diff --git a/alembic/versions/0091_platform_membership.py b/alembic/versions/0091_platform_membership.py
new file mode 100644
index 0000000..899f6e4
--- /dev/null
+++ b/alembic/versions/0091_platform_membership.py
@@ -0,0 +1,81 @@
+"""platform_membership — the learned roster of what the account actually pays for.
+
+Milestone 387, phase C. FC knows which creators it was told to follow and
+nothing about which ones the operator is subscribed to; this table is the
+memory that makes the drift in both directions observable. See the model
+docstring for why the roster is learned rather than looked up live, and why
+`status` holds the platform's own word rather than a normalised FC value.
+
+## Nothing populates this yet, on purpose
+
+The sweep that fills it (C3) depends on a client seam (C2) that depends on
+characterising Patreon's real membership response from a captured sample (C0),
+which needs the operator's authenticated browser session. The table's SHAPE
+does not wait on that: it is deliberately free-form where C0's findings would
+otherwise dictate a column — `status` is an unconstrained String and `details`
+keeps the raw payload — so no capture can invalidate what is created here.
+
+An empty table is the correct intermediate state. It is not dead code: C5 reads
+it to explain a tier-limited source, and C4 reads it to reconcile.
+
+Revision ID: 0091
+Revises: 0090
+Create Date: 2026-09-10
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0091"
+down_revision: Union[str, None] = "0090"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "platform_membership",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("platform", sa.String(length=64), nullable=False),
+        # Text, not a bounded String: an opaque upstream identifier we do not
+        # mint, and guessing a ceiling for one is how a walk dies on a silent
+        # truncation.
+        sa.Column("external_campaign_id", sa.Text(), nullable=False),
+        sa.Column("display_name", sa.Text(), nullable=True),
+        sa.Column("url", sa.Text(), nullable=True),
+        # No CHECK, deliberately (rule 36 considered and declined): the
+        # vocabulary is each platform's own and is not ours to fix before C0
+        # has characterised even one of them. The service owns the whitelist.
+        sa.Column("status", sa.String(length=32), nullable=True),
+        sa.Column("tier_names", sa.JSON(), nullable=True),
+        sa.Column("amount_cents", sa.Integer(), nullable=True),
+        sa.Column("currency", sa.String(length=8), nullable=True),
+        sa.Column(
+            "first_seen_at", sa.DateTime(timezone=True),
+            server_default=sa.text("now()"), nullable=False,
+        ),
+        sa.Column(
+            "last_seen_at", sa.DateTime(timezone=True),
+            server_default=sa.text("now()"), nullable=False,
+        ),
+        sa.Column("details", sa.JSON(), nullable=False),
+        sa.PrimaryKeyConstraint("id", name=op.f("pk_platform_membership")),
+        # The upsert's conflict target. Named explicitly because
+        # touch_membership references it by name in ON CONFLICT — an
+        # autogenerated name would make that call break on a rename nobody
+        # connected to it.
+        sa.UniqueConstraint(
+            "platform", "external_campaign_id",
+            name="uq_platform_membership_platform_campaign",
+        ),
+    )
+    # No secondary indexes. This table holds one row per subscription — tens,
+    # not millions — so every query against it is a short scan and an index
+    # would be write cost buying nothing (#3301 removed seven of that shape).
+    # The unique constraint above already backs the only lookup that matters.
+
+
+def downgrade() -> None:
+    op.drop_table("platform_membership")
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index fe4bf54..fc00a84 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -26,6 +26,7 @@ from .patreon_failed_media import PatreonFailedMedia
 from .patreon_seen_media import PatreonSeenMedia
 from .pixiv_failed_media import PixivFailedMedia
 from .pixiv_seen_media import PixivSeenMedia
+from .platform_membership import PlatformMembership
 from .post import Post
 from .post_attachment import PostAttachment, attachment_download_url
 from .presentation_review import PresentationReview
@@ -64,6 +65,7 @@ __all__ = [
     "SeriesChapter",
     "SeriesPage",
     "SeriesSuggestion",
+    "PlatformMembership",
     "ServiceSeen",
     "ImageRecord",
     "ImageProvenance",
diff --git a/backend/app/models/platform_membership.py b/backend/app/models/platform_membership.py
new file mode 100644
index 0000000..509f2ba
--- /dev/null
+++ b/backend/app/models/platform_membership.py
@@ -0,0 +1,130 @@
+"""platform_membership — the learned roster of what the account actually pays for.
