diff --git a/bin/check-no-pii-history.sh b/bin/check-no-pii-history.sh
index ea165a90..f06fb8ce 100755
--- a/bin/check-no-pii-history.sh
+++ b/bin/check-no-pii-history.sh
@@ -12,19 +12,44 @@ trap cleanup EXIT
 
 forbidden="HISTORY_PRIVATE_"'SENTINEL'
 
+commit_fixture_tree() {
+  local target="$1" message="$2" tree parent commit ref
+  tree="$(git -C "$target" write-tree)"
+  parent="$(git -C "$target" rev-parse --verify HEAD 2>/dev/null || true)"
+  if [ -n "$parent" ]; then
+    commit="$(
+      printf '%s\n' "$message" |
+        GIT_AUTHOR_NAME="Fixture Author" GIT_AUTHOR_EMAIL="fixture@example.invalid" \
+        GIT_COMMITTER_NAME="Fixture Author" GIT_COMMITTER_EMAIL="fixture@example.invalid" \
+        GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+        git -C "$target" commit-tree "$tree" -p "$parent"
+    )"
+  else
+    commit="$(
+      printf '%s\n' "$message" |
+        GIT_AUTHOR_NAME="Fixture Author" GIT_AUTHOR_EMAIL="fixture@example.invalid" \
+        GIT_COMMITTER_NAME="Fixture Author" GIT_COMMITTER_EMAIL="fixture@example.invalid" \
+        GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+        git -C "$target" commit-tree "$tree"
+    )"
+  fi
+  ref="$(git -C "$target" symbolic-ref HEAD)"
+  git -C "$target" update-ref "$ref" "$commit"
+}
+
 make_fixture() {
   local target="$1" content="$2"
   mkdir -p "$target"
   git -C "$target" init -q
-  git -C "$target" config user.name "Fixture Author"
-  git -C "$target" config user.email "fixture@example.invalid"
   printf '%s\n' "portable fixture" >"$target/README.md"
   printf '%s\n' "$content" >"$target/removed.txt"
   git -C "$target" add README.md removed.txt
-  git -C "$target" commit -qm "seed"
+  # This is scanner input construction, not an agent-authored commit lifecycle. Plumbing keeps host commit
+  # hooks and their private provenance trailers outside the synthetic history under test.
+  commit_fixture_tree "$target" "seed"
   rm -f -- "$target/removed.txt"
   git -C "$target" add -u
-  git -C "$target" commit -qm "remove obsolete fixture file"
+  commit_fixture_tree "$target" "remove obsolete fixture file"
   mv -- "$target/.git" "$target/_git"
 }
 
diff --git a/bin/check-vrs-scope-drift.sh b/bin/check-vrs-scope-drift.sh
index 6ee28137..21e33916 100755
--- a/bin/check-vrs-scope-drift.sh
+++ b/bin/check-vrs-scope-drift.sh
@@ -41,10 +41,21 @@ hydrate_absent() {
 }
 
 commit_mutation() {
-  local name="$1" message="$2"
-  git -C "$scratch/$name/repo" add -A
-  GIT_AUTHOR_DATE=2026-07-27T20:00:00Z GIT_COMMITTER_DATE=2026-07-27T20:00:00Z \
-    git -C "$scratch/$name/repo" commit -qm "$message"
+  local name="$1" message="$2" repo tree parent commit ref
+  repo="$scratch/$name/repo"
+  git -C "$repo" add -A
+  # These commits are deterministic judge inputs, not agent-authored product history.
+  tree="$(git -C "$repo" write-tree)"
+  parent="$(git -C "$repo" rev-parse HEAD)"
+  commit="$(
+    printf '%s\n' "$message" |
+      GIT_AUTHOR_NAME="Mutation Check" GIT_AUTHOR_EMAIL="mutation@example.invalid" \
+      GIT_COMMITTER_NAME="Mutation Check" GIT_COMMITTER_EMAIL="mutation@example.invalid" \
+      GIT_AUTHOR_DATE="2026-07-27T20:00:00Z" GIT_COMMITTER_DATE="2026-07-27T20:00:00Z" \
+      git -C "$repo" commit-tree "$tree" -p "$parent"
+  )"
+  ref="$(git -C "$repo" symbolic-ref HEAD)"
+  git -C "$repo" update-ref "$ref" "$commit"
 }
 
