feat(prevb): dynamic upgrade base (last-green→main→skip) + per-recipe previous/ overlay; migrate discourse off static base + leaky overlay

- resolve_upgrade_base: BasePlan(kind=version|ref|skip); last-green (warm canonical) primary,
  main-tip fallback, declared skip else. UPGRADE_BASE_VERSION retained as optional override.
- deploy_app: base_ref path (chaos-deploy a main-tip/last-green commit) + apply_previous wiring.
- lifecycle: previous/ surface (has_previous, previous_target_version, previous_status decision,
  provide/remove overlay, compose_file add/remove, recipe_branch_commit, stack_service_names).
- generic.perform_upgrade: strip previous/ overlay + COMPOSE_FILE entry before head redeploy.
- discourse: compose.ccci.yml now environmental-only (order: stop-first); removed bitnamilegacy
  pins + sidekiq + UPGRADE_BASE_VERSION; test_upgrade.py asserts head image == official 3.5.3 + no sidekiq.
- unit tests: resolve_upgrade_base matrix + previous/ apply/skip/stale + COMPOSE_FILE layering.

runner/harness/generic.py

@@ -251,6 +251,16 @@ def perform_upgrade(
     before = lifecycle.deployed_identity(domain)
     if head_ref:
         lifecycle.recipe_checkout_ref(recipe, head_ref)
+    # Phase prevb: strip the base-only `previous/` overlay before the head redeploy so the PR head
+    # runs UNMODIFIED (the version-specific repair must never leak onto the head). Delete the copied
+    # compose.previous.yml and drop it from COMPOSE_FILE in the app .env. No-op when no previous/ was
+    # applied (the file/entry are absent). The environmental compose.ccci.yml stays (all deploys).
+    lifecycle.remove_previous_overlay(recipe)
+    cf_now = abra.env_get(domain, "COMPOSE_FILE")
+    if cf_now and lifecycle.PREVIOUS_COMPOSE in cf_now:
+        cf_stripped = lifecycle.compose_file_remove(cf_now, lifecycle.PREVIOUS_COMPOSE)
+        abra.env_set(domain, "COMPOSE_FILE", cf_stripped)
+        print(f"  previous-overlay: COMPOSE_FILE for head redeploy = {cf_stripped}", flush=True)
     # UPGRADE_EXTRA_ENV (F2-14c): a recipe may need different app .env for the upgrade-TARGET deploy
     # than for the base — e.g. mumble's `compose.host-ports.yml` overlay exists ONLY in the newer
     # (target) version, so the base deploys minimally WITHOUT it and the upgrade adds it to COMPOSE_FILE

runner/harness/lifecycle.py

@@ -154,6 +154,145 @@ def provide_ccci_overlay(recipe: str) -> None:
     )
 
