alembic/versions/0090_service_seen.py

@@ -0,0 +1,64 @@
+"""service_seen — the learned roster that makes a stopped part observable.
+
+Milestone 365. Nothing in FabledCurator knew what was SUPPOSED to be running:
+`celery inspect` reports the workers that answer, so a dead worker was a
+shorter list rather than a red light, and the only surface that could tell an
+operator otherwise was Portainer. This table is the memory that turns an
+absence into something the app can see.
+
+Keyed on the queue set for a celery role and on agent_id for the GPU agent —
+NOT on the celery worker name, which here is `celery@<container id>` and is
+minted fresh on every deploy. See the model docstring for why that choice is
+the whole design.
+
+## First migration on the collapsed baseline
+
+0089 is the single generated baseline that replaced revisions 0001..0089
+(milestone 328). This is the first revision written on top of it, so it is
+also the first evidence that the chain steps forward from the collapse rather
+than merely reproducing the schema — which nothing had demonstrated yet.
+
+An existing install is at 0089 because it ran the real 0089; a fresh one is at
+0089 because it ran the baseline. Both arrive here identically, which was the
+property the collapse was designed around.
+
+Revision ID: 0090
+Revises: 0089
+Create Date: 2026-09-02
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0090"
+down_revision: Union[str, None] = "0089"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "service_seen",
+        sa.Column("key", sa.String(length=128), nullable=False),
+        sa.Column("kind", sa.String(length=16), nullable=False),
+        sa.Column("display_name", sa.String(length=64), nullable=False),
+        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("key", name=op.f("pk_service_seen")),
+    )
+    # No secondary indexes, deliberately: one row per moving part means every
+    # read is a handful of rows and an index would be write cost buying
+    # nothing (#3301 removed seven of exactly that shape).
+
+
+def downgrade() -> None:
+    op.drop_table("service_seen")

backend/app/api/__init__.py

@@ -38,6 +38,7 @@ def all_blueprints() -> list[Blueprint]:
     from .suggestions import suggestions_bp
     from .system_activity import system_activity_bp
     from .system_backup import system_backup_bp
+    from .system_health import system_health_bp
     from .tags import tags_bp
     from .thumbnails import thumbnails_bp
     return [
@@ -51,6 +52,7 @@ def all_blueprints() -> list[Blueprint]:
         showcase_bp,
         settings_bp,
         system_activity_bp,
+        system_health_bp,
         system_backup_bp,
         admin_bp,
         cleanup_bp,

backend/app/api/gpu.py

@@ -21,6 +21,7 @@ from ..services.gallery_service import image_url
 from ..services.ml.gpu_jobs import GpuJobService, error_dedupe_statements
 from ..services.ml.gpu_triage import classify_reason, recover_defective_image
 from ..services.ml.regions import RegionService
+from ..services.service_roster import touch_service
 
 gpu_bp = Blueprint("gpu", __name__, url_prefix="/api/gpu")
 
@@ -256,6 +257,18 @@ async def lease():
         if not await _agent_authed(session):
             return jsonify({"error": "unauthorized"}), 401
         jobs = await GpuJobService(session).lease(agent_id, batch_size=batch)
+        # The agent cannot be polled — it is HTTP-only and pulls from here, so
+        # web never dials it. A lease IS the check-in, and until milestone 365
+        # it was thrown away: an agent sitting idle with nothing to lease left
+        # no trace at all and was indistinguishable from one switched off a
+        # week ago. Recorded on the call that was already happening.
+        await touch_service(
+            session,
+            key=f"agent:{agent_id}",
+            kind="agent",
+            display_name="GPU agent" if agent_id == "agent" else f"GPU agent ({agent_id})",
+            details={"agent_id": agent_id, "last_call": "lease", "leased": len(jobs)},
+        )
         ml = await MLSettings.load(session)
         # image rows for url/mime in one shot
         ids = [j.image_record_id for j in jobs]
@@ -329,6 +342,13 @@ async def heartbeat():
         if not await _agent_authed(session):
             return jsonify({"error": "unauthorized"}), 401
         n = await GpuJobService(session).heartbeat(agent_id, job_ids)
+        await touch_service(
+            session,
+            key=f"agent:{agent_id}",
+            kind="agent",
+            display_name="GPU agent" if agent_id == "agent" else f"GPU agent ({agent_id})",
+            details={"agent_id": agent_id, "last_call": "heartbeat", "extended": n},
+        )
         await session.commit()
     return jsonify({"extended": n})
 

