backend/app/services/membership_reconcile.py

@@ -49,7 +49,7 @@ from .membership_roster import (
     get_sync_state,
     has_paid_access,
     identity_keys_for_source,
-    match_kind,
+    pair_sources_with_memberships,
     roster_is_fresh,
     url_tail,
 )
@@ -113,20 +113,12 @@ async def reconcile(
         .where(Source.platform == platform)
     )).all()
 
-    # Nested loop rather than a SQL join: the match is a predicate over a JSON
+    # The join itself lives in `membership_roster` beside `match_kind`, so C5's
-    # blob and a derived URL handle, neither of which is indexable, and both
+    # gated-reason annotation pairs sources with memberships by exactly the same
-    # sides are tens of rows on any real library. Keeping it in Python means ONE
+    # rule this card sorts them by. Two copies would let the Subscriptions row
-    # definition of identity (`match_kind`) instead of a second one in SQL that
+    # and this card disagree about which creator a source IS.
-    # could drift from it.
+    pairs = pair_sources_with_memberships([s for s, _a in rows], memberships)
-    pairs: dict[int, tuple[PlatformMembership, str]] = {}
+    matched_membership_ids = {m.id for m, _kind in pairs.values()}
-    matched_membership_ids: set[int] = set()
-    for source, _artist in rows:
-        for m in memberships:
-            kind = match_kind(source, m)
-            if kind:
-                pairs[source.id] = (m, kind)
-                matched_membership_ids.add(m.id)
-                break
 
     subscribed_not_tracked = []
     for m in memberships:

backend/app/services/membership_roster.py

@@ -352,6 +352,127 @@ def match_kind(source: Source, membership: PlatformMembership) -> str | None:
     return None
 
 
+def pair_sources_with_memberships(
+    sources: list[Source], memberships: list[PlatformMembership],
+) -> dict[int, tuple[PlatformMembership, str]]:
+    """Source id -> the membership it is the same creator as, and how we know.
+
+    Extracted from C4's reconcile loop when C5 became its second caller. It is
+    a nested loop rather than a SQL join because the match is a predicate over
+    a JSON blob and a derived URL handle, neither of which is indexable, and
+    both sides are tens of rows on any real library. Keeping it in Python means
+    ONE definition of identity (`match_kind`) instead of a second one in SQL
+    that could drift from it.
+
+    First match wins, which is `match_kind`'s ordering doing its job: a source
+    with a cached campaign id can only pair with the membership holding that
+    id, so an ambiguous handle never outvotes it.
+    """
+    pairs: dict[int, tuple[PlatformMembership, str]] = {}
+    for source in sources:
+        for m in memberships:
+            kind = match_kind(source, m)
+            if kind:
+                pairs[source.id] = (m, kind)
+                break
+    return pairs
+
+
+# ---------------------------------------------------------------------------
+# Why the posts are invisible (#387 C5)
+# ---------------------------------------------------------------------------
+#
+# A3 made a tier-gated source say "47 posts you can't see". These are the words
+# the roster is allowed to add to that count — and ONLY to that count.
+#
+# THE LINE: the roster ANNOTATES the gated flag, it never produces it.
+# `current_user_can_view` (read per post by `patreon_client.post_is_gated`) is
+# the authoritative per-post signal, and entitled-tier data cannot stand in for
+# it — a creator can gate a post behind an access rule that maps onto no tier
+# name at all. So nothing here may suppress a download, skip a walk, or decide