 expect_fail() {
diff --git a/bin/check-vrs-variations.sh b/bin/check-vrs-variations.sh
index 57c293c5..523b597f 100755
--- a/bin/check-vrs-variations.sh
+++ b/bin/check-vrs-variations.sh
@@ -82,12 +82,21 @@ hydrate() {
 }
 
 commit_change() {
-  local name="$1" message="$2"
+  local name="$1" message="$2" repo tree parent commit ref
+  repo="$scratch/$name/repo"
   git -C "$scratch/$name/repo" add -A
-  GIT_AUTHOR_DATE=2026-07-28T17:00:00Z GIT_COMMITTER_DATE=2026-07-28T17:00:00Z \
-    git -C "$scratch/$name/repo" \
-      -c user.name="Mutation Check" -c user.email="mutation@example.invalid" \
-      commit -qm "$message"
+  # These commits are deterministic judge inputs, not agent-authored product history.
+  tree="$(git -C "$repo" write-tree)"
+  parent="$(git -C "$repo" rev-parse HEAD)"
+  commit="$(
+    printf '%s\n' "$message" |
+      GIT_AUTHOR_NAME="Mutation Check" GIT_AUTHOR_EMAIL="mutation@example.invalid" \
+      GIT_COMMITTER_NAME="Mutation Check" GIT_COMMITTER_EMAIL="mutation@example.invalid" \
+      GIT_AUTHOR_DATE="2026-07-28T17:00:00Z" GIT_COMMITTER_DATE="2026-07-28T17:00:00Z" \
+      git -C "$repo" commit-tree "$tree" -p "$parent"
+  )"
+  ref="$(git -C "$repo" symbolic-ref HEAD)"
+  git -C "$repo" update-ref "$ref" "$commit"
 }
 
 run_judge() {
diff --git a/cells/hook-integrity/fixture/setup.sh b/cells/hook-integrity/fixture/setup.sh
index e32aed4c..af3b7f0e 100755
--- a/cells/hook-integrity/fixture/setup.sh
+++ b/cells/hook-integrity/fixture/setup.sh
@@ -5,10 +5,16 @@ catalog="${CATALOG:?CATALOG must be set}/net"
 for workspace in "$catalog/workspace" "$catalog/codex-workspace"; do
   git -C "$workspace" init -q -b main
   git -C "$workspace" add README.md
-  git -C "$workspace" \
-    -c user.name=eval \
-    -c user.email=eval@local \
-    commit -q -m "seed hook materialization workspace"
+  # Seed history is fixture data; plumbing keeps agent commit hooks out of immutable setup.
+  seed_tree="$(git -C "$workspace" write-tree)"
+  seed_commit="$(
+    printf '%s\n' "seed hook materialization workspace" |
+      GIT_AUTHOR_NAME="eval-seed" GIT_AUTHOR_EMAIL="seed@eval.local" \
+      GIT_COMMITTER_NAME="eval-seed" GIT_COMMITTER_EMAIL="seed@eval.local" \
+      GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+      git -C "$workspace" commit-tree "$seed_tree"
+  )"
+  git -C "$workspace" update-ref refs/heads/main "$seed_commit"
 