 
+# ---------------------------------------------------------------------------------------------
+# Phase prevb: dynamic upgrade base + per-recipe `previous/` overlay.
+#
+# `previous/` holds the MINIMAL config needed to deploy the *previous (last-green) version* when it
+# can't deploy as-published (e.g. an image relocation). It is applied ONLY to the base deploy and
+# ONLY when the resolved base is that exact published version; NEVER to the PR head; on a main-tip
+# base or version mismatch it is skipped + flagged stale. Mechanism mirrors the environmental
+# compose.ccci.yml overlay (copied untracked into the checkout, referenced via COMPOSE_FILE), but is
+# stripped before the head redeploy so the head runs unmodified. (plan-phase-prevb §2.)
+# ---------------------------------------------------------------------------------------------
+
+PREVIOUS_COMPOSE = "compose.previous.yml"
+
+
+def previous_dir(recipe: str) -> str:
+    return os.path.join(meta_mod.TESTS_DIR, recipe, "previous")
+
+
+def has_previous(recipe: str) -> bool:
+    """True iff the recipe ships a `tests/<recipe>/previous/` folder with a compose.previous.yml."""
+    return os.path.isfile(os.path.join(previous_dir(recipe), PREVIOUS_COMPOSE))
+
+
+def previous_target_version(recipe: str) -> str | None:
+    """The published version the recipe's `previous/` folder targets — declared in a one-line
+    `previous/VERSION` marker (first non-blank, non-`#` line). None if no marker. The harness applies
+    `previous/` ONLY when the resolved base equals this; otherwise the folder is stale and skipped."""
+    marker = os.path.join(previous_dir(recipe), "VERSION")
+    try:
+        with open(marker) as f:
+            for line in f:
+                s = line.strip()
+                if s and not s.startswith("#"):
+                    return s
+    except OSError:
+        return None
+    return None
+
+
+def previous_status(recipe: str, base_kind: str, base_version: str | None) -> dict:
+    """Decide whether `previous/` applies to this base, as a pure decision (unit-tested).
+
+    Returns {apply, stale, reason}:
+      - no `previous/` folder           → apply=False, stale=False (nothing to do).
+      - base is not a pinned published  → apply=False, stale=True  (main-tip / no base): previous/ can
+        version (kind != "version")       only repair a published base; flag for review.
+      - no `previous/VERSION` marker     → apply=False, stale=True  (undeclared: cannot version-guard).
+      - marker != resolved base version  → apply=False, stale=True  (stale: targets X, base is Y).
+      - marker == resolved base version  → apply=True,  stale=False.
+    """
+    if not has_previous(recipe):
+        return {"apply": False, "stale": False, "reason": ""}
+    if base_kind != "version" or not base_version:
+        return {
+            "apply": False,
+            "stale": True,
+            "reason": (
+                f"previous/ present but the resolved base is not a pinned published version "
+                f"(base_kind={base_kind}) — previous/ only repairs a published base; not applied"
+            ),
+        }
+    target = previous_target_version(recipe)
+    if not target:
+        return {
+            "apply": False,
+            "stale": True,
+            "reason": "previous/ has no VERSION marker — cannot version-guard; not applied",
+        }
+    if target != base_version:
+        return {
+            "apply": False,
+            "stale": True,
+            "reason": f"previous/ targets {target}, base is {base_version} — stale, remove it",
+        }
+    return {"apply": True, "stale": False, "reason": ""}
+
+
+def provide_previous_overlay(recipe: str) -> None:
+    """Copy `tests/<recipe>/previous/compose.previous.yml` into THIS run's recipe checkout so a
+    COMPOSE_FILE reference to it resolves (base deploy only). No-op if absent."""
+    src = os.path.join(previous_dir(recipe), PREVIOUS_COMPOSE)
+    if not os.path.isfile(src):
+        return
+    dest_dir = abra.recipe_dir(recipe)
+    if not os.path.isdir(dest_dir):
+        raise RuntimeError(f"recipe checkout missing for {recipe}: {dest_dir}")
+    shutil.copy(src, os.path.join(dest_dir, PREVIOUS_COMPOSE))
+    print(
+        f"  previous-overlay: provided {PREVIOUS_COMPOSE} to the {recipe} base checkout "
+        "(base-only; stripped before the head redeploy)",
+        flush=True,
+    )
+
+
+def remove_previous_overlay(recipe: str) -> None:
+    """Delete compose.previous.yml from this run's recipe checkout (called before the head redeploy so
+    the PR head NEVER sees the previous-version repair). No-op if absent."""
+    p = os.path.join(abra.recipe_dir(recipe), PREVIOUS_COMPOSE)
+    with contextlib.suppress(OSError):
+        if os.path.isfile(p):
+            os.remove(p)
+            print(
+                f"  previous-overlay: removed {PREVIOUS_COMPOSE} from the head checkout", flush=True
+            )
+
+
+def compose_file_add(compose_file: str, overlay: str) -> str:
+    """Append `overlay` to a ':'-separated COMPOSE_FILE value if absent (pure). Defaults a missing
+    value to `compose.yml` first, matching abra."""
+    parts = [p for p in (compose_file or "").split(":") if p] or ["compose.yml"]
+    if overlay not in parts:
+        parts.append(overlay)
+    return ":".join(parts)
+
+
+def compose_file_remove(compose_file: str, overlay: str) -> str:
+    """Remove `overlay` from a ':'-separated COMPOSE_FILE value (pure). Keeps order; defaults a now-
+    empty value to `compose.yml`."""
+    parts = [p for p in (compose_file or "").split(":") if p and p != overlay]
+    return ":".join(parts or ["compose.yml"])
+
+
+def recipe_branch_commit(recipe: str, branch: str = "main") -> str | None:
+    """Resolve the recipe repo's target-branch tip (the predecessor the PR merges onto) to a commit
+    SHA, for the dynamic upgrade-base main-tip fallback. The per-run tree is a full clone of the
+    mirror, so `origin/<branch>` is present. Tries origin/<branch>, then origin/master. None if
+    neither resolves (new recipe / detached state)."""
+    path = abra.recipe_dir(recipe)
+    for ref in (f"origin/{branch}", "origin/master"):
+        proc = subprocess.run(
+            ["git", "-C", path, "rev-parse", "--verify", "--quiet", ref],
+            capture_output=True,
+            text=True,
+        )
+        if proc.returncode == 0 and proc.stdout.strip():
+            return proc.stdout.strip()
+    return None
+
+
 def _run_install_steps(hook: tuple[str, str], recipe: str, domain: str) -> None:
     """Run a recipe's custom install-steps hook (install_steps.sh) during the install tier — after
     `abra app new` + env defaults + secret generate, before deploy (Phase 1d DG5). The hook gets the
@@ -234,6 +373,8 @@ def deploy_app(
     recipe: str,
     domain: str,
     version: str | None = None,
+    base_ref: str | None = None,
+    apply_previous: bool = False,
     secrets: bool = True,
     install_steps_hook: tuple[str, str] | None = None,
     deploy_timeout: int = 900,
@@ -273,7 +414,18 @@ def deploy_app(
     # Adversary F1d-2). Chaos is correct ONLY for the version=None case (deploy the current PR-head
     # checkout). Order matters: checkout before secret_generate (-C) so secrets match the pinned tree.
     chaos = version is None
-    if version:
+    if base_ref:
+        # Dynamic upgrade base = target-branch (main) tip, or a last-green commit (phase prevb): an
+        # arbitrary git ref, not a published tag. Check it out and deploy via chaos — same mechanism
+        # as the head deploy (a non-tag ref would FATA abra's pinned-deploy lint/clean-tree gate).
+        recipe_checkout_ref(recipe, base_ref)
+        chaos = True
+        print(
+            f"  deploy_app({recipe}): base = main-tip/ref {base_ref[:12]} → chaos deploy of the "
+            "checked-out ref (the PR's true predecessor; not a published pin)",
+            flush=True,
+        )
+    elif version:
         abra.recipe_checkout(recipe, version)
         # A pinned (non-chaos) deploy runs `abra recipe lint`, which FATAs R014 ('only annotated
         # tags') if the upstream recipe ships a stray lightweight version tag (e.g. lasuite-meet's
@@ -309,8 +461,19 @@ def deploy_app(
     # it ourselves is recipe-agnostic and canonical (the run domain IS the app's domain).
     abra.env_set(domain, "DOMAIN", domain)
     abra.env_set(domain, "LETS_ENCRYPT_ENV", "")
-    for k, v in meta_mod.extra_env(meta, meta_mod.hook_ctx(domain, meta)).items():
+    extra = meta_mod.extra_env(meta, meta_mod.hook_ctx(domain, meta))
+    for k, v in extra.items():
         abra.env_set(domain, k, v)
+    # Per-recipe `previous/` overlay (phase prevb): version-specific repair to deploy the *previous
+    # (last-green) version*, applied to the BASE deploy ONLY (the caller resolved apply=True only when
+    # the resolved base equals previous/VERSION). Appended on top of the recipe's COMPOSE_FILE (which
+    # may already include the environmental compose.ccci.yml). Stripped before the head redeploy
+    # (generic.perform_upgrade) so the PR head runs unmodified.
+    if apply_previous:
+        cf = compose_file_add(extra.get("COMPOSE_FILE", "compose.yml"), PREVIOUS_COMPOSE)
+        abra.env_set(domain, "COMPOSE_FILE", cf)
+        provide_previous_overlay(recipe)
+        print(f"  previous-overlay: COMPOSE_FILE for base deploy = {cf}", flush=True)
     if secrets:
         abra.secret_generate(domain)
     if install_steps_hook:
@@ -332,6 +495,24 @@ def _stack_name(domain: str) -> str:
     return domain.replace(".", "_")
 