backend/app/api/system_health.py

@@ -0,0 +1,192 @@
+"""Is every part of FabledCurator running? One verdict, one endpoint.
+
+Milestone 365. The nav indicator and the System page both read this and
+nothing else — composing a verdict is this module's job, not the UI's.
+
+## Two kinds of part, answered two different ways
+
+**Learned** — celery roles and the GPU agent, from `service_seen`. The
+question is "how long since it checked in", and these are the parts that can
+be ABSENT, which is the whole point: `celery inspect` alone reports presence,
+so a dead worker is a shorter list rather than a red light.
+
+**Probed live** — Postgres and Redis. Always expected, never learned, and a
+last-seen for them would be actively misleading: that Redis answered thirty
+seconds ago says nothing about now.
+
+## This endpoint must never fail because something it checks has failed
+
+The inversion is easy to write by accident and it destroys the feature exactly
+when it is needed — a 500 when Redis is down, instead of `redis: down`. Every
+probe is wrapped, every wait has a deadline (rule 156), and the roster refresh
+swallows its own errors. The worst case is a part reported `unknown`, which is
+a true statement.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import time
+from datetime import UTC, datetime
+
+from quart import Blueprint, jsonify
+from sqlalchemy import select, text
+
+from ..config import get_config
+from ..extensions import get_session
+from ..models import ServiceSeen
+from ..services.service_roster import refresh_if_stale
+
+log = logging.getLogger(__name__)
+
+system_health_bp = Blueprint("system_health", __name__, url_prefix="/api/system")
+
+# How long a learned part may go quiet before it is doubted, then disbelieved.
+#
+# These are deliberately generous, and the reason is a deploy rather than a
+# worker: `docker compose up -d` rolls start-first, so a role is briefly served
+# by two containers and then by neither while the old one drains. Thresholds
+# tight enough to catch a crash in seconds would paint the page red every time
+# the stack is updated, and an alarm that cries wolf on every deploy is one
+# nobody reads. Tune down only after watching a real deploy pass through.
+STALE_AFTER_SECONDS = 90
+DOWN_AFTER_SECONDS = 300
+
+# Probes cross a process boundary, so they carry deadlines. A hung Postgres
+# must make this endpoint say "postgres: down", not hang alongside it.
+PROBE_TIMEOUT_SECONDS = 2.0
+
+_OK, _STALE, _DOWN, _UNKNOWN = "ok", "stale", "down", "unknown"
+
+# Worst-first, so an overall verdict is just the max.
+_SEVERITY = {_OK: 0, _UNKNOWN: 1, _STALE: 2, _DOWN: 3}
+
+
+def _age_state(age_seconds: float) -> str:
+    if age_seconds >= DOWN_AFTER_SECONDS:
+        return _DOWN
+    if age_seconds >= STALE_AFTER_SECONDS:
+        return _STALE
+    return _OK
+
+
+def _describe_learned(name: str, state: str, age: float, details: dict) -> str:
+    """Say what the state MEANS. A red chip tells an operator less than a
+    sentence does at the moment they are deciding whether to go and look."""
+    if state == _OK:
+        replicas = details.get("replicas")
+        if replicas and replicas > 1:
+            return f"{name} is running ({replicas} replicas)"
+        return f"{name} is running"
+    mins = int(age // 60)
+    ago = f"{mins} min" if mins else f"{int(age)}s"
+    if state == _STALE:
+        return f"{name} has not checked in for {ago}"
+    return f"{name} has not checked in for {ago} — treat it as stopped"
+
+
+async def _probe_postgres(session) -> dict:
+    started = time.monotonic()
+    try:
+        await asyncio.wait_for(
+            session.execute(text("SELECT 1")), timeout=PROBE_TIMEOUT_SECONDS
+        )
+    except Exception as exc:  # noqa: BLE001 — a probe reports, it never raises
+        return {