+# a post is inaccessible. It explains a skip that ALREADY happened. Getting
+# that backwards would make FC silently stop fetching content the operator is
+# paying for, which is the worst failure available in this milestone.
+# `test_no_fetch_path_can_read_the_roster` pins that structurally.
+GATED_LAPSED = "lapsed"  # the membership ended — resubscribe, or disable
+GATED_TIER = "tier"      # paying, but this tier doesn't reach these posts
+GATED_FREE = "free"      # a current FREE follow — nobody is paying for access
+
+
+def gated_reason(
+    platform: str, status: str | None, *, is_free_member: bool = False,
+) -> str | None:
+    """Why a tier-gated source's posts are out of reach, if the roster knows.
+
+    None means "no words beyond the count" and is the answer for every case
+    where the roster is not evidence: a status this code has not been taught,
+    and (at the call site) a campaign absent from the roster or a roster too
+    stale to trust. Absence is not evidence — the same discipline as
+    `test_post_is_gated_only_on_explicit_false`.
+
+    `is_free_member` is read AFTER the status axis, not folded into it, which
+    is why `has_paid_access` is called here with it forced off. The two axes
+    are independent in Patreon's payload, and collapsing them loses a real
+    distinction: a current free follower has not lost anything, so telling them
+    "you're not a patron any more" would be a false sentence about a state they
+    were never in.
+    """
+    by_status = has_paid_access(platform, status, is_free_member=False)
+    if by_status is None:
+        return None
+    if not by_status:
+        return GATED_LAPSED
+    return GATED_FREE if is_free_member else GATED_TIER
+
+
+async def gated_reasons_for_sources(
+    session: AsyncSession, sources: list[Source], *, now: datetime | None = None,
+) -> dict[int, str]:
+    """The reason word for each of these sources, where the roster has one.
+
+    Callers pass ONLY the sources already known to be tier-gated: the question
+    "why can't I see these posts" is meaningless for a source whose posts are
+    all visible, and asking it anyway would put roster data on rows that have
+    no gated state for it to annotate.
+
+    Sources with no entry in the result get A3's bare count, which is the
+    correct degraded rendering for all three of: platform never swept, roster
+    stale, campaign not in the roster.
+    """
+    if not sources:
+        return {}
+
+    platforms = {s.platform for s in sources}
+    # Per platform, because freshness is per platform: a working Patreon sweep
+    # must not lend its credibility to a SubscribeStar roster that has never
+    # run. Same gate as C4's `tracked_not_subscribed`, for the same reason.
+    fresh = {
+        p for p in platforms
+        if roster_is_fresh(await get_sync_state(session, p), now=now)
+    }
+    if not fresh:
+        return {}
+
+    memberships = (await session.execute(
+        select(PlatformMembership).where(
+            PlatformMembership.platform.in_(sorted(fresh))
+        )
+    )).scalars().all()
+    pairs = pair_sources_with_memberships(
+        [s for s in sources if s.platform in fresh], memberships,
+    )
+
+    reasons: dict[int, str] = {}
+    for source_id, (m, _kind) in pairs.items():
+        reason = gated_reason(
+            m.platform, m.status,
+            is_free_member=bool((m.details or {}).get("is_free_member")),
+        )
+        if reason is not None:
+            reasons[source_id] = reason
+    return reasons
+
+
 async def source_for_membership(
     session: AsyncSession, membership: PlatformMembership,
 ) -> Source | None:

backend/app/services/source_service.py

@@ -19,6 +19,7 @@ from ..models import (
 )
 from .db_helpers import failing_sources_clause
 from .gallery_dl import ErrorType
+from .membership_roster import gated_reasons_for_sources
 from .platforms import known_platform_keys
 from .scheduler_service import compute_next_check_at
 
@@ -92,6 +93,12 @@ class SourceRecord:
     # source, so it is joined in by `list()` only — None everywhere else, which
     # the UI renders as the bare no-access state with no fabricated number.
     tier_gated_count: int | None = None
+    # Milestone #387 C5: WHY those posts are out of reach, when the learned
+    # roster can say — "lapsed" / "tier" / "free", or None for "no words beyond
+    # the count". Joined in by `list()` beside the count, and for the same
+    # reason: it annotates a gated state rather than producing one. Nothing on
+    # a fetch path may read it (see `membership_roster.gated_reason`).
+    gated_reason: str | None = None
 
     def to_dict(self) -> dict:
         return {
@@ -116,6 +123,7 @@ class SourceRecord:
             "backfill_recapture": self.backfill_recapture,
             "backfill_posts": self.backfill_posts,
             "tier_gated_count": self.tier_gated_count,
+            "gated_reason": self.gated_reason,
         }
 
 
@@ -243,6 +251,7 @@ class SourceService:
     def _build_record(
         self, source: Source, artist: Artist, settings: ImportSettings,
         gated_counts: dict[int, int] | None = None,
+        gated_reasons: dict[int, str] | None = None,
     ) -> SourceRecord:
         nxt = compute_next_check_at(source, artist, settings)
         co = source.config_overrides or {}
@@ -268,6 +277,7 @@ class SourceService:
             backfill_recapture=bool(co.get("_backfill_recapture")),
             backfill_posts=int(co.get("_backfill_posts", 0)),
             tier_gated_count=(gated_counts or {}).get(source.id),
+            gated_reason=(gated_reasons or {}).get(source.id),
         )
 
     async def _row_to_record(self, source: Source) -> SourceRecord:
@@ -302,12 +312,15 @@ class SourceService:
             stmt = stmt.order_by(Artist.name.asc(), Source.id.asc())
         rows = (await self.session.execute(stmt)).all()
         settings = await self._load_settings()
-        # Only tier-gated rows need the join — on a healthy library that is an
+        # Only tier-gated rows need either join — on a healthy library that is
-        # empty list and _tier_gated_counts short-circuits without a query.
+        # an empty list and both helpers short-circuit without a query.
-        gated_counts = await self._tier_gated_counts(
+        gated = [s for s, _a in rows if s.error_type == ErrorType.TIER_LIMITED]
-            [s.id for s, _a in rows if s.error_type == ErrorType.TIER_LIMITED]
+        gated_counts = await self._tier_gated_counts([s.id for s in gated])
-        )
+        gated_reasons = await gated_reasons_for_sources(self.session, gated)
-        return [self._build_record(s, a, settings, gated_counts) for s, a in rows]
+        return [
+            self._build_record(s, a, settings, gated_counts, gated_reasons)
+            for s, a in rows
+        ]
 
     async def get(self, source_id: int) -> SourceRecord | None:
         source = (await self.session.execute(

frontend/src/components/subscriptions/SourceHealthDot.vue

@@ -11,6 +11,9 @@
       <div>Last checked: {{ lastCheckedText }}</div>
       <div v-if="nextCheckText">Next check: {{ nextCheckText }}</div>
       <div v-if="noAccess" class="fc-health-tip__gated">{{ noAccessText }}</div>
+      <div v-if="noAccess && noAccessReason" class="fc-health-tip__why">
+        {{ noAccessReason }}
+      </div>
       <div v-if="(source.consecutive_failures || 0) > 0">
         Failures: {{ source.consecutive_failures }}
       </div>
@@ -53,6 +56,19 @@ const noAccessText = computed(() => {
     : "Some posts are behind a tier you don't hold"
 })
 
+// #387 C5: the learned roster's explanation for the line above, when it has
+// one. The backend sends null for every case where the roster is not evidence —
+// campaign absent, roster stale, never swept, status not yet characterised — so
+// there is deliberately NO fallback sentence here. A default would turn "we
+// don't know why" into a reason, which is the one thing this step must not do.
+const GATED_REASONS = {
+  lapsed: "You're not a patron any more — resubscribe, or disable this source.",
+  tier: "Your tier doesn't cover these posts — upgrade, or leave them be.",
+  free: "You follow this creator for free — these posts are for paying patrons.",
+}
+
+const noAccessReason = computed(() => GATED_REASONS[props.source.gated_reason] || null)
+
 const ariaLabel = computed(() => `source health: ${level.value}`)
 
 const lastCheckedText = computed(() => formatRelative(props.source.last_checked_at))
@@ -92,6 +108,12 @@ const truncatedError = computed(() => {
 .fc-health-tip__gated {
   color: rgb(var(--v-theme-info, 33 150 243));
 }
+/* The reason is subordinate to the count it explains: same block, quieter, so
+   a tooltip that has one does not read as two separate findings. */
+.fc-health-tip__why {
+  color: rgb(var(--v-theme-on-surface-variant));
+  max-width: 24rem;
+}
 .fc-health-tip__err {
   margin-top: 0.25rem;
   color: rgb(var(--v-theme-error, 244 67 54));

frontend/test/components/sourceHealthDot.spec.js

@@ -56,6 +56,69 @@ describe('SourceHealthDot', () => {
     expect(w.text()).toContain("tier you don't hold")
   })
 
