feat: implement issue #1103 — cmd_rollback moves the bare <agent>/<ring> tag, not <agent>/v<M>-<ring> — the emergency lever is a silent no-op for every v-scoped agent

scripts/canary-rollout.sh

@@ -2520,14 +2520,46 @@ cmd_rollback() {
   local target
   target="$(_gh_tag_commit "$host" "$agent/$to")"
   [ -z "$target" ] && { echo "::error::release tag $agent/$to not found on $host" >&2; return 1; }
-  echo "rolling back $agent/$ring -> $to (${target:0:12}) on $host"
+  # Resolve the RING tag with fallback (major-scoped-channels epic #657 F4): PREFER the
+  # v-scoped `<agent>/v<M>-<ring>` within the agent's current major line when it exists,
+  # else the legacy bare `<agent>/<ring>`. Moving the bare tag on a v-scoped fleet relocated
+  # a tag no caller pins and still exited 0 — a silent no-op on the emergency lever (#1103).
+  # First check if the v-scoped tier exists; if not, fall back to bare.
+  # (The `--to` release tag above is always the bare immutable `<agent>/vX.Y.Z`, so it is
+  # correctly resolved without a major.)
+  local ring_tag ring_commit
+  IFS=$'\t' read -r ring_tag ring_commit < <(_resolved_channel "$agent" "$ring")
+  # If the resolved tag (v-scoped or bare from _resolved_channel's logic) doesn't exist,
+  # and we got v-scoped, try the bare tag as a fallback. The agent may have released v<M>.*.*
+  # but not yet seeded channel tier tags, so bare still matters as an intermediate step.
+  if [ -z "$ring_commit" ] && [[ "$ring_tag" == *"/v"[0-9]* ]]; then
+    # Constructed ring_tag was v-scoped and doesn't exist; try bare.
+    local bare_commit bare_tag
+    bare_tag="$agent/$ring"
+    bare_commit="$(_channel_tag_commit "$agent" "$ring")"
+    if [ -n "$bare_commit" ]; then
+      ring_tag="$bare_tag"
+      ring_commit="$bare_commit"
+    else
+      # Both v-scoped and bare are absent; report the bare tag in the error message.
+      ring_tag="$bare_tag"
+    fi
+  fi
+  # Fail loudly rather than no-op (#1103): if BOTH v-scoped and bare (if tried) don't exist,
+  # refuse to create-and-move a channel tag nobody pins. The worst failure mode for rollback
+  # is a silent no-op that exits 0, so make it loud.
+  if [ -z "$ring_commit" ]; then
+    echo "::error::rollback target ring tag $ring_tag does not exist on $host — refusing to create-and-move a channel tag nobody pins (that would be a silent no-op). Check the ring name and the agent's major line." >&2
+    return 1
+  fi
+  echo "rolling back $ring_tag -> $to (${target:0:12}) on $host"
   if [ "$dry" = true ]; then
-    echo "[DRY-RUN] would: gh api PATCH repos/$host/git/refs/tags/$agent/$ring sha=$target (force)"
+    echo "[DRY-RUN] would: gh api PATCH repos/$host/git/refs/tags/$ring_tag sha=$target (force)"
     return 0
   fi
-  _gh_move_tag "$host" "$agent/$ring" "$target" \
-    || { echo "::error::failed to move $agent/$ring -> $to on $host" >&2; return 1; }
-  echo "rolled back $agent/$ring -> $to"
+  _gh_move_tag "$host" "$ring_tag" "$target" \
+    || { echo "::error::failed to move $ring_tag -> $to on $host" >&2; return 1; }
+  echo "rolled back $ring_tag -> $to"
 }
 
 # ── blocker-issue + fleet-status automation (auto-triage of held promotions) ────

tests/canary_rollout.bats

@@ -1205,6 +1205,92 @@ GITEOF
   ! grep -Ev '^[[:space:]]*#' "$ORCH" | grep -Eq '\bgit[[:space:]]+(tag|push)\b'
 }
 