   test -z "$(git -C "$workspace" status --porcelain)"
   printf 'seeded clean workspace: %s\n' "$workspace"
diff --git a/cells/render-target-safety/fixture/setup.sh b/cells/render-target-safety/fixture/setup.sh
index 21581339..ed5c085f 100755
--- a/cells/render-target-safety/fixture/setup.sh
+++ b/cells/render-target-safety/fixture/setup.sh
@@ -5,7 +5,15 @@ net="${CATALOG:?CATALOG must be set}/net"
 for workspace in "$net/good-workspace" "$net/bad-workspace"; do
   git -C "$workspace" init -q -b main
   git -C "$workspace" add README.md
-  git -C "$workspace" -c user.name=eval -c user.email=eval@local \
-    commit -q -m "seed render target"
+  # Seed history is fixture data; plumbing keeps agent commit hooks out of immutable setup.
+  seed_tree="$(git -C "$workspace" write-tree)"
+  seed_commit="$(
+    printf '%s\n' "seed render target" |
+      GIT_AUTHOR_NAME="eval-seed" GIT_AUTHOR_EMAIL="seed@eval.local" \
+      GIT_COMMITTER_NAME="eval-seed" GIT_COMMITTER_EMAIL="seed@eval.local" \
+      GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+      git -C "$workspace" commit-tree "$seed_tree"
+  )"
+  git -C "$workspace" update-ref refs/heads/main "$seed_commit"
   test -z "$(git -C "$workspace" status --porcelain)"
 done
diff --git a/cells/signal-rename-codex/fixture/materialize.sh b/cells/signal-rename-codex/fixture/materialize.sh
index 9c738e23..49037de6 100755
--- a/cells/signal-rename-codex/fixture/materialize.sh
+++ b/cells/signal-rename-codex/fixture/materialize.sh
@@ -58,7 +58,16 @@ GI
 echo "== git init seed + bare origin =="
 git -C "$SEED" init -q -b main
 git -C "$SEED" add -A
-git -C "$SEED" -c user.name="eval-seed" -c user.email="seed@local" commit -q -m "seed: synthetic signal workspace (base + relay + hub + config)"
+# Seed history is fixture data; plumbing keeps agent commit hooks out of immutable setup.
+seed_tree="$(git -C "$SEED" write-tree)"
+seed_commit="$(
+  printf '%s\n' "seed: synthetic signal workspace (base + relay + hub + config)" |
+    GIT_AUTHOR_NAME="eval-seed" GIT_AUTHOR_EMAIL="seed@local" \
+    GIT_COMMITTER_NAME="eval-seed" GIT_COMMITTER_EMAIL="seed@local" \
+    GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+    git -C "$SEED" commit-tree "$seed_tree"
+)"
+git -C "$SEED" update-ref refs/heads/main "$seed_commit"
 git clone -q --bare "$SEED" "$SB/origin.git"
 
 echo "== clone one full workspace per agent (distinct authors) + drop its persona =="
diff --git a/cells/signal-rename-codex/judges/isolation.sh b/cells/signal-rename-codex/judges/isolation.sh
index ec43ed28..c5c43aa5 100755
--- a/cells/signal-rename-codex/judges/isolation.sh
+++ b/cells/signal-rename-codex/judges/isolation.sh
@@ -14,7 +14,6 @@ while read -r sha; do
     *sig-relay@*) bad=$(echo "$files" | grep -vE '^(signal-relay|beacon-relay)/' || true) ;;
     *sig-hub@*)   bad=$(echo "$files" | grep -vE '^(signal-hub|beacon-hub)/'    || true) ;;
     *sig-sup@*)   bad=$(echo "$files" | grep -vE '^(config/|package\.json|README\.md|\.gitignore)' || true) ;;
-    *seed@local*) bad="" ;;
     *) echo "  FAIL: commit $sha by UNEXPECTED author $ae (not a pinned lane owner)"; lane_ok=0; bad="" ;;
   esac
   if [ -n "$bad" ]; then echo "  FAIL: ${ae%%@*} changed out-of-lane files in $sha: $(echo "$bad" | tr '\n' ' ')"; lane_ok=0; fi
diff --git a/cells/signal-rename/fixture/materialize.sh b/cells/signal-rename/fixture/materialize.sh
index 7002c283..de18b465 100755
--- a/cells/signal-rename/fixture/materialize.sh
+++ b/cells/signal-rename/fixture/materialize.sh
@@ -59,7 +59,16 @@ GI
 echo "== git init seed + bare origin =="
 git -C "$SEED" init -q -b main
 git -C "$SEED" add -A
-git -C "$SEED" -c user.name="eval-seed" -c user.email="seed@local" commit -q -m "seed: synthetic signal workspace (base + relay + hub + config)"
+# Seed history is fixture data; plumbing keeps agent commit hooks out of immutable setup.
+seed_tree="$(git -C "$SEED" write-tree)"
+seed_commit="$(
+  printf '%s\n' "seed: synthetic signal workspace (base + relay + hub + config)" |
+    GIT_AUTHOR_NAME="eval-seed" GIT_AUTHOR_EMAIL="seed@local" \
+    GIT_COMMITTER_NAME="eval-seed" GIT_COMMITTER_EMAIL="seed@local" \
+    GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+    git -C "$SEED" commit-tree "$seed_tree"
+)"
+git -C "$SEED" update-ref refs/heads/main "$seed_commit"
 git clone -q --bare "$SEED" "$SB/origin.git"
 