+  // Milestone #387 C5. The count says WHAT; these say WHY — a much stronger
+  // claim, so the cases that must stay silent are pinned alongside the ones
+  // that speak.
+
+  function gated (extra) {
+    return mountComponent(SourceHealthDot, {
+      stubs: { VTooltip: VTooltipStub },
+      props: {
+        source: {
+          ...checked, consecutive_failures: 0,
+          error_type: 'tier_limited', tier_gated_count: 47, ...extra,
+        },
+      },
+    })
+  }
+
+  it('a lapsed membership says the subscription ended', () => {
+    expect(gated({ gated_reason: 'lapsed' }).text()).toContain('not a patron any more')
+  })
+
+  it('an active membership says the tier is the limit, not the subscription', () => {
+    const text = gated({ gated_reason: 'tier' }).text()
+    expect(text).toContain("tier doesn't cover these posts")
+    expect(text).not.toContain('not a patron any more')
+  })
+
+  it('a free follow is not described as a lapsed subscription', () => {
+    const text = gated({ gated_reason: 'free' }).text()
+    expect(text).toContain('follow this creator for free')
+    expect(text).not.toContain('not a patron any more')
+  })
+
+  it('no reason means the count stands alone, with no invented explanation', () => {
+    // null covers all four not-evidence cases the backend collapses into it:
+    // campaign absent, roster stale, never swept, status uncharacterised.
+    const text = gated({ gated_reason: null }).text()
+    expect(text).toContain('47 posts')
+    expect(text).not.toContain('patron')
+    expect(text).not.toContain('tier doesn')
+  })
+
+  it('a reason the frontend has not been taught renders nothing', () => {
+    // The backend's status vocabulary grows per platform (D1). An unknown word
+    // must degrade to the bare count, never to `undefined` in the tooltip.
+    const text = gated({ gated_reason: 'some_future_word' }).text()
+    expect(text).toContain('47 posts')
+    expect(text).not.toContain('undefined')
+  })
+
+  it('a reason never appears on a source that is not gated', () => {
+    const w = mountComponent(SourceHealthDot, {
+      stubs: { VTooltip: VTooltipStub },
+      props: {
+        source: {
+          ...checked, consecutive_failures: 0,
+          error_type: null, gated_reason: 'lapsed',
+        },
+      },
+    })
+    // The roster annotates a gated state; it never asserts one on its own.
+    expect(w.text()).not.toContain('not a patron any more')
+  })
+
   it('a genuinely failing source still grades as a failure, gated or not', () => {
     const w = mountComponent(SourceHealthDot, {
       stubs: { VTooltip: VTooltipStub },

tests/roster_builders.py

@@ -0,0 +1,64 @@
+"""Row builders for the learned membership roster (#387 phase C).
+
+Three test files were each constructing `PlatformMembership` and
+`MembershipSync` rows with their own private helper — C4's reconcile tests,
+E4's suggestion tests, and C5's gated-reason tests — and the three had already
+started to drift apart in which fields they defaulted. That matters more here
+than for ordinary test plumbing: every one of these tests turns on the exact
+shape of a membership row (a `details["campaign"]["vanity"]` that the identity
+join reads, an `is_free_member` flag that changes what the operator is told),
+so three builders means three slightly different ideas of what a membership
+looks like, and a test that passes against a row the sweep would never write.
+
+`campaign=` rather than the column's own `external_campaign_id=`: it is what
+the majority of call sites already say, and the full name earns nothing in a
+builder whose only subject is memberships.
+"""
+from __future__ import annotations
+
+from datetime import UTC, datetime, timedelta
+
+from backend.app.models import MembershipSync, PlatformMembership
+
+# The shape a real Patreon sweep writes, per the C0 capture (Scribe note
+# #3886): a vanity nested under `details.campaign`, which is where
+# `PlatformMembership.vanity_or_none` reads it from.
+DEFAULT_VANITY = "maewix"
+DEFAULT_URL = f"https://www.patreon.com/{DEFAULT_VANITY}"
+
+
+async def membership(
+    db, *, campaign="c1", platform="patreon", status="active_patron",
+    display_name="Maewix", url=DEFAULT_URL, details=None, **kw,
+) -> PlatformMembership:
+    """One observed membership.
+
+    `details` defaults to the vanity-bearing shape rather than to `{}`, because
+    a row with no vanity cannot be matched by handle and would quietly make
+    every identity test a campaign-id test.
+    """
+    m = PlatformMembership(
+        platform=platform,
+        external_campaign_id=campaign,
+        status=status,
+        display_name=display_name,
+        url=url,
+        details={"campaign": {"vanity": DEFAULT_VANITY}} if details is None else details,
+        **kw,
+    )
+    db.add(m)
+    await db.flush()
+    return m
+
+
+async def synced(db, *, platform="patreon", ago=timedelta(hours=1)) -> MembershipSync:
+    """A successful sweep this recently — what makes a roster FRESH.
+
+    Pass `ago` past `ROSTER_STALE_AFTER` to build the stale case; omit the call
+    entirely for never-synced. Those are three different states and every
+    consumer of the roster has to tell them apart.
+    """
+    state = MembershipSync(platform=platform, last_success_at=datetime.now(UTC) - ago)
+    db.add(state)
+    await db.flush()
+    return state