+            "key": "postgres", "kind": "datastore", "name": "PostgreSQL",
+            "state": _DOWN, "detail": f"not answering: {type(exc).__name__}",
+        }
+    return {
+        "key": "postgres", "kind": "datastore", "name": "PostgreSQL", "state": _OK,
+        "detail": "answering", "latency_ms": round((time.monotonic() - started) * 1000, 1),
+    }
+
+
+def _ping_redis_sync() -> None:
+    import redis  # local import; mirrors system_activity's pattern
+
+    client = redis.Redis.from_url(
+        get_config().celery_broker_url,
+        socket_connect_timeout=PROBE_TIMEOUT_SECONDS,
+        socket_timeout=PROBE_TIMEOUT_SECONDS,
+    )
+    client.ping()
+
+
+async def _probe_redis() -> dict:
+    started = time.monotonic()
+    try:
+        await asyncio.wait_for(
+            asyncio.to_thread(_ping_redis_sync), timeout=PROBE_TIMEOUT_SECONDS * 2
+        )
+    except Exception as exc:  # noqa: BLE001
+        return {
+            "key": "redis", "kind": "datastore", "name": "Redis",
+            "state": _DOWN,
+            "detail": f"not answering: {type(exc).__name__} — queues and workers "
+                      f"cannot be reached either",
+        }
+    return {
+        "key": "redis", "kind": "datastore", "name": "Redis", "state": _OK,
+        "detail": "answering", "latency_ms": round((time.monotonic() - started) * 1000, 1),
+    }
+
+
+@system_health_bp.route("/health", methods=["GET"])
+async def system_health():
+    """Every part, its state, and one overall verdict.
+
+    Response: {overall, parts: [{key, kind, name, state, detail, last_seen_at,
+    …}], checked_at}
+    """
+    parts: list[dict] = []
+    now = datetime.now(UTC)
+
+    async with get_session() as session:
+        # Postgres first, and if it is unreachable nothing else can be read —
+        # say so rather than failing, because "the database is down" is the
+        # single most useful thing this endpoint can ever report.
+        pg = await _probe_postgres(session)
+        parts.append(pg)
+
+        if pg["state"] == _OK:
+            # Rate-limited inside; see service_roster on why the web process
+            # is the right observer.
+            try:
+                await refresh_if_stale(session)
+                await session.commit()
+            except Exception:  # noqa: BLE001
+                log.warning("system health: roster refresh failed", exc_info=True)
+
+            rows = (
+                await session.execute(select(ServiceSeen).order_by(ServiceSeen.display_name))
+            ).scalars().all()
+            for row in rows:
+                age = (now - row.last_seen_at).total_seconds()
+                state = _age_state(age)
+                parts.append({
+                    "key": row.key,
+                    "kind": row.kind,
+                    "name": row.display_name,
+                    "state": state,
+                    "detail": _describe_learned(row.display_name, state, age, row.details or {}),
+                    "last_seen_at": row.last_seen_at.isoformat(),
+                    "first_seen_at": row.first_seen_at.isoformat(),
+                    **{k: v for k, v in (row.details or {}).items() if k != "agent_id"},
+                })
+
+    parts.append(await _probe_redis())
+
+    overall = max((p["state"] for p in parts), key=lambda s: _SEVERITY[s], default=_UNKNOWN)
+    return jsonify({
+        "overall": overall,
+        "parts": sorted(parts, key=lambda p: (-_SEVERITY[p["state"]], p["name"])),
+        "checked_at": now.isoformat(),
+        # So the UI can explain a `stale` without hard-coding the same numbers
+        # in a second place.
+        "thresholds": {
+            "stale_after_seconds": STALE_AFTER_SECONDS,
+            "down_after_seconds": DOWN_AFTER_SECONDS,
+        },
+    })

