects, with one exception to be aware of:
+
+- **It creates a real provenance attestation.** The `Attest build provenance`
+  step runs in a dry run (on purpose — OIDC and attestation-permission failures
+  are exactly what it is there to catch). That attestation is written to the
+  repository's attestation store and to the public Sigstore transparency log —
+  it is **permanent and public**, and references the throwaway version. This is
+  harmless but not nothing, so:
+  - use a clearly fake version (`0.0.0-dry.N`) so a throwaway attestation is
+    never mistaken for a real release;
+  - run the manual dry run deliberately (before a real release, or after
+    changing `release.yml`), not casually in a loop.
+- **Nothing is published.** No package reaches nuget.org, and no GitHub Release
+  or git tag is created.
+- **The packed `.nupkg` / `.snupkg` are uploaded as workflow-run artifacts**,
+  which you can download from the run page to inspect, and which expire on the
+  repository's normal artifact retention.
+
+## When to use it
+
+- Before cutting an important release, as a final smoke test of the pipeline.
+- After changing `release.yml`, the packable `.csproj` files, or the packaging
+  configuration (`Directory.Build.props`), since those changes are otherwise
+  unverified until a real tag.
+
+## Related: the automatic dry run
+
+For the **side-effect-free** part of the pipeline — build, pack, and SBOM
+embedding — there is nothing to trigger by hand: the `release-dryrun` workflow
+(`.github/workflows/release-dryrun.yml`) runs it automatically on **every pull
+request and push to `main`**, and fails if the SBOM stops being embedded. It has
+no attestation and no publish, so it runs continuously with no side effects.
+
+Use the **manual** dry run documented here when you additionally want to rehearse
+the **attestation / OIDC** path that the automatic one deliberately leaves out.
+
+## What neither dry run can test
+
+The actual **push to nuget.org** and the **repository-signed bytes** nuget.org
+serves cannot be exercised without publishing — nuget.org has no "dry-run push".
+That final link is only ever validated by a real release.
diff --git a/maintainers/ReleaseDryRun.fr.md b/maintainers/ReleaseDryRun.fr.md
new file mode 100644
index 0000000..9850eda
--- /dev/null
+++ b/maintainers/ReleaseDryRun.fr.md
@@ -0,0 +1,102 @@
+# Répétition de release à blanc (« dry run » manuel)
+
+> Documentation technique / mainteneur. Elle ne fait **pas** partie de la
+> documentation utilisateur de la librairie, sous `doc/`.
+
+## De quoi s'agit-il
+
+Le workflow `release` (`.github/workflows/release.yml`) publie les packages
+NuGet. Il ne s'exécute normalement **que lorsqu'un tag de version est poussé**
+(`v1.2.3`) : tout son pipeline — analyse de la version, build, tests, pack,
+génération du SBOM, OIDC, attestation de provenance et étapes de publication —
+ne tourne donc *pour la première fois qu'en production, sur un tag, une seule
+fois*.
+
+Le **dry run manuel** permet de lancer ce même pipeline **à la demande**,
+jusqu'à l'attestation de provenance incluse, **sans rien publier**. C'est une
+répétition : on vérifie que la machinerie de release est saine avant que ça ne
+compte.
+
+## Ce qu'il fait — et ne fait pas
+
+| Étape | Release réelle (push de tag) | Dry run |
+| --- | --- | --- |
+| Résoudre & valider la version | ✅ | ✅ |
+| Restore, build, tests | ✅ | ✅ |
+| Packer les deux projets publiés | ✅ | ✅ |
+| Embarquer le SBOM SPDX | ✅ | ✅ |
+| Uploader les packages en artefacts de run | ✅ | ✅ |
+| **Signer l'attestation de provenance** | ✅ | ✅ (voir *Impacts*) |
+| Login NuGet (OIDC) | ✅ | ⛔ sauté |
+| **Push vers nuget.org** | ✅ | ⛔ sauté |
+| **Créer la GitHub Release** | ✅ | ⛔ sauté |
+
+Les trois étapes de publication sont conditionnées par
+`github.event_name == 'push' || inputs.dry_run == false`, donc :
+
+- un **push de tag publie toujours** — le chemin de release normal est
+  inchangé ;
+- un **lancement manuel ne publie que si tu décoches explicitement `dry_run`**.
+
+## Comment le lancer
+
+1. Sur GitHub, ouvre l'onglet **Actions**.
+2. Dans la barre latérale de gauche, sélectionne le workflow **release**.
+3. Clique **Run workflow** (en haut à droite).
+4. Renseigne les entrées :
+   - **version** — n'importe quel SemVer valide ; utilise une version
+     manifestement factice comme `0.0.0-dry.1` (rien n'est publié, la valeur
+     doit seulement être valide).
+   - **dry run** — **déjà cochée par défaut**. Laisse-la cochée.
+5. Clique **Run workflow** et observe le run.
