diff --git a/.forgejo/workflows/build.yml b/.forgejo/workflows/build.yml
index 43ab953..a641f19 100644
--- a/.forgejo/workflows/build.yml
+++ b/.forgejo/workflows/build.yml
@@ -103,6 +103,27 @@ jobs:
       # cache hit and holds AMO to one call per extension CHANGE. Only moving
       # backwards is a failure, so this runs on every path — cache hit
       # included — rather than only before a sign.
+      # --- shadow mode (milestone 313, step 2) -----------------------------
+      # Informational ONLY. Nothing reads this and it must never fail the
+      # build — no `set -e`, and every derivation falls back to UNAVAILABLE.
+      #
+      # What to watch across pushes, because this is what step 3 will trust:
+      #   * a push touching only agent/ moves the agent and leaves web and ml
+      #     STILL. If web moves, its path set is too wide.
+      #   * a push touching only docs moves nothing.
+      #   * a push touching the extension moves the extension AND web, since
+      #     web bakes in the XPI. If web does not move, its set is too narrow
+      #     — the direction that serves stale bytes on a pin.
+      #   * dev and main derive the same values for the same source.
+      - name: Shadow — derived artifact version (informational)
+        run: |
+          set -u
+          A=extension
+          T=$(sh scripts/artifacts.sh tag "$A" 2>&1 || echo UNAVAILABLE)
+          V=$(sh scripts/artifacts.sh version "$A" 2>&1 || echo UNAVAILABLE)
+          R=$(sh scripts/artifacts.sh revision "$A" 2>&1 || echo UNAVAILABLE)
+          echo "shadow: artifact=$A tag=$T version=$V revision=$R sha=$GITHUB_SHA"
+
       - name: Guard — the derived version must never go backwards
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN }}
@@ -320,6 +341,27 @@ jobs:
           # that exists perfectly well under its real name.
           fetch-depth: 0
 
+      # --- shadow mode (milestone 313, step 2) -----------------------------
+      # Informational ONLY. Nothing reads this and it must never fail the
+      # build — no `set -e`, and every derivation falls back to UNAVAILABLE.
+      #
+      # What to watch across pushes, because this is what step 3 will trust:
+      #   * a push touching only agent/ moves the agent and leaves web and ml
+      #     STILL. If web moves, its path set is too wide.
+      #   * a push touching only docs moves nothing.
+      #   * a push touching the extension moves the extension AND web, since
+      #     web bakes in the XPI. If web does not move, its set is too narrow
+      #     — the direction that serves stale bytes on a pin.
+      #   * dev and main derive the same values for the same source.
+      - name: Shadow — derived artifact version (informational)
+        run: |
+          set -u
+          A=web
+          T=$(sh scripts/artifacts.sh tag "$A" 2>&1 || echo UNAVAILABLE)
+          V=$(sh scripts/artifacts.sh version "$A" 2>&1 || echo UNAVAILABLE)
+          R=$(sh scripts/artifacts.sh revision "$A" 2>&1 || echo UNAVAILABLE)
+          echo "shadow: artifact=$A tag=$T version=$V revision=$R sha=$GITHUB_SHA"
+
       - name: Download signed XPI from Forgejo release asset
         # Fires on every trigger shape. dev and main each bundle the XPI their
         # own sign-extension just published — that is the whole point of the
@@ -486,6 +528,34 @@ jobs:
       image: git.fabledsword.com/bvandeusen/ci-python:3.14
     steps:
       - uses: actions/checkout@v4
+        with:
+          # Full history: this job derives its artifact's version from the
+          # commit its shipped files last changed in (milestone 313). A
+          # depth-1 clone cannot see that commit — it either derives a wrong,
+          # too-low value or finds nothing at all, and neither is a failure
+          # the build would otherwise notice.
+          fetch-depth: 0
+
+      # --- shadow mode (milestone 313, step 2) -----------------------------
+      # Informational ONLY. Nothing reads this and it must never fail the
+      # build — no `set -e`, and every derivation falls back to UNAVAILABLE.
+      #
+      # What to watch across pushes, because this is what step 3 will trust:
+      #   * a push touching only agent/ moves the agent and leaves web and ml
+      #     STILL. If web moves, its path set is too wide.
+      #   * a push touching only docs moves nothing.
+      #   * a push touching the extension moves the extension AND web, since
+      #     web bakes in the XPI. If web does not move, its set is too narrow
+      #     — the direction that serves stale bytes on a pin.
+      #   * dev and main derive the same values for the same source.
+      - name: Shadow — derived artifact version (informational)
+        run: |
+          set -u
+          A=ml
+          T=$(sh scripts/artifacts.sh tag "$A" 2>&1 || echo UNAVAILABLE)
+          V=$(sh scripts/artifacts.sh version "$A" 2>&1 || echo UNAVAILABLE)
+          R=$(sh scripts/artifacts.sh revision "$A" 2>&1 || echo UNAVAILABLE)
+          echo "shadow: artifact=$A tag=$T version=$V revision=$R sha=$GITHUB_SHA"
 
       - name: Determine tag
         id: tag
@@ -533,6 +603,34 @@ jobs:
       image: git.fabledsword.com/bvandeusen/ci-python:3.14
     steps:
       - uses: actions/checkout@v4
+        with:
+          # Full history: this job derives its artifact's version from the
+          # commit its shipped files last changed in (milestone 313). A
+          # depth-1 clone cannot see that commit — it either derives a wrong,
+          # too-low value or finds nothing at all, and neither is a failure
+          # the build would otherwise notice.
+          fetch-depth: 0
+
+      # --- shadow mode (milestone 313, step 2) -----------------------------
+      # Informational ONLY. Nothing reads this and it must never fail the
+      # build — no `set -e`, and every derivation falls back to UNAVAILABLE.
+      #
+      # What to watch across pushes, because this is what step 3 will trust:
+      #   * a push touching only agent/ moves the agent and leaves web and ml
+      #     STILL. If web moves, its path set is too wide.
+      #   * a push touching only docs moves nothing.
+      #   * a push touching the extension moves the extension AND web, since
+      #     web bakes in the XPI. If web does not move, its set is too narrow
+      #     — the direction that serves stale bytes on a pin.
+      #   * dev and main derive the same values for the same source.
+      - name: Shadow — derived artifact version (informational)
+        run: |
+          set -u
+          A=agent
+          T=$(sh scripts/artifacts.sh tag "$A" 2>&1 || echo UNAVAILABLE)
+          V=$(sh scripts/artifacts.sh version "$A" 2>&1 || echo UNAVAILABLE)
+          R=$(sh scripts/artifacts.sh revision "$A" 2>&1 || echo UNAVAILABLE)
+          echo "shadow: artifact=$A tag=$T version=$V revision=$R sha=$GITHUB_SHA"
 
       - name: Determine tag
         id: tag