backend/app/models/__init__.py

@@ -32,6 +32,7 @@ from .presentation_review import PresentationReview
 from .series_chapter import SeriesChapter
 from .series_page import SeriesPage
 from .series_suggestion import SeriesSuggestion
+from .service_seen import ServiceSeen
 from .source import Source
 from .subscribestar_failed_media import SubscribeStarFailedMedia
 from .subscribestar_seen_media import SubscribeStarSeenMedia
@@ -63,6 +64,7 @@ __all__ = [
     "SeriesChapter",
     "SeriesPage",
     "SeriesSuggestion",
+    "ServiceSeen",
     "ImageRecord",
     "ImageProvenance",
     "ImageRegion",

backend/app/models/service_seen.py

@@ -0,0 +1,88 @@
+"""service_seen — the learned roster of FabledCurator's own moving parts.
+
+Nothing else in this application knows what is SUPPOSED to be running.
+`celery inspect` reports the workers that answer, so a stopped worker is a
+shorter list rather than a red light, and Postgres and Redis have no
+representation at all. That is why the only place an operator could see a
+dead service was Portainer, which knows the intended set (milestone 365).
+
+This table is the memory that makes an absence observable: every part that
+has ever checked in, and when it last did. A row that stops advancing is a
+part that stopped.
+
+## Why the key is not the hostname
+
+`_read_workers_sync()` returns celery's worker names, which here are
+`celery@<container id>`. Those are minted fresh on every deploy. Keyed on
+them, this table would record a death and a birth every time the stack is
+updated — and a status page that goes red on every deploy is a status page
+nobody reads, which is worse than not having one.
+
+So a celery role is keyed on its **queue set**, which is assigned per role in
+docker-compose.yml (`CELERY_QUEUES`) and survives container replacement:
+
+    default,import,thumbnail,download  ->  worker
+    maintenance,scan                   ->  scheduler   (celery worker --beat)
+    ml                                 ->  ml-worker
+
+Two replicas of one role share a queue set and are therefore ONE row — which
+is right, because the question being answered is "is that role being served",
+not "how many containers exist". The replica count and their hostnames go in
+`details`, where they can change without the identity changing.
+
+The GPU agent is keyed on its `agent_id`, the identity its lease protocol
+already uses (`api/gpu.py`).
+
+## What is NOT in here
+
+Postgres and Redis. They are always expected and never learned, and a
+last-seen for them would be actively misleading — that one answered thirty
+seconds ago says nothing about now. They are probed live at request time.
+
+## kind
+
+Plain `String`, not a Postgres ENUM and not CHECK-gated, matching
+`gpu_job.status` and `backup_run.status`. The value set here is expected to
+grow as parts are added, and a constraint swap per new kind (rule 36) would
+be cost with no invariant behind it.
+
+    celery  — a worker role, keyed on its queue set
+    agent   — a GPU agent, keyed on its agent_id
+"""
+
+from datetime import datetime
+
+from sqlalchemy import JSON, DateTime, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from .base import Base
+
+
+class ServiceSeen(Base):
+    __tablename__ = "service_seen"
+
+    # No indexes beyond the primary key, deliberately. This table holds one row
+    # per moving part — a handful, forever — so every query against it is a
+    # full read of a few rows and an index would be write cost buying nothing
+    # (the lesson of #3301, which removed seven redundant ones).
+    key: Mapped[str] = mapped_column(String(128), primary_key=True)
+    kind: Mapped[str] = mapped_column(String(16), nullable=False)
+
+    # What to call it in the UI. Derived from the queue set where it is
+    # recognised, and falling back to the raw queue list where it is not — a
+    # deployment that slices its queues differently should still show something
+    # true rather than a name this code invented for it.
+    display_name: Mapped[str] = mapped_column(String(64), nullable=False)
+
+    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 parts that change without changing identity: replica hostnames,
+    # active task counts, the queues actually being served. Kept as a blob
+    # because it is displayed and never queried — giving it columns would
+    # invite filtering on it, which is what the activity endpoints are for.
+    details: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)