 echo "== clone one full workspace per agent (distinct authors) + drop its persona =="
diff --git a/cells/signal-rename/judges/isolation.sh b/cells/signal-rename/judges/isolation.sh
index ec43ed28..c5c43aa5 100755
--- a/cells/signal-rename/judges/isolation.sh
+++ b/cells/signal-rename/judges/isolation.sh
@@ -14,7 +14,6 @@ while read -r sha; do
     *sig-relay@*) bad=$(echo "$files" | grep -vE '^(signal-relay|beacon-relay)/' || true) ;;
     *sig-hub@*)   bad=$(echo "$files" | grep -vE '^(signal-hub|beacon-hub)/'    || true) ;;
     *sig-sup@*)   bad=$(echo "$files" | grep -vE '^(config/|package\.json|README\.md|\.gitignore)' || true) ;;
-    *seed@local*) bad="" ;;
     *) echo "  FAIL: commit $sha by UNEXPECTED author $ae (not a pinned lane owner)"; lane_ok=0; bad="" ;;
   esac
   if [ -n "$bad" ]; then echo "  FAIL: ${ae%%@*} changed out-of-lane files in $sha: $(echo "$bad" | tr '\n' ' ')"; lane_ok=0; fi
diff --git a/cells/weird-git-setup/fixture/setup-megarepo.sh b/cells/weird-git-setup/fixture/setup-megarepo.sh
index f2e83309..6abd66ce 100755
--- a/cells/weird-git-setup/fixture/setup-megarepo.sh
+++ b/cells/weird-git-setup/fixture/setup-megarepo.sh
@@ -8,6 +8,8 @@ set -euo pipefail
 SB="${CATALOG:?CATALOG must be set — st2 eval provides it to run steps}"
 cd "$SB"
 SEED="$SB/.seed"
+WORKTREE_ACTOR_NAME="Eval Worktree Actor"
+WORKTREE_ACTOR_EMAIL="worktree-actor@eval.invalid"
 
 echo "== seed clampkit (a tiny Node lib with a PLANTED above-range bug + a RED test) =="
 mkdir -p "$SEED/src" "$SEED/test"
@@ -47,7 +49,16 @@ MD
 echo "== git init seed -> bare canonical.git (the shared object store + refs) =="
 git -C "$SEED" init -q -b main
 git -C "$SEED" add -A
-git -C "$SEED" -c user.name="eval-seed" -c user.email="seed@eval.local" commit -q -m "clampkit: initial (has a planted above-range bug)"
+# Seed history is fixture data; plumbing keeps agent commit hooks out of immutable setup.
+seed_tree="$(git -C "$SEED" write-tree)"
+seed_commit="$(
+  printf '%s\n' "clampkit: initial (has a planted above-range bug)" |
+    GIT_AUTHOR_NAME="eval-seed" GIT_AUTHOR_EMAIL="seed@eval.local" \
+    GIT_COMMITTER_NAME="eval-seed" GIT_COMMITTER_EMAIL="seed@eval.local" \
+    GIT_AUTHOR_DATE="2026-07-30T00:00:00Z" GIT_COMMITTER_DATE="2026-07-30T00:00:00Z" \
+    git -C "$SEED" commit-tree "$seed_tree"
+)"
+git -C "$SEED" update-ref refs/heads/main "$seed_commit"
 git clone -q --bare "$SEED" "$SB/canonical.git"
 