 
+def stack_service_names(domain: str) -> list[str]:
+    """Short service names in this app's swarm stack (stack prefix stripped). Used by recipe overlay
+    assertions to prove a service was added/removed by an upgrade (e.g. discourse drops `sidekiq`)."""
+    stack = _stack_name(domain)
+    proc = subprocess.run(
+        ["docker", "stack", "services", stack, "--format", "{{.Name}}"],
+        capture_output=True,
+        text=True,
+    )
+    names = []
+    for ln in proc.stdout.split("\n"):
+        n = ln.strip()
+        if not n:
+            continue
+        names.append(n[len(stack) + 1 :] if n.startswith(stack + "_") else n)
+    return names
+
+
 def services_converged(domain: str) -> bool:
     """True when every service in the stack reports replicas N/N (N>0) AND no service is
     mid-rolling-update (swarm UpdateStatus settled)."""

runner/run_recipe_ci.py

@@ -38,6 +38,7 @@ import subprocess
 import sys
 import tempfile
 import time
+from typing import NamedTuple
 
 ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, os.path.join(ROOT, "runner"))
@@ -88,36 +89,66 @@ def sso_dep_unverified(declared, deps_ready: bool, requires_deps_skipped: int) -
     return bool(declared) and not deps_ready and requires_deps_skipped > 0
 
 
-def upgrade_base(stages, meta, recipe: str) -> str | None:
-    """Deploy-once base version decision (pure given meta + the published-version lookup):
-    previous published version when the upgrade tier will run and one exists (so upgrade goes
-    previous→target in place), else None (the caller falls back to the target / PR head).
-    (DECISIONS.)
+class BasePlan(NamedTuple):
+    """Resolved upgrade-base decision (phase prevb). `kind`:
+    - "version" → deploy a pinned published version (`version`): an explicit UPGRADE_BASE_VERSION
+      override, or last-green (warm-canonical) version. `previous/` may apply (version-guarded).
+    - "ref"     → deploy the target-branch (main) tip at commit `ref` (chaos): the true predecessor
+      the PR merges onto, used when there is no last-green. `previous/` never applies to a ref base.
+    - "skip"    → no upgrade base; the single deploy is the PR head and the upgrade tier records a
+      declared skip with `reason` (upgrade∉stages / EXPECTED_NA / new recipe / head==main tip)."""
 
-    A recipe may override the base via recipe_meta UPGRADE_BASE_VERSION when the harness default
-    (recipe_versions[-2]) is NOT the PR's true predecessor — e.g. a PR that adds a version ABOVE the
-    newest published tag, where the correct base is [-1] (the newest published), not [-2]. The
-    override must be an exact published version tag (deployed as a pinned base). (Adversary §7.1.)
+    kind: str
+    version: str | None
+    ref: str | None
+    reason: str
 
-    A recipe that declares the upgrade rung in EXPECTED_NA gets NO base: published versions may
-    exist yet be genuinely undeployable — e.g. bluesky-pds, where every published tag pins the
-    moving image tag `:0.4` that upstream republished with incompatible main builds, so no
-    published version can come up as an upgrade base (phase bsky, DECISIONS). Deploying one would
-    fail the INSTALL tier before the PR-head code is ever exercised. With no base, the single
-    deploy is the PR head itself and the upgrade tier records "skip", which derive_rungs
-    classifies as the DECLARED intentional skip (reason from EXPECTED_NA — visible in
-    results.json `skips.intentional`, never reported as a pass)."""
+    @property
+    def runs(self) -> bool:
+        return self.kind in ("version", "ref")
+
+
+def resolve_upgrade_base(stages, meta, recipe: str, head_ref: str | None = None) -> BasePlan:
+    """Dynamic upgrade-base resolution (phase prevb, replaces the static `recipe_versions[-2]`
+    default). Order: explicit override → last-green (warm canonical) → target-branch (main) tip →
+    skip. EXPECTED_NA[upgrade] / upgrade∉stages short-circuit to a declared skip first.
+
+    last-green is the PRIMARY base — the version cc-ci last recorded green for this recipe (the
+    warm-canonical registry record). main-tip is the FALLBACK: the recipe repo's `main` HEAD, the
+    real predecessor the PR merges on top of, used when there is no last-green. Else the tier is
+    skipped with a recorded reason (structural, declared — not a silent pass).
+
+    `UPGRADE_BASE_VERSION` is RETAINED as an optional explicit override (wins when set) for the rare
+    PR-adds-a-version-above-the-newest-tag case; it is no longer the default (DECISIONS prevb)."""
     if "upgrade" not in stages:
-        return None
-    if "upgrade" in (meta.EXPECTED_NA or {}):
+        return BasePlan("skip", None, None, "upgrade tier not in requested stages")
+    declared = (meta.EXPECTED_NA or {}).get("upgrade")
+    if declared:
         print(
-            "== upgrade tier: declared EXPECTED_NA['upgrade'] — no upgrade base will be "
-            f"deployed; the single deploy is the target/PR head. Reason: "
-            f"{(meta.EXPECTED_NA or {}).get('upgrade')}",
+            f"== upgrade tier: declared EXPECTED_NA['upgrade'] — single deploy is the PR head. "
+            f"Reason: {declared}",
             flush=True,
         )
-        return None
-    return meta.UPGRADE_BASE_VERSION or lifecycle.previous_version(recipe)
+        return BasePlan("skip", None, None, f"declared EXPECTED_NA[upgrade]: {declared}")
+    override = getattr(meta, "UPGRADE_BASE_VERSION", None)
+    if override:
+        return BasePlan("version", override, None, "explicit UPGRADE_BASE_VERSION override")
+    rec = canonical.read_registry(recipe)
+    if rec and rec.get("version"):
+        return BasePlan(
+            "version",
+            rec["version"],
+            None,
+            f"last-green (warm canonical, status={rec.get('status')})",
+        )
+    main_tip = lifecycle.recipe_branch_commit(recipe, "main")
+    if main_tip and main_tip != head_ref:
+        return BasePlan("ref", None, main_tip, "target-branch (main) tip")
+    if main_tip and main_tip == head_ref:
+        return BasePlan("skip", None, None, "head == main tip (no predecessor delta)")
+    return BasePlan(
+        "skip", None, None, "no last-green and no main tip (new recipe / no predecessor)"
+    )
 