backend/app/services/service_roster.py

@@ -0,0 +1,175 @@
+"""The learned roster: which of FabledCurator's parts have checked in, and when.
+
+Milestone 365. `celery inspect` answers "who is here"; this answers "who is
+missing", which nothing in the application could do before — see
+`models/service_seen.py` for why the identity is a queue set and not a
+worker hostname.
+
+## Who does the observing, and why it is the web process
+
+Three candidates, and the choice matters more than the code:
+
+* **A celery beat sweep.** Rejected. If the scheduler dies, the sweep stops,
+  every row goes stale, and the page reports that everything is down when one
+  thing is. An alarm that cannot distinguish "one part died" from "the
+  observer died" is worse than no alarm.
+* **A background task in web.** Rejected on a detail of how this deploys:
+  hypercorn runs `--workers 4`, so a `before_serving` loop would be FOUR
+  concurrent inspect loops hammering the broker, forever, per container.
+* **Refresh on demand, rate-limited by the data itself.** Taken. Whichever web
+  process happens to serve a health request refreshes the roster if it is
+  older than REFRESH_TTL, and otherwise reads what is already there.
+
+The third has the property the other two lack: **the observer is the thing
+serving the page.** If web is down you get a browser error rather than a
+confidently green page, which is the honest failure. It also self-limits
+without coordination — the TTL lives in the row everybody can see.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+
+from sqlalchemy import func, select
+from sqlalchemy.dialects.postgresql import insert as pg_insert
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from ..models import ServiceSeen
+
+log = logging.getLogger(__name__)
+
+# How stale the roster may be before a health request refreshes it. Comfortably
+# under the staleness thresholds that decide a service is missing, so the
+# verdict is never limited by how often anyone looked.
+REFRESH_TTL_SECONDS = 20.0
+
+# celery inspect is a broker round trip and this sits on a request path, so it
+# gets a deadline (rule 156). A broker that has stopped answering must make the
+# roster stale — which is a true statement about the system — not hang the one
+# page that exists to explain it.
+INSPECT_TIMEOUT_SECONDS = 2.0
+
+# Queue set -> the name an operator recognises. Sorted-tuple keys, because the
+# order celery reports them in is not guaranteed.
+#
+# A deployment that slices CELERY_QUEUES differently falls through to the raw
+# queue list rather than being given a name this table invented for it: a
+# wrong-but-confident label on a status page is worse than an ugly true one.
+ROLE_NAMES: dict[tuple[str, ...], str] = {
+    ("default", "download", "import", "thumbnail"): "Worker",
+    ("maintenance", "scan"): "Scheduler",
+    ("ml",): "ML worker",
+}
+
+
+def role_display_name(queues: tuple[str, ...]) -> str:
+    known = ROLE_NAMES.get(queues)
+    if known:
+        return known
+    return "Worker (" + ", ".join(queues) + ")"
+
+
+def _inspect_celery_sync() -> dict[tuple[str, ...], dict]:
+    """celery inspect, grouped by queue set rather than by worker.
+
+    Returns {queue_set: {"hostnames": [...], "active": int}}. Two replicas of
+    one role collapse into one entry on purpose — the question is whether the
+    role is being served, not how many containers exist.
+    """
+    from ..celery_app import celery as celery_app
+
+    insp = celery_app.control.inspect(timeout=INSPECT_TIMEOUT_SECONDS)
+    active_queues = insp.active_queues() or {}
+    active_tasks = insp.active() or {}
+
+    grouped: dict[tuple[str, ...], dict] = {}
+    for hostname, queues in active_queues.items():
+        key = tuple(sorted({q["name"] for q in queues}))
+        entry = grouped.setdefault(key, {"hostnames": [], "active": 0})
+        entry["hostnames"].append(hostname)
+        entry["active"] += len(active_tasks.get(hostname, []))
+    for entry in grouped.values():
+        entry["hostnames"].sort()
+    return grouped
+
+
+async def touch_service(
+    session: AsyncSession, *, key: str, kind: str, display_name: str, details: dict
+) -> None:
+    """Record that a part checked in just now.
+
+    Upsert rather than read-modify-write: several web processes and several
+    agents can be doing this at once, and the last writer is simply the most
+    recent sighting. `first_seen_at` is deliberately NOT updated — it is the
+    one field that answers "has this ever run", which the learned-roster design
+    depends on.
+    """
+    stmt = pg_insert(ServiceSeen).values(
+        key=key, kind=kind, display_name=display_name, details=details,
+    )
+    stmt = stmt.on_conflict_do_update(
+        index_elements=[ServiceSeen.key],
+        set_={
+            "kind": stmt.excluded.kind,
+            "display_name": stmt.excluded.display_name,
+            "details": stmt.excluded.details,
+            "last_seen_at": func.now(),
+        },
+    )
+    await session.execute(stmt)
+
+
+async def refresh_celery_roster(session: AsyncSession) -> None:
+    """Inspect the broker and record what answered. Never raises.
+
+    A failure here means the roster does not advance, and the rows going stale
+    is then a TRUE report about a broker nobody can reach. Letting the
+    exception out would instead break the health endpoint, which is the one
+    thing that must keep answering when the stack is unwell.
+    """
+    try:
+        grouped = await asyncio.wait_for(
+            asyncio.to_thread(_inspect_celery_sync),
+            timeout=INSPECT_TIMEOUT_SECONDS * 2,
+        )
+    except Exception:
+        log.warning("service roster: celery inspect failed; roster not refreshed", exc_info=True)
+        return
+
+    for queues, entry in grouped.items():
+        await touch_service(
+            session,
+            key="celery:" + ",".join(queues),
+            kind="celery",
+            display_name=role_display_name(queues),
+            details={
+                "queues": list(queues),
+                "hostnames": entry["hostnames"],
+                "replicas": len(entry["hostnames"]),
+                "active": entry["active"],
+            },
+        )
+
+
+async def refresh_if_stale(session: AsyncSession) -> None:
+    """Refresh the celery roster if nobody has for REFRESH_TTL_SECONDS.
+
+    Rate-limited by the data rather than by a lock: the gate is the newest
+    last_seen_at across the celery rows, which every web process can see. Two
+    processes racing through the gate costs one redundant inspect and writes
+    the same values twice, so the benign outcome needs no coordination to
+    prevent.
+    """
+    newest = (
+        await session.execute(
+            select(func.max(ServiceSeen.last_seen_at)).where(ServiceSeen.kind == "celery")
+        )
+    ).scalar_one_or_none()
+
+    if newest is not None:
+        age = (await session.execute(select(func.now()))).scalar_one() - newest
+        if age.total_seconds() < REFRESH_TTL_SECONDS:
+            return
+
+    await refresh_celery_roster(session)

frontend/src/components/TopNav.vue

@@ -5,9 +5,12 @@
         <img src="/favicon.svg" alt="" class="fc-brand__glyph" width="22" height="22" />
         <span class="fc-brand__text">FabledCurator</span>
       </RouterLink>
-      <span class="fc-health" :title="health.label">
+      <RouterLink
+        :to="{ name: 'system' }" class="fc-health" :title="health.label"
+        :aria-label="`System health: ${health.label}`"
+      >
         <v-icon size="x-small" :color="health.color">{{ health.icon }}</v-icon>
-      </span>
+      </RouterLink>
       <PipelineStatusChip />
     </div>
 