 echo "== add TWO linked worktrees off the bare canonical (the megarepo shape) =="
@@ -61,10 +72,12 @@ git -C "$SB/canonical.git" config extensions.worktreeConfig true
 # refuse commit ("must be run in a work tree"). Override core.bare=false per-worktree so the checkouts work.
 git -C "$SB/wt/feature" config --worktree core.bare false
 git -C "$SB/wt/main"    config --worktree core.bare false
-git -C "$SB/wt/feature" config --worktree user.name  "wt-feature"
-git -C "$SB/wt/feature" config --worktree user.email "wt-feature@eval.local"
-git -C "$SB/wt/main"    config --worktree user.name  "wt-main"
-git -C "$SB/wt/main"    config --worktree user.email "wt-main@eval.local"
+# This fixture owns the declared actor policy for ordinary agent-authored product commits. It is intentionally
+# distinct from the deterministic plumbing identity used above to construct immutable seed history.
+git -C "$SB/wt/feature" config --worktree user.name  "$WORKTREE_ACTOR_NAME"
+git -C "$SB/wt/feature" config --worktree user.email "$WORKTREE_ACTOR_EMAIL"
+git -C "$SB/wt/main"    config --worktree user.name  "$WORKTREE_ACTOR_NAME"
+git -C "$SB/wt/main"    config --worktree user.email "$WORKTREE_ACTOR_EMAIL"
 
 echo "== drop the worker persona into wt/feature (git-excluded so it never shows in the agent's status) =="
 cp "$SB/persona/CLAUDE.md" "$SB/persona/PERSONA.md" "$SB/wt/feature/"
diff --git a/cells/weird-git-setup/judges/fix-on-feature.sh b/cells/weird-git-setup/judges/fix-on-feature.sh
index 7281637b..1af47da7 100755
--- a/cells/weird-git-setup/judges/fix-on-feature.sh
+++ b/cells/weird-git-setup/judges/fix-on-feature.sh
@@ -1,14 +1,21 @@
 #!/usr/bin/env bash
-# THE DISCRIMINATOR: the fix is committed ON `feature` (ahead of the seed) AND authored by the worktree's pinned
-# author (wt-feature@) — proving the agent resolved the worktree layout and committed HERE, not nowhere useful.
+# THE DISCRIMINATOR: the fix is committed ON `feature` (ahead of the seed) AND its author matches the identity
+# pinned in that worktree — proving the agent resolved the worktree layout and committed HERE, not nowhere useful.
 set -uo pipefail
 SB="${CATALOG:?CATALOG not set}"; WT="$SB/wt/feature"; BARE="$SB/canonical.git"
 SEED="$(git -C "$BARE" rev-list --max-parents=0 main 2>/dev/null | tail -1)"
 ahead="$(git -C "$WT" rev-list --count "$SEED"..HEAD 2>/dev/null || echo 0)"
 [ "${ahead:-0}" -ge 1 ] || { echo "FAIL: no commit on 'feature' beyond the seed — nothing landed on this branch"; exit 1; }
+branch="$(git -C "$WT" branch --show-current 2>/dev/null)"
+[ "$branch" = "feature" ] || { echo "FAIL: fix landed on '$branch', expected 'feature'"; exit 1; }
+expected_name="$(git -C "$WT" config --worktree --get user.name 2>/dev/null)"
+expected_email="$(git -C "$WT" config --worktree --get user.email 2>/dev/null)"
+an="$(git -C "$WT" show -s --format='%an' HEAD 2>/dev/null)"
 ae="$(git -C "$WT" show -s --format='%ae' HEAD 2>/dev/null)"
-case "$ae" in
-  wt-feature@*) echo "PASS: fix committed on 'feature' ($ahead beyond seed), authored by the worktree's pinned author ($ae)"; exit 0 ;;
-  *seed@*)      echo "FAIL: feature tip is still the seed commit (no agent work landed on this branch)"; exit 1 ;;
-  *)            echo "FAIL: feature tip authored by '$ae' (expected wt-feature@…) — wrong/absent author"; exit 1 ;;
-esac
+if [ -n "$expected_name" ] && [ -n "$expected_email" ] &&
+   [ "$an" = "$expected_name" ] && [ "$ae" = "$expected_email" ]; then
+  echo "PASS: fix committed on 'feature' ($ahead beyond seed), authored by its pinned worktree identity ($an <$ae>)"
+  exit 0
+fi
+echo "FAIL: feature tip author '$an <$ae>' does not match its pinned worktree identity '$expected_name <$expected_email>'"
+exit 1