 
 def _truthy(v: str | None) -> bool:
@@ -952,8 +983,25 @@ def main() -> int:
 
     domain = naming.app_domain(recipe, os.environ.get("PR", "0"), ref)
 
-    prev = upgrade_base(stages, meta, recipe)
-    base = prev or target
+    base_plan = resolve_upgrade_base(stages, meta, recipe, head_ref=head_ref)
+    prev = base_plan.runs  # gates the upgrade tier
+    # base deploy target: a pinned published version (kind=version) or main-tip commit (kind=ref);
+    # on skip fall back to the run's VERSION/head (target=None → chaos head deploy, as before).
+    base = base_plan.version or target
+    base_ref = base_plan.ref
+    prev_status = lifecycle.previous_status(recipe, base_plan.kind, base_plan.version)
+    print(
+        f"== upgrade base: kind={base_plan.kind} "
+        f"{('version=' + base) if base_plan.kind == 'version' else ''}"
+        f"{('ref=' + (base_ref or '')[:12]) if base_plan.kind == 'ref' else ''}"
+        f"{(' SKIP: ' + base_plan.reason) if base_plan.kind == 'skip' else ''} "
+        f"({base_plan.reason if base_plan.kind != 'skip' else ''})",
+        flush=True,
+    )
+    if prev_status["stale"]:
+        print(f"!! previous/ STALE — {prev_status['reason']}", flush=True)
+    elif prev_status["apply"]:
+        print(f"== previous/ applies to the base deploy (targets {base})", flush=True)
     backup_cap = generic.backup_capable(recipe, meta)
     hook = discovery.install_steps(recipe, repo_local)
 
@@ -1051,6 +1099,8 @@ def main() -> int:
                 recipe,
                 domain,
                 version=base,
+                base_ref=base_ref,
+                apply_previous=prev_status["apply"],
                 secrets=True,
                 install_steps_hook=hook,
                 deploy_timeout=int(meta.DEPLOY_TIMEOUT),
@@ -1129,7 +1179,7 @@ def main() -> int:
                         junit_dir=junit_dir,
                     )
                     if prev
-                    else "skip"  # no upgrade base: single published version, or declared EXPECTED_NA
+                    else "skip"  # base_plan.kind == "skip": no predecessor / EXPECTED_NA / head==main
                 )
             # ---- BACKUP + RESTORE tiers (backup-capable only; else clean N/A) ----
             if "backup" in stages:

tests/discourse/compose.ccci.yml

@@ -1,57 +1,29 @@
 ---
 version: "3.8"
-# cc-ci overlay (Phase 2 Q4.6) — minimal, single-purpose: make the UPGRADE-tier BASE deploy (the
-# previous published discourse version) deployable so upgrade-to-latest can run.
+# cc-ci ENVIRONMENTAL overlay (phase prevb) — applies to ALL deploys (base + PR head). Node-reality
+# tweaks ONLY; NO version-specific image pins or service add/drop. (Version-specific repairs, when a
+# previous base can't deploy as-published, live in tests/<recipe>/previous/ — base-only. discourse
+# needs none: the dynamic base = last-green / main tip = bitnamilegacy/discourse:3.5.0 deploys clean.)
 #
-# WHY THIS OVERLAY EXISTS (plan-ccci-compose-overlay-policy.md §1 "minimal justified fallback" +
-# the §1 mandate that upgrade-to-latest must ALWAYS run): the harness base-deploys the from-version
-# (UPGRADE_BASE_VERSION = 0.7.0+3.3.1), then `deploy --chaos` to the recipe-PR head. Two blockers on
-# that published base, both resolved here, NEITHER weakening any test:
-#   1. RE-PIN: every published discourse tag pins `bitnami/discourse:3.3.1` (and 0.6.3 → 3.1.2),
-#      but Docker Hub REMOVED the bitnami/discourse namespace (404). The recipe-PR (recipe-maintainers/
-#      discourse#1) re-pins app+sidekiq to `bitnamilegacy/discourse:3.3.1` (the legit upstream
-#      relocation of the identical image). This overlay applies the SAME namespace-only re-pin to the
-#      BASE 0.7.0 (identical version 3.3.1, identical image content) so the from-version pulls — exactly
-#      the policy-blessed "minimal bitnami→bitnamilegacy re-pin overlay on the 0.7.0 from-version".
-#   2. GRACE: discourse's Rails cold first boot (DB migrate + asset precompile) is 15-25min on cc-ci,
-#      exceeding the published 5m start_period → swarm kills the still-booting app. start_period CANNOT
-#      be an env var (abra validates the literal 'duration' BEFORE substitution → FATA; Adversary-
-#      reproduced, REVIEW-2 4b862f6), so we widen it to a literal 20m on the BASE. The PR head already
-#      ships 20m, so this overlay is idempotent on the head (it persists untracked across the checkout).
-# Both changes are namespace/grace-only: identical image content, a healthy check still marks healthy
-# immediately → NO assertion is weakened and no defect is masked.
+# Fusing version-specific config into this all-deploys overlay was the prevb bug: the old overlay
+# re-pinned app+sidekiq to bitnamilegacy/discourse:3.3.1 and re-added the sidekiq service on EVERY
+# deploy, so the PR head (official discourse/discourse:3.5.3, sidekiq dropped) was silently reverted
+# to the old image and its migration never tested. Removed entirely; only the environmental tweak below
+# remains.
 #
-# NOTE (prepull): the published recipe ships `sidekiq.depends_on: [discourse]` but the main service is
-# named `app` (`discourse` is undefined), so `abra app config --images` returns invalid-compose (rc=15)
-# and the harness prepull is SKIPPED. This overlay does NOT try to override depends_on — compose
-# normalizes short-form depends_on to a map and map-merge is additive, so an override can't REMOVE the
-# bad `discourse` key. Instead the 2.4GB `bitnamilegacy/discourse:3.3.1` image is kept warm in the node
-# image cache, so the inline pull during deploy is a no-op and convergence isn't pull-bound. (swarm
-# ignores depends_on, so the dangling ref has zero runtime effect — a recipe lint nit, not a defect.)
-#
-#   3. UPGRADE ROLLOUT (dstamp 2026-06-11, direct-evidence attribution in JOURNAL-dstamp): the
-#      published app service sets `deploy.update_config: { failure_action: rollback, order:
-#      start-first }`. On the upgrade chaos redeploy (base 0.7.0 → PR head), start-first runs the OLD
-#      and NEW precompile/Rails-heavy discourse tasks CO-RESIDENT (~2x memory); under host memory
-#      pressure the NEW task intermittently OOMs/fails swarm's update monitor → `failure_action:
-#      rollback` reverts the app service to its PREVIOUS spec, INCLUDING the
-#      `coop-cloud.<stack>.chaos-version` label (head → base). Because start-first keeps the OLD task
-#      serving, wait_healthy still passes, and HC1 then reads the reverted BASE commit (eb96de9+U) and
-#      misreports it as 'the re-checkout failed' — the dstamp drift, reproduced solo (runs
-#      dstamp-repro1/4) with `.Spec.chaos-version=7ae7b0f7+U` (head applied) flipping to
-#      `.PreviousSpec=eb96de94+U` after the rollback. FIX: `order: stop-first` so the NEW task boots
-#      with the full host memory (no 2x co-residency) and genuinely becomes healthy → no spurious
-#      rollback. This is a CI deploy-rollout tweak only: the upgrade still really deploys + asserts the
-#      PR-head code under test, and `failure_action: rollback` is LEFT intact, so a genuinely broken
-#      head still rolls back and is caught (lifecycle.assert_upgrade_converged) — NO test is weakened.
-#      Trade-off: brief real downtime during the CI upgrade (covered by DEPLOY_TIMEOUT 3600).
+# WHY (environmental — depends on the cc-ci node, must apply to the head too): the upgrade chaos
+# redeploy (base bitnamilegacy:3.5.0 → PR-head official 3.5.3) runs the OLD and NEW Rails-heavy
+# (DB-migrate + asset-precompile) tasks. The published recipe sets
+# app.deploy.update_config.order: start-first, which keeps both co-resident (~2x memory); under the
+# single CI node's memory pressure the NEW task intermittently OOMs swarm's update monitor →
+# failure_action: rollback reverts the app spec (incl. the coop-cloud.<stack>.chaos-version label)
+# while the old task keeps serving, and the upgrade is misreported (dstamp finding, JOURNAL-dstamp).
+# FIX: order: stop-first so the NEW task boots with the full host memory (no 2x co-residency) and
+# genuinely becomes healthy. failure_action: rollback is LEFT intact → a genuinely broken head still
+# rolls back and is caught (lifecycle.assert_upgrade_converged) — NO test/assertion is weakened.
+# Trade-off: brief real downtime during the CI upgrade (covered by DEPLOY_TIMEOUT 3600).
 services:
   app:
-    image: bitnamilegacy/discourse:3.3.1
-    healthcheck:
-      start_period: 20m
     deploy:
       update_config:
         order: stop-first
-  sidekiq:
-    image: bitnamilegacy/discourse:3.3.1

