feat(settings): the instance reports which build it is (318 step 6)

A dim line at the foot of Settings: `FabledCurator 2026.08.28.1249 · dev`.

This is no longer a convenience. Milestone 318 stopped publishing version
image tags, so an instance's own report is the ONLY answer to "which build is
this?" — there is no registry name left to check it against. Note #3127 §5
says it directly: a wrong answer here has no second source to contradict it.

Three states, kept distinct because collapsing any two of them lies:

  not asked yet         render nothing
  asked, no version     render "unknown"
  asked, has a version  render it

A blank footer reads as "no version", which is a different claim from "I
cannot say". And a failed health call deliberately does NOT mark the build
loaded — a network blip says nothing about the image, and presenting it as
"unknown" would look like a defective build.

Carried on /api/health rather than a new route: it answers at the same cost
(two module constants, no I/O) and TopNav already fetches it app-wide, so a
separate endpoint would mean a second request for two strings.

Both fields are OMITTED when unset rather than sent empty. Absence already
means "cannot say" — an image predating the field says exactly that by not
having the key — so a second spelling would make every reader special-case
it. The pre-existing test asserting the body is EXACTLY {"status": "ok"} is
what keeps a well-meaning `or ""` default from creeping in.

FC_CHANNEL now has one definition. It was read from the environment in
extension.py and would have been read again here; the new build_info module
holds both, and extension.py binds it as a module-level name so existing
tests monkeypatch it exactly as before. Separate from config.py on purpose:
those are operator settings meant to be changed, these describe the artifact.

Channel sits beside the version, never inside it (rule 149), asserted from
both ends. A `-dev` suffix would read as a 0 segment to the extension's
parseInt comparator and make every dev build compare equal — #2993 exactly.

Not hidden, per the operator and §7: the JS bundle and asset hashes
fingerprint the build anyway, and "I'm on 2026.08.28.1249" is the single most
useful line in a bug report.

frontend/src/stores/system.js

@@ -5,6 +5,18 @@ import { useApi } from '../composables/useApi.js'
 export const useSystemStore = defineStore('system', () => {
   const api = useApi()
   const healthy = ref(null)  // null=unknown, true=ok, false=down
+  // 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.
+  //
+  // Three states, and collapsing any two of them would lie:
+  //   buildLoaded=false            we have not asked yet   -> render nothing
+  //   buildLoaded=true, version='' the build cannot say    -> render "unknown"
+  //   buildLoaded=true, version=x  this build is x
+  // A blank footer would read as "no version", which is a different claim.
+  const buildVersion = ref('')
+  const buildChannel = ref('')
+  const buildLoaded = ref(false)
   const stats = ref(null)
   const statsLoading = ref(false)
 
@@ -12,8 +24,17 @@ export const useSystemStore = defineStore('system', () => {
     try {
       const body = await api.get('/api/health')
       healthy.value = body.status === 'ok'
+      // Absent means "cannot say" — the server omits these rather than
+      // sending empty strings, so `?? ''` preserves that rather than
+      // inventing a value for it.
+      buildVersion.value = body.version ?? ''
+      buildChannel.value = body.channel ?? ''
+      buildLoaded.value = true
     } catch {
       healthy.value = false
+      // Deliberately NOT setting buildLoaded: a failed health call tells us
+      // nothing about the build, and claiming "unknown" would present a
+      // network blip as a defective image.
     }
   }
 
@@ -26,5 +47,8 @@ export const useSystemStore = defineStore('system', () => {
     }
   }
 
-  return { healthy, stats, statsLoading, refreshHealth, refreshStats }
+  return {
+    healthy, stats, statsLoading, refreshHealth, refreshStats,
+    buildVersion, buildChannel, buildLoaded,
+  }
 })

frontend/src/views/SettingsView.vue

@@ -54,6 +54,21 @@
         <MaintenancePanel />
       </v-window-item>
     </v-window>
+
+    <!-- Which build is this? With no version image tags (milestone 318) the
+         instance's own report is the only answer, so it is shown rather than
+         hidden. The instinct to treat it as information disclosure does not
+         survive contact: the JS bundle and asset hashes fingerprint the build
+         anyway, and "I'm on 2026.08.28.1249" is the single most useful line in
+         a bug report.
+
+         Channel sits BESIDE the version, never inside it (rule 149) — a
+         `-dev` suffix would read as a 0 segment to the extension's comparator
+         and make every dev build compare equal (#2993). -->
+    <div v-if="system.buildLoaded" class="text-caption text-medium-emphasis text-center mt-8">
+      FabledCurator {{ system.buildVersion || 'unknown' }}
+      <span v-if="system.buildChannel"> · {{ system.buildChannel }}</span>
+    </div>
   </v-container>
 </template>
 