tests/test_artist_membership_suggestions.py

@@ -31,6 +31,7 @@ from backend.app.services.artist_membership_service import (
     name_signal,
     weighted_score,
 )
+from tests.roster_builders import membership as _membership
 
 pytestmark = pytest.mark.integration
 
@@ -126,17 +127,6 @@ async def _artist_with_discord(db, name, slug):
     return a
 
 
-async def _membership(db, **kw):
-    kw.setdefault("platform", "patreon")
-    kw.setdefault("external_campaign_id", "c1")
-    kw.setdefault("url", "https://www.patreon.com/maewix")
-    kw.setdefault("details", {"campaign": {"vanity": "maewix"}})
-    m = PlatformMembership(**kw)
-    db.add(m)
-    await db.flush()
-    return m
-
-
 @pytest.mark.asyncio
 async def test_a_matching_name_proposes_the_link(db):
     artist = await _artist_with_discord(db, "Maewix", "maewix")

tests/test_gated_reason.py

@@ -0,0 +1,387 @@
+"""Milestone 387 C5: why the posts are invisible, in the roster's own words.
+
+A3 gave a tier-gated source a count — "47 posts you can't see". The roster can
+turn that into a reason, and the whole risk of this step is that a reason is a
+much stronger claim than a count. So most of what follows pins refusals:
+
+* an unrecognised status says NOTHING rather than guessing lapsed;
+* a campaign absent from the roster says nothing, because absence is not
+  evidence (the same discipline as `test_post_is_gated_only_on_explicit_false`);
+* a stale roster degrades to the bare count rather than asserting last week's
+  reason as today's;
+* a current FREE follower is not told they used to be a patron.
+
+And the one that matters most: no fetch path can read the roster at all. That
+is asserted structurally, not by inspection — the roster explains a skip that
+already happened, and must never be able to cause one.
+"""
+from __future__ import annotations
+
+import ast
+from datetime import timedelta
+from pathlib import Path
+
+import pytest
+
+from backend.app.models import Artist, Source
+from backend.app.services.gallery_dl import ErrorType
+from backend.app.services.membership_roster import (
+    GATED_FREE,
+    GATED_LAPSED,
+    GATED_TIER,
+    ROSTER_STALE_AFTER,
+    gated_reason,
+    gated_reasons_for_sources,
+)
+from tests.roster_builders import membership as _membership
+from tests.roster_builders import synced as _synced
+
+# --- the pure mapping: status word -> the words we are entitled to say -------
+#
+# No database, so these run in the unit lane. `gated_reason` is where the claim
+# is actually decided; everything below it is plumbing.
+
+
+def test_a_former_patron_is_told_the_membership_ended():
+    assert gated_reason("patreon", "former_patron") == GATED_LAPSED
+
+
+def test_an_active_patron_is_told_the_tier_does_not_reach_these_posts():
+    assert gated_reason("patreon", "active_patron") == GATED_TIER
+
+
+def test_a_current_free_follower_is_not_told_they_used_to_be_a_patron():
+    """`free` and `lapsed` are different states and must not share a sentence.
+
+    Both make `has_paid_access` False, which is why the reason is derived from
+    the status axis first rather than from that boolean: "you're not a patron
+    any more" is a false statement about someone who never was one.
+    """
+    assert gated_reason("patreon", "active_patron", is_free_member=True) == GATED_FREE
+    assert gated_reason("patreon", "former_patron", is_free_member=True) == GATED_LAPSED
+
+
+@pytest.mark.parametrize("status", [None, "declined_patron", "", "wat"])
+def test_an_unrecognised_status_says_nothing(status):
+    """Unknown is not lapsed.
+
+    `declined_patron` is in here on purpose: it is the plausible-looking word
+    the C0 capture proved is NOT in the `patron_status` vocabulary. If someone
+    adds it to MEMBERSHIP_STATUS on the strength of the request filter, this
+    test is where that shows up.
+    """
+    assert gated_reason("patreon", status) is None
+
+
+def test_a_platform_that_has_never_been_characterised_says_nothing():
+    """SubscribeStar and FANBOX (D1) inherit silence, not a Patreon guess."""
+    assert gated_reason("subscribestar", "active_patron") is None
+
+
+# --- the join, against the database ----------------------------------------
+
+
+async def _artist(db, name="Maewix"):
+    a = Artist(name=name, slug=name.lower().replace(" ", ""))
+    db.add(a)
+    await db.flush()
+    return a
+
+
+async def _gated_source(db, artist, *, url="https://www.patreon.com/maewix",
+                        platform="patreon", overrides=None):
+    s = Source(
+        artist_id=artist.id, platform=platform, url=url, enabled=True,
+        error_type=ErrorType.TIER_LIMITED, config_overrides=overrides,
+    )
+    db.add(s)
+    await db.flush()
+    return s
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_matched_active_membership_explains_the_gate(db):
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db)
+    await _synced(db)
+
+    assert await gated_reasons_for_sources(db, [source]) == {source.id: GATED_TIER}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_lapsed_membership_explains_the_gate(db):
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db, status="former_patron")
+    await _synced(db)
+
+    assert await gated_reasons_for_sources(db, [source]) == {source.id: GATED_LAPSED}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_campaign_absent_from_the_roster_adds_no_words(db):