tests/discourse/recipe_meta.py

@@ -21,20 +21,18 @@ HTTP_TIMEOUT = 1200
 # still marks healthy immediately → fast hosts unaffected). Precedent: lasuite-drive collabora PR.
 # TIMEOUT (abra's internal convergence wait) is raised to outlast the boot.
 #
-# UPGRADE-tier BASE (compose.ccci.yml + UPGRADE_BASE_VERSION): upgrade-to-latest must ALWAYS run
-# (plan-ccci-compose-overlay-policy.md §1). The from-version is the latest published 0.7.0+3.3.1
-# (UPGRADE_BASE_VERSION below; the PR head is 0.7.0-based, so 0.7.0 is the true predecessor — not the
-# default [-2]=0.6.3). The published 0.7.0 has TWO blockers, both resolved by the policy-blessed
-# minimal base overlay compose.ccci.yml (see its header), neither weakening a test:
-#   (1) it pins the Docker-Hub-removed `bitnami/discourse:3.3.1` (404) → overlay re-pins app+sidekiq to
-#       `bitnamilegacy/discourse:3.3.1` (namespace-only, identical image), the same re-pin the PR makes;
-#   (2) its 5m start_period is too tight for the 15-25min Rails boot → overlay widens it to 20m (grace).
-# The harness auto-provides the overlay to the checkout and auto-chaoses the base deploy
-# (first-class compose.ccci.yml, rcust P2a); it persists across the head checkout (idempotent — the
-# PR head already re-pins + ships 20m).
-# Upgrade crossover: 0.7.0 (re-pinned base) → PR head; full assertions run on the HEAD. The 0.7.0
-# *custom* tests are not separately run (custom tier runs once, on the head — policy §1 allows skip+record).
-UPGRADE_BASE_VERSION = "0.7.0+3.3.1"
+# UPGRADE-tier BASE (phase prevb — DYNAMIC, no hardcoded UPGRADE_BASE_VERSION): the base the head
+# upgrades from is resolved at run time — last-green (warm canonical) → fallback target-branch (`main`)
+# tip → else skip (run_recipe_ci.resolve_upgrade_base). discourse has no warm canonical, so the base is
+# the `main` tip = bitnamilegacy/discourse:3.5.0, which deploys clean (bitnamilegacy exists) with NO
+# `previous/` repair needed. The PR head (recipe-maintainers/discourse#4) switches app to the official
+# `discourse/discourse:3.5.3` and drops the sidekiq service, so the upgrade tier now exercises the REAL
+# bitnamilegacy→official image migration the PR claims to support.
+#
+# compose.ccci.yml is now the ENVIRONMENTAL overlay (all deploys): only app.deploy.update_config.order:
+# stop-first (node memory reality on the upgrade crossover — see its header). The version-specific
+# bitnamilegacy re-pin + sidekiq block were REMOVED (they leaked onto the head and masked the migration
+# — the prevb bug). No assertion weakened: the head runs unmodified and full assertions run on it.
 EXTRA_ENV = {
     "TIMEOUT": "3600",  # abra's internal convergence wait; matches DEPLOY_TIMEOUT (slow Rails boot headroom)
     "COMPOSE_FILE": "compose.yml:compose.ccci.yml",

tests/discourse/test_upgrade.py

@@ -0,0 +1,40 @@
+"""discourse — UPGRADE overlay (phase prevb): FAITHFULNESS assertion that the PR head genuinely ran.
+
+The whole point of phase prevb: the old all-deploys overlay re-pinned the head back to
+bitnamilegacy/discourse:3.3.1 and re-added the sidekiq service, so the head's official-image
+migration was never tested. With the version-specific config removed from the all-deploys overlay
+and the dynamic base (last-green/main = bitnamilegacy:3.5.0) deployed only as the *base*, the upgrade
+chaos redeploy must land the PR head UNMODIFIED. This overlay asserts exactly that, post-upgrade:
+
+  1. the running `app` service image IS the official discourse/discourse:3.5.3 — NOT bitnamilegacy;
+  2. the `sidekiq` service the PR deletes is GONE from the deployed stack.
+
+If either fails, the head did not really run (the overlay leaked onto it) → RED. Assertion-only,
+additive to the generic upgrade tier (which already proves reconverge/serving/moved + HC1 commit stamp).
+"""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def test_head_runs_official_image_not_bitnamilegacy(live_app):
+    image = lifecycle.deployed_identity(live_app, service="app").get("image") or ""
+    assert "bitnamilegacy" not in image, (
+        f"app image is {image!r} — the bitnamilegacy base leaked onto the PR head "
+        "(the version-specific overlay was applied to the head, the prevb bug)"
+    )
+    assert image.startswith("discourse/discourse:3.5.3"), (
+        f"app image is {image!r}, expected the PR head's official discourse/discourse:3.5.3 "
+        "— the head's image migration was not exercised"
+    )
+
+
+def test_sidekiq_service_dropped_by_head(live_app):
+    services = lifecycle.stack_service_names(live_app)
+    assert "sidekiq" not in services, (
+        f"sidekiq service still present after the upgrade to the PR head: {services} — the head "
+        "(which deletes sidekiq) did not really deploy"
+    )