frontend/test/systemBuild.spec.js

@@ -0,0 +1,96 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
+import { setActivePinia, createPinia } from 'pinia'
+import { useSystemStore } from '../src/stores/system.js'
+
+// Which build am I running? Milestone 318 stopped publishing version image
+// tags, so the instance's own report is the ONLY answer — there is no registry
+// name left to check it against. That promotes this from a convenience to the
+// mechanism, and it means the three states below have to stay distinct: a
+// wrong answer here has nothing to contradict it.
+//
+//   not asked yet        -> render nothing
+//   asked, no version    -> render "unknown"
+//   asked, has a version -> render it
+//
+// Collapsing the first two would show "unknown" during every page load, and
+// collapsing either into a blank would read as "no version", which is a
+// different and false claim.
+
+function stubHealth(body, { fail = false } = {}) {
+  globalThis.fetch = vi.fn(async () => {
+    if (fail) throw new Error('network down')
+    return {
+      ok: true, status: 200, statusText: '200',
+      text: async () => JSON.stringify(body),
+    }
+  })
+}
+
+describe('system store — build identity', () => {
+  beforeEach(() => setActivePinia(createPinia()))
+  afterEach(() => { vi.restoreAllMocks(); delete globalThis.fetch })
+
+  it('starts having asked nothing, so the footer renders nothing', () => {
+    const s = useSystemStore()
+    expect(s.buildLoaded).toBe(false)
+  })
+
+  it('reports the version and channel the instance claims', async () => {
+    stubHealth({ status: 'ok', version: '2026.08.28.1249', channel: 'dev' })
+    const s = useSystemStore()
+    await s.refreshHealth()
+
+    expect(s.buildLoaded).toBe(true)
+    expect(s.buildVersion).toBe('2026.08.28.1249')
+    expect(s.buildChannel).toBe('dev')
+  })
+
+  it('keeps the channel OUT of the version string', async () => {
+    // The tempting shortcut is a `-dev` suffix. The extension's comparator
+    // parses each dotted segment with parseInt, so a suffixed segment reads as
+    // 0 and every dev build compares equal to every other — #2993 exactly
+    // (rule 149). If anyone ever "simplifies" by folding them together, the
+    // version stops being the bare derived number and this fails.
+    stubHealth({ status: 'ok', version: '2026.08.28.1249', channel: 'dev' })
+    const s = useSystemStore()
+    await s.refreshHealth()
+
+    expect(s.buildVersion).toBe('2026.08.28.1249')
+    expect(s.buildVersion).not.toContain('dev')
+  })
+
+  it('treats an absent version as "cannot say", not as a value', async () => {
+    // A locally-built image, or one predating the field. The server omits the
+    // key rather than sending an empty string; `?? ''` must preserve that
+    // rather than inventing something. The view renders "unknown" from it.
+    stubHealth({ status: 'ok' })
+    const s = useSystemStore()
+    await s.refreshHealth()
+
+    expect(s.buildLoaded).toBe(true)
+    expect(s.buildVersion).toBe('')
+    expect(s.buildChannel).toBe('')
+  })
+
+  it('reports a version with no channel without inventing one', async () => {
+    stubHealth({ status: 'ok', version: '2026.08.28.1249' })
+    const s = useSystemStore()
+    await s.refreshHealth()
+
+    expect(s.buildVersion).toBe('2026.08.28.1249')
+    expect(s.buildChannel).toBe('')
+  })
+
+  it('does not claim "unknown" when the health call itself failed', async () => {
+    // A network blip says nothing about the build. Marking it loaded here
+    // would present a transient failure as a defective image — and since
+    // nothing else names the build, there would be no second source to
+    // correct the impression.
+    stubHealth(null, { fail: true })
+    const s = useSystemStore()
+    await s.refreshHealth()
+
+    expect(s.healthy).toBe(false)
+    expect(s.buildLoaded).toBe(false)
+  })
+})