+    """The third case in the step: absence is not evidence.
+
+    The sweep succeeded an hour ago and this creator is simply not in it. That
+    could mean the subscription lapsed — or that the sweep's pagination is
+    incomplete, or that the creator renamed. The count stands alone.
+    """
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db, campaign="somebody-else",
+                      url="https://www.patreon.com/someoneelse",
+                      details={"campaign": {"vanity": "someoneelse"}})
+    await _synced(db)
+
+    assert await gated_reasons_for_sources(db, [source]) == {}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_stale_roster_degrades_to_the_bare_count(db):
+    """Same data as the passing case, one stale sync state.
+
+    A reason is a claim about NOW. Last week's roster cannot make it.
+    """
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db, status="former_patron")
+    await _synced(db, ago=ROSTER_STALE_AFTER + timedelta(hours=1))
+
+    assert await gated_reasons_for_sources(db, [source]) == {}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_never_synced_platform_degrades_to_the_bare_count(db):
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db, status="former_patron")
+    # No MembershipSync row at all.
+
+    assert await gated_reasons_for_sources(db, [source]) == {}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_one_platforms_fresh_sweep_does_not_vouch_for_anothers(db):
+    """Freshness is per platform, so a working Patreon sweep cannot lend its
+    credibility to a SubscribeStar roster that has never run (D1's future)."""
+    artist = await _artist(db)
+    patreon = await _gated_source(db, artist)
+    other = await _gated_source(
+        db, artist, platform="subscribestar",
+        url="https://subscribestar.adult/maewix",
+    )
+    await _membership(db, status="former_patron")
+    await _membership(db, platform="subscribestar", campaign="s1",
+                      status="former_patron",
+                      url="https://subscribestar.adult/maewix",
+                      details={"campaign": {"vanity": "maewix"}})
+    await _synced(db)  # patreon only
+
+    reasons = await gated_reasons_for_sources(db, [patreon, other])
+    assert reasons == {patreon.id: GATED_LAPSED}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_the_cached_campaign_id_wins_over_a_stale_url(db):
+    """Inherited from `match_kind` via the shared join — asserted here so C5
+    keeps identity in step with C4 rather than quietly growing its own."""
+    artist = await _artist(db)
+    source = await _gated_source(
+        db, artist, url="https://www.patreon.com/old-handle",
+        overrides={"patreon_campaign_id": "c1"},
+    )
+    await _membership(db, campaign="c1", url="https://www.patreon.com/new-handle",
+                      details={"campaign": {"vanity": "new-handle"}},
+                      status="former_patron")
+    await _synced(db)
+
+    assert await gated_reasons_for_sources(db, [source]) == {source.id: GATED_LAPSED}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_no_sources_asks_the_database_nothing(db):
+    assert await gated_reasons_for_sources(db, []) == {}
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_the_source_list_carries_the_reason_to_the_ui(db):
+    """End to end through `SourceService.list`, because the field being on the
+    record is not the same as the field reaching the payload."""
+    from backend.app.services.source_service import SourceService
+
+    artist = await _artist(db)
+    source = await _gated_source(db, artist)
+    await _membership(db, status="former_patron")
+    await _synced(db)
+    await db.commit()
+
+    records = await SourceService(db).list()
+    row = next(r.to_dict() for r in records if r.id == source.id)
+    assert row["gated_reason"] == GATED_LAPSED
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_a_source_that_is_not_gated_gets_no_reason(db):
+    """The roster annotates a gated state; it never puts one on a healthy row.
+
+    A source walking fine whose creator the operator stopped paying for has
+    nothing to explain — and saying "you're not a patron any more" beside a
+    healthy row would be the roster asserting inaccessibility on its own.
+    """
+    from backend.app.services.source_service import SourceService
+
+    artist = await _artist(db)
+    source = Source(
+        artist_id=artist.id, platform="patreon", enabled=True,
+        url="https://www.patreon.com/maewix", error_type=None,
+    )
+    db.add(source)
+    await db.flush()
+    await _membership(db, status="former_patron")
+    await _synced(db)
+    await db.commit()
+
+    records = await SourceService(db).list()
+    row = next(r.to_dict() for r in records if r.id == source.id)
+    assert row["gated_reason"] is None
+    assert row["tier_gated_count"] is None
+
+
+# --- the line that must not be crossed --------------------------------------
+
+_APP = Path(__file__).resolve().parents[1] / "backend" / "app"
+
+# The modules that FETCH: the walk, the downloaders, the per-platform clients
+# and ingesters. Named as ROOTS of an import walk rather than as the place the
+# assertion looks — the check follows their transitive first-party imports, so