@@ -64,13 +67,15 @@
 </template>
 
 <script setup>
-import { computed, onBeforeUnmount, onMounted, ref } from 'vue'
+import { computed, onBeforeUnmount, onMounted, onUnmounted, ref } from 'vue'
 import { useRoute } from 'vue-router'
 import router, { FRONT_DOOR } from '../router.js'
 import { useSystemStore } from '../stores/system.js'
+import { useSystemHealthStore } from '../stores/systemHealth.js'
 import PipelineStatusChip from './PipelineStatusChip.vue'
 
 const system = useSystemStore()
+const healthStore = useSystemHealthStore()
 
 // Publish the nav's REAL height as --fc-nav-h so full-height workspaces
 // (Explore/Subscriptions) and sticky sub-headers pin to it exactly instead of a
@@ -116,15 +121,55 @@ const settingsRoute = computed(() =>
   navRoutes.value.find(r => r.name === 'settings') || null
 )
 
+// The dot beside the brand, and the only ambient signal that something in the
+// stack has stopped (milestone 365).
+//
+// It used to read /api/health — a no-DB liveness check that proves the WEB
+// container is serving and nothing else. Green there while the worker was dead
+// is exactly what it looked like, and a green dot next to the product name is
+// read as "everything is fine". It now reflects the whole-stack verdict.
+//
+// Deliberately re-using this element rather than adding a second indicator:
+// there were already three partial surfaces (this, the pipeline chip, the
+// Settings Activity tab) and a fourth would have made the question harder to
+// answer, not easier. This is the one that already occupied the slot.
 const health = computed(() => {
-  if (system.healthy === null) {
+  const overall = healthStore.overall
+  if (overall === null) {
     return { icon: 'mdi-circle-outline', color: 'on-surface', label: 'checking…' }
   }
-  if (system.healthy === true) {
-    return { icon: 'mdi-circle', color: 'success', label: 'healthy' }
+  if (overall === 'ok') {
+    return { icon: 'mdi-circle', color: 'success', label: 'All parts running' }
   }
-  return { icon: 'mdi-alert-circle', color: 'error', label: 'unreachable' }
+  // Name what is wrong in the tooltip. "Something is unhealthy" sends someone
+  // hunting; "Scheduler has not checked in for 6 min" does not.
+  const worst = healthStore.problems[0]
+  const others = healthStore.problems.length - 1
+  const suffix = others > 0 ? ` (+${others} more)` : ''
+  if (overall === 'down') {
+    return {
+      icon: 'mdi-alert-circle', color: 'error',
+      label: (worst?.detail || 'A part has stopped') + suffix,
+    }
+  }
+  if (overall === 'stale') {
+    return {
+      icon: 'mdi-alert', color: 'warning',
+      label: (worst?.detail || 'A part is quiet') + suffix,
+    }
+  }
+  return { icon: 'mdi-help-circle-outline', color: 'on-surface', label: 'Health unknown' }
 })
+
+const HEALTH_POLL_MS = 15_000
+let healthTimer = null
+onMounted(() => {
+  healthStore.refresh()
+  healthTimer = setInterval(() => {
+    if (!document.hidden) healthStore.refresh()
+  }, HEALTH_POLL_MS)
+})
+onUnmounted(() => { if (healthTimer) clearInterval(healthTimer) })
 </script>
 
 <style scoped>
@@ -237,7 +282,14 @@ const health = computed(() => {
   display: flex;
   align-items: center;
   flex-shrink: 0;
+  /* A RouterLink since milestone 365 — it is the path to /system, not just an
+     indicator. Reset the anchor so turning a span into a link changed nothing
+     about how the nav reads. */
+  text-decoration: none;
+  color: inherit;
+  border-radius: 50%;
 }
+.fc-health:hover { background: rgb(var(--v-theme-on-surface) / 0.12); }
 .fc-nav-right {
   flex: 1 1 0;
   min-width: 0;

frontend/src/router.js

@@ -1,5 +1,6 @@
 import { createRouter, createWebHistory, createMemoryHistory } from 'vue-router'
 import SettingsView from './views/SettingsView.vue'
+import SystemView from './views/SystemView.vue'
 import GalleryView from './views/GalleryView.vue'
 import ShowcaseView from './views/ShowcaseView.vue'
 import ExploreView from './views/ExploreView.vue'
@@ -45,6 +46,12 @@ const routes = [
 