+
+Milestone 387, phase C. FabledCurator knows which creators it has been TOLD to
+follow (`source`), and nothing about which ones the operator is actually
+subscribed to. Those two sets drift in both directions and the app cannot
+currently see either drift:
+
+* A subscription the operator pays for that FC does not track is content they
+  believe they are archiving and are not.
+* A source FC keeps walking after the subscription lapsed is requests spent on
+  a wall, reported as a creator who has gone quiet.
+
+This table is the memory that makes both visible — every membership the account
+has been observed to hold, and when it was last seen.
+
+## Why a learned roster rather than a live lookup
+
+Same reasoning as `service_seen` (milestone 365), and the same shape: an
+absence is only observable against a record of presence. A membership that
+stops appearing in a sweep is the signal — "you were subscribed to this, now
+you aren't" — and there is nowhere to read that from a live call, because a
+live call returns what IS, never what stopped being.
+
+It also means the reconciliation surface keeps working when Patreon is
+unreachable, degraded to a stale roster with a visible age rather than an empty
+page (rule 164).
+
+## Roster truth, NOT per-post truth
+
+The single most important thing about this table: `tier_names` says which tiers
+the account holds. It does **not** say which posts those tiers unlock. A
+creator can gate a post behind an access rule that maps onto no tier name at
+all.
+
+`current_user_can_view` — read per post by `patreon_client.post_is_gated` — is
+the authoritative signal, and phase A already turned it into a durable
+per-source state. This roster EXPLAINS that state ("you are no longer a patron"
+vs "your tier doesn't cover these posts"). It must never be used to decide
+whether to fetch something. Getting that backwards would make FC silently stop
+fetching content the operator is paying for, which is the worst failure
+available in this milestone.
+
+## status is a plain String, and deliberately the platform's own word
+
+Not a Postgres ENUM, not CHECK-gated — matching `service_seen.kind`,
+`gpu_job.status` and `source.error_type`. Two reasons, and the first is the
+real one:
+
+1. **The vocabulary is not ours to invent.** Patreon says `active_patron` /
+   `former_patron` / `declined_patron`; SubscribeStar and FANBOX will say
+   something else. Storing each platform's own word verbatim and mapping to
+   FC's meaning at the READ site keeps this table a record of what was
+   observed rather than a lossy translation of it. A lowest-common-denominator
+   enum picked before any platform has been characterised (step C0) would be a
+   guess baked into the schema.
+2. A constraint swap per new value (rule 36) would be cost with no invariant
+   behind it, exactly as `service_seen.kind` records.
+
+The service layer owns the whitelist and the mapping; the column owns the
+evidence.
+
+## Retention: aged out, never deleted on disappearance
+
+A membership that stops appearing in a sweep is NOT removed. Its disappearance
+is the fact the reconciliation surface reads, and deleting the row would
+destroy the signal at the moment it became interesting. `last_seen_at` is what
+makes "gone" decidable, and a retention policy ages rows out on time rather
+than on absence.
+"""
+
+from datetime import datetime
+
+from sqlalchemy import JSON, DateTime, Integer, String, Text, UniqueConstraint, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from .base import Base
+
+
+class PlatformMembership(Base):
+    __tablename__ = "platform_membership"
+    __table_args__ = (
+        # The natural key the sweep's upsert conflicts on. Named explicitly
+        # because `touch_membership` references it by name in ON CONFLICT.
+        UniqueConstraint(
+            "platform", "external_campaign_id",
+            name="uq_platform_membership_platform_campaign",
+        ),
+    )
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+
+    platform: Mapped[str] = mapped_column(String(64), nullable=False)
+    # The platform's own id for the thing subscribed to — a Patreon campaign
+    # id, whatever SubscribeStar and FANBOX call theirs. Text rather than a
+    # bounded String: these are opaque upstream identifiers and guessing a
+    # ceiling for a value we do not mint is how a walk dies on a truncation.