+# it still holds when the logic inside them moves (rule #167).
+_FETCH_ROOTS = [
+    "services/download_service.py",
+    "services/ingest_core.py",
+    "services/native_ingest_common.py",
+    "services/gallery_dl.py",
+    "services/refetch_service.py",
+]
+
+# Reading ANY of these is reading the roster.
+_ROSTER_MODULES = {"services.membership_roster", "services.membership_reconcile"}
+
+
+def _first_party_imports(path: Path) -> set[str]:
+    """Every `backend.app.*` module this file imports, as a dotted path
+    relative to `backend/app` — absolute and relative forms both."""
+    tree = ast.parse(path.read_text())
+    here = path.relative_to(_APP).with_suffix("").parts
+    if here and here[-1] == "__init__":
+        # A package's `__init__` IS the package, so `from .x import y` inside it
+        # resolves one level shallower than the file path suggests. Getting this
+        # wrong silently under-resolves every relative import in every package
+        # and would make the guard below unable to fail.
+        here = here[:-1]
+    out: set[str] = set()
+    for node in ast.walk(tree):
+        if isinstance(node, ast.ImportFrom):
+            if node.level:
+                # `from ..models import X` -> walk up from this module's package
+                base = list(here[: len(here) - node.level])
+                mod = base + (node.module.split(".") if node.module else [])
+            elif node.module and node.module.startswith("backend.app."):
+                mod = node.module[len("backend.app."):].split(".")
+            else:
+                continue
+            out.add(".".join(mod))
+            # `from .membership_roster import x` and
+            # `from . import membership_roster` must both resolve to the module.
+            for alias in node.names:
+                out.add(".".join([*mod, alias.name]))
+        elif isinstance(node, ast.Import):
+            for alias in node.names:
+                if alias.name.startswith("backend.app."):
+                    out.add(alias.name[len("backend.app."):])
+    return out
+
+
+def _reachable_from(roots: list[str]) -> set[str]:
+    seen: set[str] = set()
+    queue = [r[:-3].replace("/", ".") for r in roots]
+    while queue:
+        mod = queue.pop()
+        if mod in seen:
+            continue
+        seen.add(mod)
+        for candidate in (_APP / Path(*mod.split(".")) / "__init__.py",
+                          _APP / Path(*mod.split(".")).with_suffix(".py")):
+            if candidate.is_file():
+                queue.extend(_first_party_imports(candidate) - seen)
+                break
+    return seen
+
+
+def test_the_fetch_roots_all_exist():
+    """Falsifiability guard for the guard below.
+
+    A reachability check passes trivially if its roots resolve to nothing, so a
+    renamed module would silently turn the real assertion into a no-op that
+    still reads as coverage.
+    """
+    missing = [r for r in _FETCH_ROOTS if not (_APP / r).is_file()]
+    assert not missing, f"fetch roots moved or were renamed: {missing}"
+
+
+# The falsifiability controls. FC runs no local verification (rule #85), so a
+# guard cannot be falsified by hand before it is committed — it has to carry its
+# own proof that it is capable of failing, and re-prove it on every run. These
+# two assert the walker finds roster imports that ARE there, one direct and one
+# through a hop, so the real assertion below can never pass merely because the
+# walk resolved nothing.
+
+
+def test_the_walk_sees_a_direct_roster_import():
+    """`source_service` legitimately reads the roster — it is what annotates the
+    Subscriptions rows. If this stops holding the walker has gone blind, not the
+    dependency gone away."""
+    assert "services.membership_roster" in _reachable_from(["services/source_service.py"])
+
+
+def test_the_walk_follows_more_than_one_hop():
+    """api/sources.py -> services/source_service.py -> services/membership_roster.py.
+
+    A one-hop walker would pass the guard below on a fetch path that reaches the
+    roster through any intermediate module, which is the likeliest way this ever
+    actually regresses.
+    """
+    reachable = _reachable_from(["api/sources.py"])
+    assert "services.source_service" in reachable
+    assert "services.membership_roster" in reachable
+
+
+def test_no_fetch_path_can_read_the_roster():
+    """The roster explains a skip. It must never be able to cause one.
+
+    Entitled-tier data says which tiers the account holds, not which posts
+    those tiers unlock — `current_user_can_view` is the only per-post truth. A
+    fetch path that could consult the roster could decide not to fetch
+    something the operator is paying for, silently, and that is the worst
+    failure available in this milestone.
+
+    Import reachability rather than a call-site scan: a module that cannot
+    reach the roster cannot consult it, and unlike a grep for a function name
+    this keeps holding when the functions are renamed.
+    """
+    reachable = _reachable_from(_FETCH_ROOTS)
+    assert not (reachable & _ROSTER_MODULES), (
+        "a fetch path can now reach the membership roster: "
+        f"{sorted(reachable & _ROSTER_MODULES)}. The roster may annotate a "
+        "gated state, never produce one — see membership_roster.gated_reason."
+    )