   // Settings — config, pinned to the right of the nav (TopNav special-cases it).
   { path: '/settings', name: 'settings', component: SettingsView, meta: { title: 'Settings', stickyChrome: true } },
+  // Deliberately NO meta.title: TopNav builds its nav row from routes that
+  // have one, and this is reached from the health indicator beside the
+  // brand — the place someone already looks when they suspect something is
+  // wrong. A sixth top-level tab for a page you visit twice a year would
+  // cost more attention than it returns.
+  { path: '/system', name: 'system', component: SystemView },
 
   // The old standalone paths now redirect into the Browse hub, preserving any
   // deep-link query (e.g. /posts?post_id=N → /browse?tab=posts&post_id=N). The

frontend/src/stores/system.js

@@ -4,7 +4,12 @@ import { useApi } from '../composables/useApi.js'
 
 export const useSystemStore = defineStore('system', () => {
   const api = useApi()
-  const healthy = ref(null)  // null=unknown, true=ok, false=down
+  // NOT what the nav dot reads any more (milestone 365): that is the
+  // whole-stack verdict in systemHealth.js. /api/health only proves the web
+  // container is serving, which is why a green dot here sat happily beside a
+  // dead worker. refreshHealth() is still called — it is also how build/version
+  // info arrives — so this stays as its by-product rather than its purpose.
+  const healthy = ref(null)
   // What the instance says it is. Since milestone 318 stopped publishing
   // version image tags, this is the only answer to "which build is this?" —
   // there is no registry name left to check it against.

frontend/src/stores/systemHealth.js

@@ -0,0 +1,49 @@
+import { defineStore } from 'pinia'
+import { computed, ref } from 'vue'
+
+import { useApi } from '../composables/useApi.js'
+
+// Whole-stack health: is every part of FabledCurator running (milestone 365)?
+//
+// Distinct from `system.js`, which polls /api/health — a no-DB liveness check
+// that only proves the web container is serving. That endpoint answers "can I
+// reach the API"; this one answers "is anything broken", which is the question
+// a green dot beside the brand was already being read as answering.
+//
+// Also distinct from `systemActivity.js`, which is about what the pipeline is
+// DOING — queue depths, running tasks, failures. Running and alive are
+// different questions and they fail independently: a perfectly idle stack with
+// a dead worker looks identical to a healthy one on the activity surfaces.
+export const useSystemHealthStore = defineStore('systemHealth', () => {
+  const api = useApi()
+
+  const overall = ref(null)      // null until the first answer: unknown ≠ ok
+  const parts = ref([])
+  const checkedAt = ref(null)
+  const thresholds = ref(null)   // server-owned, so the UI keeps no second copy
+  const lastError = ref(null)
+
+  async function refresh() {
+    try {
+      const body = await api.get('/api/system/health')
+      overall.value = body.overall
+      parts.value = body.parts || []
+      checkedAt.value = body.checked_at
+      thresholds.value = body.thresholds || null
+      lastError.value = null
+    } catch (e) {
+      // The endpoint is built never to fail because a dependency failed, so a
+      // throw here means the API itself is unreachable — which is its own kind
+      // of unhealthy and must not be shown as "ok".
+      lastError.value = e.message
+      overall.value = 'unknown'
+    }
+    return overall.value
+  }
+
+  // The parts worth naming in a tooltip — everything that is not ok, worst
+  // first. The endpoint already sorts that way.
+  const problems = computed(() => parts.value.filter(p => p.state !== 'ok'))
+
+  return { overall, parts, checkedAt, thresholds, lastError, problems, refresh }
+})