+    external_campaign_id: Mapped[str] = mapped_column(Text, nullable=False)
+
+    # For the reconciliation UI, and for matching against Source.url — the
+    # vanity/URL is what the two sides actually have in common.
+    display_name: Mapped[str | None] = mapped_column(Text, nullable=True)
+    url: Mapped[str | None] = mapped_column(Text, nullable=True)
+
+    # The platform's own word. See the module docstring — this is evidence,
+    # not a normalised FC status.
+    status: Mapped[str | None] = mapped_column(String(32), nullable=True)
+
+    # Nullable throughout: a free follow has no tier and no money attached, and
+    # a platform may not expose an amount at all. Absent must stay
+    # distinguishable from zero — "free" and "we don't know" are different
+    # answers to "what is this costing".
+    tier_names: Mapped[list | None] = mapped_column(JSON, nullable=True)
+    amount_cents: Mapped[int | None] = mapped_column(Integer, nullable=True)
+    currency: Mapped[str | None] = mapped_column(String(8), nullable=True)
+
+    # NEVER updated after insert. The one field that answers "has this ever
+    # been true", which is what makes a disappearance readable rather than
+    # indistinguishable from never having existed. `touch_membership`
+    # deliberately excludes it from the ON CONFLICT update set.
+    first_seen_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now(),
+    )
+    last_seen_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now(),
+    )
+
+    # The raw membership as the platform returned it, so a later question can
+    # be answered without re-fetching — and so a field we did not think to
+    # model is not lost. Displayed and never queried, like service_seen.details.
+    details: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)
diff --git a/backend/app/services/membership_roster.py b/backend/app/services/membership_roster.py
new file mode 100644
index 0000000..b05bd91
--- /dev/null
+++ b/backend/app/services/membership_roster.py
@@ -0,0 +1,116 @@
+"""The learned membership roster: what the account actually subscribes to.
+
+Milestone 387, phase C. Sibling of `service_roster` (milestone 365) and built
+on the same insight — an absence is only observable against a record of
+presence. There, a stopped worker; here, a subscription that lapsed.
+
+## Nothing calls this yet
+
+`touch_membership` is written before its caller because the caller (the sweep,
+C3) needs a client seam (C2) that needs Patreon's real response characterised
+from a captured sample (C0), and that capture needs the operator's browser
+session. The write side does not depend on any of it: an upsert keyed on
+(platform, external_campaign_id) is the same regardless of what the payload
+turns out to look like, and `details` carries whatever C0 finds.
+
+## Why the whitelist lives here and not in the column
+
+`platform_membership.status` is an unconstrained String holding the PLATFORM's
+own word — `active_patron`, not some normalised FC value. The mapping from
+those words to FC's meaning is a read-site concern and belongs in code that can
+be corrected without a migration, because the vocabulary comes from whatever
+each platform says and will be discovered per platform rather than designed up
+front. `MEMBERSHIP_STATUS` below is a place for that knowledge to accumulate as
+platforms are characterised; it is deliberately empty of guesses today.
+"""
+
+from __future__ import annotations
+
+import logging
+
+from sqlalchemy import func
+from sqlalchemy.dialects.postgresql import insert as pg_insert
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from ..models import PlatformMembership
+
+log = logging.getLogger(__name__)
+
+# Platform word -> whether the account currently has paid access.
+#
+# EMPTY ON PURPOSE. Every entry here must come from a characterised response
+# (step C0), not from what the API docs or a plausible guess suggest — that is
+# the whole point of project rule 130, and inventing `active_patron` before
+# seeing it in a real payload is exactly the failure it names. Populate per
+# platform as each is characterised.
+#
+# Unknown words are NOT an error: an unrecognised status means the roster
+# records evidence it cannot yet interpret, which is a better state than
+# dropping the row or asserting a meaning for it.
+MEMBERSHIP_STATUS: dict[str, dict[str, bool]] = {}
+
+
+def has_paid_access(platform: str, status: str | None) -> bool | None:
+    """Does this status mean the account currently pays for access?
+
+    Returns None for a status this code has not been taught, which callers must
+    treat as "unknown" rather than as False. The difference matters: False says
+    the operator has lost access, and asserting that from an unrecognised word
+    would tell them to cancel a source they are still paying for.