+
+Si le run est vert jusqu'à *Attest build provenance*, le pipeline de release
+est sain.
+
+## Impacts
+
+Un dry run est *presque* sans effet de bord, avec une exception à connaître :
+
+- **Il crée une vraie attestation de provenance.** L'étape `Attest build
+  provenance` s'exécute pendant un dry run (volontairement — les échecs d'OIDC
+  ou de permission d'attestation sont précisément ce qu'elle sert à détecter).
+  Cette attestation est écrite dans le magasin d'attestations du dépôt et dans
+  le journal de transparence public Sigstore : elle est **permanente et
+  publique**, et référence la version jetable. C'est inoffensif mais pas rien,
+  donc :
+  - utilise une version clairement factice (`0.0.0-dry.N`) pour qu'une
+    attestation jetable ne soit jamais confondue avec une vraie release ;
+  - lance le dry run manuel de façon délibérée (avant une vraie release, ou
+    après avoir modifié `release.yml`), pas en boucle par réflexe.
+- **Rien n'est publié.** Aucun package n'atteint nuget.org, et aucune GitHub
+  Release ni aucun tag Git n'est créé.
+- **Les `.nupkg` / `.snupkg` produits sont uploadés en artefacts de run**, que
+  tu peux télécharger depuis la page du run pour les inspecter, et qui expirent
+  selon la rétention d'artefacts normale du dépôt.
+
+## Quand l'utiliser
+
+- Avant de sortir une release importante, comme test de fumée final du
+  pipeline.
+- Après avoir modifié `release.yml`, les `.csproj` empaquetés ou la
+  configuration de packaging (`Directory.Build.props`), puisque ces changements
+  restent sinon non vérifiés jusqu'à un vrai tag.
+
+## En rapport : le dry run automatique
+
+Pour la partie **sans effet de bord** du pipeline — build, pack et
+embarquement du SBOM — il n'y a rien à déclencher à la main : le workflow
+`release-dryrun` (`.github/workflows/release-dryrun.yml`) l'exécute
+automatiquement à **chaque pull request et push sur `main`**, et échoue si le
+SBOM cesse d'être embarqué. Il n'a ni attestation ni publication, donc il tourne
+en continu sans effet de bord.
+
+Utilise le dry run **manuel** documenté ici quand tu veux en plus répéter le
+chemin **attestation / OIDC** que l'automatique laisse volontairement de côté.
+
+## Ce qu'aucun dry run ne peut tester
+
+Le **push réel vers nuget.org** et les **octets re-signés par le dépôt** que
+nuget.org sert ne peuvent pas être exercés sans publier — nuget.org n'a pas de
+« push à blanc ». Ce dernier maillon n'est jamais validé que par une vraie
+release.
diff --git a/tools/packaging/pack.sh b/tools/packaging/pack.sh
new file mode 100755
index 0000000..967eac9
--- /dev/null
+++ b/tools/packaging/pack.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+# Single source of truth for producing the published NuGet packages.
+#
+# Both the real release (.github/workflows/release.yml) and the automatic
+# rehearsal (.github/workflows/release-dryrun.yml) call this, so the dry run can
+# never silently drift from the release it is meant to mirror: the set of packed
+# projects, the pack flags, the embedded SBOM and the "is the SBOM actually
+# there?" check all live here, once.
+#
+# It assumes the solution has already been built in Release (it packs with
+# --no-build). It writes the .nupkg / .snupkg into ./artifacts.
+#
+# Usage: tools/packaging/pack.sh <version>
+#   <version> is any valid SemVer (a real release passes the tag version; the
+#   dry run passes a throwaway like 0.0.0-dryrun).
+
+set -eu
+
+if [ "$#" -ne 1 ] || [ -z "$1" ]; then
+  echo "usage: tools/packaging/pack.sh <version>" >&2
+  exit 2
+fi
+version="$1"
+
+# The two projects that carry NuGet identity. GenerateSBOM embeds an SPDX SBOM
+# (_manifest/spdx_2.2/manifest.spdx.json) inside each package; it is passed here,
+# not hardcoded in the csproj, so local and floor-check packs stay SBOM-free.
+for project in \
+  FirstClassErrors/FirstClassErrors.csproj \
+  FirstClassErrors.Testing/FirstClassErrors.Testing.csproj
+do
+  dotnet pack "$project" -c Release --no-build -p:Version="$version" -p:GenerateSBOM=true -o artifacts
+done
+
+# Positive proof, not just a green pack: a pack that silently stopped embedding
+# the manifest (a GenerateSBOM / Microsoft.Sbom.Targets regression) would
+# otherwise pass unnoticed. Assert the SPDX file is present in every package.
+for package in artifacts/*.nupkg; do
+  if unzip -l "$package" | grep -q '_manifest/spdx_2.2/manifest.spdx.json'; then
+    echo "ok: SBOM present in $package"
+  else
+    echo "error: SBOM manifest missing from $package" >&2
+    exit 1
+  fi
+done