test(multiple-subtitles): [PKG-MULTI-SUB-09] isolate old-core source seeking from caption loss

test/README.md

@@ -221,7 +221,8 @@ Explicit single-active-cue probes record historical and candidate overlap defect
 their passing assertions do not mean simultaneous captions are compatible.
 Candidate paused Firefox offsets are corrected by CORE-SUBTITLE-OFFSET-01. Old
 Firefox hosts retain explicit defect observations; their behavior is not silently
-counted as correct. WebKit source-switch failures remain under investigation.
+counted as correct. Task09 classified the apparent WebKit source-switch caption
+loss as an old-host seek landing near zero, reproducible without any plugin.
 See `refactor/changes/2026-09-14-PKG-MULTI-SUB-05-combinations.md` before changing
 expectations. Reports include native active cues and rendered text. The new frozen
 5.1.2 core route verifies archive integrity and member hashes before serving.
@@ -235,3 +236,11 @@ without creating an Artplayer instance to compare native timing edits, cue
 reinsertion and mode toggling. It records actual time within the required interval,
 not a fabricated millisecond-exact seek landing. These diagnostic observations
 do not claim every native engine strategy is correct.
+
+`multiple-subtitles-switch.spec.js` records source Promise settlement, native
+currentTime writes/events and actual seek landing with no plugin, candidate and
+published1.2.0. Old first-seek misses are retained as observations; every candidate
+first seek must land. The caption combination fixture separately waits for native
+source seeking to finish and for fullscreen-enter notification before testing
+subsequent commands. It retains exact caption and enter/exit order assertions;
+do not add delays or plugin retries to cover old core readiness behavior.

test/browser/multiple-subtitles-combinations.spec.js

@@ -84,6 +84,7 @@ for (const core of cores.filter(core => !['published-5.1.2', 'published-5.1.7'].
     })
     await page.locator('#play').click()
     await expect.poll(() => page.evaluate(() => (document.fullscreenElement || document.webkitFullscreenElement) === window.art.template.$player)).toBe(true)
+    await expect.poll(() => page.evaluate(() => window.fullscreenEvents)).toEqual([true])
     await expect(page.locator('.art-subtitle-a')).toBeVisible()
     expect(await page.evaluate(() => (document.fullscreenElement || document.webkitFullscreenElement).contains(window.art.template.$subtitle))).toBe(true)
     await page.evaluate(() => {
@@ -94,6 +95,9 @@ for (const core of cores.filter(core => !['published-5.1.2', 'published-5.1.7'].
     await expect(page.locator('.art-subtitle-a')).toHaveCount(0)
     await expect(page.locator('.art-subtitle-b')).toHaveText('Translation')
     await page.evaluate(() => window.art.switchUrl('/test/pattern.mp4?subtitles-combination'))
+    // Old core promises can settle during their native restoration seek.
+    // The immediate-seek path is retained separately in multiple-subtitles-switch.spec.js.
+    await expect.poll(() => page.evaluate(() => window.art.video.seeking)).toBe(false)
     await seek(page, 1.5)
     await expect(page.locator('.art-subtitle-b')).toHaveText('Translation')
     await page.evaluate(() => window.art.plugins.multipleSubtitles.reset())