+    """
+    if status is None:
+        return None
+    entry = MEMBERSHIP_STATUS.get(platform, {})
+    return entry.get(status)
+
+
+async def touch_membership(
+    session: AsyncSession,
+    *,
+    platform: str,
+    external_campaign_id: str,
+    display_name: str | None = None,
+    url: str | None = None,
+    status: str | None = None,
+    tier_names: list | None = None,
+    amount_cents: int | None = None,
+    currency: str | None = None,
+    details: dict | None = None,
+) -> None:
+    """Record that this membership was observed just now.
+
+    Upsert rather than read-modify-write, for the same reason as
+    `service_roster.touch_service`: a sweep may overlap its own previous run,
+    and the last writer is simply the most recent sighting.
+
+    `first_seen_at` is deliberately NOT in the update set. It is the one field
+    that answers "has this ever been true", which is what makes a membership's
+    later DISAPPEARANCE readable as a lapse rather than indistinguishable from
+    a creator FC never knew about. Every other column is last-writer-wins,
+    including status — a membership that goes from active to former must move.
+    """
+    stmt = pg_insert(PlatformMembership).values(
+        platform=platform,
+        external_campaign_id=external_campaign_id,
+        display_name=display_name,
+        url=url,
+        status=status,
+        tier_names=tier_names,
+        amount_cents=amount_cents,
+        currency=currency,
+        details=details or {},
+    )
+    stmt = stmt.on_conflict_do_update(
+        constraint="uq_platform_membership_platform_campaign",
+        set_={
+            "display_name": stmt.excluded.display_name,
+            "url": stmt.excluded.url,
+            "status": stmt.excluded.status,
+            "tier_names": stmt.excluded.tier_names,
+            "amount_cents": stmt.excluded.amount_cents,
+            "currency": stmt.excluded.currency,
+            "details": stmt.excluded.details,
+            "last_seen_at": func.now(),
+        },
+    )
+    await session.execute(stmt)
diff --git a/tests/test_membership_roster.py b/tests/test_membership_roster.py
new file mode 100644
index 0000000..3172866
--- /dev/null
+++ b/tests/test_membership_roster.py
@@ -0,0 +1,175 @@
+"""Milestone 387 C1: the learned membership roster.
+
+The load-bearing property is that `first_seen_at` survives every re-observation
+— it is what makes a membership's later DISAPPEARANCE readable as a lapse
+rather than indistinguishable from a creator FC never knew about. Everything
+else is last-writer-wins, including status, because a membership that goes from
+active to former has to move.
+"""
+import pytest
+from sqlalchemy import select
+
+from backend.app.models import PlatformMembership
+from backend.app.services.membership_roster import (
+    MEMBERSHIP_STATUS,
+    has_paid_access,
+    touch_membership,
+)
+
+pytestmark = pytest.mark.integration
+
+
+async def _row(db, platform="patreon", campaign="c1"):
+    return (await db.execute(
+        select(PlatformMembership).where(
+            PlatformMembership.platform == platform,
+            PlatformMembership.external_campaign_id == campaign,
+        )
+    )).scalar_one()
+
+
+@pytest.mark.asyncio
+async def test_touch_inserts_a_new_membership(db):
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-new",
+        display_name="Maewix Studios", url="https://patreon.com/maewix",
+        status="some_platform_word", tier_names=["Sketches"],
+        amount_cents=500, currency="USD", details={"raw": 1},
+    )
+    await db.commit()
+
+    row = await _row(db, campaign="c-new")
+    assert row.display_name == "Maewix Studios"
+    assert row.status == "some_platform_word"
+    assert row.tier_names == ["Sketches"]
+    assert row.amount_cents == 500
+    assert row.details == {"raw": 1}
+    assert row.first_seen_at is not None
+
+
+@pytest.mark.asyncio
+async def test_re_observation_preserves_first_seen_and_advances_last_seen(db):
+    """The whole point of the table.
+
+    Committed between touches deliberately: `func.now()` is the TRANSACTION
+    timestamp in Postgres, so two touches in one transaction would share a
+    last_seen_at and this test would pass without proving anything. (That
+    sharing is correct for a sweep — every row it touches is one observation —
+    but it makes an in-transaction assertion vacuous.)
+    """
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-again", status="active_ish",
+    )
+    await db.commit()
+    original = await _row(db, campaign="c-again")
+    first_seen, first_last_seen = original.first_seen_at, original.last_seen_at
+    db.expunge_all()
+
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-again", status="former_ish",
+    )
+    await db.commit()
+
+    row = await _row(db, campaign="c-again")
+    assert row.first_seen_at == first_seen, "first_seen_at must never move"
+    assert row.last_seen_at >= first_last_seen
+    # Status is last-writer-wins: a lapse has to be able to overwrite.
+    assert row.status == "former_ish"
+
+
+@pytest.mark.asyncio
+async def test_re_observation_overwrites_the_mutable_fields(db):
+    """A creator who renames, retiers or changes price must not leave the
+    roster asserting the old value — every column except first_seen_at moves."""
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-mut",
+        display_name="Old Name", amount_cents=500, tier_names=["Cheap"],
+        details={"v": 1},
+    )
+    await db.commit()
+    db.expunge_all()
+
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-mut",
+        display_name="New Name", amount_cents=1500, tier_names=["Pricey"],
+        details={"v": 2},
+    )
+    await db.commit()
+
+    row = await _row(db, campaign="c-mut")
+    assert row.display_name == "New Name"
+    assert row.amount_cents == 1500
+    assert row.tier_names == ["Pricey"]
+    assert row.details == {"v": 2}
+
+
+@pytest.mark.asyncio
+async def test_the_same_campaign_id_on_two_platforms_is_two_rows(db):
+    """The key is (platform, external_campaign_id). Nothing stops two platforms
+    minting the same opaque id, and collapsing them would merge one creator's
+    membership into another's."""
+    await touch_membership(db, platform="patreon", external_campaign_id="shared-id")
+    await touch_membership(db, platform="subscribestar", external_campaign_id="shared-id")
+    await db.commit()
+
+    rows = (await db.execute(
+        select(PlatformMembership).where(
+            PlatformMembership.external_campaign_id == "shared-id"
+        )
+    )).scalars().all()
+    assert {r.platform for r in rows} == {"patreon", "subscribestar"}
+
+
+@pytest.mark.asyncio
+async def test_a_free_follow_keeps_absent_distinct_from_zero(db):
+    """"Free" and "we don't know what this costs" are different answers, and
+    the reconciliation UI has to be able to tell them apart."""
+    await touch_membership(
+        db, platform="patreon", external_campaign_id="c-free", status="free_ish",
+    )
+    await db.commit()
+
+    row = await _row(db, campaign="c-free")
+    assert row.amount_cents is None
+    assert row.tier_names is None
+
+
+# --- has_paid_access: unknown must never read as "lost access" -------------
+
+
+def test_unknown_status_is_unknown_not_false():
+    """The dangerous case. False means "the operator lost access", which C4
+    turns into an offer to disable the source. Asserting that from a word this
+    code simply has not been taught would tell them to cancel a subscription
+    they are still paying for."""
+    assert has_paid_access("patreon", "a_word_nobody_characterised_yet") is None
+
+
+def test_absent_status_is_unknown():
+    assert has_paid_access("patreon", None) is None
+
+
+def test_unknown_platform_is_unknown():
+    assert has_paid_access("a-platform-with-no-mapping", "active") is None
+
+
+def test_the_status_map_starts_empty_and_that_is_deliberate():
+    """Guards project rule 130 at the one place it is easiest to break.
+
+    Every entry must come from a characterised response (step C0), never from
+    API docs or a plausible-looking guess. If this assertion fails, either C0
+    happened — in which case update this test along with the map, citing the
+    capture — or somebody guessed, which is the thing the rule exists to stop.
+    """
+    assert MEMBERSHIP_STATUS == {}
+
+
+def test_the_map_is_consulted_once_it_has_entries(monkeypatch):
+    """The map is empty today, so exercise the lookup with a stand-in — proving
+    the plumbing works without pretending to know a real platform's word."""
+    monkeypatch.setitem(
+        MEMBERSHIP_STATUS, "testplat", {"paying": True, "lapsed": False},
+    )
+    assert has_paid_access("testplat", "paying") is True
+    assert has_paid_access("testplat", "lapsed") is False
+    assert has_paid_access("testplat", "something_else") is None