tests/unit/test_previous.py

@@ -0,0 +1,118 @@
+"""Unit tests for the phase-prevb `previous/` overlay surface + COMPOSE_FILE layering (lifecycle).
+
+Covers: the version-guarded apply/skip/stale decision (`previous_status`), the VERSION-marker reader
+(`previous_target_version`), folder discovery (`has_previous`), and the pure COMPOSE_FILE add/remove
+helpers used to layer compose.previous.yml onto the base deploy and strip it before the head redeploy.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+from harness import meta as meta_mod  # noqa: E402
+
+# ---- pure COMPOSE_FILE helpers --------------------------------------------------------------------
+
+
+def test_compose_file_add_appends_when_absent():
+    assert (
+        lifecycle.compose_file_add("compose.yml:compose.ccci.yml", "compose.previous.yml")
+        == "compose.yml:compose.ccci.yml:compose.previous.yml"
+    )
+
+
+def test_compose_file_add_idempotent():
+    cf = "compose.yml:compose.previous.yml"
+    assert lifecycle.compose_file_add(cf, "compose.previous.yml") == cf
+
+
+def test_compose_file_add_defaults_missing_base():
+    assert (
+        lifecycle.compose_file_add("", "compose.previous.yml") == "compose.yml:compose.previous.yml"
+    )
+
+
+def test_compose_file_remove_strips_only_overlay():
+    assert (
+        lifecycle.compose_file_remove(
+            "compose.yml:compose.ccci.yml:compose.previous.yml", "compose.previous.yml"
+        )
+        == "compose.yml:compose.ccci.yml"
+    )
+
+
+def test_compose_file_remove_keeps_compose_yml_when_emptied():
+    assert (
+        lifecycle.compose_file_remove("compose.previous.yml", "compose.previous.yml")
+        == "compose.yml"
+    )
+
+
+# ---- marker reader + discovery (filesystem, via a temp TESTS_DIR) ---------------------------------
+
+
+def _stage(monkeypatch, tmp_path, recipe, *, compose=True, marker=None):
+    monkeypatch.setattr(meta_mod, "TESTS_DIR", str(tmp_path))
+    prev = tmp_path / recipe / "previous"
+    prev.mkdir(parents=True)
+    if compose:
+        (prev / "compose.previous.yml").write_text("services: {}\n")
+    if marker is not None:
+        (prev / "VERSION").write_text(marker)
+    return prev
+
+
+def test_has_previous_true_only_with_compose(monkeypatch, tmp_path):
+    _stage(monkeypatch, tmp_path, "rx", compose=True)
+    assert lifecycle.has_previous("rx") is True
+    assert lifecycle.has_previous("other") is False
+
+
+def test_previous_target_version_reads_first_real_line(monkeypatch, tmp_path):
+    _stage(monkeypatch, tmp_path, "rx", marker="# the previous published version\n\n0.7.0+3.3.1\n")
+    assert lifecycle.previous_target_version("rx") == "0.7.0+3.3.1"
+
+
+def test_previous_target_version_none_without_marker(monkeypatch, tmp_path):
+    _stage(monkeypatch, tmp_path, "rx", marker=None)
+    assert lifecycle.previous_target_version("rx") is None
+
+
+# ---- the apply/skip/stale decision matrix ---------------------------------------------------------
+
+
+def test_previous_status_no_folder(monkeypatch):
+    monkeypatch.setattr(lifecycle, "has_previous", lambda r: False)
+    st = lifecycle.previous_status("rx", "version", "0.7.0+3.3.1")
+    assert st == {"apply": False, "stale": False, "reason": ""}
+
+
+def test_previous_status_applies_on_version_match(monkeypatch):
+    monkeypatch.setattr(lifecycle, "has_previous", lambda r: True)
+    monkeypatch.setattr(lifecycle, "previous_target_version", lambda r: "0.7.0+3.3.1")
+    st = lifecycle.previous_status("rx", "version", "0.7.0+3.3.1")
+    assert st["apply"] is True and st["stale"] is False
+
+
+def test_previous_status_stale_on_version_mismatch(monkeypatch):
+    monkeypatch.setattr(lifecycle, "has_previous", lambda r: True)
+    monkeypatch.setattr(lifecycle, "previous_target_version", lambda r: "0.6.0+3.1.1")
+    st = lifecycle.previous_status("rx", "version", "0.7.0+3.3.1")
+    assert st["apply"] is False and st["stale"] is True and "stale" in st["reason"]
+
+
+def test_previous_status_stale_on_main_tip_base(monkeypatch):
+    # previous/ can only repair a pinned published base; a main-tip (ref) base flags it for review.
+    monkeypatch.setattr(lifecycle, "has_previous", lambda r: True)
+    st = lifecycle.previous_status("rx", "ref", None)
+    assert st["apply"] is False and st["stale"] is True
+
+
+def test_previous_status_stale_without_marker(monkeypatch):
+    monkeypatch.setattr(lifecycle, "has_previous", lambda r: True)
+    monkeypatch.setattr(lifecycle, "previous_target_version", lambda r: None)
+    st = lifecycle.previous_status("rx", "version", "0.7.0+3.3.1")
+    assert st["apply"] is False and st["stale"] is True and "marker" in st["reason"]

tests/unit/test_upgrade_base.py

@@ -1,12 +1,9 @@
-"""Unit tests for `run_recipe_ci.upgrade_base` — the deploy-once base-version decision.
+"""Unit tests for `run_recipe_ci.resolve_upgrade_base` — the DYNAMIC upgrade-base decision (phase prevb).
 
-Phase bsky: a recipe whose published versions ALL pin a moving image tag that upstream
-republished with incompatible builds (bluesky-pds) has no deployable upgrade base — deploying
-one fails the INSTALL tier before the PR head is ever exercised. The sanctioned escape hatch is
-the EXISTING declared-intentional-skip mechanism: EXPECTED_NA["upgrade"] now also suppresses
-the base deploy (single deploy = PR head; the tier records "skip"; derive_rungs classifies it
-intentional with the declared reason). These tests lock the decision matrix; derive_rungs'
-classification of the resulting skip is already covered in test_results.py.
+Resolution order: upgrade∉stages / EXPECTED_NA[upgrade] (declared skip) → explicit UPGRADE_BASE_VERSION
+override → last-green (warm canonical) → target-branch (`main`) tip → skip (no predecessor). The result
+is a `BasePlan(kind, version, ref, reason)`: kind ∈ {"version", "ref", "skip"}; `.runs` is True for
+version/ref (the upgrade tier runs). Replaces the old static `recipe_versions[-2]` default.
 """
 
 from __future__ import annotations
@@ -17,63 +14,92 @@ from types import SimpleNamespace
 
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
 import run_recipe_ci  # noqa: E402
-from harness import lifecycle  # noqa: E402
+from harness import canonical, lifecycle  # noqa: E402
 
 ALL = {"install", "upgrade", "backup", "restore", "custom"}
+HEAD = "aaaa1111head"
+MAIN = "bbbb2222main"
 
 
 def _meta(expected_na=None, upgrade_base_version=None):
     return SimpleNamespace(EXPECTED_NA=expected_na, UPGRADE_BASE_VERSION=upgrade_base_version)
 
 
-def test_default_prev_published(monkeypatch):
-    # upgrade in stages, ≥2 published versions, nothing declared → recipe_versions[-2]
-    monkeypatch.setattr(lifecycle, "previous_version", lambda r: "0.1.0+v1")
-    assert run_recipe_ci.upgrade_base(ALL, _meta(), "somerecipe") == "0.1.0+v1"
+def _no_canonical(monkeypatch):
+    monkeypatch.setattr(canonical, "read_registry", lambda r: None)
 
 
-def test_single_published_version_no_base(monkeypatch):
-    monkeypatch.setattr(lifecycle, "previous_version", lambda r: None)
-    assert run_recipe_ci.upgrade_base(ALL, _meta(), "somerecipe") is None
+def _no_main(monkeypatch):
+    monkeypatch.setattr(lifecycle, "recipe_branch_commit", lambda r, b="main": None)
 