+# ── orchestrator: rollback resolves the ring tag v-scope-aware, like promote (#1103) ──
+# cmd_rollback used to move the BARE <agent>/<ring> tag regardless of the agent's major
+# line. On a v-scoped fleet (all stubs pin <agent>/v<M>-<ring>) that moved a tag nobody
+# reads and still exited 0 — a silent no-op on the emergency lever. It must resolve the
+# ring tag the SAME way cmd_promote/_resolved_channel do: prefer <agent>/v<M>-<ring>.
+
+@test "orchestrator: rollback targets the v-scoped ring tag on a v-scoped agent, not the bare tier (#1103)" {
+  # The real shape from the issue: dev-lead on major 139, the v139-* family present.
+  # `rollback dev-lead stable --to v139.8.0` MUST target dev-lead/v139-stable — the tag the
+  # fleet stubs actually pin — never the bare dev-lead/stable that nobody reads.
+  _make_stub_bin
+  cat > "$STUB_BIN/gh" <<'GHEOF'
+#!/usr/bin/env bash
+case "$*" in
+  *"matching-refs/tags/dev-lead/v"*)     printf 'refs/tags/dev-lead/v139-next\nrefs/tags/dev-lead/v139.8.0\n' ;;  # channel anchor + latest release
+  *"git/ref/tags/dev-lead/v139-next"*)   echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # channel anchor exists → major=139
+  *"git/ref/tags/dev-lead/v139-stable"*) echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # the pinned channel tag
+  *"git/ref/tags/dev-lead/v139.8.0"*)    echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # the release --to target
+  *"git/ref/tags/dev-lead/stable"*)      echo "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef commit" ;;  # bare tier — must NOT be targeted
+  *) echo "" ;;
+esac
+GHEOF
+  chmod +x "$STUB_BIN/gh"
+
+  # GITHUB_REPOSITORY=.github forces THIS_REPO=.github → dev-lead (host=.github-private) is cross-repo.
+  run env GITHUB_REPOSITORY="combsmith/.github" CANARY_RINGS="$RINGS" \
+    bash "$ORCH" rollback dev-lead stable --to v139.8.0 --dry-run
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"rolling back dev-lead/v139-stable"* ]]
+  [[ "$output" == *"refs/tags/dev-lead/v139-stable"* ]]
+  # The exact defect: the bare ring tag must never be the PATCH target.
+  [[ "$output" != *"refs/tags/dev-lead/stable"* ]]
+}
+
+@test "orchestrator: rollback fails loudly when the resolved ring tag does not exist (no silent no-op) (#1103)" {
+  # dev-lead on major 139, release v139.8.0 present, but NEITHER the v-scoped channel tag
+  # v139-stable NOR the bare stable exists. Rollback must NOT create-and-move a tag nobody
+  # pins and exit 0 — it must fail with a clear error.
+  _make_stub_bin
+  cat > "$STUB_BIN/gh" <<'GHEOF'
+#!/usr/bin/env bash
+case "$*" in
+  *"matching-refs/tags/dev-lead/v"*)  printf 'refs/tags/dev-lead/v139-next\nrefs/tags/dev-lead/v139.8.0\n' ;;  # channel anchor + release
+  *"git/ref/tags/dev-lead/v139-next"*) echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # channel anchor exists → major=139
+  *"git/ref/tags/dev-lead/v139.8.0"*) echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # release --to resolves
+  *) echo "" ;;                                                                        # every channel tag is absent
+esac
+GHEOF
+  chmod +x "$STUB_BIN/gh"
+
+  run env GITHUB_REPOSITORY="combsmith/.github" CANARY_RINGS="$RINGS" \
+    bash "$ORCH" rollback dev-lead stable --to v139.8.0 --dry-run
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::"* ]]
+  # The resolution falls back to the bare tier (v-scoped absent), so the loud error names the
+  # resolved-but-absent tag and refuses — never a "[DRY-RUN] would … (force)" success line.
+  [[ "$output" == *"dev-lead/stable does not exist"* ]]
+  [[ "$output" != *"DRY-RUN"* ]]
+}
+
+@test "orchestrator: rollback falls back to the bare ring tag when no v-scoped channel tag exists (#1103)" {
+  # Pre-F4 shape: releases exist (so a current major is derived) but the CHANNEL tags are
+  # still bare — v139-stable is absent, dev-lead/stable is what the fleet pins. Rollback must
+  # then move the bare tag, byte-identical to _resolved_channel's fall-back (matches promote).
+  _make_stub_bin
+  cat > "$STUB_BIN/gh" <<'GHEOF'
+#!/usr/bin/env bash
+case "$*" in
+  *"matching-refs/tags/dev-lead/v"*)     printf 'refs/tags/dev-lead/v139-next\nrefs/tags/dev-lead/v139.8.0\n' ;;  # channel anchor + release
+  *"git/ref/tags/dev-lead/v139-next"*)   echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # channel anchor exists → major=139
+  *"git/ref/tags/dev-lead/v139.8.0"*)    echo "90dcc01ca854d7acd65044bb8defcc32789a8335 commit" ;;  # release --to target
+  *"git/ref/tags/dev-lead/v139-stable"*) echo "" ;;                                    # v-scoped channel tag ABSENT
+  *"git/ref/tags/dev-lead/stable"*)      echo "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef commit" ;;  # bare channel tag present
+  *) echo "" ;;
+esac
+GHEOF
+  chmod +x "$STUB_BIN/gh"
+
+  run env GITHUB_REPOSITORY="combsmith/.github" CANARY_RINGS="$RINGS" \
+    bash "$ORCH" rollback dev-lead stable --to v139.8.0 --dry-run
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"rolling back dev-lead/stable"* ]]
+  [[ "$output" == *"refs/tags/dev-lead/stable"* ]]
+  [[ "$output" != *"v139-stable"* ]]
+}
+
 # ── orchestrator: full graduated verdicts (cut date + gh run data → gate state) ─
 # Lay out next = candidate (cccc); ring0/ring1/stable = prior (bbbb): frontier = ring0,
 # transition next->ring0, source = next. The release tag cccc is dated `cut_days` ago,