tests/test_membership_reconcile.py

@@ -10,11 +10,11 @@ So most of what follows pins refusals: the gate that empties the bucket when the
 roster cannot be trusted, the tri-state that keeps "unknown" out of "lapsed",
 and the per-row basis that stops the weakest claim sounding like the strongest.
 """
-from datetime import UTC, datetime, timedelta
+from datetime import timedelta
 
 import pytest
 
-from backend.app.models import Artist, MembershipSync, PlatformMembership, Source
+from backend.app.models import Artist, MembershipSync, Source
 from backend.app.services.membership_reconcile import (
     BASIS_ABSENT_EXACT,
     BASIS_ABSENT_HANDLE,
@@ -23,6 +23,8 @@ from backend.app.services.membership_reconcile import (
     reconcile_all,
 )
 from backend.app.services.membership_roster import ROSTER_STALE_AFTER
+from tests.roster_builders import membership as _membership
+from tests.roster_builders import synced as _synced
 
 pytestmark = pytest.mark.integration
 
@@ -44,25 +46,6 @@ async def _source(db, artist, *, url, platform="patreon", enabled=True, override
     return s
 
 
-async def _membership(
-    db, *, campaign="c1", platform="patreon", status="active_patron",
-    display_name="Maewix", url="https://www.patreon.com/maewix", details=None,
-):
-    m = PlatformMembership(
-        platform=platform, external_campaign_id=campaign, status=status,
-        display_name=display_name, url=url,
-        details={"campaign": {"vanity": "maewix"}} if details is None else details,
-    )
-    db.add(m)
-    await db.flush()
-    return m
-
-
-async def _synced(db, *, platform="patreon", ago=timedelta(hours=1)):
-    db.add(MembershipSync(platform=platform, last_success_at=datetime.now(UTC) - ago))
-    await db.flush()
-
-
 # --- the join --------------------------------------------------------------