 
-def test_upgrade_not_in_stages_no_base(monkeypatch):
+def test_upgrade_not_in_stages_skip(monkeypatch):
+    # never consults canonical/main when upgrade isn't requested
     monkeypatch.setattr(
-        lifecycle,
-        "previous_version",
-        lambda r: (_ for _ in ()).throw(AssertionError("not consulted")),
+        canonical, "read_registry", lambda r: (_ for _ in ()).throw(AssertionError("not consulted"))
     )
-    assert run_recipe_ci.upgrade_base(ALL - {"upgrade"}, _meta(), "somerecipe") is None
+    plan = run_recipe_ci.resolve_upgrade_base(ALL - {"upgrade"}, _meta(), "somerecipe")
+    assert plan.kind == "skip" and not plan.runs
 
 
-def test_upgrade_base_version_override_wins(monkeypatch):
+def test_expected_na_upgrade_skip_even_with_canonical_and_override(monkeypatch):
+    # EXPECTED_NA[upgrade] is the strongest, declared fact — short-circuits before override/canonical.
     monkeypatch.setattr(
-        lifecycle,
-        "previous_version",
-        lambda r: (_ for _ in ()).throw(AssertionError("not consulted")),
+        canonical, "read_registry", lambda r: {"version": "9.9.9", "status": "warm"}
     )
-    meta = _meta(upgrade_base_version="0.7.0+3.3.1")
-    assert run_recipe_ci.upgrade_base(ALL, meta, "discourse") == "0.7.0+3.3.1"
-
-
-def test_expected_na_upgrade_suppresses_base(monkeypatch):
-    # bluesky-pds shape: published versions exist but are undeployable — declared EXPECTED_NA
-    # upgrade → NO base (single deploy is the PR head), even though previous_version would
-    # return one and even if UPGRADE_BASE_VERSION is set (the declaration is the stronger,
-    # documented fact).
-    monkeypatch.setattr(lifecycle, "previous_version", lambda r: "0.1.1+v0.4")
     declared = {"upgrade": "no deployable upgrade base (moving tag republished)"}
-    assert run_recipe_ci.upgrade_base(ALL, _meta(expected_na=declared), "bluesky-pds") is None
-    assert (
-        run_recipe_ci.upgrade_base(
-            ALL, _meta(expected_na=declared, upgrade_base_version="0.2.0+v0.4"), "bluesky-pds"
-        )
-        is None
+    plan = run_recipe_ci.resolve_upgrade_base(
+        ALL, _meta(expected_na=declared, upgrade_base_version="0.2.0+v0.4"), "bluesky-pds"
     )
+    assert plan.kind == "skip" and "EXPECTED_NA" in plan.reason
 
 
-def test_expected_na_other_rung_does_not_suppress(monkeypatch):
-    # an EXPECTED_NA for backup_restore (custom-html-tiny shape) must NOT touch the upgrade base
-    monkeypatch.setattr(lifecycle, "previous_version", lambda r: "0.1.0+v1")
-    meta = _meta(expected_na={"backup_restore": "stateless"})
-    assert run_recipe_ci.upgrade_base(ALL, meta, "custom-html-tiny") == "0.1.0+v1"
+def test_explicit_override_wins_over_canonical(monkeypatch):
+    monkeypatch.setattr(
+        canonical, "read_registry", lambda r: {"version": "9.9.9", "status": "warm"}
+    )
+    monkeypatch.setattr(
+        lifecycle,
+        "recipe_branch_commit",
+        lambda r, b="main": (_ for _ in ()).throw(AssertionError("not consulted")),
+    )
+    plan = run_recipe_ci.resolve_upgrade_base(
+        ALL, _meta(upgrade_base_version="0.7.0+3.3.1"), "discourse"
+    )
+    assert plan.kind == "version" and plan.version == "0.7.0+3.3.1" and plan.runs
+
+
+def test_last_green_warm_canonical_is_primary(monkeypatch):
+    # no override → last-green (warm canonical version) is the PRIMARY base; main is not consulted.
+    monkeypatch.setattr(
+        canonical, "read_registry", lambda r: {"version": "0.6.0+3.1.1", "status": "idle"}
+    )
+    monkeypatch.setattr(
+        lifecycle,
+        "recipe_branch_commit",
+        lambda r, b="main": (_ for _ in ()).throw(AssertionError("not consulted")),
+    )
+    plan = run_recipe_ci.resolve_upgrade_base(ALL, _meta(), "keycloak", head_ref=HEAD)
+    assert plan.kind == "version" and plan.version == "0.6.0+3.1.1" and "last-green" in plan.reason
+
+
+def test_main_tip_fallback_when_no_last_green(monkeypatch):
+    _no_canonical(monkeypatch)
+    monkeypatch.setattr(lifecycle, "recipe_branch_commit", lambda r, b="main": MAIN)
+    plan = run_recipe_ci.resolve_upgrade_base(ALL, _meta(), "discourse", head_ref=HEAD)
+    assert plan.kind == "ref" and plan.ref == MAIN and plan.version is None and plan.runs
+
+
+def test_head_equals_main_tip_skip(monkeypatch):
+    # the PR head IS the main tip (empty PR / LATEST run) → no real predecessor → declared skip.
+    _no_canonical(monkeypatch)
+    monkeypatch.setattr(lifecycle, "recipe_branch_commit", lambda r, b="main": HEAD)
+    plan = run_recipe_ci.resolve_upgrade_base(ALL, _meta(), "discourse", head_ref=HEAD)
+    assert plan.kind == "skip" and "main tip" in plan.reason and not plan.runs
+
+
+def test_no_canonical_no_main_skip(monkeypatch):
+    _no_canonical(monkeypatch)
+    _no_main(monkeypatch)
+    plan = run_recipe_ci.resolve_upgrade_base(ALL, _meta(), "brandnew", head_ref=HEAD)
+    assert plan.kind == "skip" and "no predecessor" in plan.reason