test/browser/multiple-subtitles-switch.spec.js

@@ -0,0 +1,84 @@
+import { hash } from '../../refactor/scripts/releases.mjs'
+import { multipleSubtitlesCandidate, multipleSubtitlesHistorical } from '../helpers/multiple-subtitles.js'
+import { expect, test } from './fixtures.js'
+
+const candidate = await multipleSubtitlesCandidate()
+const published = (await multipleSubtitlesHistorical()).find(item => item.name === 'published-1.2.0-main')
+const variants = [null, candidate, published]
+
+for (const core of ['published-5.3.0', 'published', 'candidate']) {
+  for (const implementation of variants) {
+    test(`Source seek ordering / ${core} / ${implementation?.name || 'no-plugin'}`, async ({ page, browser }, testInfo) => {
+      await page.route('**/test/switch-caption.vtt', route => route.fulfill({ contentType: 'text/vtt', body: 'WEBVTT\n\n00:01.000 --> 00:03.000\nCaption\n' }))
+      await page.goto(`/test/player.html?core=${core}`)
+      if (implementation)
+        await page.addScriptTag({ content: `(() => { const module = { exports: {} }; const exports = module.exports; ${implementation.code}; window.multipleFactory = module.exports.default || module.exports; })();` })
+      await page.evaluate(() => {
+        window.createPlayer('/test/pattern.mp4')
+        const video = window.art.video
+        window.switchTrace = []
+        window.switchState = () => ({ time: video.currentTime, seeking: video.seeking, duration: video.duration, readyState: video.readyState, paused: video.paused, source: video.currentSrc, active: Array.from(window.art.template.$track.track.activeCues || [], cue => cue.text), displayed: window.art.template.$subtitle.textContent })
+        const record = (event, value) => window.switchTrace.push({ event, value, ...window.switchState() })
+        const descriptor = Object.getOwnPropertyDescriptor(HTMLMediaElement.prototype, 'currentTime')
+        Object.defineProperty(video, 'currentTime', {
+          configurable: true,
+          get() { return descriptor.get.call(this) },
+          set(value) {
+            record('write-currentTime', value)
+            descriptor.set.call(this, value)
+          },
+        })
+        for (const event of ['loadedmetadata', 'loadeddata', 'canplay', 'seeking', 'seeked', 'emptied', 'pause'])
+          video.addEventListener(event, () => record(event))
+      })
+      await expect.poll(() => page.evaluate(() => window.art.isReady)).toBe(true)
+      if (implementation) {
+        await page.evaluate(async () => {
+          await window.art.plugins.add(window.multipleFactory({ subtitles: [{ name: 'caption', url: '/test/switch-caption.vtt' }] }))
+        })
+        await expect.poll(() => page.evaluate(() => window.art.template.$track.track.cues?.length)).toBe(1)
+      }
+      await page.locator('#play').click()
+      await expect.poll(() => page.evaluate(() => window.art.currentTime)).toBeGreaterThan(0.1)
+      await page.locator('#pause').click()
+      await page.evaluate(() => {
+        document.querySelector('#play').onclick = () => {
+          window.art.fullscreen = true
+        }
+      })
+      await page.locator('#play').click()
+      await expect.poll(() => page.evaluate(() => Boolean(document.fullscreenElement || document.webkitFullscreenElement))).toBe(true)
+      await page.evaluate(() => {
+        window.art.fullscreen = false
+      })
+      await expect.poll(() => page.evaluate(() => Boolean(document.fullscreenElement || document.webkitFullscreenElement))).toBe(false)
+      const outcomes = []
+      for (let round = 0; round < 3; round++) {
+        await page.evaluate(round => window.art.switchUrl(`/test/pattern.mp4?seek-order=${round}`), round)
+        const settled = await page.evaluate(() => window.switchState())
+        await page.evaluate(() => new Promise((resolve) => {
+          window.art.once('video:seeked', resolve)
+          window.art.seek = 1.5
+        }))
+        await expect.poll(() => page.evaluate(() => window.art.video.seeking)).toBe(false)
+        const firstSeek = await page.evaluate(() => window.switchState())
+        const landed = Math.abs(firstSeek.time - 1.5) < 0.05
+        if (!landed) {
+          await page.evaluate(() => new Promise((resolve) => {
+            window.art.once('video:seeked', resolve)
+            window.art.seek = 1.5
+          }))
+          await expect.poll(() => page.evaluate(() => window.art.video.seeking)).toBe(false)
+        }
+        await expect.poll(() => page.evaluate(() => Math.abs(window.art.currentTime - 1.5))).toBeLessThan(0.05)
+        if (implementation)
+          await expect(page.locator('.art-subtitle-caption')).toHaveText('Caption')
+        outcomes.push({ round, settled, firstSeek, landed, afterSettledSeek: await page.evaluate(() => window.switchState()) })
+      }
+      await testInfo.attach('source-seek-order', { contentType: 'application/json', body: JSON.stringify({ core, plugin: implementation?.name || 'none', pluginSha256: implementation ? hash(implementation.code) : null, browser: browser.version(), outcomes, trace: await page.evaluate(() => window.switchTrace), scope: 'Three real source changes with immediate versus settled seek; old misses are recorded, candidate must honor every first seek' }) })
+      if (core === 'candidate')
+        expect(outcomes.every(item => item.landed)).toBe(true)
+      await page.evaluate(() => window.art.destroy())
+    })
+  }
+}