frontend/src/views/SystemView.vue

@@ -0,0 +1,129 @@
+<template>
+  <v-container class="py-6" style="max-width: 900px">
+    <div class="d-flex align-center mb-1">
+      <h1 class="text-h5">System</h1>
+      <v-spacer />
+      <span class="fc-sys__checked">
+        {{ store.checkedAt ? `checked ${formatRelative(store.checkedAt)}` : 'checking…' }}
+      </span>
+    </div>
+
+    <p class="fc-sys__lede text-body-2 mb-5">
+      Every moving part of FabledCurator and whether it is still checking in.
+      Parts are learned as they appear, so anything that has run at least once
+      stays listed — that is what lets a stopped one be noticed rather than
+      simply vanishing.
+    </p>
+
+    <v-alert
+      v-if="store.lastError" type="error" variant="tonal" density="compact" class="mb-4"
+    >
+      Could not reach FabledCurator: {{ store.lastError }}
+    </v-alert>
+
+    <v-card v-else variant="flat" class="fc-sys__card">
+      <div v-if="!store.parts.length" class="pa-6 text-center fc-sys__muted">
+        Still gathering — this fills in on the first check.
+      </div>
+
+      <div
+        v-for="part in store.parts" :key="part.key"
+        class="fc-sys__row" :class="`fc-sys__row--${part.state}`"
+      >
+        <span class="fc-sys__dot" :class="`fc-sys__dot--${part.state}`" />
+
+        <div class="fc-sys__body">
+          <div class="fc-sys__name">
+            {{ part.name }}
+            <span class="fc-sys__kind">{{ kindLabel(part.kind) }}</span>
+          </div>
+          <!-- The sentence, not just a chip. At the moment someone is deciding
+               whether to go and open Portainer, "has not checked in for 6 min"
+               is the thing that answers them. -->
+          <div class="fc-sys__detail">{{ part.detail }}</div>
+        </div>
+
+        <div class="fc-sys__meta">
+          <div v-if="part.last_seen_at" :title="part.last_seen_at">
+            seen {{ formatRelative(part.last_seen_at) }}
+          </div>
+          <div v-if="part.latency_ms != null">{{ part.latency_ms }} ms</div>
+          <div v-if="part.queues?.length" class="fc-sys__queues">{{ part.queues.join(', ') }}</div>
+        </div>
+      </div>
+    </v-card>
+
+    <p v-if="store.thresholds" class="fc-sys__foot text-caption mt-4">
+      A part is called stale after
+      {{ Math.round(store.thresholds.stale_after_seconds / 60) }} min without a
+      check-in and treated as stopped after
+      {{ Math.round(store.thresholds.down_after_seconds / 60) }} min. The window
+      is deliberately wide: a rolling deploy briefly runs two of a service and
+      then neither, and an indicator that reddened on every update would stop
+      being read.
+    </p>
+  </v-container>
+</template>
+
+<script setup>
+import { onMounted, onUnmounted } from 'vue'
+
+import { useSystemHealthStore } from '../stores/systemHealth.js'
+import { formatRelative } from '../utils/date.js'
+
+const store = useSystemHealthStore()
+
+// Slower than the pipeline chip's 8s: liveness changes on the scale of
+// container restarts, not task starts, and this page is open while someone
+// watches it.
+const POLL_MS = 10_000
+let timer = null
+
+function kindLabel(kind) {
+  if (kind === 'celery') return 'background worker'
+  if (kind === 'agent') return 'GPU agent'
+  if (kind === 'datastore') return 'datastore'
+  return kind
+}
+
+onMounted(() => {
+  store.refresh()
+  timer = setInterval(() => { if (!document.hidden) store.refresh() }, POLL_MS)
+})
+onUnmounted(() => { if (timer) clearInterval(timer) })
+</script>
+
+<style scoped>
+.fc-sys__lede, .fc-sys__muted, .fc-sys__checked, .fc-sys__foot {
+  color: rgb(var(--v-theme-on-surface) / 0.66);
+}
+.fc-sys__checked { font-size: 0.78rem; }
+.fc-sys__card { background: rgb(var(--v-theme-on-surface) / 0.04); }
+
+.fc-sys__row {
+  display: flex; align-items: center; gap: 12px;
+  padding: 12px 16px;
+  border-bottom: 1px solid rgb(var(--v-theme-on-surface) / 0.08);
+}
+.fc-sys__row:last-child { border-bottom: 0; }
+
+.fc-sys__dot { width: 9px; height: 9px; border-radius: 50%; flex: 0 0 auto; }
+.fc-sys__dot--ok      { background: rgb(var(--v-theme-success)); }
+.fc-sys__dot--stale   { background: rgb(var(--v-theme-warning)); }
+.fc-sys__dot--down    { background: rgb(var(--v-theme-error)); }
+.fc-sys__dot--unknown { background: rgb(var(--v-theme-on-surface) / 0.35); }
+
+.fc-sys__body { min-width: 0; flex: 1 1 auto; }
+.fc-sys__name { font-weight: 600; }
+.fc-sys__kind {
+  margin-left: 8px; font-weight: 400; font-size: 0.72rem; text-transform: uppercase;
+  letter-spacing: 0.04em; color: rgb(var(--v-theme-on-surface) / 0.5);
+}
+.fc-sys__detail { font-size: 0.82rem; color: rgb(var(--v-theme-on-surface) / 0.72); }
+
+.fc-sys__meta {
+  text-align: right; font-size: 0.75rem; flex: 0 0 auto;
+  font-variant-numeric: tabular-nums; color: rgb(var(--v-theme-on-surface) / 0.6);
+}
+.fc-sys__queues { opacity: 0.